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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 09:44:07 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 09:44:07 +0000
commit39ce00b8d520cbecbd6af87257e8fb11df0ec273 (patch)
tree4c21a2674c19e5c44be3b3550b476b9e63d8ae3d /doc/spec.txt
parentInitial commit. (diff)
downloadexim4-39ce00b8d520cbecbd6af87257e8fb11df0ec273.tar.xz
exim4-39ce00b8d520cbecbd6af87257e8fb11df0ec273.zip
Adding upstream version 4.94.2.upstream/4.94.2upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
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+Specification of the Exim Mail Transfer Agent
+
+Exim Maintainers
+
+Copyright (c) 2020 University of Cambridge
+
+Revision 4.94.2 30 Apr 2021 EM
+
+-------------------------------------------------------------------------------
+
+TABLE OF CONTENTS
+
+1. Introduction
+
+ 1.1. Exim documentation
+ 1.2. FTP site and websites
+ 1.3. Mailing lists
+ 1.4. Bug reports
+ 1.5. Where to find the Exim distribution
+ 1.6. Limitations
+ 1.7. Runtime configuration
+ 1.8. Calling interface
+ 1.9. Terminology
+
+2. Incorporated code
+3. How Exim receives and delivers mail
+
+ 3.1. Overall philosophy
+ 3.2. Policy control
+ 3.3. User filters
+ 3.4. Message identification
+ 3.5. Receiving mail
+ 3.6. Handling an incoming message
+ 3.7. Life of a message
+ 3.8. Processing an address for delivery
+ 3.9. Processing an address for verification
+ 3.10. Running an individual router
+ 3.11. Duplicate addresses
+ 3.12. Router preconditions
+ 3.13. Delivery in detail
+ 3.14. Retry mechanism
+ 3.15. Temporary delivery failure
+ 3.16. Permanent delivery failure
+ 3.17. Failures to deliver bounce messages
+
+4. Building and installing Exim
+
+ 4.1. Unpacking
+ 4.2. Multiple machine architectures and operating systems
+ 4.3. PCRE library
+ 4.4. DBM libraries
+ 4.5. Pre-building configuration
+ 4.6. Support for iconv()
+ 4.7. Including TLS/SSL encryption support
+ 4.8. Use of tcpwrappers
+ 4.9. Including support for IPv6
+ 4.10. Dynamically loaded lookup module support
+ 4.11. The building process
+ 4.12. Output from "make"
+ 4.13. Overriding build-time options for Exim
+ 4.14. OS-specific header files
+ 4.15. Overriding build-time options for the monitor
+ 4.16. Installing Exim binaries and scripts
+ 4.17. Installing info documentation
+ 4.18. Setting up the spool directory
+ 4.19. Testing
+ 4.20. Replacing another MTA with Exim
+ 4.21. Upgrading Exim
+ 4.22. Stopping the Exim daemon on Solaris
+
+5. The Exim command line
+
+ 5.1. Setting options by program name
+ 5.2. Trusted and admin users
+ 5.3. Command line options
+
+6. The Exim runtime configuration file
+
+ 6.1. Using a different configuration file
+ 6.2. Configuration file format
+ 6.3. File inclusions in the configuration file
+ 6.4. Macros in the configuration file
+ 6.5. Macro substitution
+ 6.6. Redefining macros
+ 6.7. Overriding macro values
+ 6.8. Example of macro usage
+ 6.9. Builtin macros
+ 6.10. Conditional skips in the configuration file
+ 6.11. Common option syntax
+ 6.12. Boolean options
+ 6.13. Integer values
+ 6.14. Octal integer values
+ 6.15. Fixed point numbers
+ 6.16. Time intervals
+ 6.17. String values
+ 6.18. Expanded strings
+ 6.19. User and group names
+ 6.20. List construction
+ 6.21. Changing list separators
+ 6.22. Empty items in lists
+ 6.23. Format of driver configurations
+
+7. The default configuration file
+
+ 7.1. Macros
+ 7.2. Main configuration settings
+ 7.3. ACL configuration
+ 7.4. Router configuration
+ 7.5. Transport configuration
+ 7.6. Default retry rule
+ 7.7. Rewriting configuration
+ 7.8. Authenticators configuration
+
+8. Regular expressions
+9. File and database lookups
+
+ 9.1. Examples of different lookup syntax
+ 9.2. Lookup types
+ 9.3. Single-key lookup types
+ 9.4. Query-style lookup types
+ 9.5. Temporary errors in lookups
+ 9.6. Default values in single-key lookups
+ 9.7. Partial matching in single-key lookups
+ 9.8. Lookup caching
+ 9.9. Quoting lookup data
+ 9.10. More about dnsdb
+ 9.11. Dnsdb lookup modifiers
+ 9.12. Pseudo dnsdb record types
+ 9.13. Multiple dnsdb lookups
+ 9.14. More about LDAP
+ 9.15. Format of LDAP queries
+ 9.16. LDAP quoting
+ 9.17. LDAP connections
+ 9.18. LDAP authentication and control information
+ 9.19. Format of data returned by LDAP
+ 9.20. More about NIS+
+ 9.21. SQL lookups
+ 9.22. More about MySQL, PostgreSQL, Oracle, InterBase, and Redis
+ 9.23. Specifying the server in the query
+ 9.24. Special MySQL features
+ 9.25. Special PostgreSQL features
+ 9.26. More about SQLite
+ 9.27. More about Redis
+
+10. Domain, host, address, and local part lists
+
+ 10.1. Expansion of lists
+ 10.2. Negated items in lists
+ 10.3. File names in lists
+ 10.4. An lsearch file is not an out-of-line list
+ 10.5. Results of list checking
+ 10.6. Named lists
+ 10.7. Named lists compared with macros
+ 10.8. Named list caching
+ 10.9. Domain lists
+ 10.10. Host lists
+ 10.11. Special host list patterns
+ 10.12. Host list patterns that match by IP address
+ 10.13. Host list patterns for single-key lookups by host address
+ 10.14. Host list patterns that match by host name
+ 10.15. Behaviour when an IP address or name cannot be found
+ 10.16. Mixing wildcarded host names and addresses in host lists
+ 10.17. Temporary DNS errors when looking up host information
+ 10.18. Host list patterns for single-key lookups by host name
+ 10.19. Host list patterns for query-style lookups
+ 10.20. Address lists
+ 10.21. Case of letters in address lists
+ 10.22. Local part lists
+
+11. String expansions
+
+ 11.1. Literal text in expanded strings
+ 11.2. Character escape sequences in expanded strings
+ 11.3. Testing string expansions
+ 11.4. Forced expansion failure
+ 11.5. Expansion items
+ 11.6. Expansion operators
+ 11.7. Expansion conditions
+ 11.8. Combining expansion conditions
+ 11.9. Expansion variables
+
+12. Embedded Perl
+
+ 12.1. Setting up so Perl can be used
+ 12.2. Calling Perl subroutines
+ 12.3. Calling Exim functions from Perl
+ 12.4. Use of standard output and error by Perl
+
+13. Starting the daemon and the use of network interfaces
+
+ 13.1. Starting a listening daemon
+ 13.2. Special IP listening addresses
+ 13.3. Overriding local_interfaces and daemon_smtp_ports
+ 13.4. Support for the submissions (aka SSMTP or SMTPS) protocol
+ 13.5. IPv6 address scopes
+ 13.6. Disabling IPv6
+ 13.7. Examples of starting a listening daemon
+ 13.8. Recognizing the local host
+ 13.9. Delivering to a remote host
+
+14. Main configuration
+
+ 14.1. Miscellaneous
+ 14.2. Exim parameters
+ 14.3. Privilege controls
+ 14.4. Logging
+ 14.5. Frozen messages
+ 14.6. Data lookups
+ 14.7. Message ids
+ 14.8. Embedded Perl Startup
+ 14.9. Daemon
+ 14.10. Resource control
+ 14.11. Policy controls
+ 14.12. Callout cache
+ 14.13. TLS
+ 14.14. Local user handling
+ 14.15. All incoming messages (SMTP and non-SMTP)
+ 14.16. Non-SMTP incoming messages
+ 14.17. Incoming SMTP messages
+ 14.18. SMTP extensions
+ 14.19. Processing messages
+ 14.20. System filter
+ 14.21. Routing and delivery
+ 14.22. Bounce and warning messages
+ 14.23. Alphabetical list of main options
+
+15. Generic options for routers
+16. The accept router
+17. The dnslookup router
+
+ 17.1. Problems with DNS lookups
+ 17.2. Declining addresses by dnslookup
+ 17.3. Private options for dnslookup
+ 17.4. Effect of qualify_single and search_parents
+
+18. The ipliteral router
+19. The iplookup router
+20. The manualroute router
+
+ 20.1. Private options for manualroute
+ 20.2. Routing rules in route_list
+ 20.3. Routing rules in route_data
+ 20.4. Format of the list of hosts
+ 20.5. Format of one host item
+ 20.6. How the list of hosts is used
+ 20.7. How the options are used
+ 20.8. Manualroute examples
+
+21. The queryprogram router
+22. The redirect router
+
+ 22.1. Redirection data
+ 22.2. Forward files and address verification
+ 22.3. Interpreting redirection data
+ 22.4. Items in a non-filter redirection list
+ 22.5. Redirecting to a local mailbox
+ 22.6. Special items in redirection lists
+ 22.7. Duplicate addresses
+ 22.8. Repeated redirection expansion
+ 22.9. Errors in redirection lists
+ 22.10. Private options for the redirect router
+
+23. Environment for running local transports
+
+ 23.1. Concurrent deliveries
+ 23.2. Uids and gids
+ 23.3. Current and home directories
+ 23.4. Expansion variables derived from the address
+
+24. Generic options for transports
+25. Address batching in local transports
+26. The appendfile transport
+
+ 26.1. The file and directory options
+ 26.2. Private options for appendfile
+ 26.3. Operational details for appending
+ 26.4. Operational details for delivery to a new file
+ 26.5. Maildir delivery
+ 26.6. Using tags to record message sizes
+ 26.7. Using a maildirsize file
+ 26.8. Mailstore delivery
+ 26.9. Non-special new file delivery
+
+27. The autoreply transport
+
+ 27.1. Private options for autoreply
+
+28. The lmtp transport
+29. The pipe transport
+
+ 29.1. Concurrent delivery
+ 29.2. Returned status and data
+ 29.3. How the command is run
+ 29.4. Environment variables
+ 29.5. Private options for pipe
+ 29.6. Using an external local delivery agent
+
+30. The smtp transport
+
+ 30.1. Multiple messages on a single connection
+ 30.2. Use of the $host and $host_address variables
+ 30.3. Use of $tls_cipher and $tls_peerdn
+ 30.4. Private options for smtp
+ 30.5. How the limits for the number of hosts to try are used
+
+31. Address rewriting
+
+ 31.1. Explicitly configured address rewriting
+ 31.2. When does rewriting happen?
+ 31.3. Testing the rewriting rules that apply on input
+ 31.4. Rewriting rules
+ 31.5. Rewriting patterns
+ 31.6. Rewriting replacements
+ 31.7. Rewriting flags
+ 31.8. Flags specifying which headers and envelope addresses to rewrite
+ 31.9. The SMTP-time rewriting flag
+ 31.10. Flags controlling the rewriting process
+ 31.11. Rewriting examples
+
+32. Retry configuration
+
+ 32.1. Changing retry rules
+ 32.2. Format of retry rules
+ 32.3. Choosing which retry rule to use for address errors
+ 32.4. Choosing which retry rule to use for host and message errors
+ 32.5. Retry rules for specific errors
+ 32.6. Retry rules for specified senders
+ 32.7. Retry parameters
+ 32.8. Retry rule examples
+ 32.9. Timeout of retry data
+ 32.10. Long-term failures
+ 32.11. Deliveries that work intermittently
+
+33. SMTP authentication
+
+ 33.1. Generic options for authenticators
+ 33.2. The AUTH parameter on MAIL commands
+ 33.3. Authentication on an Exim server
+ 33.4. Testing server authentication
+ 33.5. Authentication by an Exim client
+
+34. The plaintext authenticator
+
+ 34.1. Avoiding cleartext use
+ 34.2. Plaintext server options
+ 34.3. Using plaintext in a server
+ 34.4. The PLAIN authentication mechanism
+ 34.5. The LOGIN authentication mechanism
+ 34.6. Support for different kinds of authentication
+ 34.7. Using plaintext in a client
+
+35. The cram_md5 authenticator
+
+ 35.1. Using cram_md5 as a server
+ 35.2. Using cram_md5 as a client
+
+36. The cyrus_sasl authenticator
+
+ 36.1. Using cyrus_sasl as a server
+
+37. The dovecot authenticator
+38. The gsasl authenticator
+
+ 38.1. gsasl auth variables
+
+39. The heimdal_gssapi authenticator
+
+ 39.1. heimdal_gssapi auth variables
+
+40. The spa authenticator
+
+ 40.1. Using spa as a server
+ 40.2. Using spa as a client
+
+41. The external authenticator
+
+ 41.1. External options
+ 41.2. Using external in a server
+ 41.3. Using external in a client
+
+42. The tls authenticator
+43. Encrypted SMTP connections using TLS/SSL
+
+ 43.1. Support for the "submissions" (aka "ssmtp" and "smtps") protocol
+ 43.2. OpenSSL vs GnuTLS
+ 43.3. GnuTLS parameter computation
+ 43.4. Requiring specific ciphers in OpenSSL
+ 43.5. Requiring specific ciphers or other parameters in GnuTLS
+ 43.6. Configuring an Exim server to use TLS
+ 43.7. Requesting and verifying client certificates
+ 43.8. Revoked certificates
+ 43.9. Configuring an Exim client to use TLS
+ 43.10. Use of TLS Server Name Indication
+ 43.11. Multiple messages on the same encrypted TCP/IP connection
+ 43.12. Certificates and all that
+ 43.13. Certificate chains
+ 43.14. Self-signed certificates
+ 43.15. DANE
+
+44. Access control lists
+
+ 44.1. Testing ACLs
+ 44.2. Specifying when ACLs are used
+ 44.3. The non-SMTP ACLs
+ 44.4. The SMTP connect ACL
+ 44.5. The EHLO/HELO ACL
+ 44.6. The DATA ACLs
+ 44.7. The SMTP DKIM ACL
+ 44.8. The SMTP MIME ACL
+ 44.9. The SMTP PRDR ACL
+ 44.10. The QUIT ACL
+ 44.11. The not-QUIT ACL
+ 44.12. Finding an ACL to use
+ 44.13. ACL return codes
+ 44.14. Unset ACL options
+ 44.15. Data for message ACLs
+ 44.16. Data for non-message ACLs
+ 44.17. Format of an ACL
+ 44.18. ACL verbs
+ 44.19. ACL variables
+ 44.20. Condition and modifier processing
+ 44.21. ACL modifiers
+ 44.22. Use of the control modifier
+ 44.23. Summary of message fixup control
+ 44.24. Adding header lines in ACLs
+ 44.25. Removing header lines in ACLs
+ 44.26. ACL conditions
+ 44.27. Using DNS lists
+ 44.28. Specifying the IP address for a DNS list lookup
+ 44.29. DNS lists keyed on domain names
+ 44.30. Multiple explicit keys for a DNS list
+ 44.31. Data returned by DNS lists
+ 44.32. Variables set from DNS lists
+ 44.33. Additional matching conditions for DNS lists
+ 44.34. Negated DNS matching conditions
+ 44.35. Handling multiple DNS records from a DNS list
+ 44.36. Detailed information from merged DNS lists
+ 44.37. DNS lists and IPv6
+ 44.38. Rate limiting incoming messages
+ 44.39. Ratelimit options for what is being measured
+ 44.40. Ratelimit update modes
+ 44.41. Ratelimit options for handling fast clients
+ 44.42. Limiting the rate of different events
+ 44.43. Using rate limiting
+ 44.44. Address verification
+ 44.45. Callout verification
+ 44.46. Additional parameters for callouts
+ 44.47. Callout caching
+ 44.48. Sender address verification reporting
+ 44.49. Redirection while verifying
+ 44.50. Client SMTP authorization (CSA)
+ 44.51. Bounce address tag validation
+ 44.52. Using an ACL to control relaying
+ 44.53. Checking a relay configuration
+
+45. Content scanning at ACL time
+
+ 45.1. Scanning for viruses
+ 45.2. Scanning with SpamAssassin and Rspamd
+ 45.3. Calling SpamAssassin from an Exim ACL
+ 45.4. Scanning MIME parts
+ 45.5. Scanning with regular expressions
+
+46. Adding a local scan function to Exim
+
+ 46.1. Building Exim to use a local scan function
+ 46.2. API for local_scan()
+ 46.3. Configuration options for local_scan()
+ 46.4. Available Exim variables
+ 46.5. Structure of header lines
+ 46.6. Structure of recipient items
+ 46.7. Available Exim functions
+ 46.8. More about Exim's memory handling
+
+47. System-wide message filtering
+
+ 47.1. Specifying a system filter
+ 47.2. Testing a system filter
+ 47.3. Contents of a system filter
+ 47.4. Additional variable for system filters
+ 47.5. Defer, freeze, and fail commands for system filters
+ 47.6. Adding and removing headers in a system filter
+ 47.7. Setting an errors address in a system filter
+ 47.8. Per-address filtering
+
+48. Message processing
+
+ 48.1. Submission mode for non-local messages
+ 48.2. Line endings
+ 48.3. Unqualified addresses
+ 48.4. The UUCP From line
+ 48.5. Resent- header lines
+ 48.6. The Auto-Submitted: header line
+ 48.7. The Bcc: header line
+ 48.8. The Date: header line
+ 48.9. The Delivery-date: header line
+ 48.10. The Envelope-to: header line
+ 48.11. The From: header line
+ 48.12. The Message-ID: header line
+ 48.13. The Received: header line
+ 48.14. The References: header line
+ 48.15. The Return-path: header line
+ 48.16. The Sender: header line
+ 48.17. Adding and removing header lines in routers and transports
+ 48.18. Constructed addresses
+ 48.19. Case of local parts
+ 48.20. Dots in local parts
+ 48.21. Rewriting addresses
+
+49. SMTP processing
+
+ 49.1. Outgoing SMTP and LMTP over TCP/IP
+ 49.2. Errors in outgoing SMTP
+ 49.3. Incoming SMTP messages over TCP/IP
+ 49.4. Unrecognized SMTP commands
+ 49.5. Syntax and protocol errors in SMTP commands
+ 49.6. Use of non-mail SMTP commands
+ 49.7. The VRFY and EXPN commands
+ 49.8. The ETRN command
+ 49.9. Incoming local SMTP
+ 49.10. Outgoing batched SMTP
+ 49.11. Incoming batched SMTP
+
+50. Customizing bounce and warning messages
+
+ 50.1. Customizing bounce messages
+ 50.2. Customizing warning messages
+
+51. Some common configuration settings
+
+ 51.1. Sending mail to a smart host
+ 51.2. Using Exim to handle mailing lists
+ 51.3. Syntax errors in mailing lists
+ 51.4. Re-expansion of mailing lists
+ 51.5. Closed mailing lists
+ 51.6. Variable Envelope Return Paths (VERP)
+ 51.7. Virtual domains
+ 51.8. Multiple user mailboxes
+ 51.9. Simplified vacation processing
+ 51.10. Taking copies of mail
+ 51.11. Intermittently connected hosts
+ 51.12. Exim on the upstream server host
+ 51.13. Exim on the intermittently connected client host
+
+52. Using Exim as a non-queueing client
+53. Log files
+
+ 53.1. Where the logs are written
+ 53.2. Logging to local files that are periodically "cycled"
+ 53.3. Datestamped log files
+ 53.4. Logging to syslog
+ 53.5. Log line flags
+ 53.6. Logging message reception
+ 53.7. Logging deliveries
+ 53.8. Discarded deliveries
+ 53.9. Deferred deliveries
+ 53.10. Delivery failures
+ 53.11. Fake deliveries
+ 53.12. Completion
+ 53.13. Summary of Fields in Log Lines
+ 53.14. Other log entries
+ 53.15. Reducing or increasing what is logged
+ 53.16. Message log
+
+54. Exim utilities
+
+ 54.1. Finding out what Exim processes are doing (exiwhat)
+ 54.2. Selective queue listing (exiqgrep)
+ 54.3. Summarizing the queue (exiqsumm)
+ 54.4. Extracting specific information from the log (exigrep)
+ 54.5. Selecting messages by various criteria (exipick)
+ 54.6. Cycling log files (exicyclog)
+ 54.7. Mail statistics (eximstats)
+ 54.8. Checking access policy (exim_checkaccess)
+ 54.9. Making DBM files (exim_dbmbuild)
+ 54.10. Finding individual retry times (exinext)
+ 54.11. Hints database maintenance
+ 54.12. exim_dumpdb
+ 54.13. exim_tidydb
+ 54.14. exim_fixdb
+ 54.15. Mailbox maintenance (exim_lock)
+
+55. The Exim monitor
+
+ 55.1. Running the monitor
+ 55.2. The stripcharts
+ 55.3. Main action buttons
+ 55.4. The log display
+ 55.5. The queue display
+ 55.6. The queue menu
+
+56. Security considerations
+
+ 56.1. Building a more "hardened" Exim
+ 56.2. Root privilege
+ 56.3. Running Exim without privilege
+ 56.4. Delivering to local files
+ 56.5. Running local commands
+ 56.6. Trust in configuration data
+ 56.7. IPv4 source routing
+ 56.8. The VRFY, EXPN, and ETRN commands in SMTP
+ 56.9. Privileged users
+ 56.10. Spool files
+ 56.11. Use of argv[0]
+ 56.12. Use of %f formatting
+ 56.13. Embedded Exim path
+ 56.14. Dynamic module directory
+ 56.15. Use of sprintf()
+ 56.16. Use of debug_printf() and log_write()
+ 56.17. Use of strcat() and strcpy()
+
+57. Format of spool files
+
+ 57.1. Format of the -H file
+ 57.2. Format of the -D file
+
+58. DKIM, SPF and DMARC
+
+ 58.1. DKIM (DomainKeys Identified Mail)
+ 58.2. Signing outgoing messages
+ 58.3. Verifying DKIM signatures in incoming mail
+ 58.4. SPF (Sender Policy Framework)
+ 58.5. DMARC
+
+59. Proxies
+
+ 59.1. Inbound proxies
+ 59.2. Outbound proxies
+ 59.3. Logging
+
+60. Internationalisation
+
+ 60.1. MTA operations
+ 60.2. MDA operations
+
+61. Events
+62. Adding new drivers or lookup types
+
+
+
+===============================================================================
+1. INTRODUCTION
+
+Exim is a mail transfer agent (MTA) for hosts that are running Unix or
+Unix-like operating systems. It was designed on the assumption that it would be
+run on hosts that are permanently connected to the Internet. However, it can be
+used on intermittently connected hosts with suitable configuration adjustments.
+
+Configuration files currently exist for the following operating systems: AIX,
+BSD/OS (aka BSDI), Darwin (Mac OS X), DGUX, Dragonfly, FreeBSD, GNU/Hurd, GNU/
+Linux, HI-OSF (Hitachi), HI-UX, HP-UX, IRIX, MIPS RISCOS, NetBSD, OpenBSD,
+OpenUNIX, QNX, SCO, SCO SVR4.2 (aka UNIX-SV), Solaris (aka SunOS5), SunOS4,
+Tru64-Unix (formerly Digital UNIX, formerly DEC-OSF1), Ultrix, and UnixWare.
+Some of these operating systems are no longer current and cannot easily be
+tested, so the configuration files may no longer work in practice.
+
+There are also configuration files for compiling Exim in the Cygwin environment
+that can be installed on systems running Windows. However, this document does
+not contain any information about running Exim in the Cygwin environment.
+
+The terms and conditions for the use and distribution of Exim are contained in
+the file NOTICE. Exim is distributed under the terms of the GNU General Public
+Licence, a copy of which may be found in the file LICENCE.
+
+The use, supply, or promotion of Exim for the purpose of sending bulk,
+unsolicited electronic mail is incompatible with the basic aims of Exim, which
+revolve around the free provision of a service that enhances the quality of
+personal communications. The author of Exim regards indiscriminate mass-mailing
+as an antisocial, irresponsible abuse of the Internet.
+
+Exim owes a great deal to Smail 3 and its author, Ron Karr. Without the
+experience of running and working on the Smail 3 code, I could never have
+contemplated starting to write a new MTA. Many of the ideas and user interfaces
+were originally taken from Smail 3, though the actual code of Exim is entirely
+new, and has developed far beyond the initial concept.
+
+Many people, both in Cambridge and around the world, have contributed to the
+development and the testing of Exim, and to porting it to various operating
+systems. I am grateful to them all. The distribution now contains a file called
+ACKNOWLEDGMENTS, in which I have started recording the names of contributors.
+
+
+1.1 Exim documentation
+----------------------
+
+This edition of the Exim specification applies to version 4.94.2 of Exim.
+Substantive changes from the 4.93 edition are marked in some renditions of this
+document; this paragraph is so marked if the rendition is capable of showing a
+change indicator.
+
+This document is very much a reference manual; it is not a tutorial. The reader
+is expected to have some familiarity with the SMTP mail transfer protocol and
+with general Unix system administration. Although there are some discussions
+and examples in places, the information is mostly organized in a way that makes
+it easy to look up, rather than in a natural order for sequential reading.
+Furthermore, this manual aims to cover every aspect of Exim in detail,
+including a number of rarely-used, special-purpose features that are unlikely
+to be of very wide interest.
+
+An "easier" discussion of Exim which provides more in-depth explanatory,
+introductory, and tutorial material can be found in a book entitled The Exim
+SMTP Mail Server (second edition, 2007), published by UIT Cambridge (https://
+www.uit.co.uk/exim-book/).
+
+The book also contains a chapter that gives a general introduction to SMTP and
+Internet mail. Inevitably, however, the book is unlikely to be fully up-to-date
+with the latest release of Exim. (Note that the earlier book about Exim,
+published by O'Reilly, covers Exim 3, and many things have changed in Exim 4.)
+
+If you are using a Debian distribution of Exim, you will find information about
+Debian-specific features in the file /usr/share/doc/exim4-base/README.Debian.
+The command man update-exim.conf is another source of Debian-specific
+information.
+
+As Exim develops, there may be features in newer versions that have not yet
+made it into this document, which is updated only when the most significant
+digit of the fractional part of the version number changes. Specifications of
+new features that are not yet in this manual are placed in the file doc/
+NewStuff in the Exim distribution.
+
+Some features may be classified as "experimental". These may change
+incompatibly while they are developing, or even be withdrawn. For this reason,
+they are not documented in this manual. Information about experimental features
+can be found in the file doc/experimental.txt.
+
+All changes to Exim (whether new features, bug fixes, or other kinds of change)
+are noted briefly in the file called doc/ChangeLog.
+
+This specification itself is available as an ASCII file in doc/spec.txt so that
+it can easily be searched with a text editor. Other files in the doc directory
+are:
+
+OptionLists.txt list of all options in alphabetical order
+dbm.discuss.txt discussion about DBM libraries
+exim.8 a man page of Exim's command line options
+experimental.txt documentation of experimental features
+filter.txt specification of the filter language
+Exim3.upgrade upgrade notes from release 2 to release 3
+Exim4.upgrade upgrade notes from release 3 to release 4
+openssl.txt installing a current OpenSSL release
+
+The main specification and the specification of the filtering language are also
+available in other formats (HTML, PostScript, PDF, and Texinfo). Section 1.5
+below tells you how to get hold of these.
+
+
+1.2 FTP site and websites
+-------------------------
+
+The primary site for Exim source distributions is the exim.org FTP site,
+available over HTTPS, HTTP and FTP. These services, and the exim.org website,
+are hosted at the University of Cambridge.
+
+As well as Exim distribution tar files, the Exim website contains a number of
+differently formatted versions of the documentation. A recent addition to the
+online information is the Exim wiki (https://wiki.exim.org), which contains
+what used to be a separate FAQ, as well as various other examples, tips, and
+know-how that have been contributed by Exim users. The wiki site should always
+redirect to the correct place, which is currently provided by GitHub, and is
+open to editing by anyone with a GitHub account.
+
+An Exim Bugzilla exists at https://bugs.exim.org. You can use this to report
+bugs, and also to add items to the wish list. Please search first to check that
+you are not duplicating a previous entry. Please do not ask for configuration
+help in the bug-tracker.
+
+
+1.3 Mailing lists
+-----------------
+
+The following Exim mailing lists exist:
+
+exim-announce@exim.org Moderated, low volume announcements list
+exim-users@exim.org General discussion list
+exim-dev@exim.org Discussion of bugs, enhancements, etc.
+exim-cvs@exim.org Automated commit messages from the VCS
+
+You can subscribe to these lists, change your existing subscriptions, and view
+or search the archives via the mailing lists link on the Exim home page. If you
+are using a Debian distribution of Exim, you may wish to subscribe to the
+Debian-specific mailing list pkg-exim4-users@lists.alioth.debian.org via this
+web page:
+
+https://alioth-lists.debian.net/cgi-bin/mailman/listinfo/pkg-exim4-users
+
+Please ask Debian-specific questions on that list and not on the general Exim
+lists.
+
+
+1.4 Bug reports
+---------------
+
+Reports of obvious bugs can be emailed to bugs@exim.org or reported via the
+Bugzilla (https://bugs.exim.org). However, if you are unsure whether some
+behaviour is a bug or not, the best thing to do is to post a message to the
+exim-dev mailing list and have it discussed.
+
+
+1.5 Where to find the Exim distribution
+---------------------------------------
+
+The master distribution site for the Exim distribution is
+
+https://downloads.exim.org/
+
+The service is available over HTTPS, HTTP and FTP. We encourage people to
+migrate to HTTPS.
+
+The content served at https://downloads.exim.org/ is identical to the content
+served at https://ftp.exim.org/pub/exim and ftp://ftp.exim.org/pub/exim.
+
+If accessing via a hostname containing ftp, then the file references that
+follow are relative to the exim directories at these sites. If accessing via
+the hostname downloads then the subdirectories described here are top-level
+directories.
+
+There are now quite a number of independent mirror sites around the world.
+Those that I know about are listed in the file called Mirrors.
+
+Within the top exim directory there are subdirectories called exim3 (for
+previous Exim 3 distributions), exim4 (for the latest Exim 4 distributions),
+and Testing for testing versions. In the exim4 subdirectory, the current
+release can always be found in files called
+
+exim-n.nn.tar.xz
+exim-n.nn.tar.gz
+exim-n.nn.tar.bz2
+
+where n.nn is the highest such version number in the directory. The three files
+contain identical data; the only difference is the type of compression. The .xz
+file is usually the smallest, while the .gz file is the most portable to old
+systems.
+
+The distributions will be PGP signed by an individual key of the Release
+Coordinator. This key will have a uid containing an email address in the
+exim.org domain and will have signatures from other people, including other
+Exim maintainers. We expect that the key will be in the "strong set" of PGP
+keys. There should be a trust path to that key from the Exim Maintainer's PGP
+keys, a version of which can be found in the release directory in the file
+Exim-Maintainers-Keyring.asc. All keys used will be available in public
+keyserver pools, such as pool.sks-keyservers.net.
+
+At the time of the last update, releases were being made by Jeremy Harris and
+signed with key 0xBCE58C8CE41F32DF. Other recent keys used for signing are
+those of Heiko Schlittermann, 0x26101B62F69376CE, and of Phil Pennock,
+0x4D1E900E14C1CC04.
+
+The signatures for the tar bundles are in:
+
+exim-n.nn.tar.xz.asc
+exim-n.nn.tar.gz.asc
+exim-n.nn.tar.bz2.asc
+
+For each released version, the log of changes is made available in a separate
+file in the directory ChangeLogs so that it is possible to find out what has
+changed without having to download the entire distribution.
+
+The main distribution contains ASCII versions of this specification and other
+documentation; other formats of the documents are available in separate files
+inside the exim4 directory of the FTP site:
+
+exim-html-n.nn.tar.gz
+exim-pdf-n.nn.tar.gz
+exim-postscript-n.nn.tar.gz
+exim-texinfo-n.nn.tar.gz
+
+These tar files contain only the doc directory, not the complete distribution,
+and are also available in .bz2 and .xz forms.
+
+
+1.6 Limitations
+---------------
+
+ * Exim is designed for use as an Internet MTA, and therefore handles
+ addresses in RFC 2822 domain format only. It cannot handle UUCP "bang
+ paths", though simple two-component bang paths can be converted by a
+ straightforward rewriting configuration. This restriction does not prevent
+ Exim from being interfaced to UUCP as a transport mechanism, provided that
+ domain addresses are used.
+
+ * Exim insists that every address it handles has a domain attached. For
+ incoming local messages, domainless addresses are automatically qualified
+ with a configured domain value. Configuration options specify from which
+ remote systems unqualified addresses are acceptable. These are then
+ qualified on arrival.
+
+ * The only external transport mechanisms that are currently implemented are
+ SMTP and LMTP over a TCP/IP network (including support for IPv6). However,
+ a pipe transport is available, and there are facilities for writing
+ messages to files and pipes, optionally in batched SMTP format; these
+ facilities can be used to send messages to other transport mechanisms such
+ as UUCP, provided they can handle domain-style addresses. Batched SMTP
+ input is also catered for.
+
+ * Exim is not designed for storing mail for dial-in hosts. When the volumes
+ of such mail are large, it is better to get the messages "delivered" into
+ files (that is, off Exim's queue) and subsequently passed on to the dial-in
+ hosts by other means.
+
+ * Although Exim does have basic facilities for scanning incoming messages,
+ these are not comprehensive enough to do full virus or spam scanning. Such
+ operations are best carried out using additional specialized software
+ packages. If you compile Exim with the content-scanning extension,
+ straightforward interfaces to a number of common scanners are provided.
+
+
+1.7 Runtime configuration
+-------------------------
+
+Exim's runtime configuration is held in a single text file that is divided into
+a number of sections. The entries in this file consist of keywords and values,
+in the style of Smail 3 configuration files. A default configuration file which
+is suitable for simple online installations is provided in the distribution,
+and is described in chapter 7 below.
+
+
+1.8 Calling interface
+---------------------
+
+Like many MTAs, Exim has adopted the Sendmail command line interface so that it
+can be a straight replacement for /usr/lib/sendmail or /usr/sbin/sendmail when
+sending mail, but you do not need to know anything about Sendmail in order to
+run Exim. For actions other than sending messages, Sendmail-compatible options
+also exist, but those that produce output (for example, -bp, which lists the
+messages in the queue) do so in Exim's own format. There are also some
+additional options that are compatible with Smail 3, and some further options
+that are new to Exim. Chapter 5 documents all Exim's command line options. This
+information is automatically made into the man page that forms part of the Exim
+distribution.
+
+Control of messages in the queue can be done via certain privileged command
+line options. There is also an optional monitor program called eximon, which
+displays current information in an X window, and which contains a menu
+interface to Exim's command line administration options.
+
+
+1.9 Terminology
+---------------
+
+The body of a message is the actual data that the sender wants to transmit. It
+is the last part of a message and is separated from the header (see below) by a
+blank line.
+
+When a message cannot be delivered, it is normally returned to the sender in a
+delivery failure message or a "non-delivery report" (NDR). The term bounce is
+commonly used for this action, and the error reports are often called bounce
+messages. This is a convenient shorthand for "delivery failure error report".
+Such messages have an empty sender address in the message's envelope (see
+below) to ensure that they cannot themselves give rise to further bounce
+messages.
+
+The term default appears frequently in this manual. It is used to qualify a
+value which is used in the absence of any setting in the configuration. It may
+also qualify an action which is taken unless a configuration setting specifies
+otherwise.
+
+The term defer is used when the delivery of a message to a specific destination
+cannot immediately take place for some reason (a remote host may be down, or a
+user's local mailbox may be full). Such deliveries are deferred until a later
+time.
+
+The word domain is sometimes used to mean all but the first component of a
+host's name. It is not used in that sense here, where it normally refers to the
+part of an email address following the @ sign.
+
+A message in transit has an associated envelope, as well as a header and a
+body. The envelope contains a sender address (to which bounce messages should
+be delivered), and any number of recipient addresses. References to the sender
+or the recipients of a message usually mean the addresses in the envelope. An
+MTA uses these addresses for delivery, and for returning bounce messages, not
+the addresses that appear in the header lines.
+
+The header of a message is the first part of a message's text, consisting of a
+number of lines, each of which has a name such as From:, To:, Subject:, etc.
+Long header lines can be split over several text lines by indenting the
+continuations. The header is separated from the body by a blank line.
+
+The term local part, which is taken from RFC 2822, is used to refer to the part
+of an email address that precedes the @ sign. The part that follows the @ sign
+is called the domain or mail domain.
+
+The terms local delivery and remote delivery are used to distinguish delivery
+to a file or a pipe on the local host from delivery by SMTP over TCP/IP to
+another host. As far as Exim is concerned, all hosts other than the host it is
+running on are remote.
+
+Return path is another name that is used for the sender address in a message's
+envelope.
+
+The term queue is used to refer to the set of messages awaiting delivery
+because this term is in widespread use in the context of MTAs. However, in
+Exim's case, the reality is more like a pool than a queue, because there is
+normally no ordering of waiting messages.
+
+The term queue runner is used to describe a process that scans the queue and
+attempts to deliver those messages whose retry times have come. This term is
+used by other MTAs and also relates to the command runq, but in Exim the
+waiting messages are normally processed in an unpredictable order.
+
+The term spool directory is used for a directory in which Exim keeps the
+messages in its queue - that is, those that it is in the process of delivering.
+This should not be confused with the directory in which local mailboxes are
+stored, which is called a "spool directory" by some people. In the Exim
+documentation, "spool" is always used in the first sense.
+
+
+
+===============================================================================
+2. INCORPORATED CODE
+
+A number of pieces of external code are included in the Exim distribution.
+
+ * Regular expressions are supported in the main Exim program and in the Exim
+ monitor using the freely-distributable PCRE library, copyright (c)
+ University of Cambridge. The source to PCRE is no longer shipped with Exim,
+ so you will need to use the version of PCRE shipped with your system, or
+ obtain and install the full version of the library from ftp://
+ ftp.csx.cam.ac.uk/pub/software/programming/pcre.
+
+ * Support for the cdb (Constant DataBase) lookup method is provided by code
+ contributed by Nigel Metheringham of (at the time he contributed it) Planet
+ Online Ltd. The implementation is completely contained within the code of
+ Exim. It does not link against an external cdb library. The code contains
+ the following statements:
+
+ Copyright (c) 1998 Nigel Metheringham, Planet Online Ltd
+
+ This program is free software; you can redistribute it and/or modify it
+ under the terms of the GNU General Public License as published by the
+ Free Software Foundation; either version 2 of the License, or (at your
+ option) any later version. This code implements Dan Bernstein's
+ Constant DataBase (cdb) spec. Information, the spec and sample code for
+ cdb can be obtained from https://cr.yp.to/cdb.html. This implementation
+ borrows some code from Dan Bernstein's implementation (which has no
+ license restrictions applied to it).
+
+ * Client support for Microsoft's Secure Password Authentication is provided
+ by code contributed by Marc Prud'hommeaux. Server support was contributed
+ by Tom Kistner. This includes code taken from the Samba project, which is
+ released under the Gnu GPL.
+
+ * Support for calling the Cyrus pwcheck and saslauthd daemons is provided by
+ code taken from the Cyrus-SASL library and adapted by Alexander S.
+ Sabourenkov. The permission notice appears below, in accordance with the
+ conditions expressed therein.
+
+ Copyright (c) 2001 Carnegie Mellon University. All rights reserved.
+
+ Redistribution and use in source and binary forms, with or without
+ modification, are permitted provided that the following conditions are
+ met:
+
+ 1. Redistributions of source code must retain the above copyright
+ notice, this list of conditions and the following disclaimer.
+
+ 2. Redistributions in binary form must reproduce the above copyright
+ notice, this list of conditions and the following disclaimer in the
+ documentation and/or other materials provided with the
+ distribution.
+
+ 3. The name "Carnegie Mellon University" must not be used to endorse
+ or promote products derived from this software without prior
+ written permission. For permission or any other legal details,
+ please contact
+
+ Office of Technology Transfer
+ Carnegie Mellon University
+ 5000 Forbes Avenue
+ Pittsburgh, PA 15213-3890
+ (412) 268-4387, fax: (412) 268-7395
+ tech-transfer@andrew.cmu.edu
+
+ 4. Redistributions of any form whatsoever must retain the following
+ acknowledgment:
+
+ "This product includes software developed by Computing Services at
+ Carnegie Mellon University (https://www.cmu.edu/computing/."
+
+ CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO
+ THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ AND FITNESS, IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY BE LIABLE
+ FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
+ AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
+ OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
+ SOFTWARE.
+
+ * The Exim Monitor program, which is an X-Window application, includes
+ modified versions of the Athena StripChart and TextPop widgets. This code
+ is copyright by DEC and MIT, and their permission notice appears below, in
+ accordance with the conditions expressed therein.
+
+ Copyright 1987, 1988 by Digital Equipment Corporation, Maynard,
+ Massachusetts, and the Massachusetts Institute of Technology,
+ Cambridge, Massachusetts.
+
+ All Rights Reserved
+
+ Permission to use, copy, modify, and distribute this software and its
+ documentation for any purpose and without fee is hereby granted,
+ provided that the above copyright notice appear in all copies and that
+ both that copyright notice and this permission notice appear in
+ supporting documentation, and that the names of Digital or MIT not be
+ used in advertising or publicity pertaining to distribution of the
+ software without specific, written prior permission.
+
+ DIGITAL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+ INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
+ EVENT SHALL DIGITAL BE LIABLE FOR ANY SPECIAL, INDIRECT OR
+ CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
+ USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+ OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ PERFORMANCE OF THIS SOFTWARE.
+
+ * The DMARC implementation uses the OpenDMARC library which is Copyrighted by
+ The Trusted Domain Project. Portions of Exim source which use OpenDMARC
+ derived code are indicated in the respective source files. The full
+ OpenDMARC license is provided in the LICENSE.opendmarc file contained in
+ the distributed source code.
+
+ * Many people have contributed code fragments, some large, some small, that
+ were not covered by any specific license requirements. It is assumed that
+ the contributors are happy to see their code incorporated into Exim under
+ the GPL.
+
+
+
+===============================================================================
+3. HOW EXIM RECEIVES AND DELIVERS MAIL
+
+
+3.1 Overall philosophy
+----------------------
+
+Exim is designed to work efficiently on systems that are permanently connected
+to the Internet and are handling a general mix of mail. In such circumstances,
+most messages can be delivered immediately. Consequently, Exim does not
+maintain independent queues of messages for specific domains or hosts, though
+it does try to send several messages in a single SMTP connection after a host
+has been down, and it also maintains per-host retry information.
+
+
+3.2 Policy control
+------------------
+
+Policy controls are now an important feature of MTAs that are connected to the
+Internet. Perhaps their most important job is to stop MTAs from being abused as
+"open relays" by misguided individuals who send out vast amounts of unsolicited
+junk and want to disguise its source. Exim provides flexible facilities for
+specifying policy controls on incoming mail:
+
+ * Exim 4 (unlike previous versions of Exim) implements policy controls on
+ incoming mail by means of Access Control Lists (ACLs). Each list is a
+ series of statements that may either grant or deny access. ACLs can be used
+ at several places in the SMTP dialogue while receiving a message from a
+ remote host. However, the most common places are after each RCPT command,
+ and at the very end of the message. The sysadmin can specify conditions for
+ accepting or rejecting individual recipients or the entire message,
+ respectively, at these two points (see chapter 44). Denial of access
+ results in an SMTP error code.
+
+ * An ACL is also available for locally generated, non-SMTP messages. In this
+ case, the only available actions are to accept or deny the entire message.
+
+ * When Exim is compiled with the content-scanning extension, facilities are
+ provided in the ACL mechanism for passing the message to external virus and
+ /or spam scanning software. The result of such a scan is passed back to the
+ ACL, which can then use it to decide what to do with the message.
+
+ * When a message has been received, either from a remote host or from the
+ local host, but before the final acknowledgment has been sent, a locally
+ supplied C function called local_scan() can be run to inspect the message
+ and decide whether to accept it or not (see chapter 46). If the message is
+ accepted, the list of recipients can be modified by the function.
+
+ * Using the local_scan() mechanism is another way of calling external scanner
+ software. The SA-Exim add-on package works this way. It does not require
+ Exim to be compiled with the content-scanning extension.
+
+ * After a message has been accepted, a further checking mechanism is
+ available in the form of the system filter (see chapter 47). This runs at
+ the start of every delivery process.
+
+
+3.3 User filters
+----------------
+
+In a conventional Exim configuration, users are able to run private filters by
+setting up appropriate .forward files in their home directories. See chapter 22
+(about the redirect router) for the configuration needed to support this, and
+the separate document entitled Exim's interfaces to mail filtering for user
+details. Two different kinds of filtering are available:
+
+ * Sieve filters are written in the standard filtering language that is
+ defined by RFC 3028.
+
+ * Exim filters are written in a syntax that is unique to Exim, but which is
+ more powerful than Sieve, which it pre-dates.
+
+User filters are run as part of the routing process, described below.
+
+
+3.4 Message identification
+--------------------------
+
+Every message handled by Exim is given a message id which is sixteen characters
+long. It is divided into three parts, separated by hyphens, for example
+"16VDhn-0001bo-D3". Each part is a sequence of letters and digits, normally
+encoding numbers in base 62. However, in the Darwin operating system (Mac OS X)
+and when Exim is compiled to run under Cygwin, base 36 (avoiding the use of
+lower case letters) is used instead, because the message id is used to
+construct filenames, and the names of files in those systems are not always
+case-sensitive.
+
+The detail of the contents of the message id have changed as Exim has evolved.
+Earlier versions relied on the operating system not re-using a process id (pid)
+within one second. On modern operating systems, this assumption can no longer
+be made, so the algorithm had to be changed. To retain backward compatibility,
+the format of the message id was retained, which is why the following rules are
+somewhat eccentric:
+
+ * The first six characters of the message id are the time at which the
+ message started to be received, to a granularity of one second. That is,
+ this field contains the number of seconds since the start of the epoch (the
+ normal Unix way of representing the date and time of day).
+
+ * After the first hyphen, the next six characters are the id of the process
+ that received the message.
+
+ * There are two different possibilities for the final two characters:
+
+ 1. If localhost_number is not set, this value is the fractional part of
+ the time of reception, normally in units of 1/2000 of a second, but for
+ systems that must use base 36 instead of base 62 (because of
+ case-insensitive file systems), the units are 1/1000 of a second.
+
+ 2. If localhost_number is set, it is multiplied by 200 (100) and added to
+ the fractional part of the time, which in this case is in units of 1/
+ 200 (1/100) of a second.
+
+After a message has been received, Exim waits for the clock to tick at the
+appropriate resolution before proceeding, so that if another message is
+received by the same process, or by another process with the same (re-used)
+pid, it is guaranteed that the time will be different. In most cases, the clock
+will already have ticked while the message was being received.
+
+
+3.5 Receiving mail
+------------------
+
+The only way Exim can receive mail from another host is using SMTP over TCP/IP,
+in which case the sender and recipient addresses are transferred using SMTP
+commands. However, from a locally running process (such as a user's MUA), there
+are several possibilities:
+
+ * If the process runs Exim with the -bm option, the message is read
+ non-interactively (usually via a pipe), with the recipients taken from the
+ command line, or from the body of the message if -t is also used.
+
+ * If the process runs Exim with the -bS option, the message is also read
+ non-interactively, but in this case the recipients are listed at the start
+ of the message in a series of SMTP RCPT commands, terminated by a DATA
+ command. This is called "batch SMTP" format, but it isn't really SMTP. The
+ SMTP commands are just another way of passing envelope addresses in a
+ non-interactive submission.
+
+ * If the process runs Exim with the -bs option, the message is read
+ interactively, using the SMTP protocol. A two-way pipe is normally used for
+ passing data between the local process and the Exim process. This is "real"
+ SMTP and is handled in the same way as SMTP over TCP/IP. For example, the
+ ACLs for SMTP commands are used for this form of submission.
+
+ * A local process may also make a TCP/IP call to the host's loopback address
+ (127.0.0.1) or any other of its IP addresses. When receiving messages, Exim
+ does not treat the loopback address specially. It treats all such
+ connections in the same way as connections from other hosts.
+
+In the three cases that do not involve TCP/IP, the sender address is
+constructed from the login name of the user that called Exim and a default
+qualification domain (which can be set by the qualify_domain configuration
+option). For local or batch SMTP, a sender address that is passed using the
+SMTP MAIL command is ignored. However, the system administrator may allow
+certain users ("trusted users") to specify a different sender addresses
+unconditionally, or all users to specify certain forms of different sender
+address. The -f option or the SMTP MAIL command is used to specify these
+different addresses. See section 5.2 for details of trusted users, and the
+untrusted_set_sender option for a way of allowing untrusted users to change
+sender addresses.
+
+Messages received by either of the non-interactive mechanisms are subject to
+checking by the non-SMTP ACL if one is defined. Messages received using SMTP
+(either over TCP/IP or interacting with a local process) can be checked by a
+number of ACLs that operate at different times during the SMTP session. Either
+individual recipients or the entire message can be rejected if local policy
+requirements are not met. The local_scan() function (see chapter 46) is run for
+all incoming messages.
+
+Exim can be configured not to start a delivery process when a message is
+received; this can be unconditional, or depend on the number of incoming SMTP
+connections or the system load. In these situations, new messages wait on the
+queue until a queue runner process picks them up. However, in standard
+configurations under normal conditions, delivery is started as soon as a
+message is received.
+
+
+3.6 Handling an incoming message
+--------------------------------
+
+When Exim accepts a message, it writes two files in its spool directory. The
+first contains the envelope information, the current status of the message, and
+the header lines, and the second contains the body of the message. The names of
+the two spool files consist of the message id, followed by "-H" for the file
+containing the envelope and header, and "-D" for the data file.
+
+By default, all these message files are held in a single directory called input
+inside the general Exim spool directory. Some operating systems do not perform
+very well if the number of files in a directory gets large; to improve
+performance in such cases, the split_spool_directory option can be used. This
+causes Exim to split up the input files into 62 sub-directories whose names are
+single letters or digits. When this is done, the queue is processed one
+sub-directory at a time instead of all at once, which can improve overall
+performance even when there are not enough files in each directory to affect
+file system performance.
+
+The envelope information consists of the address of the message's sender and
+the addresses of the recipients. This information is entirely separate from any
+addresses contained in the header lines. The status of the message includes a
+list of recipients who have already received the message. The format of the
+first spool file is described in chapter 57.
+
+Address rewriting that is specified in the rewrite section of the configuration
+(see chapter 31) is done once and for all on incoming addresses, both in the
+header lines and the envelope, at the time the message is accepted. If during
+the course of delivery additional addresses are generated (for example, via
+aliasing), these new addresses are rewritten as soon as they are generated. At
+the time a message is actually delivered (transported) further rewriting can
+take place; because this is a transport option, it can be different for
+different forms of delivery. It is also possible to specify the addition or
+removal of certain header lines at the time the message is delivered (see
+chapters 15 and 24).
+
+
+3.7 Life of a message
+---------------------
+
+A message remains in the spool directory until it is completely delivered to
+its recipients or to an error address, or until it is deleted by an
+administrator or by the user who originally created it. In cases when delivery
+cannot proceed - for example when a message can neither be delivered to its
+recipients nor returned to its sender, the message is marked "frozen" on the
+spool, and no more deliveries are attempted.
+
+An administrator can "thaw" such messages when the problem has been corrected,
+and can also freeze individual messages by hand if necessary. In addition, an
+administrator can force a delivery error, causing a bounce message to be sent.
+
+There are options called ignore_bounce_errors_after and timeout_frozen_after,
+which discard frozen messages after a certain time. The first applies only to
+frozen bounces, the second to all frozen messages.
+
+While Exim is working on a message, it writes information about each delivery
+attempt to its main log file. This includes successful, unsuccessful, and
+delayed deliveries for each recipient (see chapter 53). The log lines are also
+written to a separate message log file for each message. These logs are solely
+for the benefit of the administrator and are normally deleted along with the
+spool files when processing of a message is complete. The use of individual
+message logs can be disabled by setting no_message_logs; this might give an
+improvement in performance on very busy systems.
+
+All the information Exim itself needs to set up a delivery is kept in the first
+spool file, along with the header lines. When a successful delivery occurs, the
+address is immediately written at the end of a journal file, whose name is the
+message id followed by "-J". At the end of a delivery run, if there are some
+addresses left to be tried again later, the first spool file (the "-H" file) is
+updated to indicate which these are, and the journal file is then deleted.
+Updating the spool file is done by writing a new file and renaming it, to
+minimize the possibility of data loss.
+
+Should the system or Exim crash after a successful delivery but before the
+spool file has been updated, the journal is left lying around. The next time
+Exim attempts to deliver the message, it reads the journal file and updates the
+spool file before proceeding. This minimizes the chances of double deliveries
+caused by crashes.
+
+
+3.8 Processing an address for delivery
+--------------------------------------
+
+The main delivery processing elements of Exim are called routers and transports
+, and collectively these are known as drivers. Code for a number of them is
+provided in the source distribution, and compile-time options specify which
+ones are included in the binary. Runtime options specify which ones are
+actually used for delivering messages.
+
+Each driver that is specified in the runtime configuration is an instance of
+that particular driver type. Multiple instances are allowed; for example, you
+can set up several different smtp transports, each with different option values
+that might specify different ports or different timeouts. Each instance has its
+own identifying name. In what follows we will normally use the instance name
+when discussing one particular instance (that is, one specific configuration of
+the driver), and the generic driver name when discussing the driver's features
+in general.
+
+A router is a driver that operates on an address, either determining how its
+delivery should happen, by assigning it to a specific transport, or converting
+the address into one or more new addresses (for example, via an alias file). A
+router may also explicitly choose to fail an address, causing it to be bounced.
+
+A transport is a driver that transmits a copy of the message from Exim's spool
+to some destination. There are two kinds of transport: for a local transport,
+the destination is a file or a pipe on the local host, whereas for a remote
+transport the destination is some other host. A message is passed to a specific
+transport as a result of successful routing. If a message has several
+recipients, it may be passed to a number of different transports.
+
+An address is processed by passing it to each configured router instance in
+turn, subject to certain preconditions, until a router accepts the address or
+specifies that it should be bounced. We will describe this process in more
+detail shortly. First, as a simple example, we consider how each recipient
+address in a message is processed in a small configuration of three routers.
+
+To make this a more concrete example, it is described in terms of some actual
+routers, but remember, this is only an example. You can configure Exim's
+routers in many different ways, and there may be any number of routers in a
+configuration.
+
+The first router that is specified in a configuration is often one that handles
+addresses in domains that are not recognized specifically by the local host.
+Typically these are addresses for arbitrary domains on the Internet. A
+precondition is set up which looks for the special domains known to the host
+(for example, its own domain name), and the router is run for addresses that do
+not match. Typically, this is a router that looks up domains in the DNS in
+order to find the hosts to which this address routes. If it succeeds, the
+address is assigned to a suitable SMTP transport; if it does not succeed, the
+router is configured to fail the address.
+
+The second router is reached only when the domain is recognized as one that
+"belongs" to the local host. This router does redirection - also known as
+aliasing and forwarding. When it generates one or more new addresses from the
+original, each of them is routed independently from the start. Otherwise, the
+router may cause an address to fail, or it may simply decline to handle the
+address, in which case the address is passed to the next router.
+
+The final router in many configurations is one that checks to see if the
+address belongs to a local mailbox. The precondition may involve a check to see
+if the local part is the name of a login account, or it may look up the local
+part in a file or a database. If its preconditions are not met, or if the
+router declines, we have reached the end of the routers. When this happens, the
+address is bounced.
+
+
+3.9 Processing an address for verification
+------------------------------------------
+
+As well as being used to decide how to deliver to an address, Exim's routers
+are also used for address verification. Verification can be requested as one of
+the checks to be performed in an ACL for incoming messages, on both sender and
+recipient addresses, and it can be tested using the -bv and -bvs command line
+options.
+
+When an address is being verified, the routers are run in "verify mode". This
+does not affect the way the routers work, but it is a state that can be
+detected. By this means, a router can be skipped or made to behave differently
+when verifying. A common example is a configuration in which the first router
+sends all messages to a message-scanning program unless they have been
+previously scanned. Thus, the first router accepts all addresses without any
+checking, making it useless for verifying. Normally, the no_verify option would
+be set for such a router, causing it to be skipped in verify mode.
+
+
+3.10 Running an individual router
+---------------------------------
+
+As explained in the example above, a number of preconditions are checked before
+running a router. If any are not met, the router is skipped, and the address is
+passed to the next router. When all the preconditions on a router are met, the
+router is run. What happens next depends on the outcome, which is one of the
+following:
+
+ * accept: The router accepts the address, and either assigns it to a
+ transport or generates one or more "child" addresses. Processing the
+ original address ceases unless the unseen option is set on the router. This
+ option can be used to set up multiple deliveries with different routing
+ (for example, for keeping archive copies of messages). When unseen is set,
+ the address is passed to the next router. Normally, however, an accept
+ return marks the end of routing.
+
+ Any child addresses generated by the router are processed independently,
+ starting with the first router by default. It is possible to change this by
+ setting the redirect_router option to specify which router to start at for
+ child addresses. Unlike pass_router (see below) the router specified by
+ redirect_router may be anywhere in the router configuration.
+
+ * pass: The router recognizes the address, but cannot handle it itself. It
+ requests that the address be passed to another router. By default, the
+ address is passed to the next router, but this can be changed by setting
+ the pass_router option. However, (unlike redirect_router) the named router
+ must be below the current router (to avoid loops).
+
+ * decline: The router declines to accept the address because it does not
+ recognize it at all. By default, the address is passed to the next router,
+ but this can be prevented by setting the no_more option. When no_more is
+ set, all the remaining routers are skipped. In effect, no_more converts
+ decline into fail.
+
+ * fail: The router determines that the address should fail, and queues it for
+ the generation of a bounce message. There is no further processing of the
+ original address unless unseen is set on the router.
+
+ * defer: The router cannot handle the address at the present time. (A
+ database may be offline, or a DNS lookup may have timed out.) No further
+ processing of the address happens in this delivery attempt. It is tried
+ again next time the message is considered for delivery.
+
+ * error: There is some error in the router (for example, a syntax error in
+ its configuration). The action is as for defer.
+
+If an address reaches the end of the routers without having been accepted by
+any of them, it is bounced as unrouteable. The default error message in this
+situation is "unrouteable address", but you can set your own message by making
+use of the cannot_route_message option. This can be set for any router; the
+value from the last router that "saw" the address is used.
+
+Sometimes while routing you want to fail a delivery when some conditions are
+met but others are not, instead of passing the address on for further routing.
+You can do this by having a second router that explicitly fails the delivery
+when the relevant conditions are met. The redirect router has a "fail" facility
+for this purpose.
+
+
+3.11 Duplicate addresses
+------------------------
+
+Once routing is complete, Exim scans the addresses that are assigned to local
+and remote transports and discards any duplicates that it finds. During this
+check, local parts are treated case-sensitively. This happens only when
+actually delivering a message; when testing routers with -bt, all the routed
+addresses are shown.
+
+
+3.12 Router preconditions
+-------------------------
+
+The preconditions that are tested for each router are listed below, in the
+order in which they are tested. The individual configuration options are
+described in more detail in chapter 15.
+
+ * The local_part_prefix and local_part_suffix options can specify that the
+ local parts handled by the router may or must have certain prefixes and/or
+ suffixes. If a mandatory affix (prefix or suffix) is not present, the
+ router is skipped. These conditions are tested first. When an affix is
+ present, it is removed from the local part before further processing,
+ including the evaluation of any other conditions.
+
+ * Routers can be designated for use only when not verifying an address, that
+ is, only when routing it for delivery (or testing its delivery routing). If
+ the verify option is set false, the router is skipped when Exim is
+ verifying an address. Setting the verify option actually sets two options,
+ verify_sender and verify_recipient, which independently control the use of
+ the router for sender and recipient verification. You can set these options
+ directly if you want a router to be used for only one type of verification.
+ Note that cutthrough delivery is classed as a recipient verification for
+ this purpose.
+
+ * If the address_test option is set false, the router is skipped when Exim is
+ run with the -bt option to test an address routing. This can be helpful
+ when the first router sends all new messages to a scanner of some sort; it
+ makes it possible to use -bt to test subsequent delivery routing without
+ having to simulate the effect of the scanner.
+
+ * Routers can be designated for use only when verifying an address, as
+ opposed to routing it for delivery. The verify_only option controls this.
+ Again, cutthrough delivery counts as a verification.
+
+ * Individual routers can be explicitly skipped when running the routers to
+ check an address given in the SMTP EXPN command (see the expn option).
+
+ * If the domains option is set, the domain of the address must be in the set
+ of domains that it defines.
+
+ * If the local_parts option is set, the local part of the address must be in
+ the set of local parts that it defines. If local_part_prefix or
+ local_part_suffix is in use, the prefix or suffix is removed from the local
+ part before this check. If you want to do precondition tests on local parts
+ that include affixes, you can do so by using a condition option (see below)
+
+ that uses the variables $local_part, $local_part_prefix,
+ $local_part_prefix_v, $local_part_suffix and $local_part_suffix_v as
+ necessary.
+
+ * If the check_local_user option is set, the local part must be the name of
+ an account on the local host. If this check succeeds, the uid and gid of
+ the local user are placed in $local_user_uid and $local_user_gid and the
+ user's home directory is placed in $home; these values can be used in the
+ remaining preconditions.
+
+ * If the router_home_directory option is set, it is expanded at this point,
+ because it overrides the value of $home. If this expansion were left till
+ later, the value of $home as set by check_local_user would be used in
+ subsequent tests. Having two different values of $home in the same router
+ could lead to confusion.
+
+ * If the senders option is set, the envelope sender address must be in the
+ set of addresses that it defines.
+
+ * If the require_files option is set, the existence or non-existence of
+ specified files is tested.
+
+ * If the condition option is set, it is evaluated and tested. This option
+ uses an expanded string to allow you to set up your own custom
+ preconditions. Expanded strings are described in chapter 11.
+
+Note that require_files comes near the end of the list, so you cannot use it to
+check for the existence of a file in which to lookup up a domain, local part,
+or sender. However, as these options are all expanded, you can use the exists
+expansion condition to make such tests within each condition. The require_files
+option is intended for checking files that the router may be going to use
+internally, or which are needed by a specific transport (for example,
+.procmailrc).
+
+
+3.13 Delivery in detail
+-----------------------
+
+When a message is to be delivered, the sequence of events is as follows:
+
+ * If a system-wide filter file is specified, the message is passed to it. The
+ filter may add recipients to the message, replace the recipients, discard
+ the message, cause a new message to be generated, or cause the message
+ delivery to fail. The format of the system filter file is the same as for
+ Exim user filter files, described in the separate document entitled Exim's
+ interfaces to mail filtering. (Note: Sieve cannot be used for system filter
+ files.)
+
+ Some additional features are available in system filters - see chapter 47
+ for details. Note that a message is passed to the system filter only once
+ per delivery attempt, however many recipients it has. However, if there are
+ several delivery attempts because one or more addresses could not be
+ immediately delivered, the system filter is run each time. The filter
+ condition first_delivery can be used to detect the first run of the system
+ filter.
+
+ * Each recipient address is offered to each configured router, in turn,
+ subject to its preconditions, until one is able to handle it. If no router
+ can handle the address, that is, if they all decline, the address is
+ failed. Because routers can be targeted at particular domains, several
+ locally handled domains can be processed entirely independently of each
+ other.
+
+ * A router that accepts an address may assign it to a local or a remote
+ transport. However, the transport is not run at this time. Instead, the
+ address is placed on a list for the particular transport, which will be run
+ later. Alternatively, the router may generate one or more new addresses
+ (typically from alias, forward, or filter files). New addresses are fed
+ back into this process from the top, but in order to avoid loops, a router
+ ignores any address which has an identically-named ancestor that was
+ processed by itself.
+
+ * When all the routing has been done, addresses that have been successfully
+ handled are passed to their assigned transports. When local transports are
+ doing real local deliveries, they handle only one address at a time, but if
+ a local transport is being used as a pseudo-remote transport (for example,
+ to collect batched SMTP messages for transmission by some other means)
+ multiple addresses can be handled. Remote transports can always handle more
+ than one address at a time, but can be configured not to do so, or to
+ restrict multiple addresses to the same domain.
+
+ * Each local delivery to a file or a pipe runs in a separate process under a
+ non-privileged uid, and these deliveries are run one at a time. Remote
+ deliveries also run in separate processes, normally under a uid that is
+ private to Exim ("the Exim user"), but in this case, several remote
+ deliveries can be run in parallel. The maximum number of simultaneous
+ remote deliveries for any one message is set by the remote_max_parallel
+ option. The order in which deliveries are done is not defined, except that
+ all local deliveries happen before any remote deliveries.
+
+ * When it encounters a local delivery during a queue run, Exim checks its
+ retry database to see if there has been a previous temporary delivery
+ failure for the address before running the local transport. If there was a
+ previous failure, Exim does not attempt a new delivery until the retry time
+ for the address is reached. However, this happens only for delivery
+ attempts that are part of a queue run. Local deliveries are always
+ attempted when delivery immediately follows message reception, even if
+ retry times are set for them. This makes for better behaviour if one
+ particular message is causing problems (for example, causing quota
+ overflow, or provoking an error in a filter file).
+
+ * Remote transports do their own retry handling, since an address may be
+ deliverable to one of a number of hosts, each of which may have a different
+ retry time. If there have been previous temporary failures and no host has
+ reached its retry time, no delivery is attempted, whether in a queue run or
+ not. See chapter 32 for details of retry strategies.
+
+ * If there were any permanent errors, a bounce message is returned to an
+ appropriate address (the sender in the common case), with details of the
+ error for each failing address. Exim can be configured to send copies of
+ bounce messages to other addresses.
+
+ * If one or more addresses suffered a temporary failure, the message is left
+ on the queue, to be tried again later. Delivery of these addresses is said
+ to be deferred.
+
+ * When all the recipient addresses have either been delivered or bounced,
+ handling of the message is complete. The spool files and message log are
+ deleted, though the message log can optionally be preserved if required.
+
+
+3.14 Retry mechanism
+--------------------
+
+Exim's mechanism for retrying messages that fail to get delivered at the first
+attempt is the queue runner process. You must either run an Exim daemon that
+uses the -q option with a time interval to start queue runners at regular
+intervals or use some other means (such as cron) to start them. If you do not
+arrange for queue runners to be run, messages that fail temporarily at the
+first attempt will remain in your queue forever. A queue runner process works
+its way through the queue, one message at a time, trying each delivery that has
+passed its retry time. You can run several queue runners at once.
+
+Exim uses a set of configured rules to determine when next to retry the failing
+address (see chapter 32). These rules also specify when Exim should give up
+trying to deliver to the address, at which point it generates a bounce message.
+If no retry rules are set for a particular host, address, and error
+combination, no retries are attempted, and temporary errors are treated as
+permanent.
+
+
+3.15 Temporary delivery failure
+-------------------------------
+
+There are many reasons why a message may not be immediately deliverable to a
+particular address. Failure to connect to a remote machine (because it, or the
+connection to it, is down) is one of the most common. Temporary failures may be
+detected during routing as well as during the transport stage of delivery.
+Local deliveries may be delayed if NFS files are unavailable, or if a mailbox
+is on a file system where the user is over quota. Exim can be configured to
+impose its own quotas on local mailboxes; where system quotas are set they will
+also apply.
+
+If a host is unreachable for a period of time, a number of messages may be
+waiting for it by the time it recovers, and sending them in a single SMTP
+connection is clearly beneficial. Whenever a delivery to a remote host is
+deferred, Exim makes a note in its hints database, and whenever a successful
+SMTP delivery has happened, it looks to see if any other messages are waiting
+for the same host. If any are found, they are sent over the same SMTP
+connection, subject to a configuration limit as to the maximum number in any
+one connection.
+
+
+3.16 Permanent delivery failure
+-------------------------------
+
+When a message cannot be delivered to some or all of its intended recipients, a
+bounce message is generated. Temporary delivery failures turn into permanent
+errors when their timeout expires. All the addresses that fail in a given
+delivery attempt are listed in a single message. If the original message has
+many recipients, it is possible for some addresses to fail in one delivery
+attempt and others to fail subsequently, giving rise to more than one bounce
+message. The wording of bounce messages can be customized by the administrator.
+See chapter 50 for details.
+
+Bounce messages contain an X-Failed-Recipients: header line that lists the
+failed addresses, for the benefit of programs that try to analyse such messages
+automatically.
+
+A bounce message is normally sent to the sender of the original message, as
+obtained from the message's envelope. For incoming SMTP messages, this is the
+address given in the MAIL command. However, when an address is expanded via a
+forward or alias file, an alternative address can be specified for delivery
+failures of the generated addresses. For a mailing list expansion (see section
+51.2) it is common to direct bounce messages to the manager of the list.
+
+
+3.17 Failures to deliver bounce messages
+----------------------------------------
+
+If a bounce message (either locally generated or received from a remote host)
+itself suffers a permanent delivery failure, the message is left in the queue,
+but it is frozen, awaiting the attention of an administrator. There are options
+that can be used to make Exim discard such failed messages, or to keep them for
+only a short time (see timeout_frozen_after and ignore_bounce_errors_after).
+
+
+
+===============================================================================
+4. BUILDING AND INSTALLING EXIM
+
+
+4.1 Unpacking
+-------------
+
+Exim is distributed as a gzipped or bzipped tar file which, when unpacked,
+creates a directory with the name of the current release (for example,
+exim-4.94.2) into which the following files are placed:
+
+ ACKNOWLEDGMENTS contains some acknowledgments
+ CHANGES contains a reference to where changes are documented
+ LICENCE the GNU General Public Licence
+ Makefile top-level make file
+ NOTICE conditions for the use of Exim
+ README list of files, directories and simple build instructions
+
+Other files whose names begin with README may also be present. The following
+subdirectories are created:
+
+ Local an empty directory for local configuration files
+ OS OS-specific files
+ doc documentation files
+ exim_monitor source files for the Exim monitor
+ scripts scripts used in the build process
+ src remaining source files
+ util independent utilities
+
+The main utility programs are contained in the src directory and are built with
+the Exim binary. The util directory contains a few optional scripts that may be
+useful to some sites.
+
+
+4.2 Multiple machine architectures and operating systems
+--------------------------------------------------------
+
+The building process for Exim is arranged to make it easy to build binaries for
+a number of different architectures and operating systems from the same set of
+source files. Compilation does not take place in the src directory. Instead, a
+build directory is created for each architecture and operating system. Symbolic
+links to the sources are installed in this directory, which is where the actual
+building takes place. In most cases, Exim can discover the machine architecture
+and operating system for itself, but the defaults can be overridden if
+necessary. A C99-capable compiler will be required for the build.
+
+
+4.3 PCRE library
+----------------
+
+Exim no longer has an embedded PCRE library as the vast majority of modern
+systems include PCRE as a system library, although you may need to install the
+PCRE package or the PCRE development package for your operating system. If your
+system has a normal PCRE installation the Exim build process will need no
+further configuration. If the library or the headers are in an unusual location
+you will need to either set the PCRE_LIBS and INCLUDE directives appropriately,
+or set PCRE_CONFIG=yes to use the installed pcre-config command. If your
+operating system has no PCRE support then you will need to obtain and build the
+current PCRE from ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/. More
+information on PCRE is available at https://www.pcre.org/.
+
+
+4.4 DBM libraries
+-----------------
+
+Even if you do not use any DBM files in your configuration, Exim still needs a
+DBM library in order to operate, because it uses indexed files for its hints
+databases. Unfortunately, there are a number of DBM libraries in existence, and
+different operating systems often have different ones installed.
+
+If you are using Solaris, IRIX, one of the modern BSD systems, or a modern
+Linux distribution, the DBM configuration should happen automatically, and you
+may be able to ignore this section. Otherwise, you may have to learn more than
+you would like about DBM libraries from what follows.
+
+Licensed versions of Unix normally contain a library of DBM functions operating
+via the ndbm interface, and this is what Exim expects by default. Free versions
+of Unix seem to vary in what they contain as standard. In particular, some
+early versions of Linux have no default DBM library, and different distributors
+have chosen to bundle different libraries with their packaged versions.
+However, the more recent releases seem to have standardized on the Berkeley DB
+library.
+
+Different DBM libraries have different conventions for naming the files they
+use. When a program opens a file called dbmfile, there are several
+possibilities:
+
+ 1. A traditional ndbm implementation, such as that supplied as part of
+ Solaris, operates on two files called dbmfile.dir and dbmfile.pag.
+
+ 2. The GNU library, gdbm, operates on a single file. If used via its ndbm
+ compatibility interface it makes two different hard links to it with names
+ dbmfile.dir and dbmfile.pag, but if used via its native interface, the
+ filename is used unmodified.
+
+ 3. The Berkeley DB package, if called via its ndbm compatibility interface,
+ operates on a single file called dbmfile.db, but otherwise looks to the
+ programmer exactly the same as the traditional ndbm implementation.
+
+ 4. If the Berkeley package is used in its native mode, it operates on a single
+ file called dbmfile; the programmer's interface is somewhat different to
+ the traditional ndbm interface.
+
+ 5. To complicate things further, there are several very different versions of
+ the Berkeley DB package. Version 1.85 was stable for a very long time,
+ releases 2.x and 3.x were current for a while, but the latest versions when
+ Exim last revamped support were numbered 4.x. Maintenance of some of the
+ earlier releases has ceased. All versions of Berkeley DB could be obtained
+ from http://www.sleepycat.com/, which is now a redirect to their new
+ owner's page with far newer versions listed. It is probably wise to plan to
+ move your storage configurations away from Berkeley DB format, as today
+ there are smaller and simpler alternatives more suited to Exim's usage
+ model.
+
+ 6. Yet another DBM library, called tdb, is available from https://
+ sourceforge.net/projects/tdb/files/. It has its own interface, and also
+ operates on a single file.
+
+Exim and its utilities can be compiled to use any of these interfaces. In order
+to use any version of the Berkeley DB package in native mode, you must set
+USE_DB in an appropriate configuration file (typically Local/Makefile). For
+example:
+
+USE_DB=yes
+
+Similarly, for gdbm you set USE_GDBM, and for tdb you set USE_TDB. An error is
+diagnosed if you set more than one of these.
+
+At the lowest level, the build-time configuration sets none of these options,
+thereby assuming an interface of type (1). However, some operating system
+configuration files (for example, those for the BSD operating systems and
+Linux) assume type (4) by setting USE_DB as their default, and the
+configuration files for Cygwin set USE_GDBM. Anything you set in Local/Makefile
+, however, overrides these system defaults.
+
+As well as setting USE_DB, USE_GDBM, or USE_TDB, it may also be necessary to
+set DBMLIB, to cause inclusion of the appropriate library, as in one of these
+lines:
+
+DBMLIB = -ldb
+DBMLIB = -ltdb
+
+Settings like that will work if the DBM library is installed in the standard
+place. Sometimes it is not, and the library's header file may also not be in
+the default path. You may need to set INCLUDE to specify where the header file
+is, and to specify the path to the library more fully in DBMLIB, as in this
+example:
+
+INCLUDE=-I/usr/local/include/db-4.1
+DBMLIB=/usr/local/lib/db-4.1/libdb.a
+
+There is further detailed discussion about the various DBM libraries in the
+file doc/dbm.discuss.txt in the Exim distribution.
+
+
+4.5 Pre-building configuration
+------------------------------
+
+Before building Exim, a local configuration file that specifies options
+independent of any operating system has to be created with the name Local/
+Makefile. A template for this file is supplied as the file src/EDITME, and it
+contains full descriptions of all the option settings therein. These
+descriptions are therefore not repeated here. If you are building Exim for the
+first time, the simplest thing to do is to copy src/EDITME to Local/Makefile,
+then read it and edit it appropriately.
+
+There are three settings that you must supply, because Exim will not build
+without them. They are the location of the runtime configuration file
+(CONFIGURE_FILE), the directory in which Exim binaries will be installed
+(BIN_DIRECTORY), and the identity of the Exim user (EXIM_USER and maybe
+EXIM_GROUP as well). The value of CONFIGURE_FILE can in fact be a
+colon-separated list of filenames; Exim uses the first of them that exists.
+
+There are a few other parameters that can be specified either at build time or
+at runtime, to enable the same binary to be used on a number of different
+machines. However, if the locations of Exim's spool directory and log file
+directory (if not within the spool directory) are fixed, it is recommended that
+you specify them in Local/Makefile instead of at runtime, so that errors
+detected early in Exim's execution (such as a malformed configuration file) can
+be logged.
+
+Exim's interfaces for calling virus and spam scanning software directly from
+access control lists are not compiled by default. If you want to include these
+facilities, you need to set
+
+WITH_CONTENT_SCAN=yes
+
+in your Local/Makefile. For details of the facilities themselves, see chapter
+45.
+
+If you are going to build the Exim monitor, a similar configuration process is
+required. The file exim_monitor/EDITME must be edited appropriately for your
+installation and saved under the name Local/eximon.conf. If you are happy with
+the default settings described in exim_monitor/EDITME, Local/eximon.conf can be
+empty, but it must exist.
+
+This is all the configuration that is needed in straightforward cases for known
+operating systems. However, the building process is set up so that it is easy
+to override options that are set by default or by operating-system-specific
+configuration files, for example, to change the C compiler, which defaults to
+gcc. See section 4.13 below for details of how to do this.
+
+
+4.6 Support for iconv()
+-----------------------
+
+The contents of header lines in messages may be encoded according to the rules
+described RFC 2047. This makes it possible to transmit characters that are not
+in the ASCII character set, and to label them as being in a particular
+character set. When Exim is inspecting header lines by means of the $h_
+mechanism, it decodes them, and translates them into a specified character set
+(default is set at build time). The translation is possible only if the
+operating system supports the iconv() function.
+
+However, some of the operating systems that supply iconv() do not support very
+many conversions. The GNU libiconv library (available from https://www.gnu.org/
+software/libiconv/) can be installed on such systems to remedy this deficiency,
+as well as on systems that do not supply iconv() at all. After installing
+libiconv, you should add
+
+HAVE_ICONV=yes
+
+to your Local/Makefile and rebuild Exim.
+
+
+4.7 Including TLS/SSL encryption support
+----------------------------------------
+
+Exim is usually built to support encrypted SMTP connections, using the STARTTLS
+command as per RFC 2487. It can also support clients that expect to start a TLS
+session immediately on connection to a non-standard port (see the
+tls_on_connect_ports runtime option and the -tls-on-connect command line
+option).
+
+If you want to build Exim with TLS support, you must first install either the
+OpenSSL or GnuTLS library. There is no cryptographic code in Exim itself for
+implementing SSL.
+
+If you do not want TLS support you should set
+
+DISABLE_TLS=yes
+
+in Local/Makefile.
+
+If OpenSSL is installed, you should set
+
+USE_OPENSL=yes
+TLS_LIBS=-lssl -lcrypto
+
+in Local/Makefile. You may also need to specify the locations of the OpenSSL
+library and include files. For example:
+
+USE_OPENSSL=yes
+TLS_LIBS=-L/usr/local/openssl/lib -lssl -lcrypto
+TLS_INCLUDE=-I/usr/local/openssl/include/
+
+If you have pkg-config available, then instead you can just use:
+
+USE_OPENSSL=yes
+USE_OPENSSL_PC=openssl
+
+If GnuTLS is installed, you should set
+
+USE_GNUTLS=yes
+TLS_LIBS=-lgnutls -ltasn1 -lgcrypt
+
+in Local/Makefile, and again you may need to specify the locations of the
+library and include files. For example:
+
+USE_GNUTLS=yes
+TLS_LIBS=-L/usr/gnu/lib -lgnutls -ltasn1 -lgcrypt
+TLS_INCLUDE=-I/usr/gnu/include
+
+If you have pkg-config available, then instead you can just use:
+
+USE_GNUTLS=yes
+USE_GNUTLS_PC=gnutls
+
+You do not need to set TLS_INCLUDE if the relevant directory is already
+specified in INCLUDE. Details of how to configure Exim to make use of TLS are
+given in chapter 43.
+
+
+4.8 Use of tcpwrappers
+----------------------
+
+Exim can be linked with the tcpwrappers library in order to check incoming SMTP
+calls using the tcpwrappers control files. This may be a convenient alternative
+to Exim's own checking facilities for installations that are already making use
+of tcpwrappers for other purposes. To do this, you should set USE_TCP_WRAPPERS
+in Local/Makefile, arrange for the file tcpd.h to be available at compile time,
+and also ensure that the library libwrap.a is available at link time, typically
+by including -lwrap in EXTRALIBS_EXIM. For example, if tcpwrappers is installed
+in /usr/local, you might have
+
+USE_TCP_WRAPPERS=yes
+CFLAGS=-O -I/usr/local/include
+EXTRALIBS_EXIM=-L/usr/local/lib -lwrap
+
+in Local/Makefile. The daemon name to use in the tcpwrappers control files is
+"exim". For example, the line
+
+exim : LOCAL 192.168.1. .friendly.domain.example
+
+in your /etc/hosts.allow file allows connections from the local host, from the
+subnet 192.168.1.0/24, and from all hosts in friendly.domain.example. All other
+connections are denied. The daemon name used by tcpwrappers can be changed at
+build time by setting TCP_WRAPPERS_DAEMON_NAME in Local/Makefile, or by setting
+tcp_wrappers_daemon_name in the configure file. Consult the tcpwrappers
+documentation for further details.
+
+
+4.9 Including support for IPv6
+------------------------------
+
+Exim contains code for use on systems that have IPv6 support. Setting
+"HAVE_IPV6=YES" in Local/Makefile causes the IPv6 code to be included; it may
+also be necessary to set IPV6_INCLUDE and IPV6_LIBS on systems where the IPv6
+support is not fully integrated into the normal include and library files.
+
+Two different types of DNS record for handling IPv6 addresses have been
+defined. AAAA records (analogous to A records for IPv4) are in use, and are
+currently seen as the mainstream. Another record type called A6 was proposed as
+better than AAAA because it had more flexibility. However, it was felt to be
+over-complex, and its status was reduced to "experimental". Exim used to have a
+compile option for including A6 record support but this has now been withdrawn.
+
+
+4.10 Dynamically loaded lookup module support
+---------------------------------------------
+
+On some platforms, Exim supports not compiling all lookup types directly into
+the main binary, instead putting some into external modules which can be loaded
+on demand. This permits packagers to build Exim with support for lookups with
+extensive library dependencies without requiring all users to install all of
+those dependencies. Most, but not all, lookup types can be built this way.
+
+Set "LOOKUP_MODULE_DIR" to the directory into which the modules will be
+installed; Exim will only load modules from that directory, as a security
+measure. You will need to set "CFLAGS_DYNAMIC" if not already defined for your
+OS; see OS/Makefile-Linux for an example. Some other requirements for adjusting
+"EXTRALIBS" may also be necessary, see src/EDITME for details.
+
+Then, for each module to be loaded dynamically, define the relevant "LOOKUP_"<
+lookup_type> flags to have the value "2" instead of "yes". For example, this
+will build in lsearch but load sqlite and mysql support on demand:
+
+LOOKUP_LSEARCH=yes
+LOOKUP_SQLITE=2
+LOOKUP_MYSQL=2
+
+
+4.11 The building process
+-------------------------
+
+Once Local/Makefile (and Local/eximon.conf, if required) have been created, run
+make at the top level. It determines the architecture and operating system
+types, and creates a build directory if one does not exist. For example, on a
+Sun system running Solaris 8, the directory build-SunOS5-5.8-sparc is created.
+Symbolic links to relevant source files are installed in the build directory.
+
+If this is the first time make has been run, it calls a script that builds a
+make file inside the build directory, using the configuration files from the
+Local directory. The new make file is then passed to another instance of make.
+This does the real work, building a number of utility scripts, and then
+compiling and linking the binaries for the Exim monitor (if configured), a
+number of utility programs, and finally Exim itself. The command "make
+makefile" can be used to force a rebuild of the make file in the build
+directory, should this ever be necessary.
+
+If you have problems building Exim, check for any comments there may be in the
+README file concerning your operating system, and also take a look at the FAQ,
+where some common problems are covered.
+
+
+4.12 Output from "make"
+-----------------------
+
+The output produced by the make process for compile lines is often very
+unreadable, because these lines can be very long. For this reason, the normal
+output is suppressed by default, and instead output similar to that which
+appears when compiling the 2.6 Linux kernel is generated: just a short line for
+each module that is being compiled or linked. However, it is still possible to
+get the full output, by calling make like this:
+
+FULLECHO='' make -e
+
+The value of FULLECHO defaults to "@", the flag character that suppresses
+command reflection in make. When you ask for the full output, it is given in
+addition to the short output.
+
+
+4.13 Overriding build-time options for Exim
+-------------------------------------------
+
+The main make file that is created at the beginning of the building process
+consists of the concatenation of a number of files which set configuration
+values, followed by a fixed set of make instructions. If a value is set more
+than once, the last setting overrides any previous ones. This provides a
+convenient way of overriding defaults. The files that are concatenated are, in
+order:
+
+OS/Makefile-Default
+OS/Makefile-<ostype>
+Local/Makefile
+Local/Makefile-<ostype>
+Local/Makefile-<archtype>
+Local/Makefile-<ostype>-<archtype>
+OS/Makefile-Base
+
+where <ostype> is the operating system type and <archtype> is the architecture
+type. Local/Makefile is required to exist, and the building process fails if it
+is absent. The other three Local files are optional, and are often not needed.
+
+The values used for <ostype> and <archtype> are obtained from scripts called
+scripts/os-type and scripts/arch-type respectively. If either of the
+environment variables EXIM_OSTYPE or EXIM_ARCHTYPE is set, their values are
+used, thereby providing a means of forcing particular settings. Otherwise, the
+scripts try to get values from the uname command. If this fails, the shell
+variables OSTYPE and ARCHTYPE are inspected. A number of ad hoc transformations
+are then applied, to produce the standard names that Exim expects. You can run
+these scripts directly from the shell in order to find out what values are
+being used on your system.
+
+OS/Makefile-Default contains comments about the variables that are set therein.
+Some (but not all) are mentioned below. If there is something that needs
+changing, review the contents of this file and the contents of the make file
+for your operating system (OS/Makefile-<ostype>) to see what the default values
+are.
+
+If you need to change any of the values that are set in OS/Makefile-Default or
+in OS/Makefile-<ostype>, or to add any new definitions, you do not need to
+change the original files. Instead, you should make the changes by putting the
+new values in an appropriate Local file. For example, when building Exim in
+many releases of the Tru64-Unix (formerly Digital UNIX, formerly DEC-OSF1)
+operating system, it is necessary to specify that the C compiler is called cc
+rather than gcc. Also, the compiler must be called with the option -std1, to
+make it recognize some of the features of Standard C that Exim uses. (Most
+other compilers recognize Standard C by default.) To do this, you should create
+a file called Local/Makefile-OSF1 containing the lines
+
+CC=cc
+CFLAGS=-std1
+
+If you are compiling for just one operating system, it may be easier to put
+these lines directly into Local/Makefile.
+
+Keeping all your local configuration settings separate from the distributed
+files makes it easy to transfer them to new versions of Exim simply by copying
+the contents of the Local directory.
+
+Exim contains support for doing LDAP, NIS, NIS+, and other kinds of file
+lookup, but not all systems have these components installed, so the default is
+not to include the relevant code in the binary. All the different kinds of file
+and database lookup that Exim supports are implemented as separate code modules
+which are included only if the relevant compile-time options are set. In the
+case of LDAP, NIS, and NIS+, the settings for Local/Makefile are:
+
+LOOKUP_LDAP=yes
+LOOKUP_NIS=yes
+LOOKUP_NISPLUS=yes
+
+and similar settings apply to the other lookup types. They are all listed in
+src/EDITME. In many cases the relevant include files and interface libraries
+need to be installed before compiling Exim. However, there are some optional
+lookup types (such as cdb) for which the code is entirely contained within
+Exim, and no external include files or libraries are required. When a lookup
+type is not included in the binary, attempts to configure Exim to use it cause
+runtime configuration errors.
+
+Many systems now use a tool called pkg-config to encapsulate information about
+how to compile against a library; Exim has some initial support for being able
+to use pkg-config for lookups and authenticators. For any given makefile
+variable which starts "LOOKUP_" or "AUTH_", you can add a new variable with the
+"_PC" suffix in the name and assign as the value the name of the package to be
+queried. The results of querying via the pkg-config command will be added to
+the appropriate Makefile variables with "+=" directives, so your version of
+make will need to support that syntax. For instance:
+
+LOOKUP_SQLITE=yes
+LOOKUP_SQLITE_PC=sqlite3
+AUTH_GSASL=yes
+AUTH_GSASL_PC=libgsasl
+AUTH_HEIMDAL_GSSAPI=yes
+AUTH_HEIMDAL_GSSAPI_PC=heimdal-gssapi
+
+Exim can be linked with an embedded Perl interpreter, allowing Perl subroutines
+to be called during string expansion. To enable this facility,
+
+EXIM_PERL=perl.o
+
+must be defined in Local/Makefile. Details of this facility are given in
+chapter 12.
+
+The location of the X11 libraries is something that varies a lot between
+operating systems, and there may be different versions of X11 to cope with.
+Exim itself makes no use of X11, but if you are compiling the Exim monitor, the
+X11 libraries must be available. The following three variables are set in OS/
+Makefile-Default:
+
+X11=/usr/X11R6
+XINCLUDE=-I$(X11)/include
+XLFLAGS=-L$(X11)/lib
+
+These are overridden in some of the operating-system configuration files. For
+example, in OS/Makefile-SunOS5 there is
+
+X11=/usr/openwin
+XINCLUDE=-I$(X11)/include
+XLFLAGS=-L$(X11)/lib -R$(X11)/lib
+
+If you need to override the default setting for your operating system, place a
+definition of all three of these variables into your Local/Makefile-<ostype>
+file.
+
+If you need to add any extra libraries to the link steps, these can be put in a
+variable called EXTRALIBS, which appears in all the link commands, but by
+default is not defined. In contrast, EXTRALIBS_EXIM is used only on the command
+for linking the main Exim binary, and not for any associated utilities.
+
+There is also DBMLIB, which appears in the link commands for binaries that use
+DBM functions (see also section 4.4). Finally, there is EXTRALIBS_EXIMON, which
+appears only in the link step for the Exim monitor binary, and which can be
+used, for example, to include additional X11 libraries.
+
+The make file copes with rebuilding Exim correctly if any of the configuration
+files are edited. However, if an optional configuration file is deleted, it is
+necessary to touch the associated non-optional file (that is, Local/Makefile or
+Local/eximon.conf) before rebuilding.
+
+
+4.14 OS-specific header files
+-----------------------------
+
+The OS directory contains a number of files with names of the form os.h-
+<ostype>. These are system-specific C header files that should not normally
+need to be changed. There is a list of macro settings that are recognized in
+the file OS/os.configuring, which should be consulted if you are porting Exim
+to a new operating system.
+
+
+4.15 Overriding build-time options for the monitor
+--------------------------------------------------
+
+A similar process is used for overriding things when building the Exim monitor,
+where the files that are involved are
+
+OS/eximon.conf-Default
+OS/eximon.conf-<ostype>
+Local/eximon.conf
+Local/eximon.conf-<ostype>
+Local/eximon.conf-<archtype>
+Local/eximon.conf-<ostype>-<archtype>
+
+As with Exim itself, the final three files need not exist, and in this case the
+OS/eximon.conf-<ostype> file is also optional. The default values in OS/
+eximon.conf-Default can be overridden dynamically by setting environment
+variables of the same name, preceded by EXIMON_. For example, setting
+EXIMON_LOG_DEPTH in the environment overrides the value of LOG_DEPTH at
+runtime.
+
+
+4.16 Installing Exim binaries and scripts
+-----------------------------------------
+
+The command "make install" runs the exim_install script with no arguments. The
+script copies binaries and utility scripts into the directory whose name is
+specified by the BIN_DIRECTORY setting in Local/Makefile. The install script
+copies files only if they are newer than the files they are going to replace.
+The Exim binary is required to be owned by root and have the setuid bit set,
+for normal configurations. Therefore, you must run "make install" as root so
+that it can set up the Exim binary in this way. However, in some special
+situations (for example, if a host is doing no local deliveries) it may be
+possible to run Exim without making the binary setuid root (see chapter 56 for
+details).
+
+Exim's runtime configuration file is named by the CONFIGURE_FILE setting in
+Local/Makefile. If this names a single file, and the file does not exist, the
+default configuration file src/configure.default is copied there by the
+installation script. If a runtime configuration file already exists, it is left
+alone. If CONFIGURE_FILE is a colon-separated list, naming several alternative
+files, no default is installed.
+
+One change is made to the default configuration file when it is installed: the
+default configuration contains a router that references a system aliases file.
+The path to this file is set to the value specified by SYSTEM_ALIASES_FILE in
+Local/Makefile (/etc/aliases by default). If the system aliases file does not
+exist, the installation script creates it, and outputs a comment to the user.
+
+The created file contains no aliases, but it does contain comments about the
+aliases a site should normally have. Mail aliases have traditionally been kept
+in /etc/aliases. However, some operating systems are now using /etc/mail/
+aliases. You should check if yours is one of these, and change Exim's
+configuration if necessary.
+
+The default configuration uses the local host's name as the only local domain,
+and is set up to do local deliveries into the shared directory /var/mail,
+running as the local user. System aliases and .forward files in users' home
+directories are supported, but no NIS or NIS+ support is configured. Domains
+other than the name of the local host are routed using the DNS, with delivery
+over SMTP.
+
+It is possible to install Exim for special purposes (such as building a binary
+distribution) in a private part of the file system. You can do this by a
+command such as
+
+make DESTDIR=/some/directory/ install
+
+This has the effect of pre-pending the specified directory to all the file
+paths, except the name of the system aliases file that appears in the default
+configuration. (If a default alias file is created, its name is modified.) For
+backwards compatibility, ROOT is used if DESTDIR is not set, but this usage is
+deprecated.
+
+Running make install does not copy the Exim 4 conversion script convert4r4. You
+will probably run this only once if you are upgrading from Exim 3. None of the
+documentation files in the doc directory are copied, except for the info files
+when you have set INFO_DIRECTORY, as described in section 4.17 below.
+
+For the utility programs, old versions are renamed by adding the suffix .O to
+their names. The Exim binary itself, however, is handled differently. It is
+installed under a name that includes the version number and the compile number,
+for example, exim-4.94.2-1. The script then arranges for a symbolic link called
+exim to point to the binary. If you are updating a previous version of Exim,
+the script takes care to ensure that the name exim is never absent from the
+directory (as seen by other processes).
+
+If you want to see what the make install will do before running it for real,
+you can pass the -n option to the installation script by this command:
+
+make INSTALL_ARG=-n install
+
+The contents of the variable INSTALL_ARG are passed to the installation script.
+You do not need to be root to run this test. Alternatively, you can run the
+installation script directly, but this must be from within the build directory.
+For example, from the top-level Exim directory you could use this command:
+
+(cd build-SunOS5-5.5.1-sparc; ../scripts/exim_install -n)
+
+There are two other options that can be supplied to the installation script.
+
+ * -no_chown bypasses the call to change the owner of the installed binary to
+ root, and the call to make it a setuid binary.
+
+ * -no_symlink bypasses the setting up of the symbolic link exim to the
+ installed binary.
+
+INSTALL_ARG can be used to pass these options to the script. For example:
+
+make INSTALL_ARG=-no_symlink install
+
+The installation script can also be given arguments specifying which files are
+to be copied. For example, to install just the Exim binary, and nothing else,
+without creating the symbolic link, you could use:
+
+make INSTALL_ARG='-no_symlink exim' install
+
+
+4.17 Installing info documentation
+----------------------------------
+
+Not all systems use the GNU info system for documentation, and for this reason,
+the Texinfo source of Exim's documentation is not included in the main
+distribution. Instead it is available separately from the FTP site (see section
+1.5).
+
+If you have defined INFO_DIRECTORY in Local/Makefile and the Texinfo source of
+the documentation is found in the source tree, running "make install"
+automatically builds the info files and installs them.
+
+
+4.18 Setting up the spool directory
+-----------------------------------
+
+When it starts up, Exim tries to create its spool directory if it does not
+exist. The Exim uid and gid are used for the owner and group of the spool
+directory. Sub-directories are automatically created in the spool directory as
+necessary.
+
+
+4.19 Testing
+------------
+
+Having installed Exim, you can check that the runtime configuration file is
+syntactically valid by running the following command, which assumes that the
+Exim binary directory is within your PATH environment variable:
+
+exim -bV
+
+If there are any errors in the configuration file, Exim outputs error messages.
+Otherwise it outputs the version number and build date, the DBM library that is
+being used, and information about which drivers and other optional code modules
+are included in the binary. Some simple routing tests can be done by using the
+address testing option. For example,
+
+exim -bt <local username>
+
+should verify that it recognizes a local mailbox, and
+
+exim -bt <remote address>
+
+a remote one. Then try getting it to deliver mail, both locally and remotely.
+This can be done by passing messages directly to Exim, without going through a
+user agent. For example:
+
+exim -v postmaster@your.domain.example
+From: user@your.domain.example
+To: postmaster@your.domain.example
+Subject: Testing Exim
+
+This is a test message.
+^D
+
+The -v option causes Exim to output some verification of what it is doing. In
+this case you should see copies of three log lines, one for the message's
+arrival, one for its delivery, and one containing "Completed".
+
+If you encounter problems, look at Exim's log files (mainlog and paniclog) to
+see if there is any relevant information there. Another source of information
+is running Exim with debugging turned on, by specifying the -d option. If a
+message is stuck on Exim's spool, you can force a delivery with debugging
+turned on by a command of the form
+
+exim -d -M <exim-message-id>
+
+You must be root or an "admin user" in order to do this. The -d option produces
+rather a lot of output, but you can cut this down to specific areas. For
+example, if you use -d-all+route only the debugging information relevant to
+routing is included. (See the -d option in chapter 5 for more details.)
+
+One specific problem that has shown up on some sites is the inability to do
+local deliveries into a shared mailbox directory, because it does not have the
+"sticky bit" set on it. By default, Exim tries to create a lock file before
+writing to a mailbox file, and if it cannot create the lock file, the delivery
+is deferred. You can get round this either by setting the "sticky bit" on the
+directory, or by setting a specific group for local deliveries and allowing
+that group to create files in the directory (see the comments above the
+local_delivery transport in the default configuration file). Another approach
+is to configure Exim not to use lock files, but just to rely on fcntl() locking
+instead. However, you should do this only if all user agents also use fcntl()
+locking. For further discussion of locking issues, see chapter 26.
+
+One thing that cannot be tested on a system that is already running an MTA is
+the receipt of incoming SMTP mail on the standard SMTP port. However, the -oX
+option can be used to run an Exim daemon that listens on some other port, or
+inetd can be used to do this. The -bh option and the exim_checkaccess utility
+can be used to check out policy controls on incoming SMTP mail.
+
+Testing a new version on a system that is already running Exim can most easily
+be done by building a binary with a different CONFIGURE_FILE setting. From
+within the runtime configuration, all other file and directory names that Exim
+uses can be altered, in order to keep it entirely clear of the production
+version.
+
+
+4.20 Replacing another MTA with Exim
+------------------------------------
+
+Building and installing Exim for the first time does not of itself put it in
+general use. The name by which the system's MTA is called by mail user agents
+is either /usr/sbin/sendmail, or /usr/lib/sendmail (depending on the operating
+system), and it is necessary to make this name point to the exim binary in
+order to get the user agents to pass messages to Exim. This is normally done by
+renaming any existing file and making /usr/sbin/sendmail or /usr/lib/sendmail a
+symbolic link to the exim binary. It is a good idea to remove any setuid
+privilege and executable status from the old MTA. It is then necessary to stop
+and restart the mailer daemon, if one is running.
+
+Some operating systems have introduced alternative ways of switching MTAs. For
+example, if you are running FreeBSD, you need to edit the file /etc/mail/
+mailer.conf instead of setting up a symbolic link as just described. A typical
+example of the contents of this file for running Exim is as follows:
+
+sendmail /usr/exim/bin/exim
+send-mail /usr/exim/bin/exim
+mailq /usr/exim/bin/exim -bp
+newaliases /usr/bin/true
+
+Once you have set up the symbolic link, or edited /etc/mail/mailer.conf, your
+Exim installation is "live". Check it by sending a message from your favourite
+user agent.
+
+You should consider what to tell your users about the change of MTA. Exim may
+have different capabilities to what was previously running, and there are
+various operational differences such as the text of messages produced by
+command line options and in bounce messages. If you allow your users to make
+use of Exim's filtering capabilities, you should make the document entitled
+Exim's interface to mail filtering available to them.
+
+
+4.21 Upgrading Exim
+-------------------
+
+If you are already running Exim on your host, building and installing a new
+version automatically makes it available to MUAs, or any other programs that
+call the MTA directly. However, if you are running an Exim daemon, you do need
+to send it a HUP signal, to make it re-execute itself, and thereby pick up the
+new binary. You do not need to stop processing mail in order to install a new
+version of Exim. The install script does not modify an existing runtime
+configuration file.
+
+
+4.22 Stopping the Exim daemon on Solaris
+----------------------------------------
+
+The standard command for stopping the mailer daemon on Solaris is
+
+/etc/init.d/sendmail stop
+
+If /usr/lib/sendmail has been turned into a symbolic link, this script fails to
+stop Exim because it uses the command ps -e and greps the output for the text
+"sendmail"; this is not present because the actual program name (that is,
+"exim") is given by the ps command with these options. A solution is to replace
+the line that finds the process id with something like
+
+pid=`cat /var/spool/exim/exim-daemon.pid`
+
+to obtain the daemon's pid directly from the file that Exim saves it in.
+
+Note, however, that stopping the daemon does not "stop Exim". Messages can
+still be received from local processes, and if automatic delivery is configured
+(the normal case), deliveries will still occur.
+
+
+
+===============================================================================
+5. THE EXIM COMMAND LINE
+
+Exim's command line takes the standard Unix form of a sequence of options, each
+starting with a hyphen character, followed by a number of arguments. The
+options are compatible with the main options of Sendmail, and there are also
+some additional options, some of which are compatible with Smail 3. Certain
+combinations of options do not make sense, and provoke an error if used. The
+form of the arguments depends on which options are set.
+
+
+5.1 Setting options by program name
+-----------------------------------
+
+If Exim is called under the name mailq, it behaves as if the option -bp were
+present before any other options. The -bp option requests a listing of the
+contents of the mail queue on the standard output. This feature is for
+compatibility with some systems that contain a command of that name in one of
+the standard libraries, symbolically linked to /usr/sbin/sendmail or /usr/lib/
+sendmail.
+
+If Exim is called under the name rsmtp it behaves as if the option -bS were
+present before any other options, for compatibility with Smail. The -bS option
+is used for reading in a number of messages in batched SMTP format.
+
+If Exim is called under the name rmail it behaves as if the -i and -oee options
+were present before any other options, for compatibility with Smail. The name
+rmail is used as an interface by some UUCP systems.
+
+If Exim is called under the name runq it behaves as if the option -q were
+present before any other options, for compatibility with Smail. The -q option
+causes a single queue runner process to be started.
+
+If Exim is called under the name newaliases it behaves as if the option -bi
+were present before any other options, for compatibility with Sendmail. This
+option is used for rebuilding Sendmail's alias file. Exim does not have the
+concept of a single alias file, but can be configured to run a given command if
+called with the -bi option.
+
+
+5.2 Trusted and admin users
+---------------------------
+
+Some Exim options are available only to trusted users and others are available
+only to admin users. In the description below, the phrases "Exim user" and
+"Exim group" mean the user and group defined by EXIM_USER and EXIM_GROUP in
+Local/Makefile or set by the exim_user and exim_group options. These do not
+necessarily have to use the name "exim".
+
+ * The trusted users are root, the Exim user, any user listed in the
+ trusted_users configuration option, and any user whose current group or any
+ supplementary group is one of those listed in the trusted_groups
+ configuration option. Note that the Exim group is not automatically
+ trusted.
+
+ Trusted users are always permitted to use the -f option or a leading
+ "From " line to specify the envelope sender of a message that is passed to
+ Exim through the local interface (see the -bm and -f options below). See
+ the untrusted_set_sender option for a way of permitting non-trusted users
+ to set envelope senders.
+
+ For a trusted user, there is never any check on the contents of the From:
+ header line, and a Sender: line is never added. Furthermore, any existing
+ Sender: line in incoming local (non-TCP/IP) messages is not removed.
+
+ Trusted users may also specify a host name, host address, interface
+ address, protocol name, ident value, and authentication data when
+ submitting a message locally. Thus, they are able to insert messages into
+ Exim's queue locally that have the characteristics of messages received
+ from a remote host. Untrusted users may in some circumstances use -f, but
+ can never set the other values that are available to trusted users.
+
+ * The admin users are root, the Exim user, and any user that is a member of
+ the Exim group or of any group listed in the admin_groups configuration
+ option. The current group does not have to be one of these groups.
+
+ Admin users are permitted to list the queue, and to carry out certain
+ operations on messages, for example, to force delivery failures. It is also
+ necessary to be an admin user in order to see the full information provided
+ by the Exim monitor, and full debugging output.
+
+ By default, the use of the -M, -q, -R, and -S options to cause Exim to
+ attempt delivery of messages on its queue is restricted to admin users.
+ However, this restriction can be relaxed by setting the prod_requires_admin
+ option false (that is, specifying no_prod_requires_admin).
+
+ Similarly, the use of the -bp option to list all the messages in the queue
+ is restricted to admin users unless queue_list_requires_admin is set false.
+
+Warning: If you configure your system so that admin users are able to edit
+Exim's configuration file, you are giving those users an easy way of getting
+root. There is further discussion of this issue at the start of chapter 6.
+
+
+5.3 Command line options
+------------------------
+
+Exim's command line options are described in alphabetical order below. If none
+of the options that specifies a specific action (such as starting the daemon or
+a queue runner, or testing an address, or receiving a message in a specific
+format, or listing the queue) are present, and there is at least one argument
+on the command line, -bm (accept a local message on the standard input, with
+the arguments specifying the recipients) is assumed. Otherwise, Exim outputs a
+brief message about itself and exits.
+
+--
+
+ This is a pseudo-option whose only purpose is to terminate the options and
+ therefore to cause subsequent command line items to be treated as arguments
+ rather than options, even if they begin with hyphens.
+
+--help
+
+ This option causes Exim to output a few sentences stating what it is. The
+ same output is generated if the Exim binary is called with no options and
+ no arguments.
+
+--version
+
+ This option is an alias for -bV and causes version information to be
+ displayed.
+
+-Ac, -Am
+
+ These options are used by Sendmail for selecting configuration files and
+ are ignored by Exim.
+
+-B<type>
+
+ This is a Sendmail option for selecting 7 or 8 bit processing. Exim is
+ 8-bit clean; it ignores this option.
+
+-bd
+
+ This option runs Exim as a daemon, awaiting incoming SMTP connections.
+ Usually the -bd option is combined with the -q<time> option, to specify
+ that the daemon should also initiate periodic queue runs.
+
+ The -bd option can be used only by an admin user. If either of the -d
+ (debugging) or -v (verifying) options are set, the daemon does not
+ disconnect from the controlling terminal. When running this way, it can be
+ stopped by pressing ctrl-C.
+
+ By default, Exim listens for incoming connections to the standard SMTP port
+ on all the host's running interfaces. However, it is possible to listen on
+ other ports, on multiple ports, and only on specific interfaces. Chapter 13
+ contains a description of the options that control this.
+
+ When a listening daemon is started without the use of -oX (that is, without
+ overriding the normal configuration), it writes its process id to a file
+ called exim-daemon.pid in Exim's spool directory. This location can be
+ overridden by setting PID_FILE_PATH in Local/Makefile. The file is written
+ while Exim is still running as root.
+
+ When -oX is used on the command line to start a listening daemon, the
+ process id is not written to the normal pid file path. However, -oP can be
+ used to specify a path on the command line if a pid file is required.
+
+ The SIGHUP signal can be used to cause the daemon to re-execute itself.
+ This should be done whenever Exim's configuration file, or any file that is
+ incorporated into it by means of the .include facility, is changed, and
+ also whenever a new version of Exim is installed. It is not necessary to do
+ this when other files that are referenced from the configuration (for
+ example, alias files) are changed, because these are reread each time they
+ are used.
+
+-bdf
+
+ This option has the same effect as -bd except that it never disconnects
+ from the controlling terminal, even when no debugging is specified.
+
+-be
+
+ Run Exim in expansion testing mode. Exim discards its root privilege, to
+ prevent ordinary users from using this mode to read otherwise inaccessible
+ files. If no arguments are given, Exim runs interactively, prompting for
+ lines of data. Otherwise, it processes each argument in turn.
+
+ If Exim was built with USE_READLINE=yes in Local/Makefile, it tries to load
+ the libreadline library dynamically whenever the -be option is used without
+ command line arguments. If successful, it uses the readline() function,
+ which provides extensive line-editing facilities, for reading the test
+ data. A line history is supported.
+
+ Long expansion expressions can be split over several lines by using
+ backslash continuations. As in Exim's runtime configuration, white space at
+ the start of continuation lines is ignored. Each argument or data line is
+ passed through the string expansion mechanism, and the result is output.
+ Variable values from the configuration file (for example, $qualify_domain)
+ are available, but no message-specific values (such as $message_exim_id)
+ are set, because no message is being processed (but see -bem and -Mset).
+
+ Note: If you use this mechanism to test lookups, and you change the data
+ files or databases you are using, you must exit and restart Exim before
+ trying the same lookup again. Otherwise, because each Exim process caches
+ the results of lookups, you will just get the same result as before.
+
+ Macro processing is done on lines before string-expansion: new macros can
+ be defined and macros will be expanded. Because macros in the config file
+ are often used for secrets, those are only available to admin users.
+
+-bem <filename>
+
+ This option operates like -be except that it must be followed by the name
+ of a file. For example:
+
+ exim -bem /tmp/testmessage
+
+ The file is read as a message (as if receiving a locally-submitted non-SMTP
+ message) before any of the test expansions are done. Thus, message-specific
+ variables such as $message_size and $header_from: are available. However,
+ no Received: header is added to the message. If the -t option is set,
+ recipients are read from the headers in the normal way, and are shown in
+ the $recipients variable. Note that recipients cannot be given on the
+ command line, because further arguments are taken as strings to expand
+ (just like -be).
+
+-bF <filename>
+
+ This option is the same as -bf except that it assumes that the filter being
+ tested is a system filter. The additional commands that are available only
+ in system filters are recognized.
+
+-bf <filename>
+
+ This option runs Exim in user filter testing mode; the file is the filter
+ file to be tested, and a test message must be supplied on the standard
+ input. If there are no message-dependent tests in the filter, an empty file
+ can be supplied.
+
+ If you want to test a system filter file, use -bF instead of -bf. You can
+ use both -bF and -bf on the same command, in order to test a system filter
+ and a user filter in the same run. For example:
+
+ exim -bF /system/filter -bf /user/filter </test/message
+
+ This is helpful when the system filter adds header lines or sets filter
+ variables that are used by the user filter.
+
+ If the test filter file does not begin with one of the special lines
+
+ # Exim filter
+ # Sieve filter
+
+ it is taken to be a normal .forward file, and is tested for validity under
+ that interpretation. See sections 22.4 to 22.6 for a description of the
+ possible contents of non-filter redirection lists.
+
+ The result of an Exim command that uses -bf, provided no errors are
+ detected, is a list of the actions that Exim would try to take if presented
+ with the message for real. More details of filter testing are given in the
+ separate document entitled Exim's interfaces to mail filtering.
+
+ When testing a filter file, the envelope sender can be set by the -f
+ option, or by a "From " line at the start of the test message. Various
+ parameters that would normally be taken from the envelope recipient address
+ of the message can be set by means of additional command line options (see
+ the next four options).
+
+-bfd <domain>
+
+ This sets the domain of the recipient address when a filter file is being
+ tested by means of the -bf option. The default is the value of
+ $qualify_domain.
+
+-bfl <local part>
+
+ This sets the local part of the recipient address when a filter file is
+ being tested by means of the -bf option. The default is the username of the
+ process that calls Exim. A local part should be specified with any prefix
+ or suffix stripped, because that is how it appears to the filter when a
+ message is actually being delivered.
+
+-bfp <prefix>
+
+ This sets the prefix of the local part of the recipient address when a
+ filter file is being tested by means of the -bf option. The default is an
+ empty prefix.
+
+-bfs <suffix>
+
+ This sets the suffix of the local part of the recipient address when a
+ filter file is being tested by means of the -bf option. The default is an
+ empty suffix.
+
+-bh <IP address>
+
+ This option runs a fake SMTP session as if from the given IP address, using
+ the standard input and output. The IP address may include a port number at
+ the end, after a full stop. For example:
+
+ exim -bh 10.9.8.7.1234
+ exim -bh fe80::a00:20ff:fe86:a061.5678
+
+ When an IPv6 address is given, it is converted into canonical form. In the
+ case of the second example above, the value of $sender_host_address after
+ conversion to the canonical form is
+ "fe80:0000:0000:0a00:20ff:fe86:a061.5678".
+
+ Comments as to what is going on are written to the standard error file.
+ These include lines beginning with "LOG" for anything that would have been
+ logged. This facility is provided for testing configuration options for
+ incoming messages, to make sure they implement the required policy. For
+ example, you can test your relay controls using -bh.
+
+ Warning 1: You can test features of the configuration that rely on ident
+ (RFC 1413) information by using the -oMt option. However, Exim cannot
+ actually perform an ident callout when testing using -bh because there is
+ no incoming SMTP connection.
+
+ Warning 2: Address verification callouts (see section 44.45) are also
+ skipped when testing using -bh. If you want these callouts to occur, use
+ -bhc instead.
+
+ Messages supplied during the testing session are discarded, and nothing is
+ written to any of the real log files. There may be pauses when DNS (and
+ other) lookups are taking place, and of course these may time out. The -oMi
+ option can be used to specify a specific IP interface and port if this is
+ important, and -oMaa and -oMai can be used to set parameters as if the SMTP
+ session were authenticated.
+
+ The exim_checkaccess utility is a "packaged" version of -bh whose output
+ just states whether a given recipient address from a given host is
+ acceptable or not. See section 54.8.
+
+ Features such as authentication and encryption, where the client input is
+ not plain text, cannot easily be tested with -bh. Instead, you should use a
+ specialized SMTP test program such as swaks.
+
+-bhc <IP address>
+
+ This option operates in the same way as -bh, except that address
+ verification callouts are performed if required. This includes consulting
+ and updating the callout cache database.
+
+-bi
+
+ Sendmail interprets the -bi option as a request to rebuild its alias file.
+ Exim does not have the concept of a single alias file, and so it cannot
+ mimic this behaviour. However, calls to /usr/lib/sendmail with the -bi
+ option tend to appear in various scripts such as NIS make files, so the
+ option must be recognized.
+
+ If -bi is encountered, the command specified by the bi_command
+ configuration option is run, under the uid and gid of the caller of Exim.
+ If the -oA option is used, its value is passed to the command as an
+ argument. The command set by bi_command may not contain arguments. The
+ command can use the exim_dbmbuild utility, or some other means, to rebuild
+ alias files if this is required. If the bi_command option is not set,
+ calling Exim with -bi is a no-op.
+
+-bI:help
+
+ We shall provide various options starting "-bI:" for querying Exim for
+ information. The output of many of these will be intended for machine
+ consumption. This one is not. The -bI:help option asks Exim for a synopsis
+ of supported options beginning "-bI:". Use of any of these options shall
+ cause Exim to exit after producing the requested output.
+
+-bI:dscp
+
+ This option causes Exim to emit an alphabetically sorted list of all
+ recognised DSCP names.
+
+-bI:sieve
+
+ This option causes Exim to emit an alphabetically sorted list of all
+ supported Sieve protocol extensions on stdout, one per line. This is
+ anticipated to be useful for ManageSieve (RFC 5804) implementations, in
+ providing that protocol's "SIEVE" capability response line. As the precise
+ list may depend upon compile-time build options, which this option will
+ adapt to, this is the only way to guarantee a correct response.
+
+-bm
+
+ This option runs an Exim receiving process that accepts an incoming,
+ locally-generated message on the standard input. The recipients are given
+ as the command arguments (except when -t is also present - see below). Each
+ argument can be a comma-separated list of RFC 2822 addresses. This is the
+ default option for selecting the overall action of an Exim call; it is
+ assumed if no other conflicting option is present.
+
+ If any addresses in the message are unqualified (have no domain), they are
+ qualified by the values of the qualify_domain or qualify_recipient options,
+ as appropriate. The -bnq option (see below) provides a way of suppressing
+ this for special cases.
+
+ Policy checks on the contents of local messages can be enforced by means of
+ the non-SMTP ACL. See chapter 44 for details.
+
+ The return code is zero if the message is successfully accepted. Otherwise,
+ the action is controlled by the -oex option setting - see below.
+
+ The format of the message must be as defined in RFC 2822, except that, for
+ compatibility with Sendmail and Smail, a line in one of the forms
+
+ From sender Fri Jan 5 12:55 GMT 1997
+ From sender Fri, 5 Jan 97 12:55:01
+
+ (with the weekday optional, and possibly with additional text after the
+ date) is permitted to appear at the start of the message. There appears to
+ be no authoritative specification of the format of this line. Exim
+ recognizes it by matching against the regular expression defined by the
+ uucp_from_pattern option, which can be changed if necessary.
+
+ The specified sender is treated as if it were given as the argument to the
+ -f option, but if a -f option is also present, its argument is used in
+ preference to the address taken from the message. The caller of Exim must
+ be a trusted user for the sender of a message to be set in this way.
+
+-bmalware <filename>
+
+ This debugging option causes Exim to scan the given file or directory
+ (depending on the used scanner interface), using the malware scanning
+ framework. The option of av_scanner influences this option, so if
+ av_scanner's value is dependent upon an expansion then the expansion should
+ have defaults which apply to this invocation. ACLs are not invoked, so if
+ av_scanner references an ACL variable then that variable will never be
+ populated and -bmalware will fail.
+
+ Exim will have changed working directory before resolving the filename, so
+ using fully qualified pathnames is advisable. Exim will be running as the
+ Exim user when it tries to open the file, rather than as the invoking user.
+ This option requires admin privileges.
+
+ The -bmalware option will not be extended to be more generally useful,
+ there are better tools for file-scanning. This option exists to help
+ administrators verify their Exim and AV scanner configuration.
+
+-bnq
+
+ By default, Exim automatically qualifies unqualified addresses (those
+ without domains) that appear in messages that are submitted locally (that
+ is, not over TCP/IP). This qualification applies both to addresses in
+ envelopes, and addresses in header lines. Sender addresses are qualified
+ using qualify_domain, and recipient addresses using qualify_recipient
+ (which defaults to the value of qualify_domain).
+
+ Sometimes, qualification is not wanted. For example, if -bS (batch SMTP) is
+ being used to re-submit messages that originally came from remote hosts
+ after content scanning, you probably do not want to qualify unqualified
+ addresses in header lines. (Such lines will be present only if you have not
+ enabled a header syntax check in the appropriate ACL.)
+
+ The -bnq option suppresses all qualification of unqualified addresses in
+ messages that originate on the local host. When this is used, unqualified
+ addresses in the envelope provoke errors (causing message rejection) and
+ unqualified addresses in header lines are left alone.
+
+-bP
+
+ If this option is given with no arguments, it causes the values of all
+ Exim's main configuration options to be written to the standard output. The
+ values of one or more specific options can be requested by giving their
+ names as arguments, for example:
+
+ exim -bP qualify_domain hold_domains
+
+ However, any option setting that is preceded by the word "hide" in the
+ configuration file is not shown in full, except to an admin user. For other
+ users, the output is as in this example:
+
+ mysql_servers = <value not displayable>
+
+ If config is given as an argument, the config is output, as it was parsed,
+ any include file resolved, any comment removed.
+
+ If config_file is given as an argument, the name of the runtime
+ configuration file is output. (configure_file works too, for backward
+ compatibility.) If a list of configuration files was supplied, the value
+ that is output here is the name of the file that was actually used.
+
+ If the -n flag is given, then for most modes of -bP operation the name will
+ not be output.
+
+ If log_file_path or pid_file_path are given, the names of the directories
+ where log files and daemon pid files are written are output, respectively.
+ If these values are unset, log files are written in a sub-directory of the
+ spool directory called log, and the pid file is written directly into the
+ spool directory.
+
+ If -bP is followed by a name preceded by "+", for example,
+
+ exim -bP +local_domains
+
+ it searches for a matching named list of any type (domain, host, address,
+ or local part) and outputs what it finds.
+
+ If one of the words router, transport, or authenticator is given, followed
+ by the name of an appropriate driver instance, the option settings for that
+ driver are output. For example:
+
+ exim -bP transport local_delivery
+
+ The generic driver options are output first, followed by the driver's
+ private options. A list of the names of drivers of a particular type can be
+ obtained by using one of the words router_list, transport_list, or
+ authenticator_list, and a complete list of all drivers with their option
+ settings can be obtained by using routers, transports, or authenticators.
+
+ If environment is given as an argument, the set of environment variables is
+ output, line by line. Using the -n flag suppresses the value of the
+ variables.
+
+ If invoked by an admin user, then macro, macro_list and macros are
+ available, similarly to the drivers. Because macros are sometimes used for
+ storing passwords, this option is restricted. The output format is one item
+ per line. For the "-bP macro <name>" form, if no such macro is found the
+ exit status will be nonzero.
+
+-bp
+
+ This option requests a listing of the contents of the mail queue on the
+ standard output. If the -bp option is followed by a list of message ids,
+ just those messages are listed. By default, this option can be used only by
+ an admin user. However, the queue_list_requires_admin option can be set
+ false to allow any user to see the queue.
+
+ Each message in the queue is displayed as in the following example:
+
+ 25m 2.9K 0t5C6f-0000c8-00 <alice@wonderland.fict.example>
+ red.king@looking-glass.fict.example
+ <other addresses>
+
+ The first line contains the length of time the message has been in the
+ queue (in this case 25 minutes), the size of the message (2.9K), the unique
+ local identifier for the message, and the message sender, as contained in
+ the envelope. For bounce messages, the sender address is empty, and appears
+ as "<>". If the message was submitted locally by an untrusted user who
+ overrode the default sender address, the user's login name is shown in
+ parentheses before the sender address.
+
+ If the message is frozen (attempts to deliver it are suspended) then the
+ text "*** frozen ***" is displayed at the end of this line.
+
+ The recipients of the message (taken from the envelope, not the headers)
+ are displayed on subsequent lines. Those addresses to which the message has
+ already been delivered are marked with the letter D. If an original address
+ gets expanded into several addresses via an alias or forward file, the
+ original is displayed with a D only when deliveries for all of its child
+ addresses are complete.
+
+-bpa
+
+ This option operates like -bp, but in addition it shows delivered addresses
+ that were generated from the original top level address(es) in each message
+ by alias or forwarding operations. These addresses are flagged with "+D"
+ instead of just "D".
+
+-bpc
+
+ This option counts the number of messages in the queue, and writes the
+ total to the standard output. It is restricted to admin users, unless
+ queue_list_requires_admin is set false.
+
+-bpr
+
+ This option operates like -bp, but the output is not sorted into
+ chronological order of message arrival. This can speed it up when there are
+ lots of messages in the queue, and is particularly useful if the output is
+ going to be post-processed in a way that doesn't need the sorting.
+
+-bpra
+
+ This option is a combination of -bpr and -bpa.
+
+-bpru
+
+ This option is a combination of -bpr and -bpu.
+
+-bpu
+
+ This option operates like -bp but shows only undelivered top-level
+ addresses for each message displayed. Addresses generated by aliasing or
+ forwarding are not shown, unless the message was deferred after processing
+ by a router with the one_time option set.
+
+-brt
+
+ This option is for testing retry rules, and it must be followed by up to
+ three arguments. It causes Exim to look for a retry rule that matches the
+ values and to write it to the standard output. For example:
+
+ exim -brt bach.comp.mus.example
+ Retry rule: *.comp.mus.example F,2h,15m; F,4d,30m;
+
+ See chapter 32 for a description of Exim's retry rules. The first argument,
+ which is required, can be a complete address in the form local_part@domain,
+ or it can be just a domain name. If the second argument contains a dot, it
+ is interpreted as an optional second domain name; if no retry rule is found
+ for the first argument, the second is tried. This ties in with Exim's
+ behaviour when looking for retry rules for remote hosts - if no rule is
+ found that matches the host, one that matches the mail domain is sought.
+ Finally, an argument that is the name of a specific delivery error, as used
+ in setting up retry rules, can be given. For example:
+
+ exim -brt haydn.comp.mus.example quota_3d
+ Retry rule: *@haydn.comp.mus.example quota_3d F,1h,15m
+
+-brw
+
+ This option is for testing address rewriting rules, and it must be followed
+ by a single argument, consisting of either a local part without a domain,
+ or a complete address with a fully qualified domain. Exim outputs how this
+ address would be rewritten for each possible place it might appear. See
+ chapter 31 for further details.
+
+-bS
+
+ This option is used for batched SMTP input, which is an alternative
+ interface for non-interactive local message submission. A number of
+ messages can be submitted in a single run. However, despite its name, this
+ is not really SMTP input. Exim reads each message's envelope from SMTP
+ commands on the standard input, but generates no responses. If the caller
+ is trusted, or untrusted_set_sender is set, the senders in the SMTP MAIL
+ commands are believed; otherwise the sender is always the caller of Exim.
+
+ The message itself is read from the standard input, in SMTP format (leading
+ dots doubled), terminated by a line containing just a single dot. An error
+ is provoked if the terminating dot is missing. A further message may then
+ follow.
+
+ As for other local message submissions, the contents of incoming batch SMTP
+ messages can be checked using the non-SMTP ACL (see chapter 44).
+ Unqualified addresses are automatically qualified using qualify_domain and
+ qualify_recipient, as appropriate, unless the -bnq option is used.
+
+ Some other SMTP commands are recognized in the input. HELO and EHLO act as
+ RSET; VRFY, EXPN, ETRN, and HELP act as NOOP; QUIT quits, ignoring the rest
+ of the standard input.
+
+ If any error is encountered, reports are written to the standard output and
+ error streams, and Exim gives up immediately. The return code is 0 if no
+ error was detected; it is 1 if one or more messages were accepted before
+ the error was detected; otherwise it is 2.
+
+ More details of input using batched SMTP are given in section 49.11.
+
+-bs
+
+ This option causes Exim to accept one or more messages by reading SMTP
+ commands on the standard input, and producing SMTP replies on the standard
+ output. SMTP policy controls, as defined in ACLs (see chapter 44) are
+ applied. Some user agents use this interface as a way of passing
+ locally-generated messages to the MTA.
+
+ In this usage, if the caller of Exim is trusted, or untrusted_set_sender is
+ set, the senders of messages are taken from the SMTP MAIL commands.
+ Otherwise the content of these commands is ignored and the sender is set up
+ as the calling user. Unqualified addresses are automatically qualified
+ using qualify_domain and qualify_recipient, as appropriate, unless the -bnq
+ option is used.
+
+ The -bs option is also used to run Exim from inetd, as an alternative to
+ using a listening daemon. Exim can distinguish the two cases by checking
+ whether the standard input is a TCP/IP socket. When Exim is called from
+ inetd, the source of the mail is assumed to be remote, and the comments
+ above concerning senders and qualification do not apply. In this situation,
+ Exim behaves in exactly the same way as it does when receiving a message
+ via the listening daemon.
+
+-bt
+
+ This option runs Exim in address testing mode, in which each argument is
+ taken as a recipient address to be tested for deliverability. The results
+ are written to the standard output. If a test fails, and the caller is not
+ an admin user, no details of the failure are output, because these might
+ contain sensitive information such as usernames and passwords for database
+ lookups.
+
+ If no arguments are given, Exim runs in an interactive manner, prompting
+ with a right angle bracket for addresses to be tested.
+
+ Unlike the -be test option, you cannot arrange for Exim to use the readline
+ () function, because it is running as root and there are security issues.
+
+ Each address is handled as if it were the recipient address of a message
+ (compare the -bv option). It is passed to the routers and the result is
+ written to the standard output. However, any router that has
+ no_address_test set is bypassed. This can make -bt easier to use for
+ genuine routing tests if your first router passes everything to a scanner
+ program.
+
+ The return code is 2 if any address failed outright; it is 1 if no address
+ failed outright but at least one could not be resolved for some reason.
+ Return code 0 is given only when all addresses succeed.
+
+ Note: When actually delivering a message, Exim removes duplicate recipient
+ addresses after routing is complete, so that only one delivery takes place.
+ This does not happen when testing with -bt; the full results of routing are
+ always shown.
+
+ Warning: -bt can only do relatively simple testing. If any of the routers
+ in the configuration makes any tests on the sender address of a message,
+ you can use the -f option to set an appropriate sender when running -bt
+ tests. Without it, the sender is assumed to be the calling user at the
+ default qualifying domain. However, if you have set up (for example)
+ routers whose behaviour depends on the contents of an incoming message, you
+ cannot test those conditions using -bt. The -N option provides a possible
+ way of doing such tests.
+
+-bV
+
+ This option causes Exim to write the current version number, compilation
+ number, and compilation date of the exim binary to the standard output. It
+ also lists the DBM library that is being used, the optional modules (such
+ as specific lookup types), the drivers that are included in the binary, and
+ the name of the runtime configuration file that is in use.
+
+ As part of its operation, -bV causes Exim to read and syntax check its
+ configuration file. However, this is a static check only. It cannot check
+ values that are to be expanded. For example, although a misspelt ACL verb
+ is detected, an error in the verb's arguments is not. You cannot rely on
+ -bV alone to discover (for example) all the typos in the configuration;
+ some realistic testing is needed. The -bh and -N options provide more
+ dynamic testing facilities.
+
+-bv
+
+ This option runs Exim in address verification mode, in which each argument
+ is taken as a recipient address to be verified by the routers. (This does
+ not involve any verification callouts). During normal operation,
+ verification happens mostly as a consequence processing a verify condition
+ in an ACL (see chapter 44). If you want to test an entire ACL, possibly
+ including callouts, see the -bh and -bhc options.
+
+ If verification fails, and the caller is not an admin user, no details of
+ the failure are output, because these might contain sensitive information
+ such as usernames and passwords for database lookups.
+
+ If no arguments are given, Exim runs in an interactive manner, prompting
+ with a right angle bracket for addresses to be verified.
+
+ Unlike the -be test option, you cannot arrange for Exim to use the readline
+ () function, because it is running as exim and there are security issues.
+
+ Verification differs from address testing (the -bt option) in that routers
+ that have no_verify set are skipped, and if the address is accepted by a
+ router that has fail_verify set, verification fails. The address is
+ verified as a recipient if -bv is used; to test verification for a sender
+ address, -bvs should be used.
+
+ If the -v option is not set, the output consists of a single line for each
+ address, stating whether it was verified or not, and giving a reason in the
+ latter case. Without -v, generating more than one address by redirection
+ causes verification to end successfully, without considering the generated
+ addresses. However, if just one address is generated, processing continues,
+ and the generated address must verify successfully for the overall
+ verification to succeed.
+
+ When -v is set, more details are given of how the address has been handled,
+ and in the case of address redirection, all the generated addresses are
+ also considered. Verification may succeed for some and fail for others.
+
+ The return code is 2 if any address failed outright; it is 1 if no address
+ failed outright but at least one could not be resolved for some reason.
+ Return code 0 is given only when all addresses succeed.
+
+ If any of the routers in the configuration makes any tests on the sender
+ address of a message, you should use the -f option to set an appropriate
+ sender when running -bv tests. Without it, the sender is assumed to be the
+ calling user at the default qualifying domain.
+
+-bvs
+
+ This option acts like -bv, but verifies the address as a sender rather than
+ a recipient address. This affects any rewriting and qualification that
+ might happen.
+
+-bw
+
+ This option runs Exim as a daemon, awaiting incoming SMTP connections,
+ similarly to the -bd option. All port specifications on the command-line
+ and in the configuration file are ignored. Queue-running may not be
+ specified.
+
+ In this mode, Exim expects to be passed a socket as fd 0 (stdin) which is
+ listening for connections. This permits the system to start up and have
+ inetd (or equivalent) listen on the SMTP ports, starting an Exim daemon for
+ each port only when the first connection is received.
+
+ If the option is given as -bw<time> then the time is a timeout, after which
+ the daemon will exit, which should cause inetd to listen once more.
+
+-C <filelist>
+
+ This option causes Exim to find the runtime configuration file from the
+ given list instead of from the list specified by the CONFIGURE_FILE
+ compile-time setting. Usually, the list will consist of just a single
+ filename, but it can be a colon-separated list of names. In this case, the
+ first file that exists is used. Failure to open an existing file stops Exim
+ from proceeding any further along the list, and an error is generated.
+
+ When this option is used by a caller other than root, and the list is
+ different from the compiled-in list, Exim gives up its root privilege
+ immediately, and runs with the real and effective uid and gid set to those
+ of the caller. However, if a TRUSTED_CONFIG_LIST file is defined in Local/
+ Makefile, that file contains a list of full pathnames, one per line, for
+ configuration files which are trusted. Root privilege is retained for any
+ configuration file so listed, as long as the caller is the Exim user (or
+ the user specified in the CONFIGURE_OWNER option, if any), and as long as
+ the configuration file is not writeable by inappropriate users or groups.
+
+ Leaving TRUSTED_CONFIG_LIST unset precludes the possibility of testing a
+ configuration using -C right through message reception and delivery, even
+ if the caller is root. The reception works, but by that time, Exim is
+ running as the Exim user, so when it re-executes to regain privilege for
+ the delivery, the use of -C causes privilege to be lost. However, root can
+ test reception and delivery using two separate commands (one to put a
+ message in the queue, using -odq, and another to do the delivery, using -M
+ ).
+
+ If ALT_CONFIG_PREFIX is defined in Local/Makefile, it specifies a prefix
+ string with which any file named in a -C command line option must start. In
+ addition, the filename must not contain the sequence "/../". However, if
+ the value of the -C option is identical to the value of CONFIGURE_FILE in
+ Local/Makefile, Exim ignores -C and proceeds as usual. There is no default
+ setting for ALT_CONFIG_PREFIX; when it is unset, any filename can be used
+ with -C.
+
+ ALT_CONFIG_PREFIX can be used to confine alternative configuration files to
+ a directory to which only root has access. This prevents someone who has
+ broken into the Exim account from running a privileged Exim with an
+ arbitrary configuration file.
+
+ The -C facility is useful for ensuring that configuration files are
+ syntactically correct, but cannot be used for test deliveries, unless the
+ caller is privileged, or unless it is an exotic configuration that does not
+ require privilege. No check is made on the owner or group of the files
+ specified by this option.
+
+-D<macro>=<value>
+
+ This option can be used to override macro definitions in the configuration
+ file (see section 6.4). However, like -C, if it is used by an unprivileged
+ caller, it causes Exim to give up its root privilege. If DISABLE_D_OPTION
+ is defined in Local/Makefile, the use of -D is completely disabled, and its
+ use causes an immediate error exit.
+
+ If WHITELIST_D_MACROS is defined in Local/Makefile then it should be a
+ colon-separated list of macros which are considered safe and, if -D only
+ supplies macros from this list, and the values are acceptable, then Exim
+ will not give up root privilege if the caller is root, the Exim run-time
+ user, or the CONFIGURE_OWNER, if set. This is a transition mechanism and is
+ expected to be removed in the future. Acceptable values for the macros
+ satisfy the regexp: "^[A-Za-z0-9_/.-]*$"
+
+ The entire option (including equals sign if present) must all be within one
+ command line item. -D can be used to set the value of a macro to the empty
+ string, in which case the equals sign is optional. These two commands are
+ synonymous:
+
+ exim -DABC ...
+ exim -DABC= ...
+
+ To include spaces in a macro definition item, quotes must be used. If you
+ use quotes, spaces are permitted around the macro name and the equals sign.
+ For example:
+
+ exim '-D ABC = something' ...
+
+ -D may be repeated up to 10 times on a command line. Only macro names up to
+ 22 letters long can be set.
+
+-d<debug options>
+
+ This option causes debugging information to be written to the standard
+ error stream. It is restricted to admin users because debugging output may
+ show database queries that contain password information. Also, the details
+ of users' filter files should be protected. If a non-admin user uses -d,
+ Exim writes an error message to the standard error stream and exits with a
+ non-zero return code.
+
+ When -d is used, -v is assumed. If -d is given on its own, a lot of
+ standard debugging data is output. This can be reduced, or increased to
+ include some more rarely needed information, by directly following -d with
+ a string made up of names preceded by plus or minus characters. These add
+ or remove sets of debugging data, respectively. For example, -d+filter adds
+ filter debugging, whereas -d-all+filter selects only filter debugging. Note
+ that no spaces are allowed in the debug setting. The available debugging
+ categories are:
+
+ acl ACL interpretation
+ auth authenticators
+ deliver general delivery logic
+ dns DNS lookups (see also resolver)
+ dnsbl DNS black list (aka RBL) code
+ exec arguments for execv() calls
+ expand detailed debugging for string expansions
+ filter filter handling
+ hints_lookup hints data lookups
+ host_lookup all types of name-to-IP address handling
+ ident ident lookup
+ interface lists of local interfaces
+ lists matching things in lists
+ load system load checks
+ local_scan can be used by local_scan() (see chapter 46)
+ lookup general lookup code and all lookups
+ memory memory handling
+ noutf8 modifier: avoid UTF-8 line-drawing
+ pid modifier: add pid to debug output lines
+ process_info setting info for the process log
+ queue_run queue runs
+ receive general message reception logic
+ resolver turn on the DNS resolver's debugging output
+ retry retry handling
+ rewrite address rewriting
+ route address routing
+ timestamp modifier: add timestamp to debug output lines
+ tls TLS logic
+ transport transports
+ uid changes of uid/gid and looking up uid/gid
+ verify address verification logic
+ all almost all of the above (see below), and also -v
+
+ The "all" option excludes "memory" when used as "+all", but includes it for
+ "-all". The reason for this is that "+all" is something that people tend to
+ use when generating debug output for Exim maintainers. If "+memory" is
+ included, an awful lot of output that is very rarely of interest is
+ generated, so it now has to be explicitly requested. However, "-all" does
+ turn everything off.
+
+ The "resolver" option produces output only if the DNS resolver was compiled
+ with DEBUG enabled. This is not the case in some operating systems. Also,
+ unfortunately, debugging output from the DNS resolver is written to stdout
+ rather than stderr.
+
+ The default (-d with no argument) omits "expand", "filter", "interface",
+ "load", "memory", "pid", "resolver", and "timestamp". However, the "pid"
+ selector is forced when debugging is turned on for a daemon, which then
+ passes it on to any re-executed Exims. Exim also automatically adds the pid
+ to debug lines when several remote deliveries are run in parallel.
+
+ The "timestamp" selector causes the current time to be inserted at the
+ start of all debug output lines. This can be useful when trying to track
+ down delays in processing.
+
+ The "noutf8" selector disables the use of UTF-8 line-drawing characters to
+ group related information. When disabled. ascii-art is used instead. Using
+ the "+all" option does not set this modifier,
+
+ If the debug_print option is set in any driver, it produces output whenever
+ any debugging is selected, or if -v is used.
+
+-dd<debug options>
+
+ This option behaves exactly like -d except when used on a command that
+ starts a daemon process. In that case, debugging is turned off for the
+ subprocesses that the daemon creates. Thus, it is useful for monitoring the
+ behaviour of the daemon without creating as much output as full debugging
+ does.
+
+-dropcr
+
+ This is an obsolete option that is now a no-op. It used to affect the way
+ Exim handled CR and LF characters in incoming messages. What happens now is
+ described in section 48.2.
+
+-E
+
+ This option specifies that an incoming message is a locally-generated
+ delivery failure report. It is used internally by Exim when handling
+ delivery failures and is not intended for external use. Its only effect is
+ to stop Exim generating certain messages to the postmaster, as otherwise
+ message cascades could occur in some situations. As part of the same
+ option, a message id may follow the characters -E. If it does, the log
+ entry for the receipt of the new message contains the id, following "R=",
+ as a cross-reference.
+
+-ex
+
+ There are a number of Sendmail options starting with -oe which seem to be
+ called by various programs without the leading o in the option. For
+ example, the vacation program uses -eq. Exim treats all options of the form
+ -ex as synonymous with the corresponding -oex options.
+
+-F <string>
+
+ This option sets the sender's full name for use when a locally-generated
+ message is being accepted. In the absence of this option, the user's gecos
+ entry from the password data is used. As users are generally permitted to
+ alter their gecos entries, no security considerations are involved. White
+ space between -F and the <string> is optional.
+
+-f <address>
+
+ This option sets the address of the envelope sender of a locally-generated
+ message (also known as the return path). The option can normally be used
+ only by a trusted user, but untrusted_set_sender can be set to allow
+ untrusted users to use it.
+
+ Processes running as root or the Exim user are always trusted. Other
+ trusted users are defined by the trusted_users or trusted_groups options.
+ In the absence of -f, or if the caller is not trusted, the sender of a
+ local message is set to the caller's login name at the default qualify
+ domain.
+
+ There is one exception to the restriction on the use of -f: an empty sender
+ can be specified by any user, trusted or not, to create a message that can
+ never provoke a bounce. An empty sender can be specified either as an empty
+ string, or as a pair of angle brackets with nothing between them, as in
+ these examples of shell commands:
+
+ exim -f '<>' user@domain
+ exim -f "" user@domain
+
+ In addition, the use of -f is not restricted when testing a filter file
+ with -bf or when testing or verifying addresses using the -bt or -bv
+ options.
+
+ Allowing untrusted users to change the sender address does not of itself
+ make it possible to send anonymous mail. Exim still checks that the From:
+ header refers to the local user, and if it does not, it adds a Sender:
+ header, though this can be overridden by setting no_local_from_check.
+
+ White space between -f and the <address> is optional (that is, they can be
+ given as two arguments or one combined argument). The sender of a
+ locally-generated message can also be set (when permitted) by an initial
+ "From " line in the message - see the description of -bm above - but if -f
+ is also present, it overrides "From ".
+
+-G
+
+ This option is equivalent to an ACL applying:
+
+ control = suppress_local_fixups
+
+ for every message received. Note that Sendmail will complain about such bad
+ formatting, where Exim silently just does not fix it up. This may change in
+ future.
+
+ As this affects audit information, the caller must be a trusted user to use
+ this option.
+
+-h <number>
+
+ This option is accepted for compatibility with Sendmail, but has no effect.
+ (In Sendmail it overrides the "hop count" obtained by counting Received:
+ headers.)
+
+-i
+
+ This option, which has the same effect as -oi, specifies that a dot on a
+ line by itself should not terminate an incoming, non-SMTP message. I can
+ find no documentation for this option in Solaris 2.4 Sendmail, but the
+ mailx command in Solaris 2.4 uses it. See also -ti.
+
+-L <tag>
+
+ This option is equivalent to setting syslog_processname in the config file
+ and setting log_file_path to "syslog". Its use is restricted to
+ administrators. The configuration file has to be read and parsed, to
+ determine access rights, before this is set and takes effect, so early
+ configuration file errors will not honour this flag.
+
+ The tag should not be longer than 32 characters.
+
+-M <message id> <message id> ...
+
+ This option requests Exim to run a delivery attempt on each message in
+ turn. If any of the messages are frozen, they are automatically thawed
+ before the delivery attempt. The settings of queue_domains,
+ queue_smtp_domains, and hold_domains are ignored.
+
+ Retry hints for any of the addresses are overridden - Exim tries to deliver
+ even if the normal retry time has not yet been reached. This option
+ requires the caller to be an admin user. However, there is an option called
+ prod_requires_admin which can be set false to relax this restriction (and
+ also the same requirement for the -q, -R, and -S options).
+
+ The deliveries happen synchronously, that is, the original Exim process
+ does not terminate until all the delivery attempts have finished. No output
+ is produced unless there is a serious error. If you want to see what is
+ happening, use the -v option as well, or inspect Exim's main log.
+
+-Mar <message id> <address> <address> ...
+
+ This option requests Exim to add the addresses to the list of recipients of
+ the message ("ar" for "add recipients"). The first argument must be a
+ message id, and the remaining ones must be email addresses. However, if the
+ message is active (in the middle of a delivery attempt), it is not altered.
+ This option can be used only by an admin user.
+
+-MC <transport> <hostname> <host IP> <sequence number> <message id>
+
+ This option is not intended for use by external callers. It is used
+ internally by Exim to invoke another instance of itself to deliver a
+ waiting message using an existing SMTP connection, which is passed as the
+ standard input. Details are given in chapter 49. This must be the final
+ option, and the caller must be root or the Exim user in order to use it.
+
+-MCA
+
+ This option is not intended for use by external callers. It is used
+ internally by Exim in conjunction with the -MC option. It signifies that
+ the connection to the remote host has been authenticated.
+
+-MCD
+
+ This option is not intended for use by external callers. It is used
+ internally by Exim in conjunction with the -MC option. It signifies that
+ the remote host supports the ESMTP DSN extension.
+
+-MCd
+
+ This option is not intended for use by external callers. It is used
+ internally by Exim in conjunction with the -d option to pass on an
+ information string on the purpose of the process.
+
+-MCG <queue name>
+
+ This option is not intended for use by external callers. It is used
+ internally by Exim in conjunction with the -MC option. It signifies that an
+ alternate queue is used, named by the following argument.
+
+-MCK
+
+ This option is not intended for use by external callers. It is used
+ internally by Exim in conjunction with the -MC option. It signifies that a
+ remote host supports the ESMTP CHUNKING extension.
+
+-MCP
+
+ This option is not intended for use by external callers. It is used
+ internally by Exim in conjunction with the -MC option. It signifies that
+ the server to which Exim is connected supports pipelining.
+
+-MCQ <process id> <pipe fd>
+
+ This option is not intended for use by external callers. It is used
+ internally by Exim in conjunction with the -MC option when the original
+ delivery was started by a queue runner. It passes on the process id of the
+ queue runner, together with the file descriptor number of an open pipe.
+ Closure of the pipe signals the final completion of the sequence of
+ processes that are passing messages through the same SMTP connection.
+
+-MCS
+
+ This option is not intended for use by external callers. It is used
+ internally by Exim in conjunction with the -MC option, and passes on the
+ fact that the ESMTP SIZE option should be used on messages delivered down
+ the existing connection.
+
+-MCT
+
+ This option is not intended for use by external callers. It is used
+ internally by Exim in conjunction with the -MC option, and passes on the
+ fact that the host to which Exim is connected supports TLS encryption.
+
+-MCr <SNI>, -MCs <SNI>
+
+ These options are not intended for use by external callers. It is used
+ internally by Exim in conjunction with the -MCt option, and passes on the
+ fact that a TLS Server Name Indication was sent as part of the channel
+ establishment. The argument gives the SNI string. The "r" variant indicates
+ a DANE-verified connection.
+
+-MCt <IP address> <port> <cipher>
+
+ This option is not intended for use by external callers. It is used
+ internally by Exim in conjunction with the -MC option, and passes on the
+ fact that the connection is being proxied by a parent process for handling
+ TLS encryption. The arguments give the local address and port being
+ proxied, and the TLS cipher.
+
+-Mc <message id> <message id> ...
+
+ This option requests Exim to run a delivery attempt on each message, in
+ turn, but unlike the -M option, it does check for retry hints, and respects
+ any that are found. This option is not very useful to external callers. It
+ is provided mainly for internal use by Exim when it needs to re-invoke
+ itself in order to regain root privilege for a delivery (see chapter 56).
+ However, -Mc can be useful when testing, in order to run a delivery that
+ respects retry times and other options such as hold_domains that are
+ overridden when -M is used. Such a delivery does not count as a queue run.
+ If you want to run a specific delivery as if in a queue run, you should use
+ -q with a message id argument. A distinction between queue run deliveries
+ and other deliveries is made in one or two places.
+
+-Mes <message id> <address>
+
+ This option requests Exim to change the sender address in the message to
+ the given address, which must be a fully qualified address or "<>" ("es"
+ for "edit sender"). There must be exactly two arguments. The first argument
+ must be a message id, and the second one an email address. However, if the
+ message is active (in the middle of a delivery attempt), its status is not
+ altered. This option can be used only by an admin user.
+
+-Mf <message id> <message id> ...
+
+ This option requests Exim to mark each listed message as "frozen". This
+ prevents any delivery attempts taking place until the message is "thawed",
+ either manually or as a result of the auto_thaw configuration option.
+ However, if any of the messages are active (in the middle of a delivery
+ attempt), their status is not altered. This option can be used only by an
+ admin user.
+
+-Mg <message id> <message id> ...
+
+ This option requests Exim to give up trying to deliver the listed messages,
+ including any that are frozen. However, if any of the messages are active,
+ their status is not altered. For non-bounce messages, a delivery error
+ message is sent to the sender, containing the text "cancelled by
+ administrator". Bounce messages are just discarded. This option can be used
+ only by an admin user.
+
+-MG <queue name> <message id> <message id> ...
+
+ This option requests that each listed message be moved from its current
+ queue to the given named queue. The destination queue name argument is
+ required, but can be an empty string to define the default queue. If the
+ messages are not currently located in the default queue, a -qG<name> option
+ will be required to define the source queue.
+
+-Mmad <message id> <message id> ...
+
+ This option requests Exim to mark all the recipient addresses in the
+ messages as already delivered ("mad" for "mark all delivered"). However, if
+ any message is active (in the middle of a delivery attempt), its status is
+ not altered. This option can be used only by an admin user.
+
+-Mmd <message id> <address> <address> ...
+
+ This option requests Exim to mark the given addresses as already delivered
+ ("md" for "mark delivered"). The first argument must be a message id, and
+ the remaining ones must be email addresses. These are matched to recipient
+ addresses in the message in a case-sensitive manner. If the message is
+ active (in the middle of a delivery attempt), its status is not altered.
+ This option can be used only by an admin user.
+
+-Mrm <message id> <message id> ...
+
+ This option requests Exim to remove the given messages from the queue. No
+ bounce messages are sent; each message is simply forgotten. However, if any
+ of the messages are active, their status is not altered. This option can be
+ used only by an admin user or by the user who originally caused the message
+ to be placed in the queue.
+
+-Mset <message id>
+
+ This option is useful only in conjunction with -be (that is, when testing
+ string expansions). Exim loads the given message from its spool before
+ doing the test expansions, thus setting message-specific variables such as
+ $message_size and the header variables. The $recipients variable is made
+ available. This feature is provided to make it easier to test expansions
+ that make use of these variables. However, this option can be used only by
+ an admin user. See also -bem.
+
+-Mt <message id> <message id> ...
+
+ This option requests Exim to "thaw" any of the listed messages that are
+ "frozen", so that delivery attempts can resume. However, if any of the
+ messages are active, their status is not altered. This option can be used
+ only by an admin user.
+
+-Mvb <message id>
+
+ This option causes the contents of the message body (-D) spool file to be
+ written to the standard output. This option can be used only by an admin
+ user.
+
+-Mvc <message id>
+
+ This option causes a copy of the complete message (header lines plus body)
+ to be written to the standard output in RFC 2822 format. This option can be
+ used only by an admin user.
+
+-Mvh <message id>
+
+ This option causes the contents of the message headers (-H) spool file to
+ be written to the standard output. This option can be used only by an admin
+ user.
+
+-Mvl <message id>
+
+ This option causes the contents of the message log spool file to be written
+ to the standard output. This option can be used only by an admin user.
+
+-m
+
+ This is apparently a synonym for -om that is accepted by Sendmail, so Exim
+ treats it that way too.
+
+-N
+
+ This is a debugging option that inhibits delivery of a message at the
+ transport level. It implies -v. Exim goes through many of the motions of
+ delivery - it just doesn't actually transport the message, but instead
+ behaves as if it had successfully done so. However, it does not make any
+ updates to the retry database, and the log entries for deliveries are
+ flagged with "*>" rather than "=>".
+
+ Because -N discards any message to which it applies, only root or the Exim
+ user are allowed to use it with -bd, -q, -R or -M. In other words, an
+ ordinary user can use it only when supplying an incoming message to which
+ it will apply. Although transportation never fails when -N is set, an
+ address may be deferred because of a configuration problem on a transport,
+ or a routing problem. Once -N has been used for a delivery attempt, it
+ sticks to the message, and applies to any subsequent delivery attempts that
+ may happen for that message.
+
+-n
+
+ This option is interpreted by Sendmail to mean "no aliasing". For normal
+ modes of operation, it is ignored by Exim. When combined with -bP it makes
+ the output more terse (suppresses option names, environment values and
+ config pretty printing).
+
+-O <data>
+
+ This option is interpreted by Sendmail to mean "set option". It is ignored
+ by Exim.
+
+-oA <file name>
+
+ This option is used by Sendmail in conjunction with -bi to specify an
+ alternative alias filename. Exim handles -bi differently; see the
+ description above.
+
+-oB <n>
+
+ This is a debugging option which limits the maximum number of messages that
+ can be delivered down one SMTP connection, overriding the value set in any
+ smtp transport. If <n> is omitted, the limit is set to 1.
+
+-odb
+
+ This option applies to all modes in which Exim accepts incoming messages,
+ including the listening daemon. It requests "background" delivery of such
+ messages, which means that the accepting process automatically starts a
+ delivery process for each message received, but does not wait for the
+ delivery processes to finish.
+
+ When all the messages have been received, the reception process exits,
+ leaving the delivery processes to finish in their own time. The standard
+ output and error streams are closed at the start of each delivery process.
+ This is the default action if none of the -od options are present.
+
+ If one of the queueing options in the configuration file (queue_only or
+ queue_only_file, for example) is in effect, -odb overrides it if
+ queue_only_override is set true, which is the default setting. If
+ queue_only_override is set false, -odb has no effect.
+
+-odf
+
+ This option requests "foreground" (synchronous) delivery when Exim has
+ accepted a locally-generated message. (For the daemon it is exactly the
+ same as -odb.) A delivery process is automatically started to deliver the
+ message, and Exim waits for it to complete before proceeding.
+
+ The original Exim reception process does not finish until the delivery
+ process for the final message has ended. The standard error stream is left
+ open during deliveries.
+
+ However, like -odb, this option has no effect if queue_only_override is
+ false and one of the queueing options in the configuration file is in
+ effect.
+
+ If there is a temporary delivery error during foreground delivery, the
+ message is left in the queue for later delivery, and the original reception
+ process exits. See chapter 52 for a way of setting up a restricted
+ configuration that never queues messages.
+
+-odi
+
+ This option is synonymous with -odf. It is provided for compatibility with
+ Sendmail.
+
+-odq
+
+ This option applies to all modes in which Exim accepts incoming messages,
+ including the listening daemon. It specifies that the accepting process
+ should not automatically start a delivery process for each message
+ received. Messages are placed in the queue, and remain there until a
+ subsequent queue runner process encounters them. There are several
+ configuration options (such as queue_only) that can be used to queue
+ incoming messages under certain conditions. This option overrides all of
+ them and also -odqs. It always forces queueing.
+
+-odqs
+
+ This option is a hybrid between -odb/-odi and -odq. However, like -odb and
+ -odi, this option has no effect if queue_only_override is false and one of
+ the queueing options in the configuration file is in effect.
+
+ When -odqs does operate, a delivery process is started for each incoming
+ message, in the background by default, but in the foreground if -odi is
+ also present. The recipient addresses are routed, and local deliveries are
+ done in the normal way. However, if any SMTP deliveries are required, they
+ are not done at this time, so the message remains in the queue until a
+ subsequent queue runner process encounters it. Because routing was done,
+ Exim knows which messages are waiting for which hosts, and so a number of
+ messages for the same host can be sent in a single SMTP connection. The
+ queue_smtp_domains configuration option has the same effect for specific
+ domains. See also the -qq option.
+
+-oee
+
+ If an error is detected while a non-SMTP message is being received (for
+ example, a malformed address), the error is reported to the sender in a
+ mail message.
+
+ Provided this error message is successfully sent, the Exim receiving
+ process exits with a return code of zero. If not, the return code is 2 if
+ the problem is that the original message has no recipients, or 1 for any
+ other error. This is the default -oex option if Exim is called as rmail.
+
+-oem
+
+ This is the same as -oee, except that Exim always exits with a non-zero
+ return code, whether or not the error message was successfully sent. This
+ is the default -oex option, unless Exim is called as rmail.
+
+-oep
+
+ If an error is detected while a non-SMTP message is being received, the
+ error is reported by writing a message to the standard error file (stderr).
+ The return code is 1 for all errors.
+
+-oeq
+
+ This option is supported for compatibility with Sendmail, but has the same
+ effect as -oep.
+
+-oew
+
+ This option is supported for compatibility with Sendmail, but has the same
+ effect as -oem.
+
+-oi
+
+ This option, which has the same effect as -i, specifies that a dot on a
+ line by itself should not terminate an incoming, non-SMTP message.
+ Otherwise, a single dot does terminate, though Exim does no special
+ processing for other lines that start with a dot. This option is set by
+ default if Exim is called as rmail. See also -ti.
+
+-oitrue
+
+ This option is treated as synonymous with -oi.
+
+-oMa <host address>
+
+ A number of options starting with -oM can be used to set values associated
+ with remote hosts on locally-submitted messages (that is, messages not
+ received over TCP/IP). These options can be used by any caller in
+ conjunction with the -bh, -be, -bf, -bF, -bt, or -bv testing options. In
+ other circumstances, they are ignored unless the caller is trusted.
+
+ The -oMa option sets the sender host address. This may include a port
+ number at the end, after a full stop (period). For example:
+
+ exim -bs -oMa 10.9.8.7.1234
+
+ An alternative syntax is to enclose the IP address in square brackets,
+ followed by a colon and the port number:
+
+ exim -bs -oMa [10.9.8.7]:1234
+
+ The IP address is placed in the $sender_host_address variable, and the
+ port, if present, in $sender_host_port. If both -oMa and -bh are present on
+ the command line, the sender host IP address is taken from whichever one is
+ last.
+
+-oMaa <name>
+
+ See -oMa above for general remarks about the -oM options. The -oMaa option
+ sets the value of $sender_host_authenticated (the authenticator name). See
+ chapter 33 for a discussion of SMTP authentication. This option can be used
+ with -bh and -bs to set up an authenticated SMTP session without actually
+ using the SMTP AUTH command.
+
+-oMai <string>
+
+ See -oMa above for general remarks about the -oM options. The -oMai option
+ sets the value of $authenticated_id (the id that was authenticated). This
+ overrides the default value (the caller's login id, except with -bh, where
+ there is no default) for messages from local sources. See chapter 33 for a
+ discussion of authenticated ids.
+
+-oMas <address>
+
+ See -oMa above for general remarks about the -oM options. The -oMas option
+ sets the authenticated sender value in $authenticated_sender. It overrides
+ the sender address that is created from the caller's login id for messages
+ from local sources, except when -bh is used, when there is no default. For
+ both -bh and -bs, an authenticated sender that is specified on a MAIL
+ command overrides this value. See chapter 33 for a discussion of
+ authenticated senders.
+
+-oMi <interface address>
+
+ See -oMa above for general remarks about the -oM options. The -oMi option
+ sets the IP interface address value. A port number may be included, using
+ the same syntax as for -oMa. The interface address is placed in
+ $received_ip_address and the port number, if present, in $received_port.
+
+-oMm <message reference>
+
+ See -oMa above for general remarks about the -oM options. The -oMm option
+ sets the message reference, e.g. message-id, and is logged during delivery.
+ This is useful when some kind of audit trail is required to tie messages
+ together. The format of the message reference is checked and will abort if
+ the format is invalid. The option will only be accepted if exim is running
+ in trusted mode, not as any regular user.
+
+ The best example of a message reference is when Exim sends a bounce
+ message. The message reference is the message-id of the original message
+ for which Exim is sending the bounce.
+
+-oMr <protocol name>
+
+ See -oMa above for general remarks about the -oM options. The -oMr option
+ sets the received protocol value that is stored in $received_protocol.
+ However, it does not apply (and is ignored) when -bh or -bs is used. For
+ -bh, the protocol is forced to one of the standard SMTP protocol names (see
+ the description of $received_protocol in section 11.9). For -bs, the
+ protocol is always "local-" followed by one of those same names. For -bS
+ (batched SMTP) however, the protocol can be set by -oMr. Repeated use of
+ this option is not supported.
+
+-oMs <host name>
+
+ See -oMa above for general remarks about the -oM options. The -oMs option
+ sets the sender host name in $sender_host_name. When this option is
+ present, Exim does not attempt to look up a host name from an IP address;
+ it uses the name it is given.
+
+-oMt <ident string>
+
+ See -oMa above for general remarks about the -oM options. The -oMt option
+ sets the sender ident value in $sender_ident. The default setting for local
+ callers is the login id of the calling process, except when -bh is used,
+ when there is no default.
+
+-om
+
+ In Sendmail, this option means "me too", indicating that the sender of a
+ message should receive a copy of the message if the sender appears in an
+ alias expansion. Exim always does this, so the option does nothing.
+
+-oo
+
+ This option is ignored. In Sendmail it specifies "old style headers",
+ whatever that means.
+
+-oP <path>
+
+ This option is useful only in conjunction with -bd or -q with a time value.
+ The option specifies the file to which the process id of the daemon is
+ written. When -oX is used with -bd, or when -q with a time is used without
+ -bd, this is the only way of causing Exim to write a pid file, because in
+ those cases, the normal pid file is not used.
+
+-oPX
+
+ This option is not intended for general use. The daemon uses it when
+ terminating due to a SIGTEM, possibly in combination with -oP <path>. It
+ causes the pid file to be removed.
+
+-or <time>
+
+ This option sets a timeout value for incoming non-SMTP messages. If it is
+ not set, Exim will wait forever for the standard input. The value can also
+ be set by the receive_timeout option. The format used for specifying times
+ is described in section 6.16.
+
+-os <time>
+
+ This option sets a timeout value for incoming SMTP messages. The timeout
+ applies to each SMTP command and block of data. The value can also be set
+ by the smtp_receive_timeout option; it defaults to 5 minutes. The format
+ used for specifying times is described in section 6.16.
+
+-ov
+
+ This option has exactly the same effect as -v.
+
+-oX <number or string>
+
+ This option is relevant only when the -bd (start listening daemon) option
+ is also given. It controls which ports and interfaces the daemon uses.
+ Details of the syntax, and how it interacts with configuration file
+ options, are given in chapter 13. When -oX is used to start a daemon, no
+ pid file is written unless -oP is also present to specify a pid filename.
+
+-pd
+
+ This option applies when an embedded Perl interpreter is linked with Exim
+ (see chapter 12). It overrides the setting of the perl_at_start option,
+ forcing the starting of the interpreter to be delayed until it is needed.
+
+-ps
+
+ This option applies when an embedded Perl interpreter is linked with Exim
+ (see chapter 12). It overrides the setting of the perl_at_start option,
+ forcing the starting of the interpreter to occur as soon as Exim is
+ started.
+
+-p<rval>:<sval>
+
+ For compatibility with Sendmail, this option is equivalent to
+
+ -oMr <rval> -oMs <sval>
+
+ It sets the incoming protocol and host name (for trusted callers). The host
+ name and its colon can be omitted when only the protocol is to be set. Note
+ the Exim already has two private options, -pd and -ps, that refer to
+ embedded Perl. It is therefore impossible to set a protocol value of "d" or
+ "s" using this option (but that does not seem a real limitation). Repeated
+ use of this option is not supported.
+
+-q
+
+ This option is normally restricted to admin users. However, there is a
+ configuration option called prod_requires_admin which can be set false to
+ relax this restriction (and also the same requirement for the -M, -R, and
+ -S options).
+
+ If other commandline options do not specify an action, the -q option starts
+ one queue runner process. This scans the queue of waiting messages, and
+ runs a delivery process for each one in turn. It waits for each delivery
+ process to finish before starting the next one. A delivery process may not
+ actually do any deliveries if the retry times for the addresses have not
+ been reached. Use -qf (see below) if you want to override this.
+
+ If the delivery process spawns other processes to deliver other messages
+ down passed SMTP connections, the queue runner waits for these to finish
+ before proceeding.
+
+ When all the queued messages have been considered, the original queue
+ runner process terminates. In other words, a single pass is made over the
+ waiting mail, one message at a time. Use -q with a time (see below) if you
+ want this to be repeated periodically.
+
+ Exim processes the waiting messages in an unpredictable order. It isn't
+ very random, but it is likely to be different each time, which is all that
+ matters. If one particular message screws up a remote MTA, other messages
+ to the same MTA have a chance of getting through if they get tried first.
+
+ It is possible to cause the messages to be processed in lexical message id
+ order, which is essentially the order in which they arrived, by setting the
+ queue_run_in_order option, but this is not recommended for normal use.
+
+-q<qflags>
+
+ The -q option may be followed by one or more flag letters that change its
+ behaviour. They are all optional, but if more than one is present, they
+ must appear in the correct order. Each flag is described in a separate item
+ below.
+
+-qq...
+
+ An option starting with -qq requests a two-stage queue run. In the first
+ stage, the queue is scanned as if the queue_smtp_domains option matched
+ every domain. Addresses are routed, local deliveries happen, but no remote
+ transports are run.
+
+ Performance will be best if the queue_run_in_order option is false.
+
+ The hints database that remembers which messages are waiting for specific
+ hosts is updated, as if delivery to those hosts had been deferred. After
+ this is complete, a second, normal queue scan happens, with routing and
+ delivery taking place as normal. Messages that are routed to the same host
+ should mostly be delivered down a single SMTP connection because of the
+ hints that were set up during the first queue scan. This option may be
+ useful for hosts that are connected to the Internet intermittently.
+
+-q[q]i...
+
+ If the i flag is present, the queue runner runs delivery processes only for
+ those messages that haven't previously been tried. (i stands for "initial
+ delivery".) This can be helpful if you are putting messages in the queue
+ using -odq and want a queue runner just to process the new messages.
+
+-q[q][i]f...
+
+ If one f flag is present, a delivery attempt is forced for each non-frozen
+ message, whereas without f only those non-frozen addresses that have passed
+ their retry times are tried.
+
+-q[q][i]ff...
+
+ If ff is present, a delivery attempt is forced for every message, whether
+ frozen or not.
+
+-q[q][i][f[f]]l
+
+ The l (the letter "ell") flag specifies that only local deliveries are to
+ be done. If a message requires any remote deliveries, it remains in the
+ queue for later delivery.
+
+-q[q][i][f[f]][l][G<name>[/<time>]]]
+
+ If the G flag and a name is present, the queue runner operates on the queue
+ with the given name rather than the default queue. The name should not
+ contain a / character. For a periodic queue run (see below) append to the
+ name a slash and a time value.
+
+ If other commandline options specify an action, a -qG<name> option will
+ specify a queue to operate on. For example:
+
+ exim -bp -qGquarantine
+ mailq -qGquarantine
+ exim -qGoffpeak -Rf @special.domain.example
+
+-q<qflags> <start id> <end id>
+
+ When scanning the queue, Exim can be made to skip over messages whose ids
+ are lexically less than a given value by following the -q option with a
+ starting message id. For example:
+
+ exim -q 0t5C6f-0000c8-00
+
+ Messages that arrived earlier than "0t5C6f-0000c8-00" are not inspected. If
+ a second message id is given, messages whose ids are lexically greater than
+ it are also skipped. If the same id is given twice, for example,
+
+ exim -q 0t5C6f-0000c8-00 0t5C6f-0000c8-00
+
+ just one delivery process is started, for that message. This differs from
+ -M in that retry data is respected, and it also differs from -Mc in that it
+ counts as a delivery from a queue run. Note that the selection mechanism
+ does not affect the order in which the messages are scanned. There are also
+ other ways of selecting specific sets of messages for delivery in a queue
+ run - see -R and -S.
+
+-q<qflags><time>
+
+ When a time value is present, the -q option causes Exim to run as a daemon,
+ starting a queue runner process at intervals specified by the given time
+ value (whose format is described in section 6.16). This form of the -q
+ option is commonly combined with the -bd option, in which case a single
+ daemon process handles both functions. A common way of starting up a
+ combined daemon at system boot time is to use a command such as
+
+ /usr/exim/bin/exim -bd -q30m
+
+ Such a daemon listens for incoming SMTP calls, and also starts a queue
+ runner process every 30 minutes.
+
+ When a daemon is started by -q with a time value, but without -bd, no pid
+ file is written unless one is explicitly requested by the -oP option.
+
+-qR<rsflags> <string>
+
+ This option is synonymous with -R. It is provided for Sendmail
+ compatibility.
+
+-qS<rsflags> <string>
+
+ This option is synonymous with -S.
+
+-R<rsflags> <string>
+
+ The <rsflags> may be empty, in which case the white space before the string
+ is optional, unless the string is f, ff, r, rf, or rff, which are the
+ possible values for <rsflags>. White space is required if <rsflags> is not
+ empty.
+
+ This option is similar to -q with no time value, that is, it causes Exim to
+ perform a single queue run, except that, when scanning the messages on the
+ queue, Exim processes only those that have at least one undelivered
+ recipient address containing the given string, which is checked in a
+ case-independent way. If the <rsflags> start with r, <string> is
+ interpreted as a regular expression; otherwise it is a literal string.
+
+ If you want to do periodic queue runs for messages with specific
+ recipients, you can combine -R with -q and a time value. For example:
+
+ exim -q25m -R @special.domain.example
+
+ This example does a queue run for messages with recipients in the given
+ domain every 25 minutes. Any additional flags that are specified with -q
+ are applied to each queue run.
+
+ Once a message is selected for delivery by this mechanism, all its
+ addresses are processed. For the first selected message, Exim overrides any
+ retry information and forces a delivery attempt for each undelivered
+ address. This means that if delivery of any address in the first message is
+ successful, any existing retry information is deleted, and so delivery
+ attempts for that address in subsequently selected messages (which are
+ processed without forcing) will run. However, if delivery of any address
+ does not succeed, the retry information is updated, and in subsequently
+ selected messages, the failing address will be skipped.
+
+ If the <rsflags> contain f or ff, the delivery forcing applies to all
+ selected messages, not just the first; frozen messages are included when ff
+ is present.
+
+ The -R option makes it straightforward to initiate delivery of all messages
+ to a given domain after a host has been down for some time. When the SMTP
+ command ETRN is accepted by its ACL (see chapter 44), its default effect is
+ to run Exim with the -R option, but it can be configured to run an
+ arbitrary command instead.
+
+-r
+
+ This is a documented (for Sendmail) obsolete alternative name for -f.
+
+-S<rsflags> <string>
+
+ This option acts like -R except that it checks the string against each
+ message's sender instead of against the recipients. If -R is also set, both
+ conditions must be met for a message to be selected. If either of the
+ options has f or ff in its flags, the associated action is taken.
+
+-Tqt <times>
+
+ This is an option that is exclusively for use by the Exim testing suite. It
+ is not recognized when Exim is run normally. It allows for the setting up
+ of explicit "queue times" so that various warning/retry features can be
+ tested.
+
+-t
+
+ When Exim is receiving a locally-generated, non-SMTP message on its
+ standard input, the -t option causes the recipients of the message to be
+ obtained from the To:, Cc:, and Bcc: header lines in the message instead of
+ from the command arguments. The addresses are extracted before any
+ rewriting takes place and the Bcc: header line, if present, is then
+ removed.
+
+ If the command has any arguments, they specify addresses to which the
+ message is not to be delivered. That is, the argument addresses are removed
+ from the recipients list obtained from the headers. This is compatible with
+ Smail 3 and in accordance with the documented behaviour of several versions
+ of Sendmail, as described in man pages on a number of operating systems
+ (e.g. Solaris 8, IRIX 6.5, HP-UX 11). However, some versions of Sendmail
+ add argument addresses to those obtained from the headers, and the O'Reilly
+ Sendmail book documents it that way. Exim can be made to add argument
+ addresses instead of subtracting them by setting the option
+ extract_addresses_remove_arguments false.
+
+ If there are any Resent- header lines in the message, Exim extracts
+ recipients from all Resent-To:, Resent-Cc:, and Resent-Bcc: header lines
+ instead of from To:, Cc:, and Bcc:. This is for compatibility with Sendmail
+ and other MTAs. (Prior to release 4.20, Exim gave an error if -t was used
+ in conjunction with Resent- header lines.)
+
+ RFC 2822 talks about different sets of Resent- header lines (for when a
+ message is resent several times). The RFC also specifies that they should
+ be added at the front of the message, and separated by Received: lines. It
+ is not at all clear how -t should operate in the present of multiple sets,
+ nor indeed exactly what constitutes a "set". In practice, it seems that
+ MUAs do not follow the RFC. The Resent- lines are often added at the end of
+ the header, and if a message is resent more than once, it is common for the
+ original set of Resent- headers to be renamed as X-Resent- when a new set
+ is added. This removes any possible ambiguity.
+
+-ti
+
+ This option is exactly equivalent to -t -i. It is provided for
+ compatibility with Sendmail.
+
+-tls-on-connect
+
+ This option is available when Exim is compiled with TLS support. It forces
+ all incoming SMTP connections to behave as if the incoming port is listed
+ in the tls_on_connect_ports option. See section 13.4 and chapter 43 for
+ further details.
+
+-U
+
+ Sendmail uses this option for "initial message submission", and its
+ documentation states that in future releases, it may complain about
+ syntactically invalid messages rather than fixing them when this flag is
+ not set. Exim ignores this option.
+
+-v
+
+ This option causes Exim to write information to the standard error stream,
+ describing what it is doing. In particular, it shows the log lines for
+ receiving and delivering a message, and if an SMTP connection is made, the
+ SMTP dialogue is shown. Some of the log lines shown may not actually be
+ written to the log if the setting of log_selector discards them. Any
+ relevant selectors are shown with each log line. If none are shown, the
+ logging is unconditional.
+
+-x
+
+ AIX uses -x for a private purpose ("mail from a local mail program has
+ National Language Support extended characters in the body of the mail
+ item"). It sets -x when calling the MTA from its mail command. Exim ignores
+ this option.
+
+-X <logfile>
+
+ This option is interpreted by Sendmail to cause debug information to be
+ sent to the named file. It is ignored by Exim.
+
+-z <log-line>
+
+ This option writes its argument to Exim's logfile. Use is restricted to
+ administrators; the intent is for operational notes. Quotes should be used
+ to maintain a multi-word item as a single argument, under most shells.
+
+
+
+===============================================================================
+6. THE EXIM RUNTIME CONFIGURATION FILE
+
+Exim uses a single runtime configuration file that is read whenever an Exim
+binary is executed. Note that in normal operation, this happens frequently,
+because Exim is designed to operate in a distributed manner, without central
+control.
+
+If a syntax error is detected while reading the configuration file, Exim writes
+a message on the standard error, and exits with a non-zero return code. The
+message is also written to the panic log. Note: Only simple syntax errors can
+be detected at this time. The values of any expanded options are not checked
+until the expansion happens, even when the expansion does not actually alter
+the string.
+
+The name of the configuration file is compiled into the binary for security
+reasons, and is specified by the CONFIGURE_FILE compilation option. In most
+configurations, this specifies a single file. However, it is permitted to give
+a colon-separated list of filenames, in which case Exim uses the first existing
+file in the list.
+
+The runtime configuration file must be owned by root or by the user that is
+specified at compile time by the CONFIGURE_OWNER option (if set). The
+configuration file must not be world-writeable, or group-writeable unless its
+group is the root group or the one specified at compile time by the
+CONFIGURE_GROUP option.
+
+Warning: In a conventional configuration, where the Exim binary is setuid to
+root, anybody who is able to edit the runtime configuration file has an easy
+way to run commands as root. If you specify a user or group in the
+CONFIGURE_OWNER or CONFIGURE_GROUP options, then that user and/or any users who
+are members of that group will trivially be able to obtain root privileges.
+
+Up to Exim version 4.72, the runtime configuration file was also permitted to
+be writeable by the Exim user and/or group. That has been changed in Exim 4.73
+since it offered a simple privilege escalation for any attacker who managed to
+compromise the Exim user account.
+
+A default configuration file, which will work correctly in simple situations,
+is provided in the file src/configure.default. If CONFIGURE_FILE defines just
+one filename, the installation process copies the default configuration to a
+new file of that name if it did not previously exist. If CONFIGURE_FILE is a
+list, no default is automatically installed. Chapter 7 is a "walk-through"
+discussion of the default configuration.
+
+
+6.1 Using a different configuration file
+----------------------------------------
+
+A one-off alternate configuration can be specified by the -C command line
+option, which may specify a single file or a list of files. However, when -C is
+used, Exim gives up its root privilege, unless called by root (or unless the
+argument for -C is identical to the built-in value from CONFIGURE_FILE), or is
+listed in the TRUSTED_CONFIG_LIST file and the caller is the Exim user or the
+user specified in the CONFIGURE_OWNER setting. -C is useful mainly for checking
+the syntax of configuration files before installing them. No owner or group
+checks are done on a configuration file specified by -C, if root privilege has
+been dropped.
+
+Even the Exim user is not trusted to specify an arbitrary configuration file
+with the -C option to be used with root privileges, unless that file is listed
+in the TRUSTED_CONFIG_LIST file. This locks out the possibility of testing a
+configuration using -C right through message reception and delivery, even if
+the caller is root. The reception works, but by that time, Exim is running as
+the Exim user, so when it re-execs to regain privilege for the delivery, the
+use of -C causes privilege to be lost. However, root can test reception and
+delivery using two separate commands (one to put a message in the queue, using
+-odq, and another to do the delivery, using -M).
+
+If ALT_CONFIG_PREFIX is defined in Local/Makefile, it specifies a prefix string
+with which any file named in a -C command line option must start. In addition,
+the filename must not contain the sequence "/../". There is no default setting
+for ALT_CONFIG_PREFIX; when it is unset, any filename can be used with -C.
+
+One-off changes to a configuration can be specified by the -D command line
+option, which defines and overrides values for macros used inside the
+configuration file. However, like -C, the use of this option by a
+non-privileged user causes Exim to discard its root privilege. If
+DISABLE_D_OPTION is defined in Local/Makefile, the use of -D is completely
+disabled, and its use causes an immediate error exit.
+
+The WHITELIST_D_MACROS option in Local/Makefile permits the binary builder to
+declare certain macro names trusted, such that root privilege will not
+necessarily be discarded. WHITELIST_D_MACROS defines a colon-separated list of
+macros which are considered safe and, if -D only supplies macros from this
+list, and the values are acceptable, then Exim will not give up root privilege
+if the caller is root, the Exim run-time user, or the CONFIGURE_OWNER, if set.
+This is a transition mechanism and is expected to be removed in the future.
+Acceptable values for the macros satisfy the regexp: "^[A-Za-z0-9_/.-]*$"
+
+Some sites may wish to use the same Exim binary on different machines that
+share a file system, but to use different configuration files on each machine.
+If CONFIGURE_FILE_USE_NODE is defined in Local/Makefile, Exim first looks for a
+file whose name is the configuration filename followed by a dot and the
+machine's node name, as obtained from the uname() function. If this file does
+not exist, the standard name is tried. This processing occurs for each filename
+in the list given by CONFIGURE_FILE or -C.
+
+In some esoteric situations different versions of Exim may be run under
+different effective uids and the CONFIGURE_FILE_USE_EUID is defined to help
+with this. See the comments in src/EDITME for details.
+
+
+6.2 Configuration file format
+-----------------------------
+
+Exim's configuration file is divided into a number of different parts. General
+option settings must always appear at the start of the file. The other parts
+are all optional, and may appear in any order. Each part other than the first
+is introduced by the word "begin" followed by at least one literal space, and
+the name of the part. The optional parts are:
+
+ * ACL: Access control lists for controlling incoming SMTP mail (see chapter
+ 44).
+
+ * authenticators: Configuration settings for the authenticator drivers. These
+ are concerned with the SMTP AUTH command (see chapter 33).
+
+ * routers: Configuration settings for the router drivers. Routers process
+ addresses and determine how the message is to be delivered (see chapters 15
+ -22).
+
+ * transports: Configuration settings for the transport drivers. Transports
+ define mechanisms for copying messages to destinations (see chapters 24-30
+ ).
+
+ * retry: Retry rules, for use when a message cannot be delivered immediately.
+ If there is no retry section, or if it is empty (that is, no retry rules
+ are defined), Exim will not retry deliveries. In this situation, temporary
+ errors are treated the same as permanent errors. Retry rules are discussed
+ in chapter 32.
+
+ * rewrite: Global address rewriting rules, for use when a message arrives and
+ when new addresses are generated during delivery. Rewriting is discussed in
+ chapter 31.
+
+ * local_scan: Private options for the local_scan() function. If you want to
+ use this feature, you must set
+
+ LOCAL_SCAN_HAS_OPTIONS=yes
+
+ in Local/Makefile before building Exim. Details of the local_scan()
+ facility are given in chapter 46.
+
+Leading and trailing white space in configuration lines is always ignored.
+
+Blank lines in the file, and lines starting with a # character (ignoring
+leading white space) are treated as comments and are ignored. Note: A #
+character other than at the beginning of a line is not treated specially, and
+does not introduce a comment.
+
+Any non-comment line can be continued by ending it with a backslash. Note that
+the general rule for white space means that trailing white space after the
+backslash and leading white space at the start of continuation lines is
+ignored. Comment lines beginning with # (but not empty lines) may appear in the
+middle of a sequence of continuation lines.
+
+A convenient way to create a configuration file is to start from the default,
+which is supplied in src/configure.default, and add, delete, or change settings
+as required.
+
+The ACLs, retry rules, and rewriting rules have their own syntax which is
+described in chapters 44, 32, and 31, respectively. The other parts of the
+configuration file have some syntactic items in common, and these are described
+below, from section 6.11 onwards. Before that, the inclusion, macro, and
+conditional facilities are described.
+
+
+6.3 File inclusions in the configuration file
+---------------------------------------------
+
+You can include other files inside Exim's runtime configuration file by using
+this syntax:
+
+.include <filename>
+.include_if_exists <filename>
+
+on a line by itself. Double quotes round the filename are optional. If you use
+the first form, a configuration error occurs if the file does not exist; the
+second form does nothing for non-existent files. The first form allows a
+relative name. It is resolved relative to the directory of the including file.
+For the second form an absolute filename is required.
+
+Includes may be nested to any depth, but remember that Exim reads its
+configuration file often, so it is a good idea to keep them to a minimum. If
+you change the contents of an included file, you must HUP the daemon, because
+an included file is read only when the configuration itself is read.
+
+The processing of inclusions happens early, at a physical line level, so, like
+comment lines, an inclusion can be used in the middle of an option setting, for
+example:
+
+hosts_lookup = a.b.c \
+ .include /some/file
+
+Include processing happens after macro processing (see below). Its effect is to
+process the lines of the included file as if they occurred inline where the
+inclusion appears.
+
+
+6.4 Macros in the configuration file
+------------------------------------
+
+If a line in the main part of the configuration (that is, before the first
+"begin" line) begins with an upper case letter, it is taken as a macro
+definition, and must be of the form
+
+<name> = <rest of line>
+
+The name must consist of letters, digits, and underscores, and need not all be
+in upper case, though that is recommended. The rest of the line, including any
+continuations, is the replacement text, and has leading and trailing white
+space removed. Quotes are not removed. The replacement text can never end with
+a backslash character, but this doesn't seem to be a serious limitation.
+
+Macros may also be defined between router, transport, authenticator, or ACL
+definitions. They may not, however, be defined within an individual driver or
+ACL, or in the local_scan, retry, or rewrite sections of the configuration.
+
+
+6.5 Macro substitution
+----------------------
+
+Once a macro is defined, all subsequent lines in the file (and any included
+files) are scanned for the macro name; if there are several macros, the line is
+scanned for each, in turn, in the order in which the macros are defined. The
+replacement text is not re-scanned for the current macro, though it is scanned
+for subsequently defined macros. For this reason, a macro name may not contain
+the name of a previously defined macro as a substring. You could, for example,
+define
+
+ABCD_XYZ = <something>
+ABCD = <something else>
+
+but putting the definitions in the opposite order would provoke a configuration
+error. Macro expansion is applied to individual physical lines from the file,
+before checking for line continuation or file inclusion (see above). If a line
+consists solely of a macro name, and the expansion of the macro is empty, the
+line is ignored. A macro at the start of a line may turn the line into a
+comment line or a ".include" line.
+
+
+6.6 Redefining macros
+---------------------
+
+Once defined, the value of a macro can be redefined later in the configuration
+(or in an included file). Redefinition is specified by using == instead of =.
+For example:
+
+MAC = initial value
+...
+MAC == updated value
+
+Redefinition does not alter the order in which the macros are applied to the
+subsequent lines of the configuration file. It is still the same order in which
+the macros were originally defined. All that changes is the macro's value.
+Redefinition makes it possible to accumulate values. For example:
+
+MAC = initial value
+...
+MAC == MAC and something added
+
+This can be helpful in situations where the configuration file is built from a
+number of other files.
+
+
+6.7 Overriding macro values
+---------------------------
+
+The values set for macros in the configuration file can be overridden by the -D
+command line option, but Exim gives up its root privilege when -D is used,
+unless called by root or the Exim user. A definition on the command line using
+the -D option causes all definitions and redefinitions within the file to be
+ignored.
+
+
+6.8 Example of macro usage
+--------------------------
+
+As an example of macro usage, consider a configuration where aliases are looked
+up in a MySQL database. It helps to keep the file less cluttered if long
+strings such as SQL statements are defined separately as macros, for example:
+
+ALIAS_QUERY = select mailbox from user where \
+ login='${quote_mysql:$local_part}';
+
+This can then be used in a redirect router setting like this:
+
+data = ${lookup mysql{ALIAS_QUERY}}
+
+In earlier versions of Exim macros were sometimes used for domain, host, or
+address lists. In Exim 4 these are handled better by named lists - see section
+10.6.
+
+
+6.9 Builtin macros
+------------------
+
+Exim defines some macros depending on facilities available, which may differ
+due to build-time definitions and from one release to another. All of these
+macros start with an underscore. They can be used to conditionally include
+parts of a configuration (see below).
+
+The following classes of macros are defined:
+
+ _HAVE_* build-time defines
+ _DRIVER_ROUTER_* router drivers
+ _DRIVER_TRANSPORT_* transport drivers
+ _DRIVER_AUTHENTICATOR_* authenticator drivers
+ _LOG_* log_selector values
+ _OPT_MAIN_* main config options
+ _OPT_ROUTERS_* generic router options
+ _OPT_TRANSPORTS_* generic transport options
+ _OPT_AUTHENTICATORS_* generic authenticator options
+ _OPT_ROUTER_*_* private router options
+ _OPT_TRANSPORT_*_* private transport options
+ _OPT_AUTHENTICATOR_*_* private authenticator options
+
+Use an "exim -bP macros" command to get the list of macros.
+
+
+6.10 Conditional skips in the configuration file
+------------------------------------------------
+
+You can use the directives ".ifdef", ".ifndef", ".elifdef", ".elifndef",
+".else", and ".endif" to dynamically include or exclude portions of the
+configuration file. The processing happens whenever the file is read (that is,
+when an Exim binary starts to run).
+
+The implementation is very simple. Instances of the first four directives must
+be followed by text that includes the names of one or macros. The condition
+that is tested is whether or not any macro substitution has taken place in the
+line. Thus:
+
+.ifdef AAA
+message_size_limit = 50M
+.else
+message_size_limit = 100M
+.endif
+
+sets a message size limit of 50M if the macro "AAA" is defined (or "A" or
+"AA"), and 100M otherwise. If there is more than one macro named on the line,
+the condition is true if any of them are defined. That is, it is an "or"
+condition. To obtain an "and" condition, you need to use nested ".ifdef"s.
+
+Although you can use a macro expansion to generate one of these directives, it
+is not very useful, because the condition "there was a macro substitution in
+this line" will always be true.
+
+Text following ".else" and ".endif" is ignored, and can be used as comment to
+clarify complicated nestings.
+
+
+6.11 Common option syntax
+-------------------------
+
+For the main set of options, driver options, and local_scan() options, each
+setting is on a line by itself, and starts with a name consisting of lower-case
+letters and underscores. Many options require a data value, and in these cases
+the name must be followed by an equals sign (with optional white space) and
+then the value. For example:
+
+qualify_domain = mydomain.example.com
+
+Some option settings may contain sensitive data, for example, passwords for
+accessing databases. To stop non-admin users from using the -bP command line
+option to read these values, you can precede the option settings with the word
+"hide". For example:
+
+hide mysql_servers = localhost/users/admin/secret-password
+
+For non-admin users, such options are displayed like this:
+
+mysql_servers = <value not displayable>
+
+If "hide" is used on a driver option, it hides the value of that option on all
+instances of the same driver.
+
+The following sections describe the syntax used for the different data types
+that are found in option settings.
+
+
+6.12 Boolean options
+--------------------
+
+Options whose type is given as boolean are on/off switches. There are two
+different ways of specifying such options: with and without a data value. If
+the option name is specified on its own without data, the switch is turned on;
+if it is preceded by "no_" or "not_" the switch is turned off. However, boolean
+options may be followed by an equals sign and one of the words "true", "false",
+"yes", or "no", as an alternative syntax. For example, the following two
+settings have exactly the same effect:
+
+queue_only
+queue_only = true
+
+The following two lines also have the same (opposite) effect:
+
+no_queue_only
+queue_only = false
+
+You can use whichever syntax you prefer.
+
+
+6.13 Integer values
+-------------------
+
+If an option's type is given as "integer", the value can be given in decimal,
+hexadecimal, or octal. If it starts with a digit greater than zero, a decimal
+number is assumed. Otherwise, it is treated as an octal number unless it starts
+with the characters "0x", in which case the remainder is interpreted as a
+hexadecimal number.
+
+If an integer value is followed by the letter K, it is multiplied by 1024; if
+it is followed by the letter M, it is multiplied by 1024x1024; if by the letter
+G, 1024x1024x1024. When the values of integer option settings are output,
+values which are an exact multiple of 1024 or 1024x1024 are sometimes, but not
+always, printed using the letters K and M. The printing style is independent of
+the actual input format that was used.
+
+
+6.14 Octal integer values
+-------------------------
+
+If an option's type is given as "octal integer", its value is always
+interpreted as an octal number, whether or not it starts with the digit zero.
+Such options are always output in octal.
+
+
+6.15 Fixed point numbers
+------------------------
+
+If an option's type is given as "fixed-point", its value must be a decimal
+integer, optionally followed by a decimal point and up to three further digits.
+
+
+6.16 Time intervals
+-------------------
+
+A time interval is specified as a sequence of numbers, each followed by one of
+the following letters, with no intervening white space:
+
+ s seconds
+ m minutes
+ h hours
+ d days
+ w weeks
+
+For example, "3h50m" specifies 3 hours and 50 minutes. The values of time
+intervals are output in the same format. Exim does not restrict the values; it
+is perfectly acceptable, for example, to specify "90m" instead of "1h30m".
+
+
+6.17 String values
+------------------
+
+If an option's type is specified as "string", the value can be specified with
+or without double-quotes. If it does not start with a double-quote, the value
+consists of the remainder of the line plus any continuation lines, starting at
+the first character after any leading white space, with trailing white space
+removed, and with no interpretation of the characters in the string. Because
+Exim removes comment lines (those beginning with #) at an early stage, they can
+appear in the middle of a multi-line string. The following two settings are
+therefore equivalent:
+
+trusted_users = uucp:mail
+trusted_users = uucp:\
+ # This comment line is ignored
+ mail
+
+If a string does start with a double-quote, it must end with a closing
+double-quote, and any backslash characters other than those used for line
+continuation are interpreted as escape characters, as follows:
+
+ "\\" single backslash
+ "\n" newline
+ "\r" carriage return
+ "\t" tab
+ "\"<octal digits> up to 3 octal digits specify one character
+ "\x"<hex digits> up to 2 hexadecimal digits specify one character
+
+If a backslash is followed by some other character, including a double-quote
+character, that character replaces the pair.
+
+Quoting is necessary only if you want to make use of the backslash escapes to
+insert special characters, or if you need to specify a value with leading or
+trailing spaces. These cases are rare, so quoting is almost never needed in
+current versions of Exim. In versions of Exim before 3.14, quoting was required
+in order to continue lines, so you may come across older configuration files
+and examples that apparently quote unnecessarily.
+
+
+6.18 Expanded strings
+---------------------
+
+Some strings in the configuration file are subjected to string expansion, by
+which means various parts of the string may be changed according to the
+circumstances (see chapter 11). The input syntax for such strings is as just
+described; in particular, the handling of backslashes in quoted strings is done
+as part of the input process, before expansion takes place. However, backslash
+is also an escape character for the expander, so any backslashes that are
+required for that reason must be doubled if they are within a quoted
+configuration string.
+
+
+6.19 User and group names
+-------------------------
+
+User and group names are specified as strings, using the syntax described
+above, but the strings are interpreted specially. A user or group name must
+either consist entirely of digits, or be a name that can be looked up using the
+getpwnam() or getgrnam() function, as appropriate.
+
+
+6.20 List construction
+----------------------
+
+The data for some configuration options is a list of items, with colon as the
+default separator. Many of these options are shown with type "string list" in
+the descriptions later in this document. Others are listed as "domain list",
+"host list", "address list", or "local part list". Syntactically, they are all
+the same; however, those other than "string list" are subject to particular
+kinds of interpretation, as described in chapter 10.
+
+In all these cases, the entire list is treated as a single string as far as the
+input syntax is concerned. The trusted_users setting in section 6.17 above is
+an example. If a colon is actually needed in an item in a list, it must be
+entered as two colons. Leading and trailing white space on each item in a list
+is ignored. This makes it possible to include items that start with a colon,
+and in particular, certain forms of IPv6 address. For example, the list
+
+local_interfaces = 127.0.0.1 : ::::1
+
+contains two IP addresses, the IPv4 address 127.0.0.1 and the IPv6 address ::1.
+
+Note: Although leading and trailing white space is ignored in individual list
+items, it is not ignored when parsing the list. The space after the first colon
+in the example above is necessary. If it were not there, the list would be
+interpreted as the two items 127.0.0.1:: and 1.
+
+
+6.21 Changing list separators
+-----------------------------
+
+Doubling colons in IPv6 addresses is an unwelcome chore, so a mechanism was
+introduced to allow the separator character to be changed. If a list begins
+with a left angle bracket, followed by any punctuation character, that
+character is used instead of colon as the list separator. For example, the list
+above can be rewritten to use a semicolon separator like this:
+
+local_interfaces = <; 127.0.0.1 ; ::1
+
+This facility applies to all lists, with the exception of the list in
+log_file_path. It is recommended that the use of non-colon separators be
+confined to circumstances where they really are needed.
+
+It is also possible to use newline and other control characters (those with
+code values less than 32, plus DEL) as separators in lists. Such separators
+must be provided literally at the time the list is processed. For options that
+are string-expanded, you can write the separator using a normal escape
+sequence. This will be processed by the expander before the string is
+interpreted as a list. For example, if a newline-separated list of domains is
+generated by a lookup, you can process it directly by a line such as this:
+
+domains = <\n ${lookup mysql{.....}}
+
+This avoids having to change the list separator in such data. You are unlikely
+to want to use a control character as a separator in an option that is not
+expanded, because the value is literal text. However, it can be done by giving
+the value in quotes. For example:
+
+local_interfaces = "<\n 127.0.0.1 \n ::1"
+
+Unlike printing character separators, which can be included in list items by
+doubling, it is not possible to include a control character as data when it is
+set as the separator. Two such characters in succession are interpreted as
+enclosing an empty list item.
+
+
+6.22 Empty items in lists
+-------------------------
+
+An empty item at the end of a list is always ignored. In other words, trailing
+separator characters are ignored. Thus, the list in
+
+senders = user@domain :
+
+contains only a single item. If you want to include an empty string as one item
+in a list, it must not be the last item. For example, this list contains three
+items, the second of which is empty:
+
+senders = user1@domain : : user2@domain
+
+Note: There must be white space between the two colons, as otherwise they are
+interpreted as representing a single colon data character (and the list would
+then contain just one item). If you want to specify a list that contains just
+one, empty item, you can do it as in this example:
+
+senders = :
+
+In this case, the first item is empty, and the second is discarded because it
+is at the end of the list.
+
+
+6.23 Format of driver configurations
+------------------------------------
+
+There are separate parts in the configuration for defining routers, transports,
+and authenticators. In each part, you are defining a number of driver
+instances, each with its own set of options. Each driver instance is defined by
+a sequence of lines like this:
+
+<instance name>:
+ <option>
+ ...
+ <option>
+
+In the following example, the instance name is localuser, and it is followed by
+three options settings:
+
+localuser:
+ driver = accept
+ check_local_user
+ transport = local_delivery
+
+For each driver instance, you specify which Exim code module it uses - by the
+setting of the driver option - and (optionally) some configuration settings.
+For example, in the case of transports, if you want a transport to deliver with
+SMTP you would use the smtp driver; if you want to deliver to a local file you
+would use the appendfile driver. Each of the drivers is described in detail in
+its own separate chapter later in this manual.
+
+You can have several routers, transports, or authenticators that are based on
+the same underlying driver (each must have a different instance name).
+
+The order in which routers are defined is important, because addresses are
+passed to individual routers one by one, in order. The order in which
+transports are defined does not matter at all. The order in which
+authenticators are defined is used only when Exim, as a client, is searching
+them to find one that matches an authentication mechanism offered by the
+server.
+
+Within a driver instance definition, there are two kinds of option: generic and
+private. The generic options are those that apply to all drivers of the same
+type (that is, all routers, all transports or all authenticators). The driver
+option is a generic option that must appear in every definition. The private
+options are special for each driver, and none need appear, because they all
+have default values.
+
+The options may appear in any order, except that the driver option must precede
+any private options, since these depend on the particular driver. For this
+reason, it is recommended that driver always be the first option.
+
+Driver instance names, which are used for reference in log entries and
+elsewhere, can be any sequence of letters, digits, and underscores (starting
+with a letter) and must be unique among drivers of the same type. A router and
+a transport (for example) can each have the same name, but no two router
+instances can have the same name. The name of a driver instance should not be
+confused with the name of the underlying driver module. For example, the
+configuration lines:
+
+remote_smtp:
+ driver = smtp
+
+create an instance of the smtp transport driver whose name is remote_smtp. The
+same driver code can be used more than once, with different instance names and
+different option settings each time. A second instance of the smtp transport,
+with different options, might be defined thus:
+
+special_smtp:
+ driver = smtp
+ port = 1234
+ command_timeout = 10s
+
+The names remote_smtp and special_smtp would be used to reference these
+transport instances from routers, and these names would appear in log lines.
+
+Comment lines may be present in the middle of driver specifications. The full
+list of option settings for any particular driver instance, including all the
+defaulted values, can be extracted by making use of the -bP command line
+option.
+
+
+
+===============================================================================
+7. THE DEFAULT CONFIGURATION FILE
+
+The default configuration file supplied with Exim as src/configure.default is
+sufficient for a host with simple mail requirements. As an introduction to the
+way Exim is configured, this chapter "walks through" the default configuration,
+giving brief explanations of the settings. Detailed descriptions of the options
+are given in subsequent chapters. The default configuration file itself
+contains extensive comments about ways you might want to modify the initial
+settings. However, note that there are many options that are not mentioned at
+all in the default configuration.
+
+
+7.1 Macros
+----------
+
+All macros should be defined before any options.
+
+One macro is specified, but commented out, in the default configuration:
+
+# ROUTER_SMARTHOST=MAIL.HOSTNAME.FOR.CENTRAL.SERVER.EXAMPLE
+
+If all off-site mail is expected to be delivered to a "smarthost", then set the
+hostname here and uncomment the macro. This will affect which router is used
+later on. If this is left commented out, then Exim will perform direct-to-MX
+deliveries using a dnslookup router.
+
+In addition to macros defined here, Exim includes a number of built-in macros
+to enable configuration to be guarded by a binary built with support for a
+given feature. See section 6.9 for more details.
+
+
+7.2 Main configuration settings
+-------------------------------
+
+The main (global) configuration option settings section must always come first
+in the file, after the macros. The first thing you'll see in the file, after
+some initial comments, is the line
+
+# primary_hostname =
+
+This is a commented-out setting of the primary_hostname option. Exim needs to
+know the official, fully qualified name of your host, and this is where you can
+specify it. However, in most cases you do not need to set this option. When it
+is unset, Exim uses the uname() system function to obtain the host name.
+
+The first three non-comment configuration lines are as follows:
+
+domainlist local_domains = @
+domainlist relay_to_domains =
+hostlist relay_from_hosts = 127.0.0.1
+
+These are not, in fact, option settings. They are definitions of two named
+domain lists and one named host list. Exim allows you to give names to lists of
+domains, hosts, and email addresses, in order to make it easier to manage the
+configuration file (see section 10.6).
+
+The first line defines a domain list called local_domains; this is used later
+in the configuration to identify domains that are to be delivered on the local
+host.
+
+There is just one item in this list, the string "@". This is a special form of
+entry which means "the name of the local host". Thus, if the local host is
+called a.host.example, mail to any.user@a.host.example is expected to be
+delivered locally. Because the local host's name is referenced indirectly, the
+same configuration file can be used on different hosts.
+
+The second line defines a domain list called relay_to_domains, but the list
+itself is empty. Later in the configuration we will come to the part that
+controls mail relaying through the local host; it allows relaying to any
+domains in this list. By default, therefore, no relaying on the basis of a mail
+domain is permitted.
+
+The third line defines a host list called relay_from_hosts. This list is used
+later in the configuration to permit relaying from any host or IP address that
+matches the list. The default contains just the IP address of the IPv4 loopback
+interface, which means that processes on the local host are able to submit mail
+for relaying by sending it over TCP/IP to that interface. No other hosts are
+permitted to submit messages for relaying.
+
+Just to be sure there's no misunderstanding: at this point in the configuration
+we aren't actually setting up any controls. We are just defining some domains
+and hosts that will be used in the controls that are specified later.
+
+The next two configuration lines are genuine option settings:
+
+acl_smtp_rcpt = acl_check_rcpt
+acl_smtp_data = acl_check_data
+
+These options specify Access Control Lists (ACLs) that are to be used during an
+incoming SMTP session for every recipient of a message (every RCPT command),
+and after the contents of the message have been received, respectively. The
+names of the lists are acl_check_rcpt and acl_check_data, and we will come to
+their definitions below, in the ACL section of the configuration. The RCPT ACL
+controls which recipients are accepted for an incoming message - if a
+configuration does not provide an ACL to check recipients, no SMTP mail can be
+accepted. The DATA ACL allows the contents of a message to be checked.
+
+Two commented-out option settings are next:
+
+# av_scanner = clamd:/tmp/clamd
+# spamd_address = 127.0.0.1 783
+
+These are example settings that can be used when Exim is compiled with the
+content-scanning extension. The first specifies the interface to the virus
+scanner, and the second specifies the interface to SpamAssassin. Further
+details are given in chapter 45.
+
+Three more commented-out option settings follow:
+
+# tls_advertise_hosts = *
+# tls_certificate = /etc/ssl/exim.crt
+# tls_privatekey = /etc/ssl/exim.pem
+
+These are example settings that can be used when Exim is compiled with support
+for TLS (aka SSL) as described in section 4.7. The first one specifies the list
+of clients that are allowed to use TLS when connecting to this server; in this
+case, the wildcard means all clients. The other options specify where Exim
+should find its TLS certificate and private key, which together prove the
+server's identity to any clients that connect. More details are given in
+chapter 43.
+
+Another two commented-out option settings follow:
+
+# daemon_smtp_ports = 25 : 465 : 587
+# tls_on_connect_ports = 465
+
+These options provide better support for roaming users who wish to use this
+server for message submission. They are not much use unless you have turned on
+TLS (as described in the previous paragraph) and authentication (about which
+more in section 7.8). Mail submission from mail clients (MUAs) should be
+separate from inbound mail to your domain (MX delivery) for various good
+reasons (eg, ability to impose much saner TLS protocol and ciphersuite
+requirements without unintended consequences). RFC 6409 (previously 4409)
+specifies use of port 587 for SMTP Submission, which uses STARTTLS, so this is
+the "submission" port. RFC 8314 specifies use of port 465 as the "submissions"
+protocol, which should be used in preference to 587. You should also consider
+deploying SRV records to help clients find these ports. Older names for
+"submissions" are "smtps" and "ssmtp".
+
+Two more commented-out options settings follow:
+
+# qualify_domain =
+# qualify_recipient =
+
+The first of these specifies a domain that Exim uses when it constructs a
+complete email address from a local login name. This is often needed when Exim
+receives a message from a local process. If you do not set qualify_domain, the
+value of primary_hostname is used. If you set both of these options, you can
+have different qualification domains for sender and recipient addresses. If you
+set only the first one, its value is used in both cases.
+
+The following line must be uncommented if you want Exim to recognize addresses
+of the form user@[10.11.12.13] that is, with a "domain literal" (an IP address
+within square brackets) instead of a named domain.
+
+# allow_domain_literals
+
+The RFCs still require this form, but many people think that in the modern
+Internet it makes little sense to permit mail to be sent to specific hosts by
+quoting their IP addresses. This ancient format has been used by people who try
+to abuse hosts by using them for unwanted relaying. However, some people
+believe there are circumstances (for example, messages addressed to postmaster)
+where domain literals are still useful.
+
+The next configuration line is a kind of trigger guard:
+
+never_users = root
+
+It specifies that no delivery must ever be run as the root user. The normal
+convention is to set up root as an alias for the system administrator. This
+setting is a guard against slips in the configuration. The list of users
+specified by never_users is not, however, the complete list; the build-time
+configuration in Local/Makefile has an option called FIXED_NEVER_USERS
+specifying a list that cannot be overridden. The contents of never_users are
+added to this list. By default FIXED_NEVER_USERS also specifies root.
+
+When a remote host connects to Exim in order to send mail, the only information
+Exim has about the host's identity is its IP address. The next configuration
+line,
+
+host_lookup = *
+
+specifies that Exim should do a reverse DNS lookup on all incoming connections,
+in order to get a host name. This improves the quality of the logging
+information, but if you feel it is too expensive, you can remove it entirely,
+or restrict the lookup to hosts on "nearby" networks. Note that it is not
+always possible to find a host name from an IP address, because not all DNS
+reverse zones are maintained, and sometimes DNS servers are unreachable.
+
+The next two lines are concerned with ident callbacks, as defined by RFC 1413
+(hence their names):
+
+rfc1413_hosts = *
+rfc1413_query_timeout = 0s
+
+These settings cause Exim to avoid ident callbacks for all incoming SMTP calls.
+Few hosts offer RFC1413 service these days; calls have to be terminated by a
+timeout and this needlessly delays the startup of an incoming SMTP connection.
+If you have hosts for which you trust RFC1413 and need this information, you
+can change this.
+
+This line enables an efficiency SMTP option. It is negotiated by clients and
+not expected to cause problems but can be disabled if needed.
+
+prdr_enable = true
+
+When Exim receives messages over SMTP connections, it expects all addresses to
+be fully qualified with a domain, as required by the SMTP definition. However,
+if you are running a server to which simple clients submit messages, you may
+find that they send unqualified addresses. The two commented-out options:
+
+# sender_unqualified_hosts =
+# recipient_unqualified_hosts =
+
+show how you can specify hosts that are permitted to send unqualified sender
+and recipient addresses, respectively.
+
+The log_selector option is used to increase the detail of logging over the
+default:
+
+log_selector = +smtp_protocol_error +smtp_syntax_error \
+ +tls_certificate_verified
+
+The percent_hack_domains option is also commented out:
+
+# percent_hack_domains =
+
+It provides a list of domains for which the "percent hack" is to operate. This
+is an almost obsolete form of explicit email routing. If you do not know
+anything about it, you can safely ignore this topic.
+
+The next two settings in the main part of the default configuration are
+concerned with messages that have been "frozen" on Exim's queue. When a message
+is frozen, Exim no longer continues to try to deliver it. Freezing occurs when
+a bounce message encounters a permanent failure because the sender address of
+the original message that caused the bounce is invalid, so the bounce cannot be
+delivered. This is probably the most common case, but there are also other
+conditions that cause freezing, and frozen messages are not always bounce
+messages.
+
+ignore_bounce_errors_after = 2d
+timeout_frozen_after = 7d
+
+The first of these options specifies that failing bounce messages are to be
+discarded after 2 days in the queue. The second specifies that any frozen
+message (whether a bounce message or not) is to be timed out (and discarded)
+after a week. In this configuration, the first setting ensures that no failing
+bounce message ever lasts a week.
+
+Exim queues it's messages in a spool directory. If you expect to have large
+queues, you may consider using this option. It splits the spool directory into
+subdirectories to avoid file system degradation from many files in a single
+directory, resulting in better performance. Manual manipulation of queued
+messages becomes more complex (though fortunately not often needed).
+
+# split_spool_directory = true
+
+In an ideal world everybody follows the standards. For non-ASCII messages RFC
+2047 is a standard, allowing a maximum line length of 76 characters. Exim
+adheres that standard and won't process messages which violate this standard.
+(Even ${rfc2047:...} expansions will fail.) In particular, the Exim maintainers
+have had multiple reports of problems from Russian administrators of issues
+until they disable this check, because of some popular, yet buggy, mail
+composition software.
+
+# check_rfc2047_length = false
+
+If you need to be strictly RFC compliant you may wish to disable the 8BITMIME
+advertisement. Use this, if you exchange mails with systems that are not 8-bit
+clean.
+
+# accept_8bitmime = false
+
+Libraries you use may depend on specific environment settings. This imposes a
+security risk (e.g. PATH). There are two lists: keep_environment for the
+variables to import as they are, and add_environment for variables we want to
+set to a fixed value. Note that TZ is handled separately, by the $%timezone%$
+runtime option and by the TIMEZONE_DEFAULT buildtime option.
+
+# keep_environment = ^LDAP
+# add_environment = PATH=/usr/bin::/bin
+
+
+7.3 ACL configuration
+---------------------
+
+In the default configuration, the ACL section follows the main configuration.
+It starts with the line
+
+begin acl
+
+and it contains the definitions of two ACLs, called acl_check_rcpt and
+acl_check_data, that were referenced in the settings of acl_smtp_rcpt and
+acl_smtp_data above.
+
+The first ACL is used for every RCPT command in an incoming SMTP message. Each
+RCPT command specifies one of the message's recipients. The ACL statements are
+considered in order, until the recipient address is either accepted or
+rejected. The RCPT command is then accepted or rejected, according to the
+result of the ACL processing.
+
+acl_check_rcpt:
+
+This line, consisting of a name terminated by a colon, marks the start of the
+ACL, and names it.
+
+accept hosts = :
+
+This ACL statement accepts the recipient if the sending host matches the list.
+But what does that strange list mean? It doesn't actually contain any host
+names or IP addresses. The presence of the colon puts an empty item in the
+list; Exim matches this only if the incoming message did not come from a remote
+host, because in that case, the remote hostname is empty. The colon is
+important. Without it, the list itself is empty, and can never match anything.
+
+What this statement is doing is to accept unconditionally all recipients in
+messages that are submitted by SMTP from local processes using the standard
+input and output (that is, not using TCP/IP). A number of MUAs operate in this
+manner.
+
+deny domains = +local_domains
+ local_parts = ^[.] : ^.*[@%!/|]
+ message = Restricted characters in address
+
+deny domains = !+local_domains
+ local_parts = ^[./|] : ^.*[@%!] : ^.*/\\.\\./
+ message = Restricted characters in address
+
+These statements are concerned with local parts that contain any of the
+characters "@", "%", "!", "/", "|", or dots in unusual places. Although these
+characters are entirely legal in local parts (in the case of "@" and leading
+dots, only if correctly quoted), they do not commonly occur in Internet mail
+addresses.
+
+The first three have in the past been associated with explicitly routed
+addresses (percent is still sometimes used - see the percent_hack_domains
+option). Addresses containing these characters are regularly tried by spammers
+in an attempt to bypass relaying restrictions, and also by open relay testing
+programs. Unless you really need them it is safest to reject these characters
+at this early stage. This configuration is heavy-handed in rejecting these
+characters for all messages it accepts from remote hosts. This is a deliberate
+policy of being as safe as possible.
+
+The first rule above is stricter, and is applied to messages that are addressed
+to one of the local domains handled by this host. This is implemented by the
+first condition, which restricts it to domains that are listed in the
+local_domains domain list. The "+" character is used to indicate a reference to
+a named list. In this configuration, there is just one domain in local_domains,
+but in general there may be many.
+
+The second condition on the first statement uses two regular expressions to
+block local parts that begin with a dot or contain "@", "%", "!", "/", or "|".
+If you have local accounts that include these characters, you will have to
+modify this rule.
+
+Empty components (two dots in a row) are not valid in RFC 2822, but Exim allows
+them because they have been encountered in practice. (Consider the common
+convention of local parts constructed as "
+first-initial.second-initial.family-name" when applied to someone like the
+author of Exim, who has no second initial.) However, a local part starting with
+a dot or containing "/../" can cause trouble if it is used as part of a
+filename (for example, for a mailing list). This is also true for local parts
+that contain slashes. A pipe symbol can also be troublesome if the local part
+is incorporated unthinkingly into a shell command line.
+
+The second rule above applies to all other domains, and is less strict. This
+allows your own users to send outgoing messages to sites that use slashes and
+vertical bars in their local parts. It blocks local parts that begin with a
+dot, slash, or vertical bar, but allows these characters within the local part.
+However, the sequence "/../" is barred. The use of "@", "%", and "!" is
+blocked, as before. The motivation here is to prevent your users (or your
+users' viruses) from mounting certain kinds of attack on remote sites.
+
+accept local_parts = postmaster
+ domains = +local_domains
+
+This statement, which has two conditions, accepts an incoming address if the
+local part is postmaster and the domain is one of those listed in the
+local_domains domain list. The "+" character is used to indicate a reference to
+a named list. In this configuration, there is just one domain in local_domains,
+but in general there may be many.
+
+The presence of this statement means that mail to postmaster is never blocked
+by any of the subsequent tests. This can be helpful while sorting out problems
+in cases where the subsequent tests are incorrectly denying access.
+
+require verify = sender
+
+This statement requires the sender address to be verified before any subsequent
+ACL statement can be used. If verification fails, the incoming recipient
+address is refused. Verification consists of trying to route the address, to
+see if a bounce message could be delivered to it. In the case of remote
+addresses, basic verification checks only the domain, but callouts can be used
+for more verification if required. Section 44.44 discusses the details of
+address verification.
+
+accept hosts = +relay_from_hosts
+ control = submission
+
+This statement accepts the address if the message is coming from one of the
+hosts that are defined as being allowed to relay through this host. Recipient
+verification is omitted here, because in many cases the clients are dumb MUAs
+that do not cope well with SMTP error responses. For the same reason, the
+second line specifies "submission mode" for messages that are accepted. This is
+described in detail in section 48.1; it causes Exim to fix messages that are
+deficient in some way, for example, because they lack a Date: header line. If
+you are actually relaying out from MTAs, you should probably add recipient
+verification here, and disable submission mode.
+
+accept authenticated = *
+ control = submission
+
+This statement accepts the address if the client host has authenticated itself.
+Submission mode is again specified, on the grounds that such messages are most
+likely to come from MUAs. The default configuration does not define any
+authenticators, though it does include some nearly complete commented-out
+examples described in 7.8. This means that no client can in fact authenticate
+until you complete the authenticator definitions.
+
+require message = relay not permitted
+ domains = +local_domains : +relay_to_domains
+
+This statement rejects the address if its domain is neither a local domain nor
+one of the domains for which this host is a relay.
+
+require verify = recipient
+
+This statement requires the recipient address to be verified; if verification
+fails, the address is rejected.
+
+# deny dnslists = black.list.example
+# message = rejected because $sender_host_address \
+# is in a black list at $dnslist_domain\n\
+# $dnslist_text
+#
+# warn dnslists = black.list.example
+# add_header = X-Warning: $sender_host_address is in \
+# a black list at $dnslist_domain
+# log_message = found in $dnslist_domain
+
+These commented-out lines are examples of how you could configure Exim to check
+sending hosts against a DNS black list. The first statement rejects messages
+from blacklisted hosts, whereas the second just inserts a warning header line.
+
+# require verify = csa
+
+This commented-out line is an example of how you could turn on client SMTP
+authorization (CSA) checking. Such checks do DNS lookups for special SRV
+records.
+
+accept
+
+The final statement in the first ACL unconditionally accepts any recipient
+address that has successfully passed all the previous tests.
+
+acl_check_data:
+
+This line marks the start of the second ACL, and names it. Most of the contents
+of this ACL are commented out:
+
+# deny malware = *
+# message = This message contains a virus \
+# ($malware_name).
+
+These lines are examples of how to arrange for messages to be scanned for
+viruses when Exim has been compiled with the content-scanning extension, and a
+suitable virus scanner is installed. If the message is found to contain a
+virus, it is rejected with the given custom error message.
+
+# warn spam = nobody
+# message = X-Spam_score: $spam_score\n\
+# X-Spam_score_int: $spam_score_int\n\
+# X-Spam_bar: $spam_bar\n\
+# X-Spam_report: $spam_report
+
+These lines are an example of how to arrange for messages to be scanned by
+SpamAssassin when Exim has been compiled with the content-scanning extension,
+and SpamAssassin has been installed. The SpamAssassin check is run with
+"nobody" as its user parameter, and the results are added to the message as a
+series of extra header line. In this case, the message is not rejected,
+whatever the spam score.
+
+accept
+
+This final line in the DATA ACL accepts the message unconditionally.
+
+
+7.4 Router configuration
+------------------------
+
+The router configuration comes next in the default configuration, introduced by
+the line
+
+begin routers
+
+Routers are the modules in Exim that make decisions about where to send
+messages. An address is passed to each router, in turn, until it is either
+accepted, or failed. This means that the order in which you define the routers
+matters. Each router is fully described in its own chapter later in this
+manual. Here we give only brief overviews.
+
+# domain_literal:
+# driver = ipliteral
+# domains = !+local_domains
+# transport = remote_smtp
+
+This router is commented out because the majority of sites do not want to
+support domain literal addresses (those of the form user@[10.9.8.7]). If you
+uncomment this router, you also need to uncomment the setting of
+allow_domain_literals in the main part of the configuration.
+
+Which router is used next depends upon whether or not the ROUTER_SMARTHOST
+macro has been defined, per
+
+.ifdef ROUTER_SMARTHOST
+smarthost:
+#...
+.else
+dnslookup:
+#...
+.endif
+
+If ROUTER_SMARTHOST has been defined, either at the top of the file or on the
+command-line, then we route all non-local mail to that smarthost; otherwise,
+we'll perform DNS lookups for direct-to-MX lookup. Any mail which is to a local
+domain will skip these routers because of the domains option.
+
+smarthost:
+ driver = manualroute
+ domains = ! +local_domains
+ transport = smarthost_smtp
+ route_data = ROUTER_SMARTHOST
+ ignore_target_hosts = <; 0.0.0.0 ; 127.0.0.0/8 ; ::1
+ no_more
+
+This router only handles mail which is not to any local domains; this is
+specified by the line
+
+domains = ! +local_domains
+
+The domains option lists the domains to which this router applies, but the
+exclamation mark is a negation sign, so the router is used only for domains
+that are not in the domain list called local_domains (which was defined at the
+start of the configuration). The plus sign before local_domains indicates that
+it is referring to a named list. Addresses in other domains are passed on to
+the following routers.
+
+The name of the router driver is manualroute because we are manually specifying
+how mail should be routed onwards, instead of using DNS MX. While the name of
+this router instance is arbitrary, the driver option must be one of the driver
+modules that is in the Exim binary.
+
+With no pre-conditions other than domains, all mail for non-local domains will
+be handled by this router, and the no_more setting will ensure that no other
+routers will be used for messages matching the pre-conditions. See 3.12 for
+more on how the pre-conditions apply. For messages which are handled by this
+router, we provide a hostname to deliver to in route_data and the macro
+supplies the value; the address is then queued for the smarthost_smtp
+transport.
+
+dnslookup:
+ driver = dnslookup
+ domains = ! +local_domains
+ transport = remote_smtp
+ ignore_target_hosts = 0.0.0.0 : 127.0.0.0/8
+ no_more
+
+The domains option behaves as per smarthost, above.
+
+The name of the router driver is dnslookup, and is specified by the driver
+option. Do not be confused by the fact that the name of this router instance is
+the same as the name of the driver. The instance name is arbitrary, but the
+name set in the driver option must be one of the driver modules that is in the
+Exim binary.
+
+The dnslookup router routes addresses by looking up their domains in the DNS in
+order to obtain a list of hosts to which the address is routed. If the router
+succeeds, the address is queued for the remote_smtp transport, as specified by
+the transport option. If the router does not find the domain in the DNS, no
+further routers are tried because of the no_more setting, so the address fails
+and is bounced.
+
+The ignore_target_hosts option specifies a list of IP addresses that are to be
+entirely ignored. This option is present because a number of cases have been
+encountered where MX records in the DNS point to host names whose IP addresses
+are 0.0.0.0 or are in the 127 subnet (typically 127.0.0.1). Completely ignoring
+these IP addresses causes Exim to fail to route the email address, so it
+bounces. Otherwise, Exim would log a routing problem, and continue to try to
+deliver the message periodically until the address timed out.
+
+system_aliases:
+ driver = redirect
+ allow_fail
+ allow_defer
+ data = ${lookup{$local_part}lsearch{/etc/aliases}}
+# user = exim
+ file_transport = address_file
+ pipe_transport = address_pipe
+
+Control reaches this and subsequent routers only for addresses in the local
+domains. This router checks to see whether the local part is defined as an
+alias in the /etc/aliases file, and if so, redirects it according to the data
+that it looks up from that file. If no data is found for the local part, the
+value of the data option is empty, causing the address to be passed to the next
+router.
+
+/etc/aliases is a conventional name for the system aliases file that is often
+used. That is why it is referenced by from the default configuration file.
+However, you can change this by setting SYSTEM_ALIASES_FILE in Local/Makefile
+before building Exim.
+
+userforward:
+ driver = redirect
+ check_local_user
+# local_part_suffix = +* : -*
+# local_part_suffix_optional
+ file = $home/.forward
+# allow_filter
+ no_verify
+ no_expn
+ check_ancestor
+ file_transport = address_file
+ pipe_transport = address_pipe
+ reply_transport = address_reply
+
+This is the most complicated router in the default configuration. It is another
+redirection router, but this time it is looking for forwarding data set up by
+individual users. The check_local_user setting specifies a check that the local
+part of the address is the login name of a local user. If it is not, the router
+is skipped. The two commented options that follow check_local_user, namely:
+
+# local_part_suffix = +* : -*
+# local_part_suffix_optional
+
+show how you can specify the recognition of local part suffixes. If the first
+is uncommented, a suffix beginning with either a plus or a minus sign, followed
+by any sequence of characters, is removed from the local part and placed in the
+variable $local_part_suffix. The second suffix option specifies that the
+presence of a suffix in the local part is optional. When a suffix is present,
+the check for a local login uses the local part with the suffix removed.
+
+When a local user account is found, the file called .forward in the user's home
+directory is consulted. If it does not exist, or is empty, the router declines.
+Otherwise, the contents of .forward are interpreted as redirection data (see
+chapter 22 for more details).
+
+Traditional .forward files contain just a list of addresses, pipes, or files.
+Exim supports this by default. However, if allow_filter is set (it is commented
+out by default), the contents of the file are interpreted as a set of Exim or
+Sieve filtering instructions, provided the file begins with "#Exim filter" or "
+#Sieve filter", respectively. User filtering is discussed in the separate
+document entitled Exim's interfaces to mail filtering.
+
+The no_verify and no_expn options mean that this router is skipped when
+verifying addresses, or when running as a consequence of an SMTP EXPN command.
+There are two reasons for doing this:
+
+ 1. Whether or not a local user has a .forward file is not really relevant when
+ checking an address for validity; it makes sense not to waste resources
+ doing unnecessary work.
+
+ 2. More importantly, when Exim is verifying addresses or handling an EXPN
+ command during an SMTP session, it is running as the Exim user, not as
+ root. The group is the Exim group, and no additional groups are set up. It
+ may therefore not be possible for Exim to read users' .forward files at
+ this time.
+
+The setting of check_ancestor prevents the router from generating a new address
+that is the same as any previous address that was redirected. (This works round
+a problem concerning a bad interaction between aliasing and forwarding - see
+section 22.5).
+
+The final three option settings specify the transports that are to be used when
+forwarding generates a direct delivery to a file, or to a pipe, or sets up an
+auto-reply, respectively. For example, if a .forward file contains
+
+a.nother@elsewhere.example, /home/spqr/archive
+
+the delivery to /home/spqr/archive is done by running the address_file
+transport.
+
+localuser:
+ driver = accept
+ check_local_user
+# local_part_suffix = +* : -*
+# local_part_suffix_optional
+ transport = local_delivery
+
+The final router sets up delivery into local mailboxes, provided that the local
+part is the name of a local login, by accepting the address and assigning it to
+the local_delivery transport. Otherwise, we have reached the end of the
+routers, so the address is bounced. The commented suffix settings fulfil the
+same purpose as they do for the userforward router.
+
+
+7.5 Transport configuration
+---------------------------
+
+Transports define mechanisms for actually delivering messages. They operate
+only when referenced from routers, so the order in which they are defined does
+not matter. The transports section of the configuration starts with
+
+begin transports
+
+Two remote transports and four local transports are defined.
+
+remote_smtp:
+ driver = smtp
+ message_size_limit = ${if > {$max_received_linelength}{998} {1}{0}}
+.ifdef _HAVE_PRDR
+ hosts_try_prdr = *
+.endif
+
+This transport is used for delivering messages over SMTP connections. The list
+of remote hosts comes from the router. The message_size_limit usage is a hack
+to avoid sending on messages with over-long lines.
+
+The hosts_try_prdr option enables an efficiency SMTP option. It is negotiated
+between client and server and not expected to cause problems but can be
+disabled if needed. The built-in macro _HAVE_PRDR guards the use of the
+hosts_try_prdr configuration option.
+
+The other remote transport is used when delivering to a specific smarthost with
+whom there must be some kind of existing relationship, instead of the usual
+federated system.
+
+smarthost_smtp:
+ driver = smtp
+ message_size_limit = ${if > {$max_received_linelength}{998} {1}{0}}
+ multi_domain
+ #
+.ifdef _HAVE_TLS
+ # Comment out any of these which you have to, then file a Support
+ # request with your smarthost provider to get things fixed:
+ hosts_require_tls = *
+ tls_verify_hosts = *
+ # As long as tls_verify_hosts is enabled, this won't matter, but if you
+ # have to comment it out then this will at least log whether you succeed
+ # or not:
+ tls_try_verify_hosts = *
+ #
+ # The SNI name should match the name which we'll expect to verify;
+ # many mail systems don't use SNI and this doesn't matter, but if it does,
+ # we need to send a name which the remote site will recognize.
+ # This _should_ be the name which the smarthost operators specified as
+ # the hostname for sending your mail to.
+ tls_sni = ROUTER_SMARTHOST
+ #
+.ifdef _HAVE_OPENSSL
+ tls_require_ciphers = HIGH:!aNULL:@STRENGTH
+.endif
+.ifdef _HAVE_GNUTLS
+ tls_require_ciphers = SECURE192:-VERS-SSL3.0:-VERS-TLS1.0:-VERS-TLS1.1
+.endif
+.endif
+.ifdef _HAVE_PRDR
+ hosts_try_prdr = *
+.endif
+
+After the same message_size_limit hack, we then specify that this Transport can
+handle messages to multiple domains in one run. The assumption here is that
+you're routing all non-local mail to the same place and that place is happy to
+take all messages from you as quickly as possible. All other options depend
+upon built-in macros; if Exim was built without TLS support then no other
+options are defined. If TLS is available, then we configure "stronger than
+default" TLS ciphersuites and versions using the tls_require_ciphers option,
+where the value to be used depends upon the library providing TLS. Beyond that,
+the options adopt the stance that you should have TLS support available from
+your smarthost on today's Internet, so we turn on requiring TLS for the mail to
+be delivered, and requiring that the certificate be valid, and match the
+expected hostname. The tls_sni option can be used by service providers to
+select an appropriate certificate to present to you and here we re-use the
+ROUTER_SMARTHOST macro, because that is unaffected by CNAMEs present in DNS.
+You want to specify the hostname which you'll expect to validate for, and that
+should not be subject to insecure tampering via DNS results.
+
+For the hosts_try_prdr option see the previous transport.
+
+All other options are defaulted.
+
+local_delivery:
+ driver = appendfile
+ file = /var/mail/$local_part_data
+ delivery_date_add
+ envelope_to_add
+ return_path_add
+# group = mail
+# mode = 0660
+
+This appendfile transport is used for local delivery to user mailboxes in
+traditional BSD mailbox format.
+
+We prefer to avoid using $local_part directly to define the mailbox filename,
+as it is provided by a potential bad actor. Instead we use $local_part_data,
+the result of looking up $local_part in the user database (done by using
+check_local_user in the the router).
+
+By default appendfile runs under the uid and gid of the local user, which
+requires the sticky bit to be set on the /var/mail directory. Some systems use
+the alternative approach of running mail deliveries under a particular group
+instead of using the sticky bit. The commented options show how this can be
+done.
+
+Exim adds three headers to the message as it delivers it: Delivery-date:,
+Envelope-to: and Return-path:. This action is requested by the three
+similarly-named options above.
+
+address_pipe:
+ driver = pipe
+ return_output
+
+This transport is used for handling deliveries to pipes that are generated by
+redirection (aliasing or users' .forward files). The return_output option
+specifies that any output on stdout or stderr generated by the pipe is to be
+returned to the sender.
+
+address_file:
+ driver = appendfile
+ delivery_date_add
+ envelope_to_add
+ return_path_add
+
+This transport is used for handling deliveries to files that are generated by
+redirection. The name of the file is not specified in this instance of
+appendfile, because it comes from the redirect router.
+
+address_reply:
+ driver = autoreply
+
+This transport is used for handling automatic replies generated by users'
+filter files.
+
+
+7.6 Default retry rule
+----------------------
+
+The retry section of the configuration file contains rules which affect the way
+Exim retries deliveries that cannot be completed at the first attempt. It is
+introduced by the line
+
+begin retry
+
+In the default configuration, there is just one rule, which applies to all
+errors:
+
+* * F,2h,15m; G,16h,1h,1.5; F,4d,6h
+
+This causes any temporarily failing address to be retried every 15 minutes for
+2 hours, then at intervals starting at one hour and increasing by a factor of
+1.5 until 16 hours have passed, then every 6 hours up to 4 days. If an address
+is not delivered after 4 days of temporary failure, it is bounced. The time is
+measured from first failure, not from the time the message was received.
+
+If the retry section is removed from the configuration, or is empty (that is,
+if no retry rules are defined), Exim will not retry deliveries. This turns
+temporary errors into permanent errors.
+
+
+7.7 Rewriting configuration
+---------------------------
+
+The rewriting section of the configuration, introduced by
+
+begin rewrite
+
+contains rules for rewriting addresses in messages as they arrive. There are no
+rewriting rules in the default configuration file.
+
+
+7.8 Authenticators configuration
+--------------------------------
+
+The authenticators section of the configuration, introduced by
+
+begin authenticators
+
+defines mechanisms for the use of the SMTP AUTH command. The default
+configuration file contains two commented-out example authenticators which
+support plaintext username/password authentication using the standard PLAIN
+mechanism and the traditional but non-standard LOGIN mechanism, with Exim
+acting as the server. PLAIN and LOGIN are enough to support most MUA software.
+
+The example PLAIN authenticator looks like this:
+
+#PLAIN:
+# driver = plaintext
+# server_set_id = $auth2
+# server_prompts = :
+# server_condition = Authentication is not yet configured
+# server_advertise_condition = ${if def:tls_in_cipher }
+
+And the example LOGIN authenticator looks like this:
+
+#LOGIN:
+# driver = plaintext
+# server_set_id = $auth1
+# server_prompts = <| Username: | Password:
+# server_condition = Authentication is not yet configured
+# server_advertise_condition = ${if def:tls_in_cipher }
+
+The server_set_id option makes Exim remember the authenticated username in
+$authenticated_id, which can be used later in ACLs or routers. The
+server_prompts option configures the plaintext authenticator so that it
+implements the details of the specific authentication mechanism, i.e. PLAIN or
+LOGIN. The server_advertise_condition setting controls when Exim offers
+authentication to clients; in the examples, this is only when TLS or SSL has
+been started, so to enable the authenticators you also need to add support for
+TLS as described in section 7.2.
+
+The server_condition setting defines how to verify that the username and
+password are correct. In the examples it just produces an error message. To
+make the authenticators work, you can use a string expansion expression like
+one of the examples in chapter 34.
+
+Beware that the sequence of the parameters to PLAIN and LOGIN differ; the
+usercode and password are in different positions. Chapter 34 covers both.
+
+
+
+===============================================================================
+8. REGULAR EXPRESSIONS
+
+Exim supports the use of regular expressions in many of its options. It uses
+the PCRE regular expression library; this provides regular expression matching
+that is compatible with Perl 5. The syntax and semantics of regular expressions
+is discussed in online Perl manpages, in many Perl reference books, and also in
+Jeffrey Friedl's Mastering Regular Expressions, which is published by O'Reilly
+(see http://www.oreilly.com/catalog/regex2/).
+
+The documentation for the syntax and semantics of the regular expressions that
+are supported by PCRE is included in the PCRE distribution, and no further
+description is included here. The PCRE functions are called from Exim using the
+default option settings (that is, with no PCRE options set), except that the
+PCRE_CASELESS option is set when the matching is required to be
+case-insensitive.
+
+In most cases, when a regular expression is required in an Exim configuration,
+it has to start with a circumflex, in order to distinguish it from plain text
+or an "ends with" wildcard. In this example of a configuration setting, the
+second item in the colon-separated list is a regular expression.
+
+domains = a.b.c : ^\\d{3} : *.y.z : ...
+
+The doubling of the backslash is required because of string expansion that
+precedes interpretation - see section 11.1 for more discussion of this issue,
+and a way of avoiding the need for doubling backslashes. The regular expression
+that is eventually used in this example contains just one backslash. The
+circumflex is included in the regular expression, and has the normal effect of
+"anchoring" it to the start of the string that is being matched.
+
+There are, however, two cases where a circumflex is not required for the
+recognition of a regular expression: these are the match condition in a string
+expansion, and the matches condition in an Exim filter file. In these cases,
+the relevant string is always treated as a regular expression; if it does not
+start with a circumflex, the expression is not anchored, and can match anywhere
+in the subject string.
+
+In all cases, if you want a regular expression to match at the end of a string,
+you must code the $ metacharacter to indicate this. For example:
+
+domains = ^\\d{3}\\.example
+
+matches the domain 123.example, but it also matches 123.example.com. You need
+to use:
+
+domains = ^\\d{3}\\.example\$
+
+if you want example to be the top-level domain. The backslash before the $ is
+needed because string expansion also interprets dollar characters.
+
+
+
+===============================================================================
+9. FILE AND DATABASE LOOKUPS
+
+Exim can be configured to look up data in files or databases as it processes
+messages. Two different kinds of syntax are used:
+
+ 1. A string that is to be expanded may contain explicit lookup requests. These
+ cause parts of the string to be replaced by data that is obtained from the
+ lookup. Lookups of this type are conditional expansion items. Different
+ results can be defined for the cases of lookup success and failure. See
+ chapter 11, where string expansions are described in detail. The key for
+ the lookup is specified as part of the string expansion.
+
+ 2. Lists of domains, hosts, and email addresses can contain lookup requests as
+ a way of avoiding excessively long linear lists. In this case, the data
+ that is returned by the lookup is often (but not always) discarded; whether
+ the lookup succeeds or fails is what really counts. These kinds of list are
+ described in chapter 10. The key for the lookup is given by the context in
+ which the list is expanded.
+
+String expansions, lists, and lookups interact with each other in such a way
+that there is no order in which to describe any one of them that does not
+involve references to the others. Each of these three chapters makes more sense
+if you have read the other two first. If you are reading this for the first
+time, be aware that some of it will make a lot more sense after you have read
+chapters 10 and 11.
+
+
+9.1 Examples of different lookup syntax
+---------------------------------------
+
+It is easy to confuse the two different kinds of lookup, especially as the
+lists that may contain the second kind are always expanded before being
+processed as lists. Therefore, they may also contain lookups of the first kind.
+Be careful to distinguish between the following two examples:
+
+domains = ${lookup{$sender_host_address}lsearch{/some/file}}
+domains = lsearch;/some/file
+
+The first uses a string expansion, the result of which must be a domain list.
+No strings have been specified for a successful or a failing lookup; the
+defaults in this case are the looked-up data and an empty string, respectively.
+The expansion takes place before the string is processed as a list, and the
+file that is searched could contain lines like this:
+
+192.168.3.4: domain1:domain2:...
+192.168.1.9: domain3:domain4:...
+
+When the lookup succeeds, the result of the expansion is a list of domains (and
+possibly other types of item that are allowed in domain lists). The result of
+the expansion is not tainted.
+
+In the second example, the lookup is a single item in a domain list. It causes
+Exim to use a lookup to see if the domain that is being processed can be found
+in the file. The file could contains lines like this:
+
+domain1:
+domain2:
+
+Any data that follows the keys is not relevant when checking that the domain
+matches the list item.
+
+It is possible, though no doubt confusing, to use both kinds of lookup at once.
+Consider a file containing lines like this:
+
+192.168.5.6: lsearch;/another/file
+
+If the value of $sender_host_address is 192.168.5.6, expansion of the first
+domains setting above generates the second setting, which therefore causes a
+second lookup to occur.
+
+The lookup type may optionally be followed by a comma and a comma-separated
+list of options. Each option is a "name=value" pair. Whether an option is
+meaningful depands on the lookup type.
+
+The rest of this chapter describes the different lookup types that are
+available. Any of them can be used in any part of the configuration where a
+lookup is permitted.
+
+
+9.2 Lookup types
+----------------
+
+Two different types of data lookup are implemented:
+
+ * The single-key type requires the specification of a file in which to look,
+ and a single key to search for. The key must be a non-empty string for the
+ lookup to succeed. The lookup type determines how the file is searched.
+
+ The file string may not be tainted
+
+ All single-key lookups support the option "ret=key". If this is given and
+ the lookup (either underlying implementation or cached value) returns data,
+ the result is replaced with a non-tainted version of the lookup key.
+
+ * The query-style type accepts a generalized database query. No particular
+ key value is assumed by Exim for query-style lookups. You can use whichever
+ Exim variables you need to construct the database query.
+
+The code for each lookup type is in a separate source file that is included in
+the binary of Exim only if the corresponding compile-time option is set. The
+default settings in src/EDITME are:
+
+LOOKUP_DBM=yes
+LOOKUP_LSEARCH=yes
+
+which means that only linear searching and DBM lookups are included by default.
+For some types of lookup (e.g. SQL databases), you need to install appropriate
+libraries and header files before building Exim.
+
+
+9.3 Single-key lookup types
+---------------------------
+
+The following single-key lookup types are implemented:
+
+ * cdb: The given file is searched as a Constant DataBase file, using the key
+ string without a terminating binary zero. The cdb format is designed for
+ indexed files that are read frequently and never updated, except by total
+ re-creation. As such, it is particularly suitable for large files
+ containing aliases or other indexed data referenced by an MTA. Information
+ about cdb and tools for building the files can be found in several places:
+
+ https://cr.yp.to/cdb.html
+ https://www.corpit.ru/mjt/tinycdb.html
+ https://packages.debian.org/stable/utils/freecdb
+ https://github.com/philpennock/cdbtools (in Go)
+
+ A cdb distribution is not needed in order to build Exim with cdb support,
+ because the code for reading cdb files is included directly in Exim itself.
+ However, no means of building or testing cdb files is provided with Exim,
+ so you need to obtain a cdb distribution in order to do this.
+
+ * dbm: Calls to DBM library functions are used to extract data from the given
+ DBM file by looking up the record with the given key. A terminating binary
+ zero is included in the key that is passed to the DBM library. See section
+ 4.4 for a discussion of DBM libraries.
+
+ For all versions of Berkeley DB, Exim uses the DB_HASH style of database
+ when building DBM files using the exim_dbmbuild utility. However, when
+ using Berkeley DB versions 3 or 4, it opens existing databases for reading
+ with the DB_UNKNOWN option. This enables it to handle any of the types of
+ database that the library supports, and can be useful for accessing DBM
+ files created by other applications. (For earlier DB versions, DB_HASH is
+ always used.)
+
+ * dbmjz: This is the same as dbm, except that the lookup key is interpreted
+ as an Exim list; the elements of the list are joined together with ASCII
+ NUL characters to form the lookup key. An example usage would be to
+ authenticate incoming SMTP calls using the passwords from Cyrus SASL's /etc
+ /sasldb2 file with the gsasl authenticator or Exim's own cram_md5
+ authenticator.
+
+ * dbmnz: This is the same as dbm, except that a terminating binary zero is
+ not included in the key that is passed to the DBM library. You may need
+ this if you want to look up data in files that are created by or shared
+ with some other application that does not use terminating zeros. For
+ example, you need to use dbmnz rather than dbm if you want to authenticate
+ incoming SMTP calls using the passwords from Courier's /etc/
+ userdbshadow.dat file. Exim's utility program for creating DBM files (
+ exim_dbmbuild) includes the zeros by default, but has an option to omit
+ them (see section 54.9).
+
+ * dsearch: The given file must be an
+
+ absolute
+
+ directory path; this is searched for an entry whose name is the key by
+ calling the lstat() function. The key may not contain any forward slash
+ characters. If lstat() succeeds then so does the lookup.
+
+ The result is regarded as untainted.
+
+ Options for the lookup can be given by appending them after the word
+ "dsearch", separated by a comma. Options, if present, are a comma-separated
+ list having each element starting with a tag name and an equals.
+
+ Two options are supported, for the return value and for filtering match
+ candidates. The "ret" option requests an alternate result value of the
+ entire path for the entry. Example:
+
+ ${lookup {passwd} dsearch,ret=full {/etc}}
+
+ The default result is just the requested entry. The "filter" option
+ requests that only directory entries of a given type are matched. The match
+ value is one of "file", "dir" or "subdir" (the latter not matching "." or
+ ".."). Example:
+
+ ${lookup {passwd} dsearch,filter=file {/etc}}
+
+ The default matching is for any entry type, including directories and
+ symlinks.
+
+ An example of how this lookup can be used to support virtual domains is
+ given in section 51.7.
+
+ * iplsearch: The given file is a text file containing keys and data. A key is
+ terminated by a colon or white space or the end of the line. The keys in
+ the file must be IP addresses, or IP addresses with CIDR masks. Keys that
+ involve IPv6 addresses must be enclosed in quotes to prevent the first
+ internal colon being interpreted as a key terminator. For example:
+
+ 1.2.3.4: data for 1.2.3.4
+ 192.168.0.0/16: data for 192.168.0.0/16
+ "abcd::cdab": data for abcd::cdab
+ "abcd:abcd::/32" data for abcd:abcd::/32
+
+ The key for an iplsearch lookup must be an IP address (without a mask). The
+ file is searched linearly, using the CIDR masks where present, until a
+ matching key is found. The first key that matches is used; there is no
+ attempt to find a "best" match. Apart from the way the keys are matched,
+ the processing for iplsearch is the same as for lsearch.
+
+ Warning 1: Unlike most other single-key lookup types, a file of data for
+ iplsearch can not be turned into a DBM or cdb file, because those lookup
+ types support only literal keys.
+
+ Warning 2: In a host list, you must always use net-iplsearch so that the
+ implicit key is the host's IP address rather than its name (see section
+ 10.13).
+
+ Warning 3: Do not use an IPv4-mapped IPv6 address for a key; use the IPv4,
+ in dotted-quad form. (Exim converts IPv4-mapped IPv6 addresses to this
+ notation before executing the lookup.)
+
+ * json: The given file is a text file with a JSON structure. An element of
+ the structure is extracted, defined by the search key. The key is a list of
+ subelement selectors (colon-separated by default but changeable in the
+ usual way) which are applied in turn to select smaller and smaller portions
+ of the JSON structure. If a selector is numeric, it must apply to a JSON
+ array; the (zero-based) nunbered array element is selected. Otherwise it
+ must apply to a JSON object; the named element is selected. The final
+ resulting element can be a simple JSON type or a JSON object or array; for
+ the latter two a string-representation of the JSON is returned. For
+ elements of type string, the returned value is de-quoted.
+
+ * lsearch: The given file is a text file that is searched linearly for a line
+ beginning with the search key, terminated by a colon or white space or the
+ end of the line. The search is case-insensitive; that is, upper and lower
+ case letters are treated as the same. The first occurrence of the key that
+ is found in the file is used.
+
+ White space between the key and the colon is permitted. The remainder of
+ the line, with leading and trailing white space removed, is the data. This
+ can be continued onto subsequent lines by starting them with any amount of
+ white space, but only a single space character is included in the data at
+ such a junction. If the data begins with a colon, the key must be
+ terminated by a colon, for example:
+
+ baduser: :fail:
+
+ Empty lines and lines beginning with # are ignored, even if they occur in
+ the middle of an item. This is the traditional textual format of alias
+ files. Note that the keys in an lsearch file are literal strings. There is
+ no wildcarding of any kind.
+
+ In most lsearch files, keys are not required to contain colons or #
+ characters, or white space. However, if you need this feature, it is
+ available. If a key begins with a doublequote character, it is terminated
+ only by a matching quote (or end of line), and the normal escaping rules
+ apply to its contents (see section 6.17). An optional colon is permitted
+ after quoted keys (exactly as for unquoted keys). There is no special
+ handling of quotes for the data part of an lsearch line.
+
+ * nis: The given file is the name of a NIS map, and a NIS lookup is done with
+ the given key, without a terminating binary zero. There is a variant called
+ nis0 which does include the terminating binary zero in the key. This is
+ reportedly needed for Sun-style alias files. Exim does not recognize NIS
+ aliases; the full map names must be used.
+
+ * wildlsearch or nwildlsearch: These search a file linearly, like lsearch,
+ but instead of being interpreted as a literal string, each key in the file
+ may be wildcarded. The difference between these two lookup types is that
+ for wildlsearch, each key in the file is string-expanded before being used,
+ whereas for nwildlsearch, no expansion takes place.
+
+ Like lsearch, the testing is done case-insensitively. However, keys in the
+ file that are regular expressions can be made case-sensitive by the use of
+ "(-i)" within the pattern. The following forms of wildcard are recognized:
+
+ 1. The string may begin with an asterisk to mean "ends with". For example:
+
+ *.a.b.c data for anything.a.b.c
+ *fish data for anythingfish
+
+ 2. The string may begin with a circumflex to indicate a regular
+ expression. For example, for wildlsearch:
+
+ ^\N\d+\.a\.b\N data for <digits>.a.b
+
+ Note the use of "\N" to disable expansion of the contents of the
+ regular expression. If you are using nwildlsearch, where the keys are
+ not string-expanded, the equivalent entry is:
+
+ ^\d+\.a\.b data for <digits>.a.b
+
+ The case-insensitive flag is set at the start of compiling the regular
+ expression, but it can be turned off by using "(-i)" at an appropriate
+ point. For example, to make the entire pattern case-sensitive:
+
+ ^(?-i)\d+\.a\.b data for <digits>.a.b
+
+ If the regular expression contains white space or colon characters, you
+ must either quote it (see lsearch above), or represent these characters
+ in other ways. For example, "\s" can be used for white space and "\x3A"
+ for a colon. This may be easier than quoting, because if you quote, you
+ have to escape all the backslashes inside the quotes.
+
+ Note: It is not possible to capture substrings in a regular expression
+ match for later use, because the results of all lookups are cached. If
+ a lookup is repeated, the result is taken from the cache, and no actual
+ pattern matching takes place. The values of all the numeric variables
+ are unset after a (n)wildlsearch match.
+
+ 3. Although I cannot see it being of much use, the general matching
+ function that is used to implement (n)wildlsearch means that the string
+ may begin with a lookup name terminated by a semicolon, and followed by
+ lookup data. For example:
+
+ cdb;/some/file data for keys that match the file
+
+ The data that is obtained from the nested lookup is discarded.
+
+ Keys that do not match any of these patterns are interpreted literally. The
+ continuation rules for the data are the same as for lsearch, and keys may
+ be followed by optional colons.
+
+ Warning: Unlike most other single-key lookup types, a file of data for (n)
+ wildlsearch can not be turned into a DBM or cdb file, because those lookup
+ types support only literal keys.
+
+ * spf: If Exim is built with SPF support, manual lookups can be done (as
+ opposed to the standard ACL condition method). For details see section 58.4
+ .
+
+
+9.4 Query-style lookup types
+----------------------------
+
+The supported query-style lookup types are listed below. Further details about
+many of them are given in later sections.
+
+ * dnsdb: This does a DNS search for one or more records whose domain names
+ are given in the supplied query. The resulting data is the contents of the
+ records. See section 9.10.
+
+ * ibase: This does a lookup in an InterBase database.
+
+ * ldap: This does an LDAP lookup using a query in the form of a URL, and
+ returns attributes from a single entry. There is a variant called ldapm
+ that permits values from multiple entries to be returned. A third variant
+ called ldapdn returns the Distinguished Name of a single entry instead of
+ any attribute values. See section 9.14.
+
+ * mysql: The format of the query is an SQL statement that is passed to a
+ MySQL database. See section 9.21.
+
+ * nisplus: This does a NIS+ lookup using a query that can specify the name of
+ the field to be returned. See section 9.20.
+
+ * oracle: The format of the query is an SQL statement that is passed to an
+ Oracle database. See section 9.21.
+
+ * passwd is a query-style lookup with queries that are just user names. The
+ lookup calls getpwnam() to interrogate the system password data, and on
+ success, the result string is the same as you would get from an lsearch
+ lookup on a traditional /etc/passwd file, though with "*" for the password
+ value. For example:
+
+ *:42:42:King Rat:/home/kr:/bin/bash
+
+ * pgsql: The format of the query is an SQL statement that is passed to a
+ PostgreSQL database. See section 9.21.
+
+ * redis: The format of the query is either a simple get or simple set, passed
+ to a Redis database. See section 9.21.
+
+ * sqlite: The format of the query is new an optional filename
+
+ followed by an SQL statement that is passed to an SQLite database. See
+ section 9.26.
+
+ * testdb: This is a lookup type that is used for testing Exim. It is not
+ likely to be useful in normal operation.
+
+ * whoson: Whoson (http://whoson.sourceforge.net) is a protocol that allows a
+ server to check whether a particular (dynamically allocated) IP address is
+ currently allocated to a known (trusted) user and, optionally, to obtain
+ the identity of the said user. For SMTP servers, Whoson was popular at one
+ time for "POP before SMTP" authentication, but that approach has been
+ superseded by SMTP authentication. In Exim, Whoson can be used to implement
+ "POP before SMTP" checking using ACL statements such as
+
+ require condition = \
+ ${lookup whoson {$sender_host_address}{yes}{no}}
+
+ The query consists of a single IP address. The value returned is the name
+ of the authenticated user, which is stored in the variable $value. However,
+ in this example, the data in $value is not used; the result of the lookup
+ is one of the fixed strings "yes" or "no".
+
+
+9.5 Temporary errors in lookups
+-------------------------------
+
+Lookup functions can return temporary error codes if the lookup cannot be
+completed. For example, an SQL or LDAP database might be unavailable. For this
+reason, it is not advisable to use a lookup that might do this for critical
+options such as a list of local domains.
+
+When a lookup cannot be completed in a router or transport, delivery of the
+message (to the relevant address) is deferred, as for any other temporary
+error. In other circumstances Exim may assume the lookup has failed, or may
+give up altogether.
+
+
+9.6 Default values in single-key lookups
+----------------------------------------
+
+In this context, a "default value" is a value specified by the administrator
+that is to be used if a lookup fails.
+
+Note: This section applies only to single-key lookups. For query-style lookups,
+the facilities of the query language must be used. An attempt to specify a
+default for a query-style lookup provokes an error.
+
+If "*" is added to a single-key lookup type (for example, lsearch*) and the
+initial lookup fails, the key "*" is looked up in the file to provide a default
+value. See also the section on partial matching below.
+
+Alternatively, if "*@" is added to a single-key lookup type (for example dbm*@)
+then, if the initial lookup fails and the key contains an @ character, a second
+lookup is done with everything before the last @ replaced by *. This makes it
+possible to provide per-domain defaults in alias files that include the domains
+in the keys. If the second lookup fails (or doesn't take place because there is
+no @ in the key), "*" is looked up. For example, a redirect router might
+contain:
+
+data = ${lookup{$local_part@$domain}lsearch*@{/etc/mix-aliases}}
+
+Suppose the address that is being processed is jane@eyre.example. Exim looks up
+these keys, in this order:
+
+jane@eyre.example
+*@eyre.example
+*
+
+The data is taken from whichever key it finds first. Note: In an lsearch file,
+this does not mean the first of these keys in the file. A complete scan is done
+for each key, and only if it is not found at all does Exim move on to try the
+next key.
+
+
+9.7 Partial matching in single-key lookups
+------------------------------------------
+
+The normal operation of a single-key lookup is to search the file for an exact
+match with the given key. However, in a number of situations where domains are
+being looked up, it is useful to be able to do partial matching. In this case,
+information in the file that has a key starting with "*." is matched by any
+domain that ends with the components that follow the full stop. For example, if
+a key in a DBM file is
+
+*.dates.fict.example
+
+then when partial matching is enabled this is matched by (amongst others)
+2001.dates.fict.example and 1984.dates.fict.example. It is also matched by
+dates.fict.example, if that does not appear as a separate key in the file.
+
+Note: Partial matching is not available for query-style lookups. It is also not
+available for any lookup items in address lists (see section 10.20).
+
+Partial matching is implemented by doing a series of separate lookups using
+keys constructed by modifying the original subject key. This means that it can
+be used with any of the single-key lookup types, provided that partial matching
+keys beginning with a special prefix (default "*.") are included in the data
+file. Keys in the file that do not begin with the prefix are matched only by
+unmodified subject keys when partial matching is in use.
+
+Partial matching is requested by adding the string "partial-" to the front of
+the name of a single-key lookup type, for example, partial-dbm. When this is
+done, the subject key is first looked up unmodified; if that fails, "*." is
+added at the start of the subject key, and it is looked up again. If that
+fails, further lookups are tried with dot-separated components removed from the
+start of the subject key, one-by-one, and "*." added on the front of what
+remains.
+
+A minimum number of two non-* components are required. This can be adjusted by
+including a number before the hyphen in the search type. For example,
+partial3-lsearch specifies a minimum of three non-* components in the modified
+keys. Omitting the number is equivalent to "partial2-". If the subject key is
+2250.dates.fict.example then the following keys are looked up when the minimum
+number of non-* components is two:
+
+2250.dates.fict.example
+*.2250.dates.fict.example
+*.dates.fict.example
+*.fict.example
+
+As soon as one key in the sequence is successfully looked up, the lookup
+finishes.
+
+The use of "*." as the partial matching prefix is a default that can be
+changed. The motivation for this feature is to allow Exim to operate with file
+formats that are used by other MTAs. A different prefix can be supplied in
+parentheses instead of the hyphen after "partial". For example:
+
+domains = partial(.)lsearch;/some/file
+
+In this example, if the domain is a.b.c, the sequence of lookups is "a.b.c",
+".a.b.c", and ".b.c" (the default minimum of 2 non-wild components is
+unchanged). The prefix may consist of any punctuation characters other than a
+closing parenthesis. It may be empty, for example:
+
+domains = partial1()cdb;/some/file
+
+For this example, if the domain is a.b.c, the sequence of lookups is "a.b.c",
+"b.c", and "c".
+
+If "partial0" is specified, what happens at the end (when the lookup with just
+one non-wild component has failed, and the original key is shortened right down
+to the null string) depends on the prefix:
+
+ * If the prefix has zero length, the whole lookup fails.
+
+ * If the prefix has length 1, a lookup for just the prefix is done. For
+ example, the final lookup for "partial0(.)" is for "." alone.
+
+ * Otherwise, if the prefix ends in a dot, the dot is removed, and the
+ remainder is looked up. With the default prefix, therefore, the final
+ lookup is for "*" on its own.
+
+ * Otherwise, the whole prefix is looked up.
+
+If the search type ends in "*" or "*@" (see section 9.6 above), the search for
+an ultimate default that this implies happens after all partial lookups have
+failed. If "partial0" is specified, adding "*" to the search type has no effect
+with the default prefix, because the "*" key is already included in the
+sequence of partial lookups. However, there might be a use for lookup types
+such as "partial0(.)lsearch*".
+
+The use of "*" in lookup partial matching differs from its use as a wildcard in
+domain lists and the like. Partial matching works only in terms of
+dot-separated components; a key such as "*fict.example" in a database file is
+useless, because the asterisk in a partial matching subject key is always
+followed by a dot.
+
+
+9.8 Lookup caching
+------------------
+
+Exim caches all lookup results in order to avoid needless repetition of
+lookups. However, because (apart from the daemon) Exim operates as a collection
+of independent, short-lived processes, this caching applies only within a
+single Exim process. There is no inter-process lookup caching facility.
+
+For single-key lookups, Exim keeps the relevant files open in case there is
+another lookup that needs them. In some types of configuration this can lead to
+many files being kept open for messages with many recipients. To avoid hitting
+the operating system limit on the number of simultaneously open files, Exim
+closes the least recently used file when it needs to open more files than its
+own internal limit, which can be changed via the lookup_open_max option.
+
+The single-key lookup files are closed and the lookup caches are flushed at
+strategic points during delivery - for example, after all routing is complete.
+
+
+9.9 Quoting lookup data
+-----------------------
+
+When data from an incoming message is included in a query-style lookup, there
+is the possibility of special characters in the data messing up the syntax of
+the query. For example, a NIS+ query that contains
+
+[name=$local_part]
+
+will be broken if the local part happens to contain a closing square bracket.
+For NIS+, data can be enclosed in double quotes like this:
+
+[name="$local_part"]
+
+but this still leaves the problem of a double quote in the data. The rule for
+NIS+ is that double quotes must be doubled. Other lookup types have different
+rules, and to cope with the differing requirements, an expansion operator of
+the following form is provided:
+
+${quote_<lookup-type>:<string>}
+
+For example, the safest way to write the NIS+ query is
+
+[name="${quote_nisplus:$local_part}"]
+
+See chapter 11 for full coverage of string expansions. The quote operator can
+be used for all lookup types, but has no effect for single-key lookups, since
+no quoting is ever needed in their key strings.
+
+
+9.10 More about dnsdb
+---------------------
+
+The dnsdb lookup type uses the DNS as its database. A simple query consists of
+a record type and a domain name, separated by an equals sign. For example, an
+expansion string could contain:
+
+${lookup dnsdb{mx=a.b.example}{$value}fail}
+
+If the lookup succeeds, the result is placed in $value, which in this case is
+used on its own as the result. If the lookup does not succeed, the "fail"
+keyword causes a forced expansion failure - see section 11.4 for an explanation
+of what this means.
+
+The supported DNS record types are A, CNAME, MX, NS, PTR, SOA, SPF, SRV, TLSA
+and TXT, and, when Exim is compiled with IPv6 support, AAAA. If no type is
+given, TXT is assumed.
+
+For any record type, if multiple records are found, the data is returned as a
+concatenation, with newline as the default separator. The order, of course,
+depends on the DNS resolver. You can specify a different separator character
+between multiple records by putting a right angle-bracket followed immediately
+by the new separator at the start of the query. For example:
+
+${lookup dnsdb{>: a=host1.example}}
+
+It is permitted to specify a space as the separator character. Further white
+space is ignored. For lookup types that return multiple fields per record, an
+alternate field separator can be specified using a comma after the main
+separator character, followed immediately by the field separator.
+
+When the type is PTR, the data can be an IP address, written as normal;
+inversion and the addition of in-addr.arpa or ip6.arpa happens automatically.
+For example:
+
+${lookup dnsdb{ptr=192.168.4.5}{$value}fail}
+
+If the data for a PTR record is not a syntactically valid IP address, it is not
+altered and nothing is added.
+
+For an MX lookup, both the preference value and the host name are returned for
+each record, separated by a space. For an SRV lookup, the priority, weight,
+port, and host name are returned for each record, separated by spaces. The
+field separator can be modified as above.
+
+For TXT records with multiple items of data, only the first item is returned,
+unless a field separator is specified. To concatenate items without a
+separator, use a semicolon instead. For SPF records the default behaviour is to
+concatenate multiple items without using a separator.
+
+${lookup dnsdb{>\n,: txt=a.b.example}}
+${lookup dnsdb{>\n; txt=a.b.example}}
+${lookup dnsdb{spf=example.org}}
+
+It is permitted to specify a space as the separator character. Further white
+space is ignored.
+
+For an SOA lookup, while no result is obtained the lookup is redone with
+successively more leading components dropped from the given domain. Only the
+primary-nameserver field is returned unless a field separator is specified.
+
+${lookup dnsdb{>:,; soa=a.b.example.com}}
+
+
+9.11 Dnsdb lookup modifiers
+---------------------------
+
+Modifiers for dnsdb lookups are given by optional keywords, each followed by a
+comma, that may appear before the record type.
+
+The dnsdb lookup fails only if all the DNS lookups fail. If there is a
+temporary DNS error for any of them, the behaviour is controlled by a
+defer-option modifier. The possible keywords are "defer_strict", "defer_never",
+and "defer_lax". With "strict" behaviour, any temporary DNS error causes the
+whole lookup to defer. With "never" behaviour, a temporary DNS error is
+ignored, and the behaviour is as if the DNS lookup failed to find anything.
+With "lax" behaviour, all the queries are attempted, but a temporary DNS error
+causes the whole lookup to defer only if none of the other lookups succeed. The
+default is "lax", so the following lookups are equivalent:
+
+${lookup dnsdb{defer_lax,a=one.host.com:two.host.com}}
+${lookup dnsdb{a=one.host.com:two.host.com}}
+
+Thus, in the default case, as long as at least one of the DNS lookups yields
+some data, the lookup succeeds.
+
+Use of DNSSEC is controlled by a dnssec modifier. The possible keywords are
+"dnssec_strict", "dnssec_lax", and "dnssec_never". With "strict" or "lax"
+DNSSEC information is requested with the lookup. With "strict" a response from
+the DNS resolver that is not labelled as authenticated data is treated as
+equivalent to a temporary DNS error. The default is "lax".
+
+See also the $lookup_dnssec_authenticated variable.
+
+Timeout for the dnsdb lookup can be controlled by a retrans modifier. The form
+is "retrans_VAL" where VAL is an Exim time specification (e.g. "5s"). The
+default value is set by the main configuration option dns_retrans.
+
+Retries for the dnsdb lookup can be controlled by a retry modifier. The form if
+"retry_VAL" where VAL is an integer. The default count is set by the main
+configuration option dns_retry.
+
+Dnsdb lookup results are cached within a single process (and its children). The
+cache entry lifetime is limited to the smallest time-to-live (TTL) value of the
+set of returned DNS records.
+
+
+9.12 Pseudo dnsdb record types
+------------------------------
+
+By default, both the preference value and the host name are returned for each
+MX record, separated by a space. If you want only host names, you can use the
+pseudo-type MXH:
+
+${lookup dnsdb{mxh=a.b.example}}
+
+In this case, the preference values are omitted, and just the host names are
+returned.
+
+Another pseudo-type is ZNS (for "zone NS"). It performs a lookup for NS records
+on the given domain, but if none are found, it removes the first component of
+the domain name, and tries again. This process continues until NS records are
+found or there are no more components left (or there is a DNS error). In other
+words, it may return the name servers for a top-level domain, but it never
+returns the root name servers. If there are no NS records for the top-level
+domain, the lookup fails. Consider these examples:
+
+${lookup dnsdb{zns=xxx.quercite.com}}
+${lookup dnsdb{zns=xxx.edu}}
+
+Assuming that in each case there are no NS records for the full domain name,
+the first returns the name servers for quercite.com, and the second returns the
+name servers for edu.
+
+You should be careful about how you use this lookup because, unless the
+top-level domain does not exist, the lookup always returns some host names. The
+sort of use to which this might be put is for seeing if the name servers for a
+given domain are on a blacklist. You can probably assume that the name servers
+for the high-level domains such as com or co.uk are not going to be on such a
+list.
+
+A third pseudo-type is CSA (Client SMTP Authorization). This looks up SRV
+records according to the CSA rules, which are described in section 44.50.
+Although dnsdb supports SRV lookups directly, this is not sufficient because of
+the extra parent domain search behaviour of CSA. The result of a successful
+lookup such as:
+
+${lookup dnsdb {csa=$sender_helo_name}}
+
+has two space-separated fields: an authorization code and a target host name.
+The authorization code can be "Y" for yes, "N" for no, "X" for explicit
+authorization required but absent, or "?" for unknown.
+
+The pseudo-type A+ performs an AAAA and then an A lookup. All results are
+returned; defer processing (see below) is handled separately for each lookup.
+Example:
+
+${lookup dnsdb {>; a+=$sender_helo_name}}
+
+
+9.13 Multiple dnsdb lookups
+---------------------------
+
+In the previous sections, dnsdb lookups for a single domain are described.
+However, you can specify a list of domains or IP addresses in a single dnsdb
+lookup. The list is specified in the normal Exim way, with colon as the default
+separator, but with the ability to change this. For example:
+
+${lookup dnsdb{one.domain.com:two.domain.com}}
+${lookup dnsdb{a=one.host.com:two.host.com}}
+${lookup dnsdb{ptr = <; 1.2.3.4 ; 4.5.6.8}}
+
+In order to retain backwards compatibility, there is one special case: if the
+lookup type is PTR and no change of separator is specified, Exim looks to see
+if the rest of the string is precisely one IPv6 address. In this case, it does
+not treat it as a list.
+
+The data from each lookup is concatenated, with newline separators by default,
+in the same way that multiple DNS records for a single item are handled. A
+different separator can be specified, as described above.
+
+
+9.14 More about LDAP
+--------------------
+
+The original LDAP implementation came from the University of Michigan; this has
+become "Open LDAP", and there are now two different releases. Another
+implementation comes from Netscape, and Solaris 7 and subsequent releases
+contain inbuilt LDAP support. Unfortunately, though these are all compatible at
+the lookup function level, their error handling is different. For this reason
+it is necessary to set a compile-time variable when building Exim with LDAP, to
+indicate which LDAP library is in use. One of the following should appear in
+your Local/Makefile:
+
+LDAP_LIB_TYPE=UMICHIGAN
+LDAP_LIB_TYPE=OPENLDAP1
+LDAP_LIB_TYPE=OPENLDAP2
+LDAP_LIB_TYPE=NETSCAPE
+LDAP_LIB_TYPE=SOLARIS
+
+If LDAP_LIB_TYPE is not set, Exim assumes "OPENLDAP1", which has the same
+interface as the University of Michigan version.
+
+There are three LDAP lookup types in Exim. These behave slightly differently in
+the way they handle the results of a query:
+
+ * ldap requires the result to contain just one entry; if there are more, it
+ gives an error.
+
+ * ldapdn also requires the result to contain just one entry, but it is the
+ Distinguished Name that is returned rather than any attribute values.
+
+ * ldapm permits the result to contain more than one entry; the attributes
+ from all of them are returned.
+
+For ldap and ldapm, if a query finds only entries with no attributes, Exim
+behaves as if the entry did not exist, and the lookup fails. The format of the
+data returned by a successful lookup is described in the next section. First we
+explain how LDAP queries are coded.
+
+
+9.15 Format of LDAP queries
+---------------------------
+
+An LDAP query takes the form of a URL as defined in RFC 2255. For example, in
+the configuration of a redirect router one might have this setting:
+
+data = ${lookup ldap \
+ {ldap:///cn=$local_part,o=University%20of%20Cambridge,\
+ c=UK?mailbox?base?}}
+
+The URL may begin with "ldap" or "ldaps" if your LDAP library supports secure
+(encrypted) LDAP connections. The second of these ensures that an encrypted TLS
+connection is used.
+
+With sufficiently modern LDAP libraries, Exim supports forcing TLS over regular
+LDAP connections, rather than the SSL-on-connect "ldaps". See the
+ldap_start_tls option.
+
+Starting with Exim 4.83, the initialization of LDAP with TLS is more tightly
+controlled. Every part of the TLS configuration can be configured by settings
+in exim.conf. Depending on the version of the client libraries installed on
+your system, some of the initialization may have required setting options in /
+etc/ldap.conf or ~/.ldaprc to get TLS working with self-signed certificates.
+This revealed a nuance where the current UID that exim was running as could
+affect which config files it read. With Exim 4.83, these methods become
+optional, only taking effect if not specifically set in exim.conf.
+
+
+9.16 LDAP quoting
+-----------------
+
+Two levels of quoting are required in LDAP queries, the first for LDAP itself
+and the second because the LDAP query is represented as a URL. Furthermore,
+within an LDAP query, two different kinds of quoting are required. For this
+reason, there are two different LDAP-specific quoting operators.
+
+The quote_ldap operator is designed for use on strings that are part of filter
+specifications. Conceptually, it first does the following conversions on the
+string:
+
+* => \2A
+( => \28
+) => \29
+\ => \5C
+
+in accordance with RFC 2254. The resulting string is then quoted according to
+the rules for URLs, that is, all non-alphanumeric characters except
+
+! $ ' - . _ ( ) * +
+
+are converted to their hex values, preceded by a percent sign. For example:
+
+${quote_ldap: a(bc)*, a<yz>; }
+
+yields
+
+%20a%5C28bc%5C29%5C2A%2C%20a%3Cyz%3E%3B%20
+
+Removing the URL quoting, this is (with a leading and a trailing space):
+
+a\28bc\29\2A, a<yz>;
+
+The quote_ldap_dn operator is designed for use on strings that are part of base
+DN specifications in queries. Conceptually, it first converts the string by
+inserting a backslash in front of any of the following characters:
+
+, + " \ < > ;
+
+It also inserts a backslash before any leading spaces or # characters, and
+before any trailing spaces. (These rules are in RFC 2253.) The resulting string
+is then quoted according to the rules for URLs. For example:
+
+${quote_ldap_dn: a(bc)*, a<yz>; }
+
+yields
+
+%5C%20a(bc)*%5C%2C%20a%5C%3Cyz%5C%3E%5C%3B%5C%20
+
+Removing the URL quoting, this is (with a trailing space):
+
+\ a(bc)*\, a\<yz\>\;\
+
+There are some further comments about quoting in the section on LDAP
+authentication below.
+
+
+9.17 LDAP connections
+---------------------
+
+The connection to an LDAP server may either be over TCP/IP, or, when OpenLDAP
+is in use, via a Unix domain socket. The example given above does not specify
+an LDAP server. A server that is reached by TCP/IP can be specified in a query
+by starting it with
+
+ldap://<hostname>:<port>/...
+
+If the port (and preceding colon) are omitted, the standard LDAP port (389) is
+used. When no server is specified in a query, a list of default servers is
+taken from the ldap_default_servers configuration option. This supplies a
+colon-separated list of servers which are tried in turn until one successfully
+handles a query, or there is a serious error. Successful handling either
+returns the requested data, or indicates that it does not exist. Serious errors
+are syntactical, or multiple values when only a single value is expected.
+Errors which cause the next server to be tried are connection failures, bind
+failures, and timeouts.
+
+For each server name in the list, a port number can be given. The standard way
+of specifying a host and port is to use a colon separator (RFC 1738). Because
+ldap_default_servers is a colon-separated list, such colons have to be doubled.
+For example
+
+ldap_default_servers = ldap1.example.com::145:ldap2.example.com
+
+If ldap_default_servers is unset, a URL with no server name is passed to the
+LDAP library with no server name, and the library's default (normally the local
+host) is used.
+
+If you are using the OpenLDAP library, you can connect to an LDAP server using
+a Unix domain socket instead of a TCP/IP connection. This is specified by using
+"ldapi" instead of "ldap" in LDAP queries. What follows here applies only to
+OpenLDAP. If Exim is compiled with a different LDAP library, this feature is
+not available.
+
+For this type of connection, instead of a host name for the server, a pathname
+for the socket is required, and the port number is not relevant. The pathname
+can be specified either as an item in ldap_default_servers, or inline in the
+query. In the former case, you can have settings such as
+
+ldap_default_servers = /tmp/ldap.sock : backup.ldap.your.domain
+
+When the pathname is given in the query, you have to escape the slashes as
+"%2F" to fit in with the LDAP URL syntax. For example:
+
+${lookup ldap {ldapi://%2Ftmp%2Fldap.sock/o=...
+
+When Exim processes an LDAP lookup and finds that the "hostname" is really a
+pathname, it uses the Unix domain socket code, even if the query actually
+specifies "ldap" or "ldaps". In particular, no encryption is used for a socket
+connection. This behaviour means that you can use a setting of
+ldap_default_servers such as in the example above with traditional "ldap" or
+"ldaps" queries, and it will work. First, Exim tries a connection via the Unix
+domain socket; if that fails, it tries a TCP/IP connection to the backup host.
+
+If an explicit "ldapi" type is given in a query when a host name is specified,
+an error is diagnosed. However, if there are more items in ldap_default_servers
+, they are tried. In other words:
+
+ * Using a pathname with "ldap" or "ldaps" forces the use of the Unix domain
+ interface.
+
+ * Using "ldapi" with a host name causes an error.
+
+Using "ldapi" with no host or path in the query, and no setting of
+ldap_default_servers, does whatever the library does by default.
+
+
+9.18 LDAP authentication and control information
+------------------------------------------------
+
+The LDAP URL syntax provides no way of passing authentication and other control
+information to the server. To make this possible, the URL in an LDAP query may
+be preceded by any number of <name>=<value> settings, separated by spaces. If a
+value contains spaces it must be enclosed in double quotes, and when double
+quotes are used, backslash is interpreted in the usual way inside them. The
+following names are recognized:
+
+DEREFERENCE set the dereferencing parameter
+NETTIME set a timeout for a network operation
+USER set the DN, for authenticating the LDAP bind
+PASS set the password, likewise
+REFERRALS set the referrals parameter
+SERVERS set alternate server list for this query only
+SIZE set the limit for the number of entries returned
+TIME set the maximum waiting time for a query
+
+The value of the DEREFERENCE parameter must be one of the words "never",
+"searching", "finding", or "always". The value of the REFERRALS parameter must
+be "follow" (the default) or "nofollow". The latter stops the LDAP library from
+trying to follow referrals issued by the LDAP server.
+
+The name CONNECT is an obsolete name for NETTIME, retained for backwards
+compatibility. This timeout (specified as a number of seconds) is enforced from
+the client end for operations that can be carried out over a network.
+Specifically, it applies to network connections and calls to the ldap_result()
+function. If the value is greater than zero, it is used if
+LDAP_OPT_NETWORK_TIMEOUT is defined in the LDAP headers (OpenLDAP), or if
+LDAP_X_OPT_CONNECT_TIMEOUT is defined in the LDAP headers (Netscape SDK 4.1). A
+value of zero forces an explicit setting of "no timeout" for Netscape SDK; for
+OpenLDAP no action is taken.
+
+The TIME parameter (also a number of seconds) is passed to the server to set a
+server-side limit on the time taken to complete a search.
+
+The SERVERS parameter allows you to specify an alternate list of ldap servers
+to use for an individual lookup. The global ldap_default_servers option
+provides a default list of ldap servers, and a single lookup can specify a
+single ldap server to use. But when you need to do a lookup with a list of
+servers that is different than the default list (maybe different order, maybe a
+completely different set of servers), the SERVERS parameter allows you to
+specify this alternate list (colon-separated).
+
+Here is an example of an LDAP query in an Exim lookup that uses some of these
+values. This is a single line, folded to fit on the page:
+
+${lookup ldap
+ {user="cn=manager,o=University of Cambridge,c=UK" pass=secret
+ ldap:///o=University%20of%20Cambridge,c=UK?sn?sub?(cn=foo)}
+ {$value}fail}
+
+The encoding of spaces as "%20" is a URL thing which should not be done for any
+of the auxiliary data. Exim configuration settings that include lookups which
+contain password information should be preceded by "hide" to prevent non-admin
+users from using the -bP option to see their values.
+
+The auxiliary data items may be given in any order. The default is no
+connection timeout (the system timeout is used), no user or password, no limit
+on the number of entries returned, and no time limit on queries.
+
+When a DN is quoted in the USER= setting for LDAP authentication, Exim removes
+any URL quoting that it may contain before passing it LDAP. Apparently some
+libraries do this for themselves, but some do not. Removing the URL quoting has
+two advantages:
+
+ * It makes it possible to use the same quote_ldap_dn expansion for USER= DNs
+ as with DNs inside actual queries.
+
+ * It permits spaces inside USER= DNs.
+
+For example, a setting such as
+
+USER=cn=${quote_ldap_dn:$1}
+
+should work even if $1 contains spaces.
+
+Expanded data for the PASS= value should be quoted using the quote expansion
+operator, rather than the LDAP quote operators. The only reason this field
+needs quoting is to ensure that it conforms to the Exim syntax, which does not
+allow unquoted spaces. For example:
+
+PASS=${quote:$3}
+
+The LDAP authentication mechanism can be used to check passwords as part of
+SMTP authentication. See the ldapauth expansion string condition in chapter 11.
+
+
+9.19 Format of data returned by LDAP
+------------------------------------
+
+The ldapdn lookup type returns the Distinguished Name from a single entry as a
+sequence of values, for example
+
+cn=manager,o=University of Cambridge,c=UK
+
+The ldap lookup type generates an error if more than one entry matches the
+search filter, whereas ldapm permits this case, and inserts a newline in the
+result between the data from different entries. It is possible for multiple
+values to be returned for both ldap and ldapm, but in the former case you know
+that whatever values are returned all came from a single entry in the
+directory.
+
+In the common case where you specify a single attribute in your LDAP query, the
+result is not quoted, and does not contain the attribute name. If the attribute
+has multiple values, they are separated by commas. Any comma that is part of an
+attribute's value is doubled.
+
+If you specify multiple attributes, the result contains space-separated, quoted
+strings, each preceded by the attribute name and an equals sign. Within the
+quotes, the quote character, backslash, and newline are escaped with
+backslashes, and commas are used to separate multiple values for the attribute.
+Any commas in attribute values are doubled (permitting treatment of the values
+as a comma-separated list). Apart from the escaping, the string within quotes
+takes the same form as the output when a single attribute is requested.
+Specifying no attributes is the same as specifying all of an entry's
+attributes.
+
+Here are some examples of the output format. The first line of each pair is an
+LDAP query, and the second is the data that is returned. The attribute called
+attr1 has two values, one of them with an embedded comma, whereas attr2 has
+only one value. Both attributes are derived from attr (they have SUP attr in
+their schema definitions).
+
+ldap:///o=base?attr1?sub?(uid=fred)
+value1.1,value1,,2
+
+ldap:///o=base?attr2?sub?(uid=fred)
+value two
+
+ldap:///o=base?attr?sub?(uid=fred)
+value1.1,value1,,2,value two
+
+ldap:///o=base?attr1,attr2?sub?(uid=fred)
+attr1="value1.1,value1,,2" attr2="value two"
+
+ldap:///o=base??sub?(uid=fred)
+objectClass="top" attr1="value1.1,value1,,2" attr2="value two"
+
+You can make use of Exim's -be option to run expansion tests and thereby check
+the results of LDAP lookups. The extract operator in string expansions can be
+used to pick out individual fields from data that consists of key=value pairs.
+The listextract operator should be used to pick out individual values of
+attributes, even when only a single value is expected. The doubling of embedded
+commas allows you to use the returned data as a comma separated list (using the
+"<," syntax for changing the input list separator).
+
+
+9.20 More about NIS+
+--------------------
+
+NIS+ queries consist of a NIS+ indexed name followed by an optional colon and
+field name. If this is given, the result of a successful query is the contents
+of the named field; otherwise the result consists of a concatenation of
+field-name=field-value pairs, separated by spaces. Empty values and values
+containing spaces are quoted. For example, the query
+
+[name=mg1456],passwd.org_dir
+
+might return the string
+
+name=mg1456 passwd="" uid=999 gid=999 gcos="Martin Guerre"
+home=/home/mg1456 shell=/bin/bash shadow=""
+
+(split over two lines here to fit on the page), whereas
+
+[name=mg1456],passwd.org_dir:gcos
+
+would just return
+
+Martin Guerre
+
+with no quotes. A NIS+ lookup fails if NIS+ returns more than one table entry
+for the given indexed key. The effect of the quote_nisplus expansion operator
+is to double any quote characters within the text.
+
+
+9.21 SQL lookups
+----------------
+
+Exim can support lookups in InterBase, MySQL, Oracle, PostgreSQL, Redis, and
+SQLite databases. Queries for these databases contain SQL statements, so an
+example might be
+
+${lookup mysql{select mailbox from users where id='userx'}\
+ {$value}fail}
+
+If the result of the query contains more than one field, the data for each
+field in the row is returned, preceded by its name, so the result of
+
+${lookup pgsql{select home,name from users where id='userx'}\
+ {$value}}
+
+might be
+
+home=/home/userx name="Mister X"
+
+Empty values and values containing spaces are double quoted, with embedded
+quotes escaped by a backslash. If the result of the query contains just one
+field, the value is passed back verbatim, without a field name, for example:
+
+Mister X
+
+If the result of the query yields more than one row, it is all concatenated,
+with a newline between the data for each row.
+
+
+9.22 More about MySQL, PostgreSQL, Oracle, InterBase, and Redis
+---------------------------------------------------------------
+
+If any MySQL, PostgreSQL, Oracle, InterBase or Redis lookups are used, the
+mysql_servers, pgsql_servers, oracle_servers, ibase_servers, or redis_servers
+option (as appropriate) must be set to a colon-separated list of server
+information. (For MySQL and PostgreSQL, the global option need not be set if
+all queries contain their own server information - see section 9.23.) For all
+but Redis each item in the list is a slash-separated list of four items: host
+name, database name, user name, and password. In the case of Oracle, the host
+name field is used for the "service name", and the database name field is not
+used and should be empty. For example:
+
+hide oracle_servers = oracle.plc.example//userx/abcdwxyz
+
+Because password data is sensitive, you should always precede the setting with
+"hide", to prevent non-admin users from obtaining the setting via the -bP
+option. Here is an example where two MySQL servers are listed:
+
+hide mysql_servers = localhost/users/root/secret:\
+ otherhost/users/root/othersecret
+
+For MySQL and PostgreSQL, a host may be specified as <name>:<port> but because
+this is a colon-separated list, the colon has to be doubled. For each query,
+these parameter groups are tried in order until a connection is made and a
+query is successfully processed. The result of a query may be that no data is
+found, but that is still a successful query. In other words, the list of
+servers provides a backup facility, not a list of different places to look.
+
+For Redis the global option need not be specified if all queries contain their
+own server information - see section 9.23. If specified, the option must be set
+to a colon-separated list of server information. Each item in the list is a
+slash-separated list of three items: host, database number, and password.
+
+ 1. The host is required and may be either an IPv4 address and optional port
+ number (separated by a colon, which needs doubling due to the higher-level
+ list), or a Unix socket pathname enclosed in parentheses
+
+ 2. The database number is optional; if present that number is selected in the
+ backend
+
+ 3. The password is optional; if present it is used to authenticate to the
+ backend
+
+The quote_mysql, quote_pgsql, and quote_oracle expansion operators convert
+newline, tab, carriage return, and backspace to \n, \t, \r, and \b
+respectively, and the characters single-quote, double-quote, and backslash
+itself are escaped with backslashes.
+
+The quote_redis expansion operator escapes whitespace and backslash characters
+with a backslash.
+
+
+9.23 Specifying the server in the query
+---------------------------------------
+
+For MySQL, PostgreSQL and Redis lookups (but not currently for Oracle and
+InterBase), it is possible to specify a list of servers with an individual
+query. This is done by appending a comma-separated option to the query type:
+
+,servers=server1:server2:server3:...
+
+Each item in the list may take one of two forms:
+
+ 1. If it contains no slashes it is assumed to be just a host name. The
+ appropriate global option (mysql_servers or pgsql_servers) is searched for
+ a host of the same name, and the remaining parameters (database, user,
+ password) are taken from there.
+
+ 2. If it contains any slashes, it is taken as a complete parameter set.
+
+The list of servers is used in exactly the same way as the global list. Once a
+connection to a server has happened and a query has been successfully executed,
+processing of the lookup ceases.
+
+This feature is intended for use in master/slave situations where updates are
+occurring and you want to update the master rather than a slave. If the master
+is in the list as a backup for reading, you might have a global setting like
+this:
+
+mysql_servers = slave1/db/name/pw:\
+ slave2/db/name/pw:\
+ master/db/name/pw
+
+In an updating lookup, you could then write:
+
+${lookup mysql,servers=master {UPDATE ...} }
+
+That query would then be sent only to the master server. If, on the other hand,
+the master is not to be used for reading, and so is not present in the global
+option, you can still update it by a query of this form:
+
+${lookup pgsql,servers=master/db/name/pw {UPDATE ...} }
+
+An older syntax places the servers speciification before the qury, semicolon
+separated:
+
+${lookup mysql{servers=master; UPDATE ...} }
+
+The new version avoids potential issues with tainted arguments in the query,
+for explicit expansion. Note: server specifications in list-style lookups are
+still problematic.
+
+
+9.24 Special MySQL features
+---------------------------
+
+For MySQL, an empty host name or the use of "localhost" in mysql_servers causes
+a connection to the server on the local host by means of a Unix domain socket.
+An alternate socket can be specified in parentheses. An option group name for
+MySQL option files can be specified in square brackets; the default value is
+"exim". The full syntax of each item in mysql_servers is:
+
+<hostname>::<port>(<socket name>)[<option group>]/<database>/<user>/<password>
+
+Any of the four sub-parts of the first field can be omitted. For normal use on
+the local host it can be left blank or set to just "localhost".
+
+No database need be supplied - but if it is absent here, it must be given in
+the queries.
+
+If a MySQL query is issued that does not request any data (an insert, update,
+or delete command), the result of the lookup is the number of rows affected.
+
+Warning: This can be misleading. If an update does not actually change anything
+(for example, setting a field to the value it already has), the result is zero
+because no rows are affected.
+
+
+9.25 Special PostgreSQL features
+--------------------------------
+
+PostgreSQL lookups can also use Unix domain socket connections to the database.
+This is usually faster and costs less CPU time than a TCP/IP connection.
+However it can be used only if the mail server runs on the same machine as the
+database server. A configuration line for PostgreSQL via Unix domain sockets
+looks like this:
+
+hide pgsql_servers = (/tmp/.s.PGSQL.5432)/db/user/password : ...
+
+In other words, instead of supplying a host name, a path to the socket is
+given. The path name is enclosed in parentheses so that its slashes aren't
+visually confused with the delimiters for the other server parameters.
+
+If a PostgreSQL query is issued that does not request any data (an insert,
+update, or delete command), the result of the lookup is the number of rows
+affected.
+
+
+9.26 More about SQLite
+----------------------
+
+SQLite is different to the other SQL lookups because a filename is required in
+addition to the SQL query. An SQLite database is a single file, and there is no
+daemon as in the other SQL databases.
+
+The preferred way of specifying the file is by using the sqlite_dbfile option,
+set to an absolute path.
+
+A deprecated method is available, prefixing the query with the filename
+separated by white space. This means that the path name cannot contain white
+space. It also means that the query cannot use any tainted values, as that
+taints the entire query including the filename - resulting in a refusal to open
+the file.
+
+Here is a lookup expansion example:
+
+sqlite_dbfile = /some/thing/sqlitedb
+...
+${lookup sqlite {select name from aliases where id='userx';}}
+
+In a list, the syntax is similar. For example:
+
+domainlist relay_to_domains = sqlite;\
+ select * from relays where ip='$sender_host_address';
+
+The only character affected by the quote_sqlite operator is a single quote,
+which it doubles.
+
+The SQLite library handles multiple simultaneous accesses to the database
+internally. Multiple readers are permitted, but only one process can update at
+once. Attempts to access the database while it is being updated are rejected
+after a timeout period, during which the SQLite library waits for the lock to
+be released. In Exim, the default timeout is set to 5 seconds, but it can be
+changed by means of the sqlite_lock_timeout option.
+
+
+9.27 More about Redis
+---------------------
+
+Redis is a non-SQL database. Commands are simple get and set. Examples:
+
+${lookup redis{set keyname ${quote_redis:objvalue plus}}}
+${lookup redis{get keyname}}
+
+As of release 4.91, "lightweight" support for Redis Cluster is available.
+Requires redis_servers list to contain all the servers in the cluster, all of
+which must be reachable from the running exim instance. If the cluster has
+master/slave replication, the list must contain all the master and slave
+servers.
+
+When the Redis Cluster returns a "MOVED" response to a query, Exim does not
+immediately follow the redirection but treats the response as a DEFER, moving
+on to the next server in the redis_servers list until the correct server is
+reached.
+
+
+
+===============================================================================
+10. DOMAIN, HOST, ADDRESS, AND LOCAL PART LISTS
+
+A number of Exim configuration options contain lists of domains, hosts, email
+addresses, or local parts. For example, the hold_domains option contains a list
+of domains whose delivery is currently suspended. These lists are also used as
+data in ACL statements (see chapter 44), and as arguments to expansion
+conditions such as match_domain.
+
+Each item in one of these lists is a pattern to be matched against a domain,
+host, email address, or local part, respectively. In the sections below, the
+different types of pattern for each case are described, but first we cover some
+general facilities that apply to all four kinds of list.
+
+Note that other parts of Exim use a string list which does not support all the
+complexity available in domain, host, address and local part lists.
+
+
+10.1 Expansion of lists
+-----------------------
+
+Each list is expanded as a single string before it is used.
+
+Exception: the router headers_remove option, where list-item splitting is done
+before string-expansion.
+
+The result of expansion must be a list, possibly containing empty items, which
+is split up into separate items for matching. By default, colon is the
+separator character, but this can be varied if necessary. See sections 6.20 and
+6.22 for details of the list syntax; the second of these discusses the way to
+specify empty list items.
+
+If the string expansion is forced to fail, Exim behaves as if the item it is
+testing (domain, host, address, or local part) is not in the list. Other
+expansion failures cause temporary errors.
+
+If an item in a list is a regular expression, backslashes, dollars and possibly
+other special characters in the expression must be protected against
+misinterpretation by the string expander. The easiest way to do this is to use
+the "\N" expansion feature to indicate that the contents of the regular
+expression should not be expanded. For example, in an ACL you might have:
+
+deny senders = \N^\d{8}\w@.*\.baddomain\.example$\N : \
+ ${lookup{$domain}lsearch{/badsenders/bydomain}}
+
+The first item is a regular expression that is protected from expansion by "\
+N", whereas the second uses the expansion to obtain a list of unwanted senders
+based on the receiving domain.
+
+
+10.2 Negated items in lists
+---------------------------
+
+Items in a list may be positive or negative. Negative items are indicated by a
+leading exclamation mark, which may be followed by optional white space. A list
+defines a set of items (domains, etc). When Exim processes one of these lists,
+it is trying to find out whether a domain, host, address, or local part
+(respectively) is in the set that is defined by the list. It works like this:
+
+The list is scanned from left to right. If a positive item is matched, the
+subject that is being checked is in the set; if a negative item is matched, the
+subject is not in the set. If the end of the list is reached without the
+subject having matched any of the patterns, it is in the set if the last item
+was a negative one, but not if it was a positive one. For example, the list in
+
+domainlist relay_to_domains = !a.b.c : *.b.c
+
+matches any domain ending in .b.c except for a.b.c. Domains that match neither
+a.b.c nor *.b.c do not match, because the last item in the list is positive.
+However, if the setting were
+
+domainlist relay_to_domains = !a.b.c
+
+then all domains other than a.b.c would match because the last item in the list
+is negative. In other words, a list that ends with a negative item behaves as
+if it had an extra item ":*" on the end.
+
+Another way of thinking about positive and negative items in lists is to read
+the connector as "or" after a positive item and as "and" after a negative item.
+
+
+10.3 File names in lists
+------------------------
+
+If an item in a domain, host, address, or local part list is an absolute
+filename (beginning with a slash character), each line of the file is read and
+processed as if it were an independent item in the list, except that further
+filenames are not allowed, and no expansion of the data from the file takes
+place. Empty lines in the file are ignored, and the file may also contain
+comment lines:
+
+ * For domain and host lists, if a # character appears anywhere in a line of
+ the file, it and all following characters are ignored.
+
+ * Because local parts may legitimately contain # characters, a comment in an
+ address list or local part list file is recognized only if # is preceded by
+ white space or the start of the line. For example:
+
+ not#comment@x.y.z # but this is a comment
+
+Putting a filename in a list has the same effect as inserting each line of the
+file as an item in the list (blank lines and comments excepted). However, there
+is one important difference: the file is read each time the list is processed,
+so if its contents vary over time, Exim's behaviour changes.
+
+If a filename is preceded by an exclamation mark, the sense of any match within
+the file is inverted. For example, if
+
+hold_domains = !/etc/nohold-domains
+
+and the file contains the lines
+
+!a.b.c
+*.b.c
+
+then a.b.c is in the set of domains defined by hold_domains, whereas any domain
+matching "*.b.c" is not.
+
+
+10.4 An lsearch file is not an out-of-line list
+-----------------------------------------------
+
+As will be described in the sections that follow, lookups can be used in lists
+to provide indexed methods of checking list membership. There has been some
+confusion about the way lsearch lookups work in lists. Because an lsearch file
+contains plain text and is scanned sequentially, it is sometimes thought that
+it is allowed to contain wild cards and other kinds of non-constant pattern.
+This is not the case. The keys in an lsearch file are always fixed strings,
+just as for any other single-key lookup type.
+
+If you want to use a file to contain wild-card patterns that form part of a
+list, just give the filename on its own, without a search type, as described in
+the previous section. You could also use the wildlsearch or nwildlsearch, but
+there is no advantage in doing this.
+
+
+10.5 Results of list checking
+-----------------------------
+
+The primary result of doing a list check is a truth value. In some contexts
+additional information is stored about the list element that matched:
+
+hosts
+
+ A hosts ACL condition will store a result in the $host_data variable.
+
+local_parts
+
+ A local_parts router option or local_parts ACL condition will store a
+ result in the $local_part_data variable.
+
+domains
+
+ A domains router option or domains ACL condition
+
+senders
+
+ A senders router option or senders ACL condition will store a result in the
+ $sender_data variable.
+
+recipients
+
+ A recipients ACL condition will store a result in the $recipient_data
+ variable.
+
+The detail of the additional information depends on the type of match and is
+given below as the value information.
+
+
+10.6 Named lists
+----------------
+
+A list of domains, hosts, email addresses, or local parts can be given a name
+which is then used to refer to the list elsewhere in the configuration. This is
+particularly convenient if the same list is required in several different
+places. It also allows lists to be given meaningful names, which can improve
+the readability of the configuration. For example, it is conventional to define
+a domain list called local_domains for all the domains that are handled locally
+on a host, using a configuration line such as
+
+domainlist local_domains = localhost:my.dom.example
+
+Named lists are referenced by giving their name preceded by a plus sign, so,
+for example, a router that is intended to handle local domains would be
+configured with the line
+
+domains = +local_domains
+
+The first router in a configuration is often one that handles all domains
+except the local ones, using a configuration with a negated item like this:
+
+dnslookup:
+ driver = dnslookup
+ domains = ! +local_domains
+ transport = remote_smtp
+ no_more
+
+The four kinds of named list are created by configuration lines starting with
+the words domainlist, hostlist, addresslist, or localpartlist, respectively.
+Then there follows the name that you are defining, followed by an equals sign
+and the list itself. For example:
+
+hostlist relay_from_hosts = 192.168.23.0/24 : my.friend.example
+addresslist bad_senders = cdb;/etc/badsenders
+
+A named list may refer to other named lists:
+
+domainlist dom1 = first.example : second.example
+domainlist dom2 = +dom1 : third.example
+domainlist dom3 = fourth.example : +dom2 : fifth.example
+
+Warning: If the last item in a referenced list is a negative one, the effect
+may not be what you intended, because the negation does not propagate out to
+the higher level. For example, consider:
+
+domainlist dom1 = !a.b
+domainlist dom2 = +dom1 : *.b
+
+The second list specifies "either in the dom1 list or *.b". The first list
+specifies just "not a.b", so the domain x.y matches it. That means it matches
+the second list as well. The effect is not the same as
+
+domainlist dom2 = !a.b : *.b
+
+where x.y does not match. It's best to avoid negation altogether in referenced
+lists if you can.
+
+Some named list definitions may contain sensitive data, for example, passwords
+for accessing databases. To stop non-admin users from using the -bP command
+line option to read these values, you can precede the definition with the word
+"hide". For example:
+
+hide domainlist filter_for_domains = ldap;PASS=secret ldap::/// ...
+
+Named lists may have a performance advantage. When Exim is routing an address
+or checking an incoming message, it caches the result of tests on named lists.
+So, if you have a setting such as
+
+domains = +local_domains
+
+on several of your routers or in several ACL statements, the actual test is
+done only for the first one. However, the caching works only if there are no
+expansions within the list itself or any sublists that it references. In other
+words, caching happens only for lists that are known to be the same each time
+they are referenced.
+
+By default, there may be up to 16 named lists of each type. This limit can be
+extended by changing a compile-time variable. The use of domain and host lists
+is recommended for concepts such as local domains, relay domains, and relay
+hosts. The default configuration is set up like this.
+
+
+10.7 Named lists compared with macros
+-------------------------------------
+
+At first sight, named lists might seem to be no different from macros in the
+configuration file. However, macros are just textual substitutions. If you
+write
+
+ALIST = host1 : host2
+auth_advertise_hosts = !ALIST
+
+it probably won't do what you want, because that is exactly the same as
+
+auth_advertise_hosts = !host1 : host2
+
+Notice that the second host name is not negated. However, if you use a host
+list, and write
+
+hostlist alist = host1 : host2
+auth_advertise_hosts = ! +alist
+
+the negation applies to the whole list, and so that is equivalent to
+
+auth_advertise_hosts = !host1 : !host2
+
+
+10.8 Named list caching
+-----------------------
+
+While processing a message, Exim caches the result of checking a named list if
+it is sure that the list is the same each time. In practice, this means that
+the cache operates only if the list contains no $ characters, which guarantees
+that it will not change when it is expanded. Sometimes, however, you may have
+an expanded list that you know will be the same each time within a given
+message. For example:
+
+domainlist special_domains = \
+ ${lookup{$sender_host_address}cdb{/some/file}}
+
+This provides a list of domains that depends only on the sending host's IP
+address. If this domain list is referenced a number of times (for example, in
+several ACL lines, or in several routers) the result of the check is not cached
+by default, because Exim does not know that it is going to be the same list
+each time.
+
+By appending "_cache" to "domainlist" you can tell Exim to go ahead and cache
+the result anyway. For example:
+
+domainlist_cache special_domains = ${lookup{...
+
+If you do this, you should be absolutely sure that caching is going to do the
+right thing in all cases. When in doubt, leave it out.
+
+
+10.9 Domain lists
+-----------------
+
+Domain lists contain patterns that are to be matched against a mail domain. The
+following types of item may appear in domain lists:
+
+ * If a pattern consists of a single @ character, it matches the local host
+ name, as set by the primary_hostname option (or defaulted). This makes it
+ possible to use the same configuration file on several different hosts that
+ differ only in their names.
+
+ The value for a match will be the primary host name.
+
+ * If a pattern consists of the string "@[]" it matches an IP address enclosed
+ in square brackets (as in an email address that contains a domain literal),
+ but only if that IP address is recognized as local for email routing
+ purposes. The local_interfaces and extra_local_interfaces options can be
+ used to control which of a host's several IP addresses are treated as
+ local. In today's Internet, the use of domain literals is controversial;
+ see the allow_domain_literals main option.
+
+ The value for a match will be the string "@[]".
+
+ * If a pattern consists of the string "@mx_any" it matches any domain that
+ has an MX record pointing to the local host or to any host that is listed
+ in hosts_treat_as_local. The items "@mx_primary" and "@mx_secondary" are
+ similar, except that the first matches only when a primary MX target is the
+ local host, and the second only when no primary MX target is the local
+ host, but a secondary MX target is. "Primary" means an MX record with the
+ lowest preference value - there may of course be more than one of them.
+
+ The MX lookup that takes place when matching a pattern of this type is
+ performed with the resolver options for widening names turned off. Thus,
+ for example, a single-component domain will not be expanded by adding the
+ resolver's default domain. See the qualify_single and search_parents
+ options of the dnslookup router for a discussion of domain widening.
+
+ Sometimes you may want to ignore certain IP addresses when using one of
+ these patterns. You can specify this by following the pattern with "/ignore
+ ="<ip list>, where <ip list> is a list of IP addresses. These addresses are
+ ignored when processing the pattern (compare the ignore_target_hosts option
+ on a router). For example:
+
+ domains = @mx_any/ignore=127.0.0.1
+
+ This example matches any domain that has an MX record pointing to one of
+ the local host's IP addresses other than 127.0.0.1.
+
+ The list of IP addresses is in fact processed by the same code that
+ processes host lists, so it may contain CIDR-coded network specifications
+ and it may also contain negative items.
+
+ Because the list of IP addresses is a sublist within a domain list, you
+ have to be careful about delimiters if there is more than one address. Like
+ any other list, the default delimiter can be changed. Thus, you might have:
+
+ domains = @mx_any/ignore=<;127.0.0.1;0.0.0.0 : \
+ an.other.domain : ...
+
+ so that the sublist uses semicolons for delimiters. When IPv6 addresses are
+ involved, it is easiest to change the delimiter for the main list as well:
+
+ domains = <? @mx_any/ignore=<;127.0.0.1;::1 ? \
+ an.other.domain ? ...
+
+ The value for a match will be the list element string (starting "@mx_").
+
+ * If a pattern starts with an asterisk, the remaining characters of the
+ pattern are compared with the terminating characters of the domain. The use
+ of "*" in domain lists differs from its use in partial matching lookups. In
+ a domain list, the character following the asterisk need not be a dot,
+ whereas partial matching works only in terms of dot-separated components.
+ For example, a domain list item such as "*key.ex" matches donkey.ex as well
+ as cipher.key.ex.
+
+ The value for a match will be the list element string (starting with the
+ asterisk). Additionally, $0 will be set to the matched string and $1 to the
+ variable portion which the asterisk matched.
+
+ * If a pattern starts with a circumflex character, it is treated as a regular
+ expression, and matched against the domain using a regular expression
+ matching function. The circumflex is treated as part of the regular
+ expression. Email domains are case-independent, so this regular expression
+ match is by default case-independent, but you can make it case-dependent by
+ starting it with "(?-i)". References to descriptions of the syntax of
+ regular expressions are given in chapter 8.
+
+ Warning: Because domain lists are expanded before being processed, you must
+ escape any backslash and dollar characters in the regular expression, or
+ use the special "\N" sequence (see chapter 11) to specify that it is not to
+ be expanded (unless you really do want to build a regular expression by
+ expansion, of course).
+
+ The value for a match will be the list element string (starting with the
+ circumflex). Additionally, $0 will be set to the string matching the
+ regular expression, and $1 (onwards) to any submatches identified by
+ parentheses.
+
+ * If a pattern starts with the name of a single-key lookup type followed by a
+ semicolon (for example, "dbm;" or "lsearch;"), the remainder of the pattern
+ must be a filename in a suitable format for the lookup type. For example,
+ for "cdb;" it must be an absolute path:
+
+ domains = cdb;/etc/mail/local_domains.cdb
+
+ The appropriate type of lookup is done on the file using the domain name as
+ the key. In most cases, the value resulting from the lookup is not used;
+ Exim is interested only in whether or not the key is present in the file.
+ However, when a lookup is used for the domains option on a router or a
+ domains condition in an ACL statement, the value is preserved in the
+ $domain_data variable and can be referred to in other router options or
+ other statements in the same ACL. The value will be untainted.
+
+ * Any of the single-key lookup type names may be preceded by "partial"<n>"-",
+ where the <n> is optional, for example,
+
+ domains = partial-dbm;/partial/domains
+
+ This causes partial matching logic to be invoked; a description of how this
+ works is given in section 9.7.
+
+ * Any of the single-key lookup types may be followed by an asterisk. This
+ causes a default lookup for a key consisting of a single asterisk to be
+ done if the original lookup fails. This is not a useful feature when using
+ a domain list to select particular domains (because any domain would
+ match), but it might have value if the result of the lookup is being used
+ via the $domain_data expansion variable.
+
+ * If the pattern starts with the name of a query-style lookup type followed
+ by a semicolon (for example, "nisplus;" or "ldap;"), the remainder of the
+ pattern must be an appropriate query for the lookup type, as described in
+ chapter 9. For example:
+
+ hold_domains = mysql;select domain from holdlist \
+ where domain = '${quote_mysql:$domain}';
+
+ In most cases, the value resulting from the lookup is not used (so for an
+ SQL query, for example, it doesn't matter what field you select). Exim is
+ interested only in whether or not the query succeeds. However, when a
+ lookup is used for the domains option on a router, the value is preserved
+ in the $domain_data variable and can be referred to in other options. The
+ value will be untainted.
+
+ * If the pattern starts with the name of a lookup type of either kind
+ (single-key or query-style) it may be followed by a comma and options, The
+ options are lookup-type specific and consist of a comma-separated list.
+ Each item starts with a tag and and equals "=".
+
+ * If none of the above cases apply, a caseless textual comparison is made
+ between the pattern and the domain.
+
+ The value for a match will be the list element string. Note that this is
+ commonly untainted (depending on the way the list was created).
+ Specifically, explicit text in the configuration file in not tainted. This
+ is a useful way of obtaining an untainted equivalent to the domain, for
+ later operations.
+
+ However if the list (including one-element lists) is created by expanding a
+ variable containing tainted data, it is tainted and so will the match value
+ be.
+
+Here is an example that uses several different kinds of pattern:
+
+domainlist funny_domains = \
+ @ : \
+ lib.unseen.edu : \
+ *.foundation.fict.example : \
+ \N^[1-2]\d{3}\.fict\.example$\N : \
+ partial-dbm;/opt/data/penguin/book : \
+ nis;domains.byname : \
+ nisplus;[name=$domain,status=local],domains.org_dir
+
+There are obvious processing trade-offs among the various matching modes. Using
+an asterisk is faster than a regular expression, and listing a few names
+explicitly probably is too. The use of a file or database lookup is expensive,
+but may be the only option if hundreds of names are required. Because the
+patterns are tested in order, it makes sense to put the most commonly matched
+patterns earlier.
+
+
+10.10 Host lists
+----------------
+
+Host lists are used to control what remote hosts are allowed to do. For
+example, some hosts may be allowed to use the local host as a relay, and some
+may be permitted to use the SMTP ETRN command. Hosts can be identified in two
+different ways, by name or by IP address. In a host list, some types of pattern
+are matched to a host name, and some are matched to an IP address. You need to
+be particularly careful with this when single-key lookups are involved, to
+ensure that the right value is being used as the key.
+
+
+10.11 Special host list patterns
+--------------------------------
+
+If a host list item is the empty string, it matches only when no remote host is
+involved. This is the case when a message is being received from a local
+process using SMTP on the standard input, that is, when a TCP/IP connection is
+not used.
+
+The special pattern "*" in a host list matches any host or no host. Neither the
+IP address nor the name is actually inspected.
+
+
+10.12 Host list patterns that match by IP address
+-------------------------------------------------
+
+If an IPv4 host calls an IPv6 host and the call is accepted on an IPv6 socket,
+the incoming address actually appears in the IPv6 host as "::ffff:"<v4address>.
+When such an address is tested against a host list, it is converted into a
+traditional IPv4 address first. (Not all operating systems accept IPv4 calls on
+IPv6 sockets, as there have been some security concerns.)
+
+The following types of pattern in a host list check the remote host by
+inspecting its IP address:
+
+ * If the pattern is a plain domain name (not a regular expression, not
+ starting with *, not a lookup of any kind), Exim calls the operating system
+ function to find the associated IP address(es). Exim uses the newer
+ getipnodebyname() function when available, otherwise gethostbyname(). This
+ typically causes a forward DNS lookup of the name. The result is compared
+ with the IP address of the subject host.
+
+ If there is a temporary problem (such as a DNS timeout) with the host name
+ lookup, a temporary error occurs. For example, if the list is being used in
+ an ACL condition, the ACL gives a "defer" response, usually leading to a
+ temporary SMTP error code. If no IP address can be found for the host name,
+ what happens is described in section 10.15 below.
+
+ * If the pattern is "@", the primary host name is substituted and used as a
+ domain name, as just described.
+
+ * If the pattern is an IP address, it is matched against the IP address of
+ the subject host. IPv4 addresses are given in the normal "dotted-quad"
+ notation. IPv6 addresses can be given in colon-separated format, but the
+ colons have to be doubled so as not to be taken as item separators when the
+ default list separator is used. IPv6 addresses are recognized even when
+ Exim is compiled without IPv6 support. This means that if they appear in a
+ host list on an IPv4-only host, Exim will not treat them as host names.
+ They are just addresses that can never match a client host.
+
+ * If the pattern is "@[]", it matches the IP address of any IP interface on
+ the local host. For example, if the local host is an IPv4 host with one
+ interface address 10.45.23.56, these two ACL statements have the same
+ effect:
+
+ accept hosts = 127.0.0.1 : 10.45.23.56
+ accept hosts = @[]
+
+ * If the pattern is an IP address followed by a slash and a mask length (for
+ example 10.11.42.0/24), it is matched against the IP address of the subject
+ host under the given mask. This allows, an entire network of hosts to be
+ included (or excluded) by a single item. The mask uses CIDR notation; it
+ specifies the number of address bits that must match, starting from the
+ most significant end of the address.
+
+ Note: The mask is not a count of addresses, nor is it the high number of a
+ range of addresses. It is the number of bits in the network portion of the
+ address. The above example specifies a 24-bit netmask, so it matches all
+ 256 addresses in the 10.11.42.0 network. An item such as
+
+ 192.168.23.236/31
+
+ matches just two addresses, 192.168.23.236 and 192.168.23.237. A mask value
+ of 32 for an IPv4 address is the same as no mask at all; just a single
+ address matches.
+
+ Here is another example which shows an IPv4 and an IPv6 network:
+
+ recipient_unqualified_hosts = 192.168.0.0/16: \
+ 3ffe::ffff::836f::::/48
+
+ The doubling of list separator characters applies only when these items
+ appear inline in a host list. It is not required when indirecting via a
+ file. For example:
+
+ recipient_unqualified_hosts = /opt/exim/unqualnets
+
+ could make use of a file containing
+
+ 172.16.0.0/12
+ 3ffe:ffff:836f::/48
+
+ to have exactly the same effect as the previous example. When listing IPv6
+ addresses inline, it is usually more convenient to use the facility for
+ changing separator characters. This list contains the same two networks:
+
+ recipient_unqualified_hosts = <; 172.16.0.0/12; \
+ 3ffe:ffff:836f::/48
+
+ The separator is changed to semicolon by the leading "<;" at the start of
+ the list.
+
+
+10.13 Host list patterns for single-key lookups by host address
+---------------------------------------------------------------
+
+When a host is to be identified by a single-key lookup of its complete IP
+address, the pattern takes this form:
+
+net-<single-key-search-type>;<search-data>
+
+For example:
+
+hosts_lookup = net-cdb;/hosts-by-ip.db
+
+The text form of the IP address of the subject host is used as the lookup key.
+IPv6 addresses are converted to an unabbreviated form, using lower case
+letters, with dots as separators because colon is the key terminator in lsearch
+files. [Colons can in fact be used in keys in lsearch files by quoting the
+keys, but this is a facility that was added later.] The data returned by the
+lookup is not used.
+
+Single-key lookups can also be performed using masked IP addresses, using
+patterns of this form:
+
+net<number>-<single-key-search-type>;<search-data>
+
+For example:
+
+net24-dbm;/networks.db
+
+The IP address of the subject host is masked using <number> as the mask length.
+A textual string is constructed from the masked value, followed by the mask,
+and this is used as the lookup key. For example, if the host's IP address is
+192.168.34.6, the key that is looked up for the above example is "192.168.34.0/
+24".
+
+When an IPv6 address is converted to a string, dots are normally used instead
+of colons, so that keys in lsearch files need not contain colons (which
+terminate lsearch keys). This was implemented some time before the ability to
+quote keys was made available in lsearch files. However, the more recently
+implemented iplsearch files do require colons in IPv6 keys (notated using the
+quoting facility) so as to distinguish them from IPv4 keys. For this reason,
+when the lookup type is iplsearch, IPv6 addresses are converted using colons
+and not dots. In all cases except IPv4-mapped IPv6, full, unabbreviated IPv6
+addresses are always used. The latter are converted to IPv4 addresses, in
+dotted-quad form.
+
+Ideally, it would be nice to tidy up this anomalous situation by changing to
+colons in all cases, given that quoting is now available for lsearch. However,
+this would be an incompatible change that might break some existing
+configurations.
+
+Warning: Specifying net32- (for an IPv4 address) or net128- (for an IPv6
+address) is not the same as specifying just net- without a number. In the
+former case the key strings include the mask value, whereas in the latter case
+the IP address is used on its own.
+
+
+10.14 Host list patterns that match by host name
+------------------------------------------------
+
+There are several types of pattern that require Exim to know the name of the
+remote host. These are either wildcard patterns or lookups by name. (If a
+complete hostname is given without any wildcarding, it is used to find an IP
+address to match against, as described in section 10.12 above.)
+
+If the remote host name is not already known when Exim encounters one of these
+patterns, it has to be found from the IP address. Although many sites on the
+Internet are conscientious about maintaining reverse DNS data for their hosts,
+there are also many that do not do this. Consequently, a name cannot always be
+found, and this may lead to unwanted effects. Take care when configuring host
+lists with wildcarded name patterns. Consider what will happen if a name cannot
+be found.
+
+Because of the problems of determining host names from IP addresses, matching
+against host names is not as common as matching against IP addresses.
+
+By default, in order to find a host name, Exim first does a reverse DNS lookup;
+if no name is found in the DNS, the system function (gethostbyaddr() or
+getipnodebyaddr() if available) is tried. The order in which these lookups are
+done can be changed by setting the host_lookup_order option. For security, once
+Exim has found one or more names, it looks up the IP addresses for these names
+and compares them with the IP address that it started with. Only those names
+whose IP addresses match are accepted. Any other names are discarded. If no
+names are left, Exim behaves as if the host name cannot be found. In the most
+common case there is only one name and one IP address.
+
+There are some options that control what happens if a host name cannot be
+found. These are described in section 10.15 below.
+
+As a result of aliasing, hosts may have more than one name. When processing any
+of the following types of pattern, all the host's names are checked:
+
+ * If a pattern starts with "*" the remainder of the item must match the end
+ of the host name. For example, "*.b.c" matches all hosts whose names end in
+ .b.c. This special simple form is provided because this is a very common
+ requirement. Other kinds of wildcarding require the use of a regular
+ expression.
+
+ * If the item starts with "^" it is taken to be a regular expression which is
+ matched against the host name. Host names are case-independent, so this
+ regular expression match is by default case-independent, but you can make
+ it case-dependent by starting it with "(?-i)". References to descriptions
+ of the syntax of regular expressions are given in chapter 8. For example,
+
+ ^(a|b)\.c\.d$
+
+ is a regular expression that matches either of the two hosts a.c.d or b.c.d
+ . When a regular expression is used in a host list, you must take care that
+ backslash and dollar characters are not misinterpreted as part of the
+ string expansion. The simplest way to do this is to use "\N" to mark that
+ part of the string as non-expandable. For example:
+
+ sender_unqualified_hosts = \N^(a|b)\.c\.d$\N : ....
+
+ Warning: If you want to match a complete host name, you must include the
+ "$" terminating metacharacter in the regular expression, as in the above
+ example. Without it, a match at the start of the host name is all that is
+ required.
+
+
+10.15 Behaviour when an IP address or name cannot be found
+----------------------------------------------------------
+
+While processing a host list, Exim may need to look up an IP address from a
+name (see section 10.12), or it may need to look up a host name from an IP
+address (see section 10.14). In either case, the behaviour when it fails to
+find the information it is seeking is the same.
+
+Note: This section applies to permanent lookup failures. It does not apply to
+temporary DNS errors, whose handling is described in the next section.
+
+Exim parses a host list from left to right. If it encounters a permanent lookup
+failure in any item in the host list before it has found a match, Exim treats
+it as a failure and the default behavior is as if the host does not match the
+list. This may not always be what you want to happen. To change Exim's
+behaviour, the special items "+include_unknown" or "+ignore_unknown" may appear
+in the list (at top level - they are not recognized in an indirected file).
+
+ * If any item that follows "+include_unknown" requires information that
+ cannot found, Exim behaves as if the host does match the list. For example,
+
+ host_reject_connection = +include_unknown:*.enemy.ex
+
+ rejects connections from any host whose name matches "*.enemy.ex", and also
+ any hosts whose name it cannot find.
+
+ * If any item that follows "+ignore_unknown" requires information that cannot
+ be found, Exim ignores that item and proceeds to the rest of the list. For
+ example:
+
+ accept hosts = +ignore_unknown : friend.example : \
+ 192.168.4.5
+
+ accepts from any host whose name is friend.example and from 192.168.4.5,
+ whether or not its host name can be found. Without "+ignore_unknown", if no
+ name can be found for 192.168.4.5, it is rejected.
+
+Both "+include_unknown" and "+ignore_unknown" may appear in the same list. The
+effect of each one lasts until the next, or until the end of the list.
+
+
+10.16 Mixing wildcarded host names and addresses in host lists
+--------------------------------------------------------------
+
+This section explains the host/ip processing logic with the same concepts as
+the previous section, but specifically addresses what happens when a wildcarded
+hostname is one of the items in the hostlist.
+
+ * If you have name lookups or wildcarded host names and IP addresses in the
+ same host list, you should normally put the IP addresses first. For
+ example, in an ACL you could have:
+
+ accept hosts = 10.9.8.7 : *.friend.example
+
+ The reason you normally would order it this way lies in the left-to-right
+ way that Exim processes lists. It can test IP addresses without doing any
+ DNS lookups, but when it reaches an item that requires a host name, it
+ fails if it cannot find a host name to compare with the pattern. If the
+ above list is given in the opposite order, the accept statement fails for a
+ host whose name cannot be found, even if its IP address is 10.9.8.7.
+
+ * If you really do want to do the name check first, and still recognize the
+ IP address, you can rewrite the ACL like this:
+
+ accept hosts = *.friend.example
+ accept hosts = 10.9.8.7
+
+ If the first accept fails, Exim goes on to try the second one. See chapter
+ 44 for details of ACLs. Alternatively, you can use "+ignore_unknown", which
+ was discussed in depth in the first example in this section.
+
+
+10.17 Temporary DNS errors when looking up host information
+-----------------------------------------------------------
+
+A temporary DNS lookup failure normally causes a defer action (except when
+dns_again_means_nonexist converts it into a permanent error). However, host
+lists can include "+ignore_defer" and "+include_defer", analogous to
+"+ignore_unknown" and "+include_unknown", as described in the previous section.
+These options should be used with care, probably only in non-critical host
+lists such as whitelists.
+
+
+10.18 Host list patterns for single-key lookups by host name
+------------------------------------------------------------
+
+If a pattern is of the form
+
+<single-key-search-type>;<search-data>
+
+for example
+
+dbm;/host/accept/list
+
+a single-key lookup is performed, using the host name as its key. If the lookup
+succeeds, the host matches the item. The actual data that is looked up is not
+used.
+
+Reminder: With this kind of pattern, you must have host names as keys in the
+file, not IP addresses. If you want to do lookups based on IP addresses, you
+must precede the search type with "net-" (see section 10.13). There is,
+however, no reason why you could not use two items in the same list, one doing
+an address lookup and one doing a name lookup, both using the same file.
+
+
+10.19 Host list patterns for query-style lookups
+------------------------------------------------
+
+If a pattern is of the form
+
+<query-style-search-type>;<query>
+
+the query is obeyed, and if it succeeds, the host matches the item. The actual
+data that is looked up is not used. The variables $sender_host_address and
+$sender_host_name can be used in the query. For example:
+
+hosts_lookup = pgsql;\
+ select ip from hostlist where ip='$sender_host_address'
+
+The value of $sender_host_address for an IPv6 address contains colons. You can
+use the sg expansion item to change this if you need to. If you want to use
+masked IP addresses in database queries, you can use the mask expansion
+operator.
+
+If the query contains a reference to $sender_host_name, Exim automatically
+looks up the host name if it has not already done so. (See section 10.14 for
+comments on finding host names.)
+
+Historical note: prior to release 4.30, Exim would always attempt to find a
+host name before running the query, unless the search type was preceded by
+"net-". This is no longer the case. For backwards compatibility, "net-" is
+still recognized for query-style lookups, but its presence or absence has no
+effect. (Of course, for single-key lookups, "net-" is important. See section
+10.13.)
+
+
+10.20 Address lists
+-------------------
+
+Address lists contain patterns that are matched against mail addresses. There
+is one special case to be considered: the sender address of a bounce message is
+always empty. You can test for this by providing an empty item in an address
+list. For example, you can set up a router to process bounce messages by using
+this option setting:
+
+senders = :
+
+The presence of the colon creates an empty item. If you do not provide any
+data, the list is empty and matches nothing. The empty sender can also be
+detected by a regular expression that matches an empty string, and by a
+query-style lookup that succeeds when $sender_address is empty.
+
+Non-empty items in an address list can be straightforward email addresses. For
+example:
+
+senders = jbc@askone.example : hs@anacreon.example
+
+A certain amount of wildcarding is permitted. If a pattern contains an @
+character, but is not a regular expression and does not begin with a
+semicolon-terminated lookup type (described below), the local part of the
+subject address is compared with the local part of the pattern, which may start
+with an asterisk. If the local parts match, the domain is checked in exactly
+the same way as for a pattern in a domain list. For example, the domain can be
+wildcarded, refer to a named list, or be a lookup:
+
+deny senders = *@*.spamming.site:\
+ *@+hostile_domains:\
+ bozo@partial-lsearch;/list/of/dodgy/sites:\
+ *@dbm;/bad/domains.db
+
+If a local part that begins with an exclamation mark is required, it has to be
+specified using a regular expression, because otherwise the exclamation mark is
+treated as a sign of negation, as is standard in lists.
+
+If a non-empty pattern that is not a regular expression or a lookup does not
+contain an @ character, it is matched against the domain part of the subject
+address. The only two formats that are recognized this way are a literal
+domain, or a domain pattern that starts with *. In both these cases, the effect
+is the same as if "*@" preceded the pattern. For example:
+
+deny senders = enemy.domain : *.enemy.domain
+
+The following kinds of more complicated address list pattern can match any
+address, including the empty address that is characteristic of bounce message
+senders:
+
+ * If (after expansion) a pattern starts with "^", a regular expression match
+ is done against the complete address, with the pattern as the regular
+ expression. You must take care that backslash and dollar characters are not
+ misinterpreted as part of the string expansion. The simplest way to do this
+ is to use "\N" to mark that part of the string as non-expandable. For
+ example:
+
+ deny senders = \N^.*this.*@example\.com$\N : \
+ \N^\d{8}.+@spamhaus.example$\N : ...
+
+ The "\N" sequences are removed by the expansion, so these items do indeed
+ start with "^" by the time they are being interpreted as address patterns.
+
+ * Complete addresses can be looked up by using a pattern that starts with a
+ lookup type terminated by a semicolon, followed by the data for the lookup.
+ For example:
+
+ deny senders = cdb;/etc/blocked.senders : \
+ mysql;select address from blocked where \
+ address='${quote_mysql:$sender_address}'
+
+ Both query-style and single-key lookup types can be used. For a single-key
+ lookup type, Exim uses the complete address as the key. However, empty keys
+ are not supported for single-key lookups, so a match against the empty
+ address always fails. This restriction does not apply to query-style
+ lookups.
+
+ Partial matching for single-key lookups (section 9.7) cannot be used, and
+ is ignored if specified, with an entry being written to the panic log.
+ However, you can configure lookup defaults, as described in section 9.6,
+ but this is useful only for the "*@" type of default. For example, with
+ this lookup:
+
+ accept senders = lsearch*@;/some/file
+
+ the file could contains lines like this:
+
+ user1@domain1.example
+ *@domain2.example
+
+ and for the sender address nimrod@jaeger.example, the sequence of keys that
+ are tried is:
+
+ nimrod@jaeger.example
+ *@jaeger.example
+ *
+
+ Warning 1: Do not include a line keyed by "*" in the file, because that
+ would mean that every address matches, thus rendering the test useless.
+
+ Warning 2: Do not confuse these two kinds of item:
+
+ deny recipients = dbm*@;/some/file
+ deny recipients = *@dbm;/some/file
+
+ The first does a whole address lookup, with defaulting, as just described,
+ because it starts with a lookup type. The second matches the local part and
+ domain independently, as described in a bullet point below.
+
+The following kinds of address list pattern can match only non-empty addresses.
+If the subject address is empty, a match against any of these pattern types
+always fails.
+
+ * If a pattern starts with "@@" followed by a single-key lookup item (for
+ example, "@@lsearch;/some/file"), the address that is being checked is
+ split into a local part and a domain. The domain is looked up in the file.
+ If it is not found, there is no match. If it is found, the data that is
+ looked up from the file is treated as a colon-separated list of local part
+ patterns, each of which is matched against the subject local part in turn.
+
+ The lookup may be a partial one, and/or one involving a search for a
+ default keyed by "*" (see section 9.6). The local part patterns that are
+ looked up can be regular expressions or begin with "*", or even be further
+ lookups. They may also be independently negated. For example, with
+
+ deny senders = @@dbm;/etc/reject-by-domain
+
+ the data from which the DBM file is built could contain lines like
+
+ baddomain.com: !postmaster : *
+
+ to reject all senders except postmaster from that domain.
+
+ If a local part that actually begins with an exclamation mark is required,
+ it has to be specified using a regular expression. In lsearch files, an
+ entry may be split over several lines by indenting the second and
+ subsequent lines, but the separating colon must still be included at line
+ breaks. White space surrounding the colons is ignored. For example:
+
+ aol.com: spammer1 : spammer2 : ^[0-9]+$ :
+ spammer3 : spammer4
+
+ As in all colon-separated lists in Exim, a colon can be included in an item
+ by doubling.
+
+ If the last item in the list starts with a right angle-bracket, the
+ remainder of the item is taken as a new key to look up in order to obtain a
+ continuation list of local parts. The new key can be any sequence of
+ characters. Thus one might have entries like
+
+ aol.com: spammer1 : spammer 2 : >*
+ xyz.com: spammer3 : >*
+ *: ^\d{8}$
+
+ in a file that was searched with @@dbm*, to specify a match for 8-digit
+ local parts for all domains, in addition to the specific local parts listed
+ for each domain. Of course, using this feature costs another lookup each
+ time a chain is followed, but the effort needed to maintain the data is
+ reduced.
+
+ It is possible to construct loops using this facility, and in order to
+ catch them, the chains may be no more than fifty items long.
+
+ * The @@<lookup> style of item can also be used with a query-style lookup,
+ but in this case, the chaining facility is not available. The lookup can
+ only return a single list of local parts.
+
+Warning: There is an important difference between the address list items in
+these two examples:
+
+senders = +my_list
+senders = *@+my_list
+
+In the first one, "my_list" is a named address list, whereas in the second
+example it is a named domain list.
+
+
+10.21 Case of letters in address lists
+--------------------------------------
+
+Domains in email addresses are always handled caselessly, but for local parts
+case may be significant on some systems (see caseful_local_part for how Exim
+deals with this when routing addresses). However, RFC 2505 (Anti-Spam
+Recommendations for SMTP MTAs) suggests that matching of addresses to blocking
+lists should be done in a case-independent manner. Since most address lists in
+Exim are used for this kind of control, Exim attempts to do this by default.
+
+The domain portion of an address is always lowercased before matching it to an
+address list. The local part is lowercased by default, and any string
+comparisons that take place are done caselessly. This means that the data in
+the address list itself, in files included as plain filenames, and in any file
+that is looked up using the "@@" mechanism, can be in any case. However, the
+keys in files that are looked up by a search type other than lsearch (which
+works caselessly) must be in lower case, because these lookups are not
+case-independent.
+
+To allow for the possibility of caseful address list matching, if an item in an
+address list is the string "+caseful", the original case of the local part is
+restored for any comparisons that follow, and string comparisons are no longer
+case-independent. This does not affect the domain, which remains in lower case.
+However, although independent matches on the domain alone are still performed
+caselessly, regular expressions that match against an entire address become
+case-sensitive after "+caseful" has been seen.
+
+
+10.22 Local part lists
+----------------------
+
+Case-sensitivity in local part lists is handled in the same way as for address
+lists, as just described. The "+caseful" item can be used if required. In a
+setting of the local_parts option in a router with caseful_local_part set
+false, the subject is lowercased and the matching is initially
+case-insensitive. In this case, "+caseful" will restore case-sensitive matching
+in the local part list, but not elsewhere in the router. If caseful_local_part
+is set true in a router, matching in the local_parts option is case-sensitive
+from the start.
+
+If a local part list is indirected to a file (see section 10.3), comments are
+handled in the same way as address lists - they are recognized only if the # is
+preceded by white space or the start of the line. Otherwise, local part lists
+are matched in the same way as domain lists, except that the special items that
+refer to the local host ("@", "@[]", "@mx_any", "@mx_primary", and
+"@mx_secondary") are not recognized. Refer to section 10.9 for details of the
+other available item types.
+
+
+
+===============================================================================
+11. STRING EXPANSIONS
+
+Many strings in Exim's runtime configuration are expanded before use. Some of
+them are expanded every time they are used; others are expanded only once.
+
+When a string is being expanded it is copied verbatim from left to right except
+when a dollar or backslash character is encountered. A dollar specifies the
+start of a portion of the string that is interpreted and replaced as described
+below in section 11.5 onwards. Backslash is used as an escape character, as
+described in the following section.
+
+Whether a string is expanded depends upon the context. Usually this is solely
+dependent upon the option for which a value is sought; in this documentation,
+options for which string expansion is performed are marked with * after the
+data type. ACL rules always expand strings. A couple of expansion conditions do
+not expand some of the brace-delimited branches, for security reasons, and
+expansion of data deriving from the sender ("tainted data") is not permitted.
+
+
+11.1 Literal text in expanded strings
+-------------------------------------
+
+An uninterpreted dollar can be included in an expanded string by putting a
+backslash in front of it. A backslash can be used to prevent any special
+character being treated specially in an expansion, including backslash itself.
+If the string appears in quotes in the configuration file, two backslashes are
+required because the quotes themselves cause interpretation of backslashes when
+the string is read in (see section 6.17).
+
+A portion of the string can specified as non-expandable by placing it between
+two occurrences of "\N". This is particularly useful for protecting regular
+expressions, which often contain backslashes and dollar signs. For example:
+
+deny senders = \N^\d{8}[a-z]@some\.site\.example$\N
+
+On encountering the first "\N", the expander copies subsequent characters
+without interpretation until it reaches the next "\N" or the end of the string.
+
+
+11.2 Character escape sequences in expanded strings
+---------------------------------------------------
+
+A backslash followed by one of the letters "n", "r", or "t" in an expanded
+string is recognized as an escape sequence for the character newline, carriage
+return, or tab, respectively. A backslash followed by up to three octal digits
+is recognized as an octal encoding for a single character, and a backslash
+followed by "x" and up to two hexadecimal digits is a hexadecimal encoding.
+
+These escape sequences are also recognized in quoted strings when they are read
+in. Their interpretation in expansions as well is useful for unquoted strings,
+and for other cases such as looked-up strings that are then expanded.
+
+
+11.3 Testing string expansions
+------------------------------
+
+Many expansions can be tested by calling Exim with the -be option. This takes
+the command arguments, or lines from the standard input if there are no
+arguments, runs them through the string expansion code, and writes the results
+to the standard output. Variables based on configuration values are set up, but
+since no message is being processed, variables such as $local_part have no
+value. Nevertheless the -be option can be useful for checking out file and
+database lookups, and the use of expansion operators such as sg, substr and
+nhash.
+
+Exim gives up its root privilege when it is called with the -be option, and
+instead runs under the uid and gid it was called with, to prevent users from
+using -be for reading files to which they do not have access.
+
+If you want to test expansions that include variables whose values are taken
+from a message, there are two other options that can be used. The -bem option
+is like -be except that it is followed by a filename. The file is read as a
+message before doing the test expansions. For example:
+
+exim -bem /tmp/test.message '$h_subject:'
+
+The -Mset option is used in conjunction with -be and is followed by an Exim
+message identifier. For example:
+
+exim -be -Mset 1GrA8W-0004WS-LQ '$recipients'
+
+This loads the message from Exim's spool before doing the test expansions, and
+is therefore restricted to admin users.
+
+
+11.4 Forced expansion failure
+-----------------------------
+
+A number of expansions that are described in the following section have
+alternative "true" and "false" substrings, enclosed in brace characters (which
+are sometimes called "curly brackets"). Which of the two strings is used
+depends on some condition that is evaluated as part of the expansion. If,
+instead of a "false" substring, the word "fail" is used (not in braces), the
+entire string expansion fails in a way that can be detected by the code that
+requested the expansion. This is called "forced expansion failure", and its
+consequences depend on the circumstances. In some cases it is no different from
+any other expansion failure, but in others a different action may be taken.
+Such variations are mentioned in the documentation of the option that is being
+expanded.
+
+
+11.5 Expansion items
+--------------------
+
+The following items are recognized in expanded strings. White space may be used
+between sub-items that are keywords or substrings enclosed in braces inside an
+outer set of braces, to improve readability. Warning: Within braces, white
+space is significant.
+
+$<variable name> or ${<variable name>}
+
+ Substitute the contents of the named variable, for example:
+
+ $local_part
+ ${domain}
+
+ The second form can be used to separate the name from subsequent
+ alphanumeric characters. This form (using braces) is available only for
+ variables; it does not apply to message headers. The names of the variables
+ are given in section 11.9 below. If the name of a non-existent variable is
+ given, the expansion fails.
+
+${<op>:<string>}
+
+ The string is first itself expanded, and then the operation specified by <
+ op> is applied to it. For example:
+
+ ${lc:$local_part}
+
+ The string starts with the first character after the colon, which may be
+ leading white space. A list of operators is given in section 11.6 below.
+ The operator notation is used for simple expansion items that have just one
+ argument, because it reduces the number of braces and therefore makes the
+ string easier to understand.
+
+$bheader_<header name>: or $bh_<header name>:
+
+ This item inserts "basic" header lines. It is described with the header
+ expansion item below.
+
+${acl{<name>}{<arg>}...}
+
+ The name and zero to nine argument strings are first expanded separately.
+ The expanded arguments are assigned to the variables $acl_arg1 to $acl_arg9
+ in order. Any unused are made empty. The variable $acl_narg is set to the
+ number of arguments. The named ACL (see chapter 44) is called and may use
+ the variables; if another acl expansion is used the values are restored
+ after it returns. If the ACL sets a value using a "message =" modifier and
+ returns accept or deny, the value becomes the result of the expansion. If
+ no message is set and the ACL returns accept or deny the expansion result
+ is an empty string. If the ACL returns defer the result is a forced-fail.
+ Otherwise the expansion fails.
+
+${authresults{<authserv-id>}}
+
+ This item returns a string suitable for insertion as an
+ Authentication-Results: header line. The given <authserv-id> is included in
+ the result; typically this will be a domain name identifying the system
+ performing the authentications. Methods that might be present in the result
+ include:
+
+ none
+ iprev
+ auth
+ spf
+ dkim
+
+ Example use (as an ACL modifier):
+
+ add_header = :at_start:${authresults {$primary_hostname}}
+
+ This is safe even if no authentication results are available.
+
+${certextract{<field>}{<certificate>}{<string2>}{<string3>}}
+
+ The <certificate> must be a variable of type certificate. The field name is
+ expanded and used to retrieve the relevant field from the certificate.
+ Supported fields are:
+
+ version
+ serial_number
+ subject RFC4514 DN
+ issuer RFC4514 DN
+ notbefore time
+ notafter time
+ sig_algorithm
+ signature
+ subj_altname tagged list
+ ocsp_uri list
+ crl_uri list
+
+ If the field is found, <string2> is expanded, and replaces the whole item;
+ otherwise <string3> is used. During the expansion of <string2> the variable
+ $value contains the value that has been extracted. Afterwards, it is
+ restored to any previous value it might have had.
+
+ If {<string3>} is omitted, the item is replaced by an empty string if the
+ key is not found. If {<string2>} is also omitted, the value that was
+ extracted is used.
+
+ Some field names take optional modifiers, appended and separated by commas.
+
+ The field selectors marked as "RFC4514" above output a Distinguished Name
+ string which is not quite parseable by Exim as a comma-separated tagged
+ list (the exceptions being elements containing commas). RDN elements of a
+ single type may be selected by a modifier of the type label; if so the
+ expansion result is a list (newline-separated by default). The separator
+ may be changed by another modifier of a right angle-bracket followed
+ immediately by the new separator. Recognised RDN type labels include "CN",
+ "O", "OU" and "DC".
+
+ The field selectors marked as "time" above take an optional modifier of
+ "int" for which the result is the number of seconds since epoch. Otherwise
+ the result is a human-readable string in the timezone selected by the main
+ "timezone" option.
+
+ The field selectors marked as "list" above return a list, newline-separated
+ by default, (embedded separator characters in elements are doubled). The
+ separator may be changed by a modifier of a right angle-bracket followed
+ immediately by the new separator.
+
+ The field selectors marked as "tagged" above prefix each list element with
+ a type string and an equals sign. Elements of only one type may be selected
+ by a modifier which is one of "dns", "uri" or "mail"; if so the element
+ tags are omitted.
+
+ If not otherwise noted field values are presented in human-readable form.
+
+${dlfunc{<file>}{<function>}{<arg>}{<arg>}...}
+
+ This expansion dynamically loads and then calls a locally-written C
+ function. This functionality is available only if Exim is compiled with
+
+ EXPAND_DLFUNC=yes
+
+ set in Local/Makefile. Once loaded, Exim remembers the dynamically loaded
+ object so that it doesn't reload the same object file in the same Exim
+ process (but of course Exim does start new processes frequently).
+
+ There may be from zero to eight arguments to the function.
+
+ When compiling a local function that is to be called in this way, first
+ DLFUNC_IMPL should be defined, and second local_scan.h should be included.
+ The Exim variables and functions that are defined by that API are also
+ available for dynamically loaded functions. The function itself must have
+ the following type:
+
+ int dlfunction(uschar **yield, int argc, uschar *argv[])
+
+ Where "uschar" is a typedef for "unsigned char" in local_scan.h. The
+ function should return one of the following values:
+
+ "OK": Success. The string that is placed in the variable yield is put into
+ the expanded string that is being built.
+
+ "FAIL": A non-forced expansion failure occurs, with the error message taken
+ from yield, if it is set.
+
+ "FAIL_FORCED": A forced expansion failure occurs, with the error message
+ taken from yield if it is set.
+
+ "ERROR": Same as "FAIL", except that a panic log entry is written.
+
+ When compiling a function that is to be used in this way with gcc, you need
+ to add -shared to the gcc command. Also, in the Exim build-time
+ configuration, you must add -export-dynamic to EXTRALIBS.
+
+${env{<key>}{<string1>}{<string2>}}
+
+ The key is first expanded separately, and leading and trailing white space
+ removed. This is then searched for as a name in the environment. If a
+ variable is found then its value is placed in $value and <string1> is
+ expanded, otherwise <string2> is expanded.
+
+ Instead of {<string2>} the word "fail" (not in curly brackets) can appear,
+ for example:
+
+ ${env{USER}{$value} fail }
+
+ This forces an expansion failure (see section 11.4); {<string1>} must be
+ present for "fail" to be recognized.
+
+ If {<string2>} is omitted an empty string is substituted on search failure.
+ If {<string1>} is omitted the search result is substituted on search
+ success.
+
+ The environment is adjusted by the keep_environment and add_environment
+ main section options.
+
+${extract{<key>}{<string1>}{<string2>}{<string3>}}
+
+ The key and <string1> are first expanded separately. Leading and trailing
+ white space is removed from the key (but not from any of the strings). The
+ key must not be empty and must not consist entirely of digits. The expanded
+ <string1> must be of the form:
+
+ <key1> = <value1> <key2> = <value2> ...
+
+ where the equals signs and spaces (but not both) are optional. If any of
+ the values contain white space, they must be enclosed in double quotes, and
+ any values that are enclosed in double quotes are subject to escape
+ processing as described in section 6.17. The expanded <string1> is searched
+ for the value that corresponds to the key. The search is case-insensitive.
+ If the key is found, <string2> is expanded, and replaces the whole item;
+ otherwise <string3> is used. During the expansion of <string2> the variable
+ $value contains the value that has been extracted. Afterwards, it is
+ restored to any previous value it might have had.
+
+ If {<string3>} is omitted, the item is replaced by an empty string if the
+ key is not found. If {<string2>} is also omitted, the value that was
+ extracted is used. Thus, for example, these two expansions are identical,
+ and yield "2001":
+
+ ${extract{gid}{uid=1984 gid=2001}}
+ ${extract{gid}{uid=1984 gid=2001}{$value}}
+
+ Instead of {<string3>} the word "fail" (not in curly brackets) can appear,
+ for example:
+
+ ${extract{Z}{A=... B=...}{$value} fail }
+
+ This forces an expansion failure (see section 11.4); {<string2>} must be
+ present for "fail" to be recognized.
+
+${extract json{<key>}{<string1>}{<string2>}{<string3>}}, ${extract jsons{<key>}
+ {<string1>}{<string2>}{<string3>}}
+
+ The key and <string1> are first expanded separately. Leading and trailing
+ white space is removed from the key (but not from any of the strings). The
+ key must not be empty and must not consist entirely of digits. The expanded
+ <string1> must be of the form:
+
+ { <"key1"> : <value1> , <"key2"> , <value2> ... }
+
+ The braces, commas and colons, and the quoting of the member name are
+ required; the spaces are optional. Matching of the key against the member
+ names is done case-sensitively. For the "json" variant, if a returned value
+ is a JSON string, it retains its leading and trailing quotes. For the
+ "jsons" variant, which is intended for use with JSON strings, the leading
+ and trailing quotes are removed from the returned value.
+
+ The results of matching are handled as above.
+
+${extract{<number>}{<separators>}{<string1>}{<string2>}{<string3>}}
+
+ The <number> argument must consist entirely of decimal digits, apart from
+ leading and trailing white space, which is ignored. This is what
+ distinguishes this form of extract from the previous kind. It behaves in
+ the same way, except that, instead of extracting a named field, it extracts
+ from <string1> the field whose number is given as the first argument. You
+ can use $value in <string2> or "fail" instead of <string3> as before.
+
+ The fields in the string are separated by any one of the characters in the
+ separator string. These may include space or tab characters. The first
+ field is numbered one. If the number is negative, the fields are counted
+ from the end of the string, with the rightmost one numbered -1. If the
+ number given is zero, the entire string is returned. If the modulus of the
+ number is greater than the number of fields in the string, the result is
+ the expansion of <string3>, or the empty string if <string3> is not
+ provided. For example:
+
+ ${extract{2}{:}{x:42:99:& Mailer::/bin/bash}}
+
+ yields "42", and
+
+ ${extract{-4}{:}{x:42:99:& Mailer::/bin/bash}}
+
+ yields "99". Two successive separators mean that the field between them is
+ empty (for example, the fifth field above).
+
+${extract json {<number>}}{<string1>}{<string2>}{<string3>}}, ${extract jsons{<
+ number>}}{<string1>}{<string2>}{<string3>}}
+
+ The <number> argument must consist entirely of decimal digits, apart from
+ leading and trailing white space, which is ignored.
+
+ Field selection and result handling is as above; there is no choice of
+ field separator. For the "json" variant, if a returned value is a JSON
+ string, it retains its leading and trailing quotes. For the "jsons"
+ variant, which is intended for use with JSON strings, the leading and
+ trailing quotes are removed from the returned value.
+
+${filter{<string>}{<condition>}}
+
+ After expansion, <string> is interpreted as a list, colon-separated by
+ default, but the separator can be changed in the usual way (6.21). For each
+ item in this list, its value is place in $item, and then the condition is
+ evaluated. If the condition is true, $item is added to the output as an
+ item in a new list; if the condition is false, the item is discarded. The
+ separator used for the output list is the same as the one used for the
+ input, but a separator setting is not included in the output. For example:
+
+ ${filter{a:b:c}{!eq{$item}{b}}}
+
+ yields "a:c". At the end of the expansion, the value of $item is restored
+ to what it was before. See also the map and reduce expansion items.
+
+${hash{<string1>}{<string2>}{<string3>}}
+
+ This is a textual hashing function, and was the first to be implemented in
+ early versions of Exim. In current releases, there are other hashing
+ functions (numeric, MD5, and SHA-1), which are described below.
+
+ The first two strings, after expansion, must be numbers. Call them <m> and
+ <n>. If you are using fixed values for these numbers, that is, if <string1>
+ and <string2> do not change when they are expanded, you can use the simpler
+ operator notation that avoids some of the braces:
+
+ ${hash_<n>_<m>:<string>}
+
+ The second number is optional (in both notations). If <n> is greater than
+ or equal to the length of the string, the expansion item returns the
+ string. Otherwise it computes a new string of length <n> by applying a
+ hashing function to the string. The new string consists of characters taken
+ from the first <m> characters of the string
+
+ abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQWRSTUVWXYZ0123456789
+
+ If <m> is not present the value 26 is used, so that only lower case letters
+ appear. For example:
+
+ $hash{3}{monty}} yields jmg
+ $hash{5}{monty}} yields monty
+ $hash{4}{62}{monty python}} yields fbWx
+
+$header_<header name>: or $h_<header name>:, $bheader_<header name>: or $bh_<
+ header name>:, $lheader_<header name>: or $lh_<header name>:, $rheader_<
+ header name>: or $rh_<header name>:
+
+ Substitute the contents of the named message header line, for example
+
+ $header_reply-to:
+
+ The newline that terminates a header line is not included in the expansion,
+ but internal newlines (caused by splitting the header line over several
+ physical lines) may be present.
+
+ The difference between the four pairs of expansions is in the way the data
+ in the header line is interpreted.
+
+ + rheader gives the original "raw" content of the header line, with no
+ processing at all, and without the removal of leading and trailing
+ white space.
+
+ + lheader gives a colon-separated list, one element per header when there
+ are multiple headers with a given name. Any embedded colon characters
+ within an element are doubled, so normal Exim list-processing
+ facilities can be used. The terminating newline of each element is
+ removed; in other respects the content is "raw".
+
+ + bheader removes leading and trailing white space, and then decodes
+ base64 or quoted-printable MIME "words" within the header text, but
+ does no character set translation. If decoding of what looks
+ superficially like a MIME "word" fails, the raw string is returned. If
+ decoding produces a binary zero character, it is replaced by a question
+ mark - this is what Exim does for binary zeros that are actually
+ received in header lines.
+
+ + header tries to translate the string as decoded by bheader to a
+ standard character set. This is an attempt to produce the same string
+ as would be displayed on a user's MUA. If translation fails, the
+ bheader string is returned. Translation is attempted only on operating
+ systems that support the iconv() function. This is indicated by the
+ compile-time macro HAVE_ICONV in a system Makefile or in Local/Makefile
+ .
+
+ In a filter file, the target character set for header can be specified by a
+ command of the following form:
+
+ headers charset "UTF-8"
+
+ This command affects all references to $h_ (or $header_) expansions in
+ subsequently obeyed filter commands. In the absence of this command, the
+ target character set in a filter is taken from the setting of the
+ headers_charset option in the runtime configuration. The value of this
+ option defaults to the value of HEADERS_CHARSET in Local/Makefile. The
+ ultimate default is ISO-8859-1.
+
+ Header names follow the syntax of RFC 2822, which states that they may
+ contain any printing characters except space and colon. Consequently, curly
+ brackets do not terminate header names, and should not be used to enclose
+ them as if they were variables. Attempting to do so causes a syntax error.
+
+ Only header lines that are common to all copies of a message are visible to
+ this mechanism. These are the original header lines that are received with
+ the message, and any that are added by an ACL statement or by a system
+ filter. Header lines that are added to a particular copy of a message by a
+ router or transport are not accessible.
+
+ For incoming SMTP messages, no header lines are visible in ACLs that are
+ obeyed before the data phase completes, because the header structure is not
+ set up until the message is received. They are visible in DKIM, PRDR and
+ DATA ACLs. Header lines that are added in a RCPT ACL (for example) are
+ saved until the message's incoming header lines are available, at which
+ point they are added. When any of the above ACLs ar running, however,
+ header lines added by earlier ACLs are visible.
+
+ Upper case and lower case letters are synonymous in header names. If the
+ following character is white space, the terminating colon may be omitted,
+ but this is not recommended, because you may then forget it when it is
+ needed. When white space terminates the header name, this white space is
+ included in the expanded string. If the message does not contain the given
+ header, the expansion item is replaced by an empty string. (See the def
+ condition in section 11.7 for a means of testing for the existence of a
+ header.)
+
+ If there is more than one header with the same name, they are all
+ concatenated to form the substitution string, up to a maximum length of
+ 64K. Unless rheader is being used, leading and trailing white space is
+ removed from each header before concatenation, and a completely empty
+ header is ignored. A newline character is then inserted between non-empty
+ headers, but there is no newline at the very end. For the header and
+ bheader expansion, for those headers that contain lists of addresses, a
+ comma is also inserted at the junctions between headers. This does not
+ happen for the rheader expansion.
+
+ When the headers are from an incoming message, the result of expanding any
+ of these variables is tainted.
+
+${hmac{<hashname>}{<secret>}{<string>}}
+
+ This function uses cryptographic hashing (either MD5 or SHA-1) to convert a
+ shared secret and some text into a message authentication code, as
+ specified in RFC 2104. This differs from "${md5:secret_text...}" or "$
+ {sha1:secret_text...}" in that the hmac step adds a signature to the
+ cryptographic hash, allowing for authentication that is not possible with
+ MD5 or SHA-1 alone. The hash name must expand to either "md5" or "sha1" at
+ present. For example:
+
+ ${hmac{md5}{somesecret}{$primary_hostname $tod_log}}
+
+ For the hostname mail.example.com and time 2002-10-17 11:30:59, this
+ produces:
+
+ dd97e3ba5d1a61b5006108f8c8252953
+
+ As an example of how this might be used, you might put in the main part of
+ an Exim configuration:
+
+ SPAMSCAN_SECRET=cohgheeLei2thahw
+
+ In a router or a transport you could then have:
+
+ headers_add = \
+ X-Spam-Scanned: ${primary_hostname} ${message_exim_id} \
+ ${hmac{md5}{SPAMSCAN_SECRET}\
+ {${primary_hostname},${message_exim_id},$h_message-id:}}
+
+ Then given a message, you can check where it was scanned by looking at the
+ X-Spam-Scanned: header line. If you know the secret, you can check that
+ this header line is authentic by recomputing the authentication code from
+ the host name, message ID and the Message-id: header line. This can be done
+ using Exim's -be option, or by other means, for example, by using the
+ hmac_md5_hex() function in Perl.
+
+${if <condition> {<string1>}{<string2>}}
+
+ If <condition> is true, <string1> is expanded and replaces the whole item;
+ otherwise <string2> is used. The available conditions are described in
+ section 11.7 below. For example:
+
+ ${if eq {$local_part}{postmaster} {yes}{no} }
+
+ The second string need not be present; if it is not and the condition is
+ not true, the item is replaced with nothing. Alternatively, the word "fail"
+ may be present instead of the second string (without any curly brackets).
+ In this case, the expansion is forced to fail if the condition is not true
+ (see section 11.4).
+
+ If both strings are omitted, the result is the string "true" if the
+ condition is true, and the empty string if the condition is false. This
+ makes it less cumbersome to write custom ACL and router conditions. For
+ example, instead of
+
+ condition = ${if >{$acl_m4}{3}{true}{false}}
+
+ you can use
+
+ condition = ${if >{$acl_m4}{3}}
+
+${imapfolder{<foldername>}}
+
+ This item converts a (possibly multilevel, or with non-ASCII characters)
+ folder specification to a Maildir name for filesystem use. For information
+ on internationalisation support see 60.2.
+
+${length{<string1>}{<string2>}}
+
+ The length item is used to extract the initial portion of a string. Both
+ strings are expanded, and the first one must yield a number, <n>, say. If
+ you are using a fixed value for the number, that is, if <string1> does not
+ change when expanded, you can use the simpler operator notation that avoids
+ some of the braces:
+
+ ${length_<n>:<string>}
+
+ The result of this item is either the first <n> bytes or the whole of <
+ string2>, whichever is the shorter. Do not confuse length with strlen,
+ which gives the length of a string. All measurement is done in bytes and is
+ not UTF-8 aware.
+
+${listextract{<number>}{<string1>}{<string2>}{<string3>}}
+
+ The <number> argument must consist entirely of decimal digits, apart from
+ an optional leading minus, and leading and trailing white space (which is
+ ignored).
+
+ After expansion, <string1> is interpreted as a list, colon-separated by
+ default, but the separator can be changed in the usual way (6.21).
+
+ The first field of the list is numbered one. If the number is negative, the
+ fields are counted from the end of the list, with the rightmost one
+ numbered -1. The numbered element of the list is extracted and placed in
+ $value, then <string2> is expanded as the result.
+
+ If the modulus of the number is zero or greater than the number of fields
+ in the string, the result is the expansion of <string3>.
+
+ For example:
+
+ ${listextract{2}{x:42:99}}
+
+ yields "42", and
+
+ ${listextract{-3}{<, x,42,99,& Mailer,,/bin/bash}{result: $value}}
+
+ yields "result: 42".
+
+ If {<string3>} is omitted, an empty string is used for string3. If {<
+ string2>} is also omitted, the value that was extracted is used. You can
+ use "fail" instead of {<string3>} as in a string extract.
+
+${listquote{<separator>}{<string>}}
+
+ This item doubles any occurrence of the separator character in the given
+ string. An empty string is replaced with a single space. This converts the
+ string into a safe form for use as a list element, in a list using the
+ given separator.
+
+${lookup{<key>} <search type> {<file>} {<string1>} {<string2>}}
+
+ This is the first of one of two different types of lookup item, which are
+ both described in the next item.
+
+${lookup <search type> {<query>} {<string1>} {<string2>}}
+
+ The two forms of lookup item specify data lookups in files and databases,
+ as discussed in chapter 9. The first form is used for single-key lookups,
+ and the second is used for query-style lookups. The <key>, <file>, and <
+ query> strings are expanded before use.
+
+ If there is any white space in a lookup item which is part of a filter
+ command, a retry or rewrite rule, a routing rule for the manualroute
+ router, or any other place where white space is significant, the lookup
+ item must be enclosed in double quotes. The use of data lookups in users'
+ filter files may be locked out by the system administrator.
+
+ If the lookup succeeds, <string1> is expanded and replaces the entire item.
+ During its expansion, the variable $value contains the data returned by the
+ lookup. Afterwards it reverts to the value it had previously (at the outer
+ level it is empty). If the lookup fails, <string2> is expanded and replaces
+ the entire item. If {<string2>} is omitted, the replacement is the empty
+ string on failure. If <string2> is provided, it can itself be a nested
+ lookup, thus providing a mechanism for looking up a default value when the
+ original lookup fails.
+
+ If a nested lookup is used as part of <string1>, $value contains the data
+ for the outer lookup while the parameters of the second lookup are
+ expanded, and also while <string2> of the second lookup is expanded, should
+ the second lookup fail. Instead of {<string2>} the word "fail" can appear,
+ and in this case, if the lookup fails, the entire expansion is forced to
+ fail (see section 11.4). If both {<string1>} and {<string2>} are omitted,
+ the result is the looked up value in the case of a successful lookup, and
+ nothing in the case of failure.
+
+ For single-key lookups, the string "partial" is permitted to precede the
+ search type in order to do partial matching, and * or *@ may follow a
+ search type to request default lookups if the key does not match (see
+ sections 9.6 and 9.7 for details).
+
+ If a partial search is used, the variables $1 and $2 contain the wild and
+ non-wild parts of the key during the expansion of the replacement text.
+ They return to their previous values at the end of the lookup item.
+
+ This example looks up the postmaster alias in the conventional alias file:
+
+ ${lookup {postmaster} lsearch {/etc/aliases} {$value}}
+
+ This example uses NIS+ to look up the full name of the user corresponding
+ to the local part of an address, forcing the expansion to fail if it is not
+ found:
+
+ ${lookup nisplus {[name=$local_part],passwd.org_dir:gcos} \
+ {$value}fail}
+
+${map{<string1>}{<string2>}}
+
+ After expansion, <string1> is interpreted as a list, colon-separated by
+ default, but the separator can be changed in the usual way (6.21). For each
+ item in this list, its value is place in $item, and then <string2> is
+ expanded and added to the output as an item in a new list. The separator
+ used for the output list is the same as the one used for the input, but a
+ separator setting is not included in the output. For example:
+
+ ${map{a:b:c}{[$item]}} ${map{<- x-y-z}{($item)}}
+
+ expands to "[a]:[b]:[c] (x)-(y)-(z)". At the end of the expansion, the
+ value of $item is restored to what it was before. See also the filter and
+ reduce expansion items.
+
+${nhash{<string1>}{<string2>}{<string3>}}
+
+ The three strings are expanded; the first two must yield numbers. Call them
+ <n> and <m>. If you are using fixed values for these numbers, that is, if <
+ string1> and <string2> do not change when they are expanded, you can use
+ the simpler operator notation that avoids some of the braces:
+
+ ${nhash_<n>_<m>:<string>}
+
+ The second number is optional (in both notations). If there is only one
+ number, the result is a number in the range 0-<n>-1. Otherwise, the string
+ is processed by a div/mod hash function that returns two numbers, separated
+ by a slash, in the ranges 0 to <n>-1 and 0 to <m>-1, respectively. For
+ example,
+
+ ${nhash{8}{64}{supercalifragilisticexpialidocious}}
+
+ returns the string "6/33".
+
+${perl{<subroutine>}{<arg>}{<arg>}...}
+
+ This item is available only if Exim has been built to include an embedded
+ Perl interpreter. The subroutine name and the arguments are first
+ separately expanded, and then the Perl subroutine is called with those
+ arguments. No additional arguments need be given; the maximum number
+ permitted, including the name of the subroutine, is nine.
+
+ The return value of the subroutine is inserted into the expanded string,
+ unless the return value is undef. In that case, the expansion fails in the
+ same way as an explicit "fail" on a lookup item. The return value is a
+ scalar. Whatever you return is evaluated in a scalar context. For example,
+ if you return the name of a Perl vector, the return value is the size of
+ the vector, not its contents.
+
+ If the subroutine exits by calling Perl's die function, the expansion fails
+ with the error message that was passed to die. More details of the embedded
+ Perl facility are given in chapter 12.
+
+ The redirect router has an option called forbid_filter_perl which locks out
+ the use of this expansion item in filter files.
+
+${prvs{<address>}{<secret>}{<keynumber>}}
+
+ The first argument is a complete email address and the second is secret
+ keystring. The third argument, specifying a key number, is optional. If
+ absent, it defaults to 0. The result of the expansion is a prvs-signed
+ email address, to be typically used with the return_path option on an smtp
+ transport as part of a bounce address tag validation (BATV) scheme. For
+ more discussion and an example, see section 44.51.
+
+${prvscheck{<address>}{<secret>}{<string>}}
+
+ This expansion item is the complement of the prvs item. It is used for
+ checking prvs-signed addresses. If the expansion of the first argument does
+ not yield a syntactically valid prvs-signed address, the whole item expands
+ to the empty string. When the first argument does expand to a syntactically
+ valid prvs-signed address, the second argument is expanded, with the
+ prvs-decoded version of the address and the key number extracted from the
+ address in the variables $prvscheck_address and $prvscheck_keynum,
+ respectively.
+
+ These two variables can be used in the expansion of the second argument to
+ retrieve the secret. The validity of the prvs-signed address is then
+ checked against the secret. The result is stored in the variable
+ $prvscheck_result, which is empty for failure or "1" for success.
+
+ The third argument is optional; if it is missing, it defaults to an empty
+ string. This argument is now expanded. If the result is an empty string,
+ the result of the expansion is the decoded version of the address. This is
+ the case whether or not the signature was valid. Otherwise, the result of
+ the expansion is the expansion of the third argument.
+
+ All three variables can be used in the expansion of the third argument.
+ However, once the expansion is complete, only $prvscheck_result remains
+ set. For more discussion and an example, see section 44.51.
+
+${readfile{<file name>}{<eol string>}}
+
+ The filename and end-of-line string are first expanded separately. The file
+ is then read, and its contents replace the entire item. All newline
+ characters in the file are replaced by the end-of-line string if it is
+ present. Otherwise, newlines are left in the string. String expansion is
+ not applied to the contents of the file. If you want this, you must wrap
+ the item in an expand operator. If the file cannot be read, the string
+ expansion fails.
+
+ The redirect router has an option called forbid_filter_readfile which locks
+ out the use of this expansion item in filter files.
+
+${readsocket{<name>}{<request>}{<options>}{<eol string>}{<fail string>}}
+
+ This item inserts data from a Unix domain or TCP socket into the expanded
+ string. The minimal way of using it uses just two arguments, as in these
+ examples:
+
+ ${readsocket{/socket/name}{request string}}
+ ${readsocket{inet:some.host:1234}{request string}}
+
+ For a Unix domain socket, the first substring must be the path to the
+ socket. For an Internet socket, the first substring must contain "inet:"
+ followed by a host name or IP address, followed by a colon and a port,
+ which can be a number or the name of a TCP port in /etc/services. An IP
+ address may optionally be enclosed in square brackets. This is best for
+ IPv6 addresses. For example:
+
+ ${readsocket{inet:[::1]:1234}{request string}}
+
+ Only a single host name may be given, but if looking it up yields more than
+ one IP address, they are each tried in turn until a connection is made. For
+ both kinds of socket, Exim makes a connection, writes the request string
+ unless it is an empty string; and no terminating NUL is ever sent) and
+ reads from the socket until an end-of-file is read. A timeout of 5 seconds
+ is applied. Additional, optional arguments extend what can be done.
+ Firstly, you can vary the timeout. For example:
+
+ ${readsocket{/socket/name}{request string}{3s}}
+
+ The third argument is a list of options, of which the first element is the
+ timeout and must be present if any options are given. Further elements are
+ options of form name=value. Example:
+
+ ${readsocket{/socket/name}{request string}{3s:shutdown=no}}
+
+ The following option names are recognised:
+
+ + cache Defines if the result data can be cached for use by a later
+ identical request in the same process. Values are "yes" or "no" (the
+ default). If not, all cached results for this connection specification
+ will be invalidated.
+
+ + shutdown Defines whether or not a write-shutdown is done on the
+ connection after sending the request. Values are "yes" (the default) or
+ "no" (preferred, eg. by some webservers).
+
+ + tls Controls the use of TLS on the connection. Values are "yes" or "no"
+ (the default). If it is enabled, a shutdown as descripbed above is
+ never done.
+
+ A fourth argument allows you to change any newlines that are in the data
+ that is read, in the same way as for readfile (see above). This example
+ turns them into spaces:
+
+ ${readsocket{inet:127.0.0.1:3294}{request string}{3s}{ }}
+
+ As with all expansions, the substrings are expanded before the processing
+ happens. Errors in these sub-expansions cause the expansion to fail. In
+ addition, the following errors can occur:
+
+ + Failure to create a socket file descriptor;
+
+ + Failure to connect the socket;
+
+ + Failure to write the request string;
+
+ + Timeout on reading from the socket.
+
+ By default, any of these errors causes the expansion to fail. However, if
+ you supply a fifth substring, it is expanded and used when any of the above
+ errors occurs. For example:
+
+ ${readsocket{/socket/name}{request string}{3s}{\n}\
+ {socket failure}}
+
+ You can test for the existence of a Unix domain socket by wrapping this
+ expansion in "${if exists", but there is a race condition between that test
+ and the actual opening of the socket, so it is safer to use the fifth
+ argument if you want to be absolutely sure of avoiding an expansion error
+ for a non-existent Unix domain socket, or a failure to connect to an
+ Internet socket.
+
+ The redirect router has an option called forbid_filter_readsocket which
+ locks out the use of this expansion item in filter files.
+
+${reduce{<string1>}{<string2>}{<string3>}}
+
+ This operation reduces a list to a single, scalar string. After expansion,
+ <string1> is interpreted as a list, colon-separated by default, but the
+ separator can be changed in the usual way (6.21). Then <string2> is
+ expanded and assigned to the $value variable. After this, each item in the
+ <string1> list is assigned to $item, in turn, and <string3> is expanded for
+ each of them. The result of that expansion is assigned to $value before the
+ next iteration. When the end of the list is reached, the final value of
+ $value is added to the expansion output. The reduce expansion item can be
+ used in a number of ways. For example, to add up a list of numbers:
+
+ ${reduce {<, 1,2,3}{0}{${eval:$value+$item}}}
+
+ The result of that expansion would be "6". The maximum of a list of numbers
+ can be found:
+
+ ${reduce {3:0:9:4:6}{0}{${if >{$item}{$value}{$item}{$value}}}}
+
+ At the end of a reduce expansion, the values of $item and $value are
+ restored to what they were before. See also the filter and map expansion
+ items.
+
+$rheader_<header name>: or $rh_<header name>:
+
+ This item inserts "raw" header lines. It is described with the header
+ expansion item in section 11.5 above.
+
+${run{<command> <args>}{<string1>}{<string2>}}
+
+ The command and its arguments are first expanded as one string. The string
+ is split apart into individual arguments by spaces, and then the command is
+ run in a separate process, but under the same uid and gid. As in other
+ command executions from Exim, a shell is not used by default. If the
+ command requires a shell, you must explicitly code it.
+
+ Since the arguments are split by spaces, when there is a variable expansion
+ which has an empty result, it will cause the situation that the argument
+ will simply be omitted when the program is actually executed by Exim. If
+ the script/program requires a specific number of arguments and the expanded
+ variable could possibly result in this empty expansion, the variable must
+ be quoted. This is more difficult if the expanded variable itself could
+ result in a string containing quotes, because it would interfere with the
+ quotes around the command arguments. A possible guard against this is to
+ wrap the variable in the sg operator to change any quote marks to some
+ other character.
+
+ The standard input for the command exists, but is empty. The standard
+ output and standard error are set to the same file descriptor. If the
+ command succeeds (gives a zero return code) <string1> is expanded and
+ replaces the entire item; during this expansion, the standard output/error
+ from the command is in the variable $value. If the command fails, <string2
+ >, if present, is expanded and used. Once again, during the expansion, the
+ standard output/error from the command is in the variable $value.
+
+ If <string2> is absent, the result is empty. Alternatively, <string2> can
+ be the word "fail" (not in braces) to force expansion failure if the
+ command does not succeed. If both strings are omitted, the result is
+ contents of the standard output/error on success, and nothing on failure.
+
+ The standard output/error of the command is put in the variable $value. In
+ this ACL example, the output of a command is logged for the admin to
+ troubleshoot:
+
+ warn condition = ${run{/usr/bin/id}{yes}{no}}
+ log_message = Output of id: $value
+
+ If the command requires shell idioms, such as the > redirect operator, the
+ shell must be invoked directly, such as with:
+
+ ${run{/bin/bash -c "/usr/bin/id >/tmp/id"}{yes}{yes}}
+
+ The return code from the command is put in the variable $runrc, and this
+ remains set afterwards, so in a filter file you can do things like this:
+
+ if "${run{x y z}{}}$runrc" is 1 then ...
+ elif $runrc is 2 then ...
+ ...
+ endif
+
+ If execution of the command fails (for example, the command does not
+ exist), the return code is 127 - the same code that shells use for
+ non-existent commands.
+
+ Warning: In a router or transport, you cannot assume the order in which
+ option values are expanded, except for those preconditions whose order of
+ testing is documented. Therefore, you cannot reliably expect to set $runrc
+ by the expansion of one option, and use it in another.
+
+ The redirect router has an option called forbid_filter_run which locks out
+ the use of this expansion item in filter files.
+
+${sg{<subject>}{<regex>}{<replacement>}}
+
+ This item works like Perl's substitution operator (s) with the global (/g)
+ option; hence its name. However, unlike the Perl equivalent, Exim does not
+ modify the subject string; instead it returns the modified string for
+ insertion into the overall expansion. The item takes three arguments: the
+ subject string, a regular expression, and a substitution string. For
+ example:
+
+ ${sg{abcdefabcdef}{abc}{xyz}}
+
+ yields "xyzdefxyzdef". Because all three arguments are expanded before use,
+ if any $, } or \ characters are required in the regular expression or in
+ the substitution string, they have to be escaped. For example:
+
+ ${sg{abcdef}{^(...)(...)\$}{\$2\$1}}
+
+ yields "defabc", and
+
+ ${sg{1=A 4=D 3=C}{\N(\d+)=\N}{K\$1=}}
+
+ yields "K1=A K4=D K3=C". Note the use of "\N" to protect the contents of
+ the regular expression from string expansion.
+
+ The regular expression is compiled in 8-bit mode, working against bytes
+ rather than any Unicode-aware character handling.
+
+${sort{<string>}{<comparator>}{<extractor>}}
+
+ After expansion, <string> is interpreted as a list, colon-separated by
+ default, but the separator can be changed in the usual way (6.21). The <
+ comparator> argument is interpreted as the operator of a two-argument
+ expansion condition. The numeric operators plus ge, gt, le, lt (and ~i
+ variants) are supported. The comparison should return true when applied to
+ two values if the first value should sort before the second value. The <
+ extractor> expansion is applied repeatedly to elements of the list, the
+ element being placed in $item, to give values for comparison.
+
+ The item result is a sorted list, with the original list separator, of the
+ list elements (in full) of the original.
+
+ Examples:
+
+ ${sort{3:2:1:4}{<}{$item}}
+
+ sorts a list of numbers, and
+
+ ${sort {${lookup dnsdb{>:,,mx=example.com}}} {<} {${listextract{1}{<,$item}}}}
+
+ will sort an MX lookup into priority order.
+
+${substr{<string1>}{<string2>}{<string3>}}
+
+ The three strings are expanded; the first two must yield numbers. Call them
+ <n> and <m>. If you are using fixed values for these numbers, that is, if <
+ string1> and <string2> do not change when they are expanded, you can use
+ the simpler operator notation that avoids some of the braces:
+
+ ${substr_<n>_<m>:<string>}
+
+ The second number is optional (in both notations). If it is absent in the
+ simpler format, the preceding underscore must also be omitted.
+
+ The substr item can be used to extract more general substrings than length.
+ The first number, <n>, is a starting offset, and <m> is the length
+ required. For example
+
+ ${substr{3}{2}{$local_part}}
+
+ If the starting offset is greater than the string length the result is the
+ null string; if the length plus starting offset is greater than the string
+ length, the result is the right-hand part of the string, starting from the
+ given offset. The first byte (character) in the string has offset zero.
+
+ The substr expansion item can take negative offset values to count from the
+ right-hand end of its operand. The last byte (character) is offset -1, the
+ second-last is offset -2, and so on. Thus, for example,
+
+ ${substr{-5}{2}{1234567}}
+
+ yields "34". If the absolute value of a negative offset is greater than the
+ length of the string, the substring starts at the beginning of the string,
+ and the length is reduced by the amount of overshoot. Thus, for example,
+
+ ${substr{-5}{2}{12}}
+
+ yields an empty string, but
+
+ ${substr{-3}{2}{12}}
+
+ yields "1".
+
+ When the second number is omitted from substr, the remainder of the string
+ is taken if the offset is positive. If it is negative, all bytes
+ (characters) in the string preceding the offset point are taken. For
+ example, an offset of -1 and no length, as in these semantically identical
+ examples:
+
+ ${substr_-1:abcde}
+ ${substr{-1}{abcde}}
+
+ yields all but the last character of the string, that is, "abcd".
+
+ All measurement is done in bytes and is not UTF-8 aware.
+
+${tr{<subject>}{<characters>}{<replacements>}}
+
+ This item does single-character (in bytes) translation on its subject
+ string. The second argument is a list of characters to be translated in the
+ subject string. Each matching character is replaced by the corresponding
+ character from the replacement list. For example
+
+ ${tr{abcdea}{ac}{13}}
+
+ yields "1b3de1". If there are duplicates in the second character string,
+ the last occurrence is used. If the third string is shorter than the
+ second, its last character is replicated. However, if it is empty, no
+ translation takes place.
+
+ All character handling is done in bytes and is not UTF-8 aware.
+
+
+11.6 Expansion operators
+------------------------
+
+For expansion items that perform transformations on a single argument string,
+the "operator" notation is used because it is simpler and uses fewer braces.
+The substring is first expanded before the operation is applied to it. The
+following operations can be performed:
+
+${address:<string>}
+
+ The string is interpreted as an RFC 2822 address, as it might appear in a
+ header line, and the effective address is extracted from it. If the string
+ does not parse successfully, the result is empty.
+
+ The parsing correctly handles SMTPUTF8 Unicode in the string.
+
+${addresses:<string>}
+
+ The string (after expansion) is interpreted as a list of addresses in RFC
+ 2822 format, such as can be found in a To: or Cc: header line. The
+ operative address (local-part@domain) is extracted from each item, and the
+ result of the expansion is a colon-separated list, with appropriate
+ doubling of colons should any happen to be present in the email addresses.
+ Syntactically invalid RFC2822 address items are omitted from the output.
+
+ It is possible to specify a character other than colon for the output
+ separator by starting the string with > followed by the new separator
+ character. For example:
+
+ ${addresses:>& Chief <ceo@up.stairs>, sec@base.ment (dogsbody)}
+
+ expands to "ceo@up.stairs&sec@base.ment". The string is expanded first, so
+ if the expanded string starts with >, it may change the output separator
+ unintentionally. This can be avoided by setting the output separator
+ explicitly:
+
+ ${addresses:>:$h_from:}
+
+ Compare the address (singular) expansion item, which extracts the working
+ address from a single RFC2822 address. See the filter, map, and reduce
+ items for ways of processing lists.
+
+ To clarify "list of addresses in RFC 2822 format" mentioned above, Exim
+ follows a strict interpretation of header line formatting. Exim parses the
+ bare, unquoted portion of an email address and if it finds a comma, treats
+ it as an email address separator. For the example header line:
+
+ From: =?iso-8859-2?Q?Last=2C_First?= <user@example.com>
+
+ The first example below demonstrates that Q-encoded email addresses are
+ parsed properly if it is given the raw header (in this example,
+ "$rheader_from:"). It does not see the comma because it's still encoded as
+ "=2C". The second example below is passed the contents of "$header_from:",
+ meaning it gets de-mimed. Exim sees the decoded "," so it treats it as two
+ email addresses. The third example shows that the presence of a comma is
+ skipped when it is quoted. The fourth example shows SMTPUTF8 handling.
+
+ # exim -be '${addresses:From: \
+ =?iso-8859-2?Q?Last=2C_First?= <user@example.com>}'
+ user@example.com
+ # exim -be '${addresses:From: Last, First <user@example.com>}'
+ Last:user@example.com
+ # exim -be '${addresses:From: "Last, First" <user@example.com>}'
+ user@example.com
+ # exim -be '${addresses:?????? <??????????@example.jp>}'
+ ??????????@example.jp
+
+${base32:<digits>}
+
+ The string must consist entirely of decimal digits. The number is converted
+ to base 32 and output as a (empty, for zero) string of characters. Only
+ lowercase letters are used.
+
+${base32d:<base-32 digits>}
+
+ The string must consist entirely of base-32 digits. The number is converted
+ to decimal and output as a string.
+
+${base62:<digits>}
+
+ The string must consist entirely of decimal digits. The number is converted
+ to base 62 and output as a string of six characters, including leading
+ zeros. In the few operating environments where Exim uses base 36 instead of
+ base 62 for its message identifiers (because those systems do not have
+ case-sensitive filenames), base 36 is used by this operator, despite its
+ name. Note: Just to be absolutely clear: this is not base64 encoding.
+
+${base62d:<base-62 digits>}
+
+ The string must consist entirely of base-62 digits, or, in operating
+ environments where Exim uses base 36 instead of base 62 for its message
+ identifiers, base-36 digits. The number is converted to decimal and output
+ as a string.
+
+${base64:<string>}
+
+ This operator converts a string into one that is base64 encoded.
+
+ If the string is a single variable of type certificate, returns the base64
+ encoding of the DER form of the certificate.
+
+${base64d:<string>}
+
+ This operator converts a base64-encoded string into the un-coded form.
+
+${domain:<string>}
+
+ The string is interpreted as an RFC 2822 address and the domain is
+ extracted from it. If the string does not parse successfully, the result is
+ empty.
+
+${escape:<string>}
+
+ If the string contains any non-printing characters, they are converted to
+ escape sequences starting with a backslash. Whether characters with the
+ most significant bit set (so-called "8-bit characters") count as printing
+ or not is controlled by the print_topbitchars option.
+
+${escape8bit:<string>}
+
+ If the string contains and characters with the most significant bit set,
+ they are converted to escape sequences starting with a backslash.
+ Backslashes and DEL characters are also converted.
+
+${eval:<string>} and ${eval10:<string>}
+
+ These items supports simple arithmetic and bitwise logical operations in
+ expansion strings. The string (after expansion) must be a conventional
+ arithmetic expression, but it is limited to basic arithmetic operators,
+ bitwise logical operators, and parentheses. All operations are carried out
+ using integer arithmetic. The operator priorities are as follows (the same
+ as in the C programming language):
+
+ highest: not (~), negate (-)
+ multiply (*), divide (/), remainder (%)
+ plus (+), minus (-)
+ shift-left (<<), shift-right (>>)
+ and (&)
+ xor (^)
+ lowest: or (|)
+
+ Binary operators with the same priority are evaluated from left to right.
+ White space is permitted before or after operators.
+
+ For eval, numbers may be decimal, octal (starting with "0") or hexadecimal
+ (starting with "0x"). For eval10, all numbers are taken as decimal, even if
+ they start with a leading zero; hexadecimal numbers are not permitted. This
+ can be useful when processing numbers extracted from dates or times, which
+ often do have leading zeros.
+
+ A number may be followed by "K", "M" or "G" to multiply it by 1024,
+ 1024*1024 or 1024*1024*1024, respectively. Negative numbers are supported.
+ The result of the computation is a decimal representation of the answer
+ (without "K", "M" or "G"). For example:
+
+ ${eval:1+1} yields 2
+ ${eval:1+2*3} yields 7
+ ${eval:(1+2)*3} yields 9
+ ${eval:2+42%5} yields 4
+ ${eval:0xc&5} yields 4
+ ${eval:0xc|5} yields 13
+ ${eval:0xc^5} yields 9
+ ${eval:0xc>>1} yields 6
+ ${eval:0xc<<1} yields 24
+ ${eval:~255&0x1234} yields 4608
+ ${eval:-(~255&0x1234)} yields -4608
+
+ As a more realistic example, in an ACL you might have
+
+ deny condition = \
+ ${if and { \
+ {>{$rcpt_count}{10}} \
+ { \
+ < \
+ {$recipients_count} \
+ {${eval:$rcpt_count/2}} \
+ } \
+ }{yes}{no}}
+ message = Too many bad recipients
+
+ The condition is true if there have been more than 10 RCPT commands and
+ fewer than half of them have resulted in a valid recipient.
+
+${expand:<string>}
+
+ The expand operator causes a string to be expanded for a second time. For
+ example,
+
+ ${expand:${lookup{$domain}dbm{/some/file}{$value}}}
+
+ first looks up a string in a file while expanding the operand for expand,
+ and then re-expands what it has found.
+
+${from_utf8:<string>}
+
+ The world is slowly moving towards Unicode, although there are no standards
+ for email yet. However, other applications (including some databases) are
+ starting to store data in Unicode, using UTF-8 encoding. This operator
+ converts from a UTF-8 string to an ISO-8859-1 string. UTF-8 code values
+ greater than 255 are converted to underscores. The input must be a valid
+ UTF-8 string. If it is not, the result is an undefined sequence of bytes.
+
+ Unicode code points with values less than 256 are compatible with ASCII and
+ ISO-8859-1 (also known as Latin-1). For example, character 169 is the
+ copyright symbol in both cases, though the way it is encoded is different.
+ In UTF-8, more than one byte is needed for characters with code values
+ greater than 127, whereas ISO-8859-1 is a single-byte encoding (but thereby
+ limited to 256 characters). This makes translation from UTF-8 to ISO-8859-1
+ straightforward.
+
+${hash_<n>_<m>:<string>}
+
+ The hash operator is a simpler interface to the hashing function that can
+ be used when the two parameters are fixed numbers (as opposed to strings
+ that change when expanded). The effect is the same as
+
+ ${hash{<n>}{<m>}{<string>}}
+
+ See the description of the general hash item above for details. The
+ abbreviation h can be used when hash is used as an operator.
+
+${hex2b64:<hexstring>}
+
+ This operator converts a hex string into one that is base64 encoded. This
+ can be useful for processing the output of the various hashing functions.
+
+${hexquote:<string>}
+
+ This operator converts non-printable characters in a string into a hex
+ escape form. Byte values between 33 (!) and 126 (~) inclusive are left as
+ is, and other byte values are converted to "\xNN", for example, a byte
+ value 127 is converted to "\x7f".
+
+${ipv6denorm:<string>}
+
+ This expands an IPv6 address to a full eight-element colon-separated set of
+ hex digits including leading zeroes. A trailing ipv4-style dotted-decimal
+ set is converted to hex. Pure IPv4 addresses are converted to IPv4-mapped
+ IPv6.
+
+${ipv6norm:<string>}
+
+ This converts an IPv6 address to canonical form. Leading zeroes of groups
+ are omitted, and the longest set of zero-valued groups is replaced with a
+ double colon. A trailing ipv4-style dotted-decimal set is converted to hex.
+ Pure IPv4 addresses are converted to IPv4-mapped IPv6.
+
+${lc:<string>}
+
+ This forces the letters in the string into lower-case, for example:
+
+ ${lc:$local_part}
+
+ Case is defined per the system C locale.
+
+${length_<number>:<string>}
+
+ The length operator is a simpler interface to the length function that can
+ be used when the parameter is a fixed number (as opposed to a string that
+ changes when expanded). The effect is the same as
+
+ ${length{<number>}{<string>}}
+
+ See the description of the general length item above for details. Note that
+ length is not the same as strlen. The abbreviation l can be used when
+ length is used as an operator. All measurement is done in bytes and is not
+ UTF-8 aware.
+
+${listcount:<string>}
+
+ The string is interpreted as a list and the number of items is returned.
+
+${listnamed:<name>} and ${listnamed_<type>:<name>}
+
+ The name is interpreted as a named list and the content of the list is
+ returned, expanding any referenced lists, re-quoting as needed for
+ colon-separation. If the optional type is given it must be one of "a", "d",
+ "h" or "l" and selects address-, domain-, host- or localpart- lists to
+ search among respectively. Otherwise all types are searched in an undefined
+ order and the first matching list is returned.
+
+${local_part:<string>}
+
+ The string is interpreted as an RFC 2822 address and the local part is
+ extracted from it. If the string does not parse successfully, the result is
+ empty. The parsing correctly handles SMTPUTF8 Unicode in the string.
+
+${mask:<IP address>/<bit count>}
+
+ If the form of the string to be operated on is not an IP address followed
+ by a slash and an integer (that is, a network address in CIDR notation),
+ the expansion fails. Otherwise, this operator converts the IP address to
+ binary, masks off the least significant bits according to the bit count,
+ and converts the result back to text, with mask appended. For example,
+
+ ${mask:10.111.131.206/28}
+
+ returns the string "10.111.131.192/28". Since this operation is expected to
+ be mostly used for looking up masked addresses in files, the result for an
+ IPv6 address uses dots to separate components instead of colons, because
+ colon terminates a key string in lsearch files. So, for example,
+
+ ${mask:3ffe:ffff:836f:0a00:000a:0800:200a:c031/99}
+
+ returns the string
+
+ 3ffe.ffff.836f.0a00.000a.0800.2000.0000/99
+
+ Letters in IPv6 addresses are always output in lower case.
+
+${md5:<string>}
+
+ The md5 operator computes the MD5 hash value of the string, and returns it
+ as a 32-digit hexadecimal number, in which any letters are in lower case.
+
+ If the string is a single variable of type certificate, returns the MD5
+ hash fingerprint of the certificate.
+
+${nhash_<n>_<m>:<string>}
+
+ The nhash operator is a simpler interface to the numeric hashing function
+ that can be used when the two parameters are fixed numbers (as opposed to
+ strings that change when expanded). The effect is the same as
+
+ ${nhash{<n>}{<m>}{<string>}}
+
+ See the description of the general nhash item above for details.
+
+${quote:<string>}
+
+ The quote operator puts its argument into double quotes if it is an empty
+ string or contains anything other than letters, digits, underscores, dots,
+ and hyphens. Any occurrences of double quotes and backslashes are escaped
+ with a backslash. Newlines and carriage returns are converted to "\n" and "
+ \r", respectively For example,
+
+ ${quote:ab"*"cd}
+
+ becomes
+
+ "ab\"*\"cd"
+
+ The place where this is useful is when the argument is a substitution from
+ a variable or a message header.
+
+${quote_local_part:<string>}
+
+ This operator is like quote, except that it quotes the string only if
+ required to do so by the rules of RFC 2822 for quoting local parts. For
+ example, a plus sign would not cause quoting (but it would for quote). If
+ you are creating a new email address from the contents of $local_part (or
+ any other unknown data), you should always use this operator.
+
+ This quoting determination is not SMTPUTF8-aware, thus quoting non-ASCII
+ data will likely use the quoting form. Thus ${quote_local_part:??????} will
+ always become "??????".
+
+${quote_<lookup-type>:<string>}
+
+ This operator applies lookup-specific quoting rules to the string. Each
+ query-style lookup type has its own quoting rules which are described with
+ the lookups in chapter 9. For example,
+
+ ${quote_ldap:two * two}
+
+ returns
+
+ two%20%5C2A%20two
+
+ For single-key lookup types, no quoting is ever necessary and this operator
+ yields an unchanged string.
+
+${randint:<n>}
+
+ This operator returns a somewhat random number which is less than the
+ supplied number and is at least 0. The quality of this randomness depends
+ on how Exim was built; the values are not suitable for keying material. If
+ Exim is linked against OpenSSL then RAND_pseudo_bytes() is used. If Exim is
+ linked against GnuTLS then gnutls_rnd(GNUTLS_RND_NONCE) is used, for
+ versions of GnuTLS with that function. Otherwise, the implementation may be
+ arc4random(), random() seeded by srandomdev() or srandom(), or a custom
+ implementation even weaker than random().
+
+${reverse_ip:<ipaddr>}
+
+ This operator reverses an IP address; for IPv4 addresses, the result is in
+ dotted-quad decimal form, while for IPv6 addresses the result is in
+ dotted-nibble hexadecimal form. In both cases, this is the "natural" form
+ for DNS. For example,
+
+ ${reverse_ip:192.0.2.4}
+ ${reverse_ip:2001:0db8:c42:9:1:abcd:192.0.2.127}
+
+ returns
+
+ 4.2.0.192
+ f.7.2.0.0.0.0.c.d.c.b.a.1.0.0.0.9.0.0.0.2.4.c.0.8.b.d.0.1.0.0.2
+
+${rfc2047:<string>}
+
+ This operator encodes text according to the rules of RFC 2047. This is an
+ encoding that is used in header lines to encode non-ASCII characters. It is
+ assumed that the input string is in the encoding specified by the
+ headers_charset option, which gets its default at build time. If the string
+ contains only characters in the range 33-126, and no instances of the
+ characters
+
+ ? = ( ) < > @ , ; : \ " . [ ] _
+
+ it is not modified. Otherwise, the result is the RFC 2047 encoding of the
+ string, using as many "encoded words" as necessary to encode all the
+ characters.
+
+${rfc2047d:<string>}
+
+ This operator decodes strings that are encoded as per RFC 2047. Binary zero
+ bytes are replaced by question marks. Characters are converted into the
+ character set defined by headers_charset. Overlong RFC 2047 "words" are not
+ recognized unless check_rfc2047_length is set false.
+
+ Note: If you use $header_xxx: (or $h_xxx:) to access a header line, RFC
+ 2047 decoding is done automatically. You do not need to use this operator
+ as well.
+
+${rxquote:<string>}
+
+ The rxquote operator inserts a backslash before any non-alphanumeric
+ characters in its argument. This is useful when substituting the values of
+ variables or headers inside regular expressions.
+
+${sha1:<string>}
+
+ The sha1 operator computes the SHA-1 hash value of the string, and returns
+ it as a 40-digit hexadecimal number, in which any letters are in upper
+ case.
+
+ If the string is a single variable of type certificate, returns the SHA-1
+ hash fingerprint of the certificate.
+
+${sha256:<string>}, ${sha2:<string>}, ${sha2_<n>:<string>}
+
+ The sha256 operator computes the SHA-256 hash value of the string and
+ returns it as a 64-digit hexadecimal number, in which any letters are in
+ upper case.
+
+ If the string is a single variable of type certificate, returns the SHA-256
+ hash fingerprint of the certificate.
+
+ The operator can also be spelled sha2 and does the same as sha256 (except
+ for certificates, which are not supported). Finally, if an underbar and a
+ number is appended it specifies the output length, selecting a member of
+ the SHA-2 family of hash functions. Values of 256, 384 and 512 are
+ accepted, with 256 being the default.
+
+${sha3:<string>}, ${sha3_<n>:<string>}
+
+ The sha3 operator computes the SHA3-256 hash value of the string and
+ returns it as a 64-digit hexadecimal number, in which any letters are in
+ upper case.
+
+ If a number is appended, separated by an underbar, it specifies the output
+ length. Values of 224, 256, 384 and 512 are accepted; with 256 being the
+ default.
+
+ The sha3 expansion item is only supported if Exim has been compiled with
+ GnuTLS 3.5.0 or later, or OpenSSL 1.1.1 or later. The macro
+ "_CRYPTO_HASH_SHA3" will be defined if it is supported.
+
+${stat:<string>}
+
+ The string, after expansion, must be a file path. A call to the stat()
+ function is made for this path. If stat() fails, an error occurs and the
+ expansion fails. If it succeeds, the data from the stat replaces the item,
+ as a series of <name>=<value> pairs, where the values are all numerical,
+ except for the value of "smode". The names are: "mode" (giving the mode as
+ a 4-digit octal number), "smode" (giving the mode in symbolic format as a
+ 10-character string, as for the ls command), "inode", "device", "links",
+ "uid", "gid", "size", "atime", "mtime", and "ctime". You can extract
+ individual fields using the extract expansion item.
+
+ The use of the stat expansion in users' filter files can be locked out by
+ the system administrator. Warning: The file size may be incorrect on 32-bit
+ systems for files larger than 2GB.
+
+${str2b64:<string>}
+
+ Now deprecated, a synonym for the base64 expansion operator.
+
+${strlen:<string>}
+
+ The item is replace by the length of the expanded string, expressed as a
+ decimal number. Note: Do not confuse strlen with length. All measurement is
+ done in bytes and is not UTF-8 aware.
+
+${substr_<start>_<length>:<string>}
+
+ The substr operator is a simpler interface to the substr function that can
+ be used when the two parameters are fixed numbers (as opposed to strings
+ that change when expanded). The effect is the same as
+
+ ${substr{<start>}{<length>}{<string>}}
+
+ See the description of the general substr item above for details. The
+ abbreviation s can be used when substr is used as an operator. All
+ measurement is done in bytes and is not UTF-8 aware.
+
+${time_eval:<string>}
+
+ This item converts an Exim time interval such as "2d4h5m" into a number of
+ seconds.
+
+${time_interval:<string>}
+
+ The argument (after sub-expansion) must be a sequence of decimal digits
+ that represents an interval of time as a number of seconds. It is converted
+ into a number of larger units and output in Exim's normal time format, for
+ example, "1w3d4h2m6s".
+
+${uc:<string>}
+
+ This forces the letters in the string into upper-case. Case is defined per
+ the system C locale.
+
+${utf8clean:<string>}
+
+ This replaces any invalid utf-8 sequence in the string by the character "?
+ ". In versions of Exim before 4.92, this did not correctly do so for a
+ truncated final codepoint's encoding, and the character would be silently
+ dropped. If you must handle detection of this scenario across both sets of
+ Exim behavior, the complexity will depend upon the task. For instance, to
+ detect if the first character is multibyte and a 1-byte extraction can be
+ successfully used as a path component (as is common for dividing up
+ delivery folders), you might use:
+
+ condition = ${if inlist{${utf8clean:${length_1:$local_part}}}{:?}{yes}{no}}
+
+ (which will false-positive if the first character of the local part is a
+ literal question mark).
+
+${utf8_domain_to_alabel:<string>}, ${utf8_domain_from_alabel:<string>}, $
+ {utf8_localpart_to_alabel:<string>}, ${utf8_localpart_from_alabel:<string>}
+
+ These convert EAI mail name components between UTF-8 and a-label forms. For
+ information on internationalisation support see 60.1.
+
+
+11.7 Expansion conditions
+-------------------------
+
+The following conditions are available for testing by the ${if construct while
+expanding strings:
+
+!<condition>
+
+ Preceding any condition with an exclamation mark negates the result of the
+ condition.
+
+<symbolic operator> {<string1>}{<string2>}
+
+ There are a number of symbolic operators for doing numeric comparisons.
+ They are:
+
+ = equal
+ == equal
+ > greater
+ >= greater or equal
+ < less
+ <= less or equal
+
+ For example:
+
+ ${if >{$message_size}{10M} ...
+
+ Note that the general negation operator provides for inequality testing.
+ The two strings must take the form of optionally signed decimal integers,
+ optionally followed by one of the letters "K", "M" or "G" (in either upper
+ or lower case), signifying multiplication by 1024, 1024*1024 or
+ 1024*1024*1024, respectively. As a special case, the numerical value of an
+ empty string is taken as zero.
+
+ In all cases, a relative comparator OP is testing if <string1> OP <string2
+ >; the above example is checking if $message_size is larger than 10M, not
+ if 10M is larger than $message_size.
+
+acl {{<name>}{<arg1>}{<arg2>}...}
+
+ The name and zero to nine argument strings are first expanded separately.
+ The expanded arguments are assigned to the variables $acl_arg1 to $acl_arg9
+ in order. Any unused are made empty. The variable $acl_narg is set to the
+ number of arguments. The named ACL (see chapter 44) is called and may use
+ the variables; if another acl expansion is used the values are restored
+ after it returns. If the ACL sets a value using a "message =" modifier the
+ variable $value becomes the result of the expansion, otherwise it is empty.
+ If the ACL returns accept the condition is true; if deny, false. If the ACL
+ returns defer the result is a forced-fail.
+
+bool {<string>}
+
+ This condition turns a string holding a true or false representation into a
+ boolean state. It parses "true", "false", "yes" and "no"
+ (case-insensitively); also integer numbers map to true if non-zero, false
+ if zero. An empty string is treated as false. Leading and trailing
+ whitespace is ignored; thus a string consisting only of whitespace is
+ false. All other string values will result in expansion failure.
+
+ When combined with ACL variables, this expansion condition will let you
+ make decisions in one place and act on those decisions in another place.
+ For example:
+
+ ${if bool{$acl_m_privileged_sender} ...
+
+bool_lax {<string>}
+
+ Like bool, this condition turns a string into a boolean state. But where
+ bool accepts a strict set of strings, bool_lax uses the same loose
+ definition that the Router condition option uses. The empty string and the
+ values "false", "no" and "0" map to false, all others map to true. Leading
+ and trailing whitespace is ignored.
+
+ Note that where "bool{00}" is false, "bool_lax{00}" is true.
+
+crypteq {<string1>}{<string2>}
+
+ This condition is included in the Exim binary if it is built to support any
+ authentication mechanisms (see chapter 33). Otherwise, it is necessary to
+ define SUPPORT_CRYPTEQ in Local/Makefile to get crypteq included in the
+ binary.
+
+ The crypteq condition has two arguments. The first is encrypted and
+ compared against the second, which is already encrypted. The second string
+ may be in the LDAP form for storing encrypted strings, which starts with
+ the encryption type in curly brackets, followed by the data. If the second
+ string does not begin with "{" it is assumed to be encrypted with crypt()
+ or crypt16() (see below), since such strings cannot begin with "{".
+ Typically this will be a field from a password file. An example of an
+ encrypted string in LDAP form is:
+
+ {md5}CY9rzUYh03PK3k6DJie09g==
+
+ If such a string appears directly in an expansion, the curly brackets have
+ to be quoted, because they are part of the expansion syntax. For example:
+
+ ${if crypteq {test}{\{md5\}CY9rzUYh03PK3k6DJie09g==}{yes}{no}}
+
+ The following encryption types (whose names are matched case-independently)
+ are supported:
+
+ + {md5} computes the MD5 digest of the first string, and expresses this
+ as printable characters to compare with the remainder of the second
+ string. If the length of the comparison string is 24, Exim assumes that
+ it is base64 encoded (as in the above example). If the length is 32,
+ Exim assumes that it is a hexadecimal encoding of the MD5 digest. If
+ the length not 24 or 32, the comparison fails.
+
+ + {sha1} computes the SHA-1 digest of the first string, and expresses
+ this as printable characters to compare with the remainder of the
+ second string. If the length of the comparison string is 28, Exim
+ assumes that it is base64 encoded. If the length is 40, Exim assumes
+ that it is a hexadecimal encoding of the SHA-1 digest. If the length is
+ not 28 or 40, the comparison fails.
+
+ + {crypt} calls the crypt() function, which traditionally used to use
+ only the first eight characters of the password. However, in modern
+ operating systems this is no longer true, and in many cases the entire
+ password is used, whatever its length.
+
+ + {crypt16} calls the crypt16() function, which was originally created to
+ use up to 16 characters of the password in some operating systems.
+ Again, in modern operating systems, more characters may be used.
+
+ Exim has its own version of crypt16(), which is just a double call to crypt
+ (). For operating systems that have their own version, setting HAVE_CRYPT16
+ in Local/Makefile when building Exim causes it to use the operating system
+ version instead of its own. This option is set by default in the
+ OS-dependent Makefile for those operating systems that are known to support
+ crypt16().
+
+ Some years after Exim's crypt16() was implemented, a user discovered that
+ it was not using the same algorithm as some operating systems' versions. It
+ turns out that as well as crypt16() there is a function called bigcrypt()
+ in some operating systems. This may or may not use the same algorithm, and
+ both of them may be different to Exim's built-in crypt16().
+
+ However, since there is now a move away from the traditional crypt()
+ functions towards using SHA1 and other algorithms, tidying up this area of
+ Exim is seen as very low priority.
+
+ If you do not put a encryption type (in curly brackets) in a crypteq
+ comparison, the default is usually either "{crypt}" or "{crypt16}", as
+ determined by the setting of DEFAULT_CRYPT in Local/Makefile. The default
+ default is "{crypt}". Whatever the default, you can always use either
+ function by specifying it explicitly in curly brackets.
+
+def:<variable name>
+
+ The def condition must be followed by the name of one of the expansion
+ variables defined in section 11.9. The condition is true if the variable
+ does not contain the empty string. For example:
+
+ ${if def:sender_ident {from $sender_ident}}
+
+ Note that the variable name is given without a leading $ character. If the
+ variable does not exist, the expansion fails.
+
+def:header_<header name>: or def:h_<header name>:
+
+ This condition is true if a message is being processed and the named header
+ exists in the message. For example,
+
+ ${if def:header_reply-to:{$h_reply-to:}{$h_from:}}
+
+ Note: No $ appears before header_ or h_ in the condition, and the header
+ name must be terminated by a colon if white space does not follow.
+
+eq {<string1>}{<string2>}, eqi {<string1>}{<string2>}
+
+ The two substrings are first expanded. The condition is true if the two
+ resulting strings are identical. For eq the comparison includes the case of
+ letters, whereas for eqi the comparison is case-independent, where case is
+ defined per the system C locale.
+
+exists {<file name>}
+
+ The substring is first expanded and then interpreted as an absolute path.
+ The condition is true if the named file (or directory) exists. The
+ existence test is done by calling the stat() function. The use of the
+ exists test in users' filter files may be locked out by the system
+ administrator.
+
+first_delivery
+
+ This condition, which has no data, is true during a message's first
+ delivery attempt. It is false during any subsequent delivery attempts.
+
+forall{<a list>}{<a condition>}, forany{<a list>}{<a condition>}
+
+ These conditions iterate over a list. The first argument is expanded to
+ form the list. By default, the list separator is a colon, but it can be
+ changed by the normal method (6.21). The second argument is interpreted as
+ a condition that is to be applied to each item in the list in turn. During
+ the interpretation of the condition, the current list item is placed in a
+ variable called $item.
+
+ + For forany, interpretation stops if the condition is true for any item,
+ and the result of the whole condition is true. If the condition is
+ false for all items in the list, the overall condition is false.
+
+ + For forall, interpretation stops if the condition is false for any
+ item, and the result of the whole condition is false. If the condition
+ is true for all items in the list, the overall condition is true.
+
+ Note that negation of forany means that the condition must be false for all
+ items for the overall condition to succeed, and negation of forall means
+ that the condition must be false for at least one item. In this example,
+ the list separator is changed to a comma:
+
+ ${if forany{<, $recipients}{match{$item}{^user3@}}{yes}{no}}
+
+ The value of $item is saved and restored while forany or forall is being
+ processed, to enable these expansion items to be nested.
+
+ To scan a named list, expand it with the listnamed operator.
+
+forall_json{<a JSON array>}{<a condition>}, forany_json{<a JSON array>}{<a
+ condition>}, forall_jsons{<a JSON array>}{<a condition>}, forany_jsons{<a
+ JSON array>}{<a condition>}
+
+ As for the above, except that the first argument must, after expansion, be
+ a JSON array. The array separator is not changeable. For the "jsons"
+ variants the elements are expected to be JSON strings and have their quotes
+ removed before the evaluation of the condition.
+
+ge {<string1>}{<string2>}, gei {<string1>}{<string2>}
+
+ The two substrings are first expanded. The condition is true if the first
+ string is lexically greater than or equal to the second string. For ge the
+ comparison includes the case of letters, whereas for gei the comparison is
+ case-independent. Case and collation order are defined per the system C
+ locale.
+
+gt {<string1>}{<string2>}, gti {<string1>}{<string2>}
+
+ The two substrings are first expanded. The condition is true if the first
+ string is lexically greater than the second string. For gt the comparison
+ includes the case of letters, whereas for gti the comparison is
+ case-independent. Case and collation order are defined per the system C
+ locale.
+
+inlist {<string1>}{<string2>}, inlisti {<string1>}{<string2>}
+
+ Both strings are expanded; the second string is treated as a list of simple
+ strings; if the first string is a member of the second, then the condition
+ is true. For the case-independent inlisti condition, case is defined per
+ the system C locale.
+
+ These are simpler to use versions of the more powerful forany condition.
+ Examples, and the forany equivalents:
+
+ ${if inlist{needle}{foo:needle:bar}}
+ ${if forany{foo:needle:bar}{eq{$item}{needle}}}
+ ${if inlisti{Needle}{fOo:NeeDLE:bAr}}
+ ${if forany{fOo:NeeDLE:bAr}{eqi{$item}{Needle}}}
+
+isip {<string>}, isip4 {<string>}, isip6 {<string>}
+
+ The substring is first expanded, and then tested to see if it has the form
+ of an IP address. Both IPv4 and IPv6 addresses are valid for isip, whereas
+ isip4 and isip6 test specifically for IPv4 or IPv6 addresses.
+
+ For an IPv4 address, the test is for four dot-separated components, each of
+ which consists of from one to three digits. For an IPv6 address, up to
+ eight colon-separated components are permitted, each containing from one to
+ four hexadecimal digits. There may be fewer than eight components if an
+ empty component (adjacent colons) is present. Only one empty component is
+ permitted.
+
+ Note: The checks used to be just on the form of the address; actual
+ numerical values were not considered. Thus, for example, 999.999.999.999
+ passed the IPv4 check. This is no longer the case.
+
+ The main use of these tests is to distinguish between IP addresses and host
+ names, or between IPv4 and IPv6 addresses. For example, you could use
+
+ ${if isip4{$sender_host_address}...
+
+ to test which IP version an incoming SMTP connection is using.
+
+ldapauth {<ldap query>}
+
+ This condition supports user authentication using LDAP. See section 9.14
+ for details of how to use LDAP in lookups and the syntax of queries. For
+ this use, the query must contain a user name and password. The query itself
+ is not used, and can be empty. The condition is true if the password is not
+ empty, and the user name and password are accepted by the LDAP server. An
+ empty password is rejected without calling LDAP because LDAP binds with an
+ empty password are considered anonymous regardless of the username, and
+ will succeed in most configurations. See chapter 33 for details of SMTP
+ authentication, and chapter 34 for an example of how this can be used.
+
+le {<string1>}{<string2>}, lei {<string1>}{<string2>}
+
+ The two substrings are first expanded. The condition is true if the first
+ string is lexically less than or equal to the second string. For le the
+ comparison includes the case of letters, whereas for lei the comparison is
+ case-independent. Case and collation order are defined per the system C
+ locale.
+
+lt {<string1>}{<string2>}, lti {<string1>}{<string2>}
+
+ The two substrings are first expanded. The condition is true if the first
+ string is lexically less than the second string. For lt the comparison
+ includes the case of letters, whereas for lti the comparison is
+ case-independent. Case and collation order are defined per the system C
+ locale.
+
+match {<string1>}{<string2>}
+
+ The two substrings are first expanded. The second is then treated as a
+ regular expression and applied to the first. Because of the pre-expansion,
+ if the regular expression contains dollar, or backslash characters, they
+ must be escaped. Care must also be taken if the regular expression contains
+ braces (curly brackets). A closing brace must be escaped so that it is not
+ taken as a premature termination of <string2>. The easiest approach is to
+ use the "\N" feature to disable expansion of the regular expression. For
+ example,
+
+ ${if match {$local_part}{\N^\d{3}\N} ...
+
+ If the whole expansion string is in double quotes, further escaping of
+ backslashes is also required.
+
+ The condition is true if the regular expression match succeeds. The regular
+ expression is not required to begin with a circumflex metacharacter, but if
+ there is no circumflex, the expression is not anchored, and it may match
+ anywhere in the subject, not just at the start. If you want the pattern to
+ match at the end of the subject, you must include the "$" metacharacter at
+ an appropriate point. All character handling is done in bytes and is not
+ UTF-8 aware, but we might change this in a future Exim release.
+
+ At the start of an if expansion the values of the numeric variable
+ substitutions $1 etc. are remembered. Obeying a match condition that
+ succeeds causes them to be reset to the substrings of that condition and
+ they will have these values during the expansion of the success string. At
+ the end of the if expansion, the previous values are restored. After
+ testing a combination of conditions using or, the subsequent values of the
+ numeric variables are those of the condition that succeeded.
+
+match_address {<string1>}{<string2>}
+
+ See match_local_part.
+
+match_domain {<string1>}{<string2>}
+
+ See match_local_part.
+
+match_ip {<string1>}{<string2>}
+
+ This condition matches an IP address to a list of IP address patterns. It
+ must be followed by two argument strings. The first (after expansion) must
+ be an IP address or an empty string. The second (not expanded) is a
+ restricted host list that can match only an IP address, not a host name.
+ For example:
+
+ ${if match_ip{$sender_host_address}{1.2.3.4:5.6.7.8}{...}{...}}
+
+ The specific types of host list item that are permitted in the list are:
+
+ + An IP address, optionally with a CIDR mask.
+
+ + A single asterisk, which matches any IP address.
+
+ + An empty item, which matches only if the IP address is empty. This
+ could be useful for testing for a locally submitted message or one from
+ specific hosts in a single test such as
+
+ ${if match_ip{$sender_host_address}{:4.3.2.1:...}{...}{...}}
+
+ where the first item in the list is the empty string.
+
+ + The item @[] matches any of the local host's interface addresses.
+
+ + Single-key lookups are assumed to be like "net-" style lookups in host
+ lists, even if "net-" is not specified. There is never any attempt to
+ turn the IP address into a host name. The most common type of linear
+ search for match_ip is likely to be iplsearch, in which the file can
+ contain CIDR masks. For example:
+
+ ${if match_ip{$sender_host_address}{iplsearch;/some/file}...
+
+ It is of course possible to use other kinds of lookup, and in such a
+ case, you do need to specify the "net-" prefix if you want to specify a
+ specific address mask, for example:
+
+ ${if match_ip{$sender_host_address}{net24-dbm;/some/file}...
+
+ However, unless you are combining a match_ip condition with others, it
+ is just as easy to use the fact that a lookup is itself a condition,
+ and write:
+
+ ${lookup{${mask:$sender_host_address/24}}dbm{/a/file}...
+
+ Note that <string2> is not itself subject to string expansion, unless Exim
+ was built with the EXPAND_LISTMATCH_RHS option.
+
+ Consult section 10.12 for further details of these patterns.
+
+match_local_part {<string1>}{<string2>}
+
+ This condition, together with match_address and match_domain, make it
+ possible to test domain, address, and local part lists within expansions.
+ Each condition requires two arguments: an item and a list to match. A
+ trivial example is:
+
+ ${if match_domain{a.b.c}{x.y.z:a.b.c:p.q.r}{yes}{no}}
+
+ In each case, the second argument may contain any of the allowable items
+ for a list of the appropriate type. Also, because the second argument is a
+ standard form of list, it is possible to refer to a named list. Thus, you
+ can use conditions like this:
+
+ ${if match_domain{$domain}{+local_domains}{...
+
+ For address lists, the matching starts off caselessly, but the "+caseful"
+ item can be used, as in all address lists, to cause subsequent items to
+ have their local parts matched casefully. Domains are always matched
+ caselessly.
+
+ Note that <string2> is not itself subject to string expansion, unless Exim
+ was built with the EXPAND_LISTMATCH_RHS option.
+
+ Note: Host lists are not supported in this way. This is because hosts have
+ two identities: a name and an IP address, and it is not clear how to
+ specify cleanly how such a test would work. However, IP addresses can be
+ matched using match_ip.
+
+pam {<string1>:<string2>:...}
+
+ Pluggable Authentication Modules (https://mirrors.edge.kernel.org/pub/linux
+ /libs/pam/) are a facility that is available in the latest releases of
+ Solaris and in some GNU/Linux distributions. The Exim support, which is
+ intended for use in conjunction with the SMTP AUTH command, is available
+ only if Exim is compiled with
+
+ SUPPORT_PAM=yes
+
+ in Local/Makefile. You probably need to add -lpam to EXTRALIBS, and in some
+ releases of GNU/Linux -ldl is also needed.
+
+ The argument string is first expanded, and the result must be a
+ colon-separated list of strings. Leading and trailing white space is
+ ignored. The PAM module is initialized with the service name "exim" and the
+ user name taken from the first item in the colon-separated data string (<
+ string1>). The remaining items in the data string are passed over in
+ response to requests from the authentication function. In the simple case
+ there will only be one request, for a password, so the data consists of
+ just two strings.
+
+ There can be problems if any of the strings are permitted to contain colon
+ characters. In the usual way, these have to be doubled to avoid being taken
+ as separators. The listquote expansion item can be used for this. For
+ example, the configuration of a LOGIN authenticator might contain this
+ setting:
+
+ server_condition = ${if pam{$auth1:${listquote{:}{$auth2}}}}
+
+ In some operating systems, PAM authentication can be done only from a
+ process running as root. Since Exim is running as the Exim user when
+ receiving messages, this means that PAM cannot be used directly in those
+ systems.
+
+pwcheck {<string1>:<string2>}
+
+ This condition supports user authentication using the Cyrus pwcheck daemon.
+ This is one way of making it possible for passwords to be checked by a
+ process that is not running as root. Note: The use of pwcheck is now
+ deprecated. Its replacement is saslauthd (see below).
+
+ The pwcheck support is not included in Exim by default. You need to specify
+ the location of the pwcheck daemon's socket in Local/Makefile before
+ building Exim. For example:
+
+ CYRUS_PWCHECK_SOCKET=/var/pwcheck/pwcheck
+
+ You do not need to install the full Cyrus software suite in order to use
+ the pwcheck daemon. You can compile and install just the daemon alone from
+ the Cyrus SASL library. Ensure that exim is the only user that has access
+ to the /var/pwcheck directory.
+
+ The pwcheck condition takes one argument, which must be the user name and
+ password, separated by a colon. For example, in a LOGIN authenticator
+ configuration, you might have this:
+
+ server_condition = ${if pwcheck{$auth1:$auth2}}
+
+ Again, for a PLAIN authenticator configuration, this would be:
+
+ server_condition = ${if pwcheck{$auth2:$auth3}}
+
+queue_running
+
+ This condition, which has no data, is true during delivery attempts that
+ are initiated by queue runner processes, and false otherwise.
+
+radius {<authentication string>}
+
+ Radius authentication (RFC 2865) is supported in a similar way to PAM. You
+ must set RADIUS_CONFIG_FILE in Local/Makefile to specify the location of
+ the Radius client configuration file in order to build Exim with Radius
+ support.
+
+ With just that one setting, Exim expects to be linked with the radiusclient
+ library, using the original API. If you are using release 0.4.0 or later of
+ this library, you need to set
+
+ RADIUS_LIB_TYPE=RADIUSCLIENTNEW
+
+ in Local/Makefile when building Exim. You can also link Exim with the
+ libradius library that comes with FreeBSD. To do this, set
+
+ RADIUS_LIB_TYPE=RADLIB
+
+ in Local/Makefile, in addition to setting RADIUS_CONFIGURE_FILE. You may
+ also have to supply a suitable setting in EXTRALIBS so that the Radius
+ library can be found when Exim is linked.
+
+ The string specified by RADIUS_CONFIG_FILE is expanded and passed to the
+ Radius client library, which calls the Radius server. The condition is true
+ if the authentication is successful. For example:
+
+ server_condition = ${if radius{<arguments>}}
+
+saslauthd {{<user>}{<password>}{<service>}{<realm>}}
+
+ This condition supports user authentication using the Cyrus saslauthd
+ daemon. This replaces the older pwcheck daemon, which is now deprecated.
+ Using this daemon is one way of making it possible for passwords to be
+ checked by a process that is not running as root.
+
+ The saslauthd support is not included in Exim by default. You need to
+ specify the location of the saslauthd daemon's socket in Local/Makefile
+ before building Exim. For example:
+
+ CYRUS_SASLAUTHD_SOCKET=/var/state/saslauthd/mux
+
+ You do not need to install the full Cyrus software suite in order to use
+ the saslauthd daemon. You can compile and install just the daemon alone
+ from the Cyrus SASL library.
+
+ Up to four arguments can be supplied to the saslauthd condition, but only
+ two are mandatory. For example:
+
+ server_condition = ${if saslauthd{{$auth1}{$auth2}}}
+
+ The service and the realm are optional (which is why the arguments are
+ enclosed in their own set of braces). For details of the meaning of the
+ service and realm, and how to run the daemon, consult the Cyrus
+ documentation.
+
+
+11.8 Combining expansion conditions
+-----------------------------------
+
+Several conditions can be tested at once by combining them using the and and or
+combination conditions. Note that and and or are complete conditions on their
+own, and precede their lists of sub-conditions. Each sub-condition must be
+enclosed in braces within the overall braces that contain the list. No
+repetition of if is used.
+
+or {{<cond1>}{<cond2>}...}
+
+ The sub-conditions are evaluated from left to right. The condition is true
+ if any one of the sub-conditions is true. For example,
+
+ ${if or {{eq{$local_part}{spqr}}{eq{$domain}{testing.com}}}...
+
+ When a true sub-condition is found, the following ones are parsed but not
+ evaluated. If there are several "match" sub-conditions the values of the
+ numeric variables afterwards are taken from the first one that succeeds.
+
+and {{<cond1>}{<cond2>}...}
+
+ The sub-conditions are evaluated from left to right. The condition is true
+ if all of the sub-conditions are true. If there are several "match"
+ sub-conditions, the values of the numeric variables afterwards are taken
+ from the last one. When a false sub-condition is found, the following ones
+ are parsed but not evaluated.
+
+
+11.9 Expansion variables
+------------------------
+
+This section contains an alphabetical list of all the expansion variables. Some
+of them are available only when Exim is compiled with specific options such as
+support for TLS or the content scanning extension.
+
+$0, $1, etc
+
+ When a match expansion condition succeeds, these variables contain the
+ captured substrings identified by the regular expression during subsequent
+ processing of the success string of the containing if expansion item. In
+ the expansion condition case they do not retain their values afterwards; in
+ fact, their previous values are restored at the end of processing an if
+ item. The numerical variables may also be set externally by some other
+ matching process which precedes the expansion of the string. For example,
+ the commands available in Exim filter files include an if command with its
+ own regular expression matching condition.
+
+$acl_arg1, $acl_arg2, etc
+
+ Within an acl condition, expansion condition or expansion item any
+ arguments are copied to these variables, any unused variables being made
+ empty.
+
+$acl_c...
+
+ Values can be placed in these variables by the set modifier in an ACL. They
+ can be given any name that starts with $acl_c and is at least six
+ characters long, but the sixth character must be either a digit or an
+ underscore. For example: $acl_c5, $acl_c_mycount. The values of the
+ $acl_c... variables persist throughout the lifetime of an SMTP connection.
+ They can be used to pass information between ACLs and between different
+ invocations of the same ACL. When a message is received, the values of
+ these variables are saved with the message, and can be accessed by filters,
+ routers, and transports during subsequent delivery.
+
+$acl_m...
+
+ These variables are like the $acl_c... variables, except that their values
+ are reset after a message has been received. Thus, if several messages are
+ received in one SMTP connection, $acl_m... values are not passed on from
+ one message to the next, as $acl_c... values are. The $acl_m... variables
+ are also reset by MAIL, RSET, EHLO, HELO, and after starting a TLS session.
+ When a message is received, the values of these variables are saved with
+ the message, and can be accessed by filters, routers, and transports during
+ subsequent delivery.
+
+$acl_narg
+
+ Within an acl condition, expansion condition or expansion item this
+ variable has the number of arguments.
+
+$acl_verify_message
+
+ After an address verification has failed, this variable contains the
+ failure message. It retains its value for use in subsequent modifiers. The
+ message can be preserved by coding like this:
+
+ warn !verify = sender
+ set acl_m0 = $acl_verify_message
+
+ You can use $acl_verify_message during the expansion of the message or
+ log_message modifiers, to include information about the verification
+ failure.
+
+$address_data
+
+ This variable is set by means of the address_data option in routers. The
+ value then remains with the address while it is processed by subsequent
+ routers and eventually a transport. If the transport is handling multiple
+ addresses, the value from the first address is used. See chapter 15 for
+ more details. Note: The contents of $address_data are visible in user
+ filter files.
+
+ If $address_data is set when the routers are called from an ACL to verify a
+ recipient address, the final value is still in the variable for subsequent
+ conditions and modifiers of the ACL statement. If routing the address
+ caused it to be redirected to just one address, the child address is also
+ routed as part of the verification, and in this case the final value of
+ $address_data is from the child's routing.
+
+ If $address_data is set when the routers are called from an ACL to verify a
+ sender address, the final value is also preserved, but this time in
+ $sender_address_data, to distinguish it from data from a recipient address.
+
+ In both cases (recipient and sender verification), the value does not
+ persist after the end of the current ACL statement. If you want to preserve
+ these values for longer, you can save them in ACL variables.
+
+$address_file
+
+ When, as a result of aliasing, forwarding, or filtering, a message is
+ directed to a specific file, this variable holds the name of the file when
+ the transport is running. At other times, the variable is empty. For
+ example, using the default configuration, if user r2d2 has a .forward file
+ containing
+
+ /home/r2d2/savemail
+
+ then when the address_file transport is running, $address_file contains the
+ text string "/home/r2d2/savemail". For Sieve filters, the value may be
+ "inbox" or a relative folder name. It is then up to the transport
+ configuration to generate an appropriate absolute path to the relevant
+ file.
+
+$address_pipe
+
+ When, as a result of aliasing or forwarding, a message is directed to a
+ pipe, this variable holds the pipe command when the transport is running.
+
+$auth1 - $auth3
+
+ These variables are used in SMTP authenticators (see chapters 34-42).
+ Elsewhere, they are empty.
+
+$authenticated_id
+
+ When a server successfully authenticates a client it may be configured to
+ preserve some of the authentication information in the variable
+ $authenticated_id (see chapter 33). For example, a user/password
+ authenticator configuration might preserve the user name for use in the
+ routers. Note that this is not the same information that is saved in
+ $sender_host_authenticated.
+
+ When a message is submitted locally (that is, not over a TCP connection)
+ the value of $authenticated_id is normally the login name of the calling
+ process. However, a trusted user can override this by means of the -oMai
+ command line option. This second case also sets up information used by the
+ $authresults expansion item.
+
+$authenticated_fail_id
+
+ When an authentication attempt fails, the variable $authenticated_fail_id
+ will contain the failed authentication id. If more than one authentication
+ id is attempted, it will contain only the last one. The variable is
+ available for processing in the ACL's, generally the quit or notquit ACL. A
+ message to a local recipient could still be accepted without requiring
+ authentication, which means this variable could also be visible in all of
+ the ACL's as well.
+
+$authenticated_sender
+
+ When acting as a server, Exim takes note of the AUTH= parameter on an
+ incoming SMTP MAIL command if it believes the sender is sufficiently
+ trusted, as described in section 33.2. Unless the data is the string "<>",
+ it is set as the authenticated sender of the message, and the value is
+ available during delivery in the $authenticated_sender variable. If the
+ sender is not trusted, Exim accepts the syntax of AUTH=, but ignores the
+ data.
+
+ When a message is submitted locally (that is, not over a TCP connection),
+ the value of $authenticated_sender is an address constructed from the login
+ name of the calling process and $qualify_domain, except that a trusted user
+ can override this by means of the -oMas command line option.
+
+$authentication_failed
+
+ This variable is set to "1" in an Exim server if a client issues an AUTH
+ command that does not succeed. Otherwise it is set to "0". This makes it
+ possible to distinguish between "did not try to authenticate" (
+ $sender_host_authenticated is empty and $authentication_failed is set to
+ "0") and "tried to authenticate but failed" ($sender_host_authenticated is
+ empty and $authentication_failed is set to "1"). Failure includes any
+ negative response to an AUTH command, including (for example) an attempt to
+ use an undefined mechanism.
+
+$av_failed
+
+ This variable is available when Exim is compiled with the content-scanning
+ extension. It is set to "0" by default, but will be set to "1" if any
+ problem occurs with the virus scanner (specified by av_scanner) during the
+ ACL malware condition.
+
+$body_linecount
+
+ When a message is being received or delivered, this variable contains the
+ number of lines in the message's body. See also $message_linecount.
+
+$body_zerocount
+
+ When a message is being received or delivered, this variable contains the
+ number of binary zero bytes (ASCII NULs) in the message's body.
+
+$bounce_recipient
+
+ This is set to the recipient address of a bounce message while Exim is
+ creating it. It is useful if a customized bounce message text file is in
+ use (see chapter 50).
+
+$bounce_return_size_limit
+
+ This contains the value set in the bounce_return_size_limit option, rounded
+ up to a multiple of 1000. It is useful when a customized error message text
+ file is in use (see chapter 50).
+
+$caller_gid
+
+ The real group id under which the process that called Exim was running.
+ This is not the same as the group id of the originator of a message (see
+ $originator_gid). If Exim re-execs itself, this variable in the new
+ incarnation normally contains the Exim gid.
+
+$caller_uid
+
+ The real user id under which the process that called Exim was running. This
+ is not the same as the user id of the originator of a message (see
+ $originator_uid). If Exim re-execs itself, this variable in the new
+ incarnation normally contains the Exim uid.
+
+$callout_address
+
+ After a callout for verification, spamd or malware daemon service, the
+ address that was connected to.
+
+$compile_number
+
+ The building process for Exim keeps a count of the number of times it has
+ been compiled. This serves to distinguish different compilations of the
+ same version of Exim.
+
+$config_dir
+
+ The directory name of the main configuration file. That is, the content of
+ $config_file with the last component stripped. The value does not contain
+ the trailing slash. If $config_file does not contain a slash, $config_dir
+ is ".".
+
+$config_file
+
+ The name of the main configuration file Exim is using.
+
+$dkim_verify_status
+
+ Results of DKIM verification. For details see section 58.3.
+
+$dkim_cur_signer, $dkim_verify_reason, $dkim_domain, $dkim_identity,
+ $dkim_selector, $dkim_algo, $dkim_canon_body, $dkim_canon_headers,
+ $dkim_copiedheaders, $dkim_bodylength, $dkim_created, $dkim_expires,
+ $dkim_headernames, $dkim_key_testing, $dkim_key_nosubdomains,
+ $dkim_key_srvtype, $dkim_key_granularity, $dkim_key_notes, $dkim_key_length
+
+ These variables are only available within the DKIM ACL. For details see
+ section 58.3.
+
+$dkim_signers
+
+ When a message has been received this variable contains a colon-separated
+ list of signer domains and identities for the message. For details see
+ section 58.3.
+
+$dmarc_domain_policy, $dmarc_status, $dmarc_status_text, $dmarc_used_domains
+
+ Results of DMARC verification. For details see section 58.5.
+
+$dnslist_domain, $dnslist_matched, $dnslist_text, $dnslist_value
+
+ When a DNS (black) list lookup succeeds, these variables are set to contain
+ the following data from the lookup: the list's domain name, the key that
+ was looked up, the contents of any associated TXT record, and the value
+ from the main A record. See section 44.32 for more details.
+
+$domain
+
+ When an address is being routed, or delivered on its own, this variable
+ contains the domain. Uppercase letters in the domain are converted into
+ lower case for $domain.
+
+ Global address rewriting happens when a message is received, so the value
+ of $domain during routing and delivery is the value after rewriting.
+ $domain is set during user filtering, but not during system filtering,
+ because a message may have many recipients and the system filter is called
+ just once.
+
+ When more than one address is being delivered at once (for example, several
+ RCPT commands in one SMTP delivery), $domain is set only if they all have
+ the same domain. Transports can be restricted to handling only one domain
+ at a time if the value of $domain is required at transport time - this is
+ the default for local transports. For further details of the environment in
+ which local transports are run, see chapter 23.
+
+ At the end of a delivery, if all deferred addresses have the same domain,
+ it is set in $domain during the expansion of delay_warning_condition.
+
+ The $domain variable is also used in some other circumstances:
+
+ + When an ACL is running for a RCPT command, $domain contains the domain
+ of the recipient address. The domain of the sender address is in
+ $sender_address_domain at both MAIL time and at RCPT time. $domain is
+ not normally set during the running of the MAIL ACL. However, if the
+ sender address is verified with a callout during the MAIL ACL, the
+ sender domain is placed in $domain during the expansions of hosts,
+ interface, and port in the smtp transport.
+
+ + When a rewrite item is being processed (see chapter 31), $domain
+ contains the domain portion of the address that is being rewritten; it
+ can be used in the expansion of the replacement address, for example,
+ to rewrite domains by file lookup.
+
+ + With one important exception, whenever a domain list is being scanned,
+ $domain contains the subject domain. Exception: When a domain list in a
+ sender_domains condition in an ACL is being processed, the subject
+ domain is in $sender_address_domain and not in $domain. It works this
+ way so that, in a RCPT ACL, the sender domain list can be dependent on
+ the recipient domain (which is what is in $domain at this time).
+
+ + When the smtp_etrn_command option is being expanded, $domain contains
+ the complete argument of the ETRN command (see section 49.8).
+
+ If the origin of the data is an incoming message, the result of expanding
+ this variable is tainted. When un untainted version is needed, one should
+ be obtained from looking up the value in a local (therefore trusted)
+ database. Often $domain_data is usable in this role.
+
+$domain_data
+
+ When the domains condition on a router
+
+ or an ACL matches a domain against a list, the match value is copied to
+ $domain_data. This is an enhancement over previous versions of Exim, when
+ it only applied to the data read by a lookup. For details on match values
+ see section 10.5 et. al.
+
+ If the router routes the address to a transport, the value is available in
+ that transport. If the transport is handling multiple addresses, the value
+ from the first address is used.
+
+ $domain_data set in an ACL is available during the rest of the ACL
+ statement.
+
+$exim_gid
+
+ This variable contains the numerical value of the Exim group id.
+
+$exim_path
+
+ This variable contains the path to the Exim binary.
+
+$exim_uid
+
+ This variable contains the numerical value of the Exim user id.
+
+$exim_version
+
+ This variable contains the version string of the Exim build. The first
+ character is a major version number, currently 4. Then after a dot, the
+ next group of digits is a minor version number. There may be other
+ characters following the minor version. This value may be overridden by the
+ exim_version main config option.
+
+$header_<name>
+
+ This is not strictly an expansion variable. It is expansion syntax for
+ inserting the message header line with the given name. Note that the name
+ must be terminated by colon or white space, because it may contain a wide
+ variety of characters. Note also that braces must not be used. See the full
+ description in section 11.5 above.
+
+$headers_added
+
+ Within an ACL this variable contains the headers added so far by the ACL
+ modifier add_header (section 44.24). The headers are a newline-separated
+ list.
+
+$home
+
+ When the check_local_user option is set for a router, the user's home
+ directory is placed in $home when the check succeeds. In particular, this
+ means it is set during the running of users' filter files. A router may
+ also explicitly set a home directory for use by a transport; this can be
+ overridden by a setting on the transport itself.
+
+ When running a filter test via the -bf option, $home is set to the value of
+ the environment variable HOME, which is subject to the keep_environment and
+ add_environment main config options.
+
+$host
+
+ If a router assigns an address to a transport (any transport), and passes a
+ list of hosts with the address, the value of $host when the transport
+ starts to run is the name of the first host on the list. Note that this
+ applies both to local and remote transports.
+
+ For the smtp transport, if there is more than one host, the value of $host
+ changes as the transport works its way through the list. In particular,
+ when the smtp transport is expanding its options for encryption using TLS,
+ or for specifying a transport filter (see chapter 24), $host contains the
+ name of the host to which it is connected.
+
+ When used in the client part of an authenticator configuration (see chapter
+ 33), $host contains the name of the server to which the client is
+ connected.
+
+$host_address
+
+ This variable is set to the remote host's IP address whenever $host is set
+ for a remote connection. It is also set to the IP address that is being
+ checked when the ignore_target_hosts option is being processed.
+
+$host_data
+
+ If a hosts condition in an ACL is satisfied by means of a lookup, the
+ result of the lookup is made available in the $host_data variable. This
+ allows you, for example, to do things like this:
+
+ deny hosts = net-lsearch;/some/file
+ message = $host_data
+
+$host_lookup_deferred
+
+ This variable normally contains "0", as does $host_lookup_failed. When a
+ message comes from a remote host and there is an attempt to look up the
+ host's name from its IP address, and the attempt is not successful, one of
+ these variables is set to "1".
+
+ + If the lookup receives a definite negative response (for example, a DNS
+ lookup succeeded, but no records were found), $host_lookup_failed is
+ set to "1".
+
+ + If there is any kind of problem during the lookup, such that Exim
+ cannot tell whether or not the host name is defined (for example, a
+ timeout for a DNS lookup), $host_lookup_deferred is set to "1".
+
+ Looking up a host's name from its IP address consists of more than just a
+ single reverse lookup. Exim checks that a forward lookup of at least one of
+ the names it receives from a reverse lookup yields the original IP address.
+ If this is not the case, Exim does not accept the looked up name(s), and
+ $host_lookup_failed is set to "1". Thus, being able to find a name from an
+ IP address (for example, the existence of a PTR record in the DNS) is not
+ sufficient on its own for the success of a host name lookup. If the reverse
+ lookup succeeds, but there is a lookup problem such as a timeout when
+ checking the result, the name is not accepted, and $host_lookup_deferred is
+ set to "1". See also $sender_host_name.
+
+ Performing these checks sets up information used by the authresults
+ expansion item.
+
+$host_lookup_failed
+
+ See $host_lookup_deferred.
+
+$host_port
+
+ This variable is set to the remote host's TCP port whenever $host is set
+ for an outbound connection.
+
+$initial_cwd
+
+ This variable contains the full path name of the initial working directory
+ of the current Exim process. This may differ from the current working
+ directory, as Exim changes this to "/" during early startup, and to
+ $spool_directory later.
+
+$inode
+
+ The only time this variable is set is while expanding the directory_file
+ option in the appendfile transport. The variable contains the inode number
+ of the temporary file which is about to be renamed. It can be used to
+ construct a unique name for the file.
+
+$interface_address
+
+ This is an obsolete name for $received_ip_address.
+
+$interface_port
+
+ This is an obsolete name for $received_port.
+
+$item
+
+ This variable is used during the expansion of forall and forany conditions
+ (see section 11.7), and filter, map, and reduce items (see section 11.7).
+ In other circumstances, it is empty.
+
+$ldap_dn
+
+ This variable, which is available only when Exim is compiled with LDAP
+ support, contains the DN from the last entry in the most recently
+ successful LDAP lookup.
+
+$load_average
+
+ This variable contains the system load average, multiplied by 1000 so that
+ it is an integer. For example, if the load average is 0.21, the value of
+ the variable is 210. The value is recomputed every time the variable is
+ referenced.
+
+$local_part
+
+ When an address is being routed, or delivered on its own, this variable
+ contains the local part. When a number of addresses are being delivered
+ together (for example, multiple RCPT commands in an SMTP session),
+ $local_part is not set.
+
+ Global address rewriting happens when a message is received, so the value
+ of $local_part during routing and delivery is the value after rewriting.
+ $local_part is set during user filtering, but not during system filtering,
+ because a message may have many recipients and the system filter is called
+ just once.
+
+ If the origin of the data is an incoming message, the result of expanding
+ this variable is tainted.
+
+ Warning: the content of this variable is usually provided by a potential
+ attacker. Consider carefully the implications of using it unvalidated as a
+ name for file access. This presents issues for users' .forward and filter
+ files. For traditional full user accounts, use check_local_users and the
+ $local_part_data variable rather than this one. For virtual users, store a
+ suitable pathname component in the database which is used for account name
+ validation, and use that retrieved value rather than this variable. Often
+ $local_part_data is usable in this role. If needed, use a router
+ address_data or set option for the retrieved data.
+
+ When a message is being delivered to a file, pipe, or autoreply transport
+ as a result of aliasing or forwarding, $local_part is set to the local part
+ of the parent address, not to the filename or command (see $address_file
+ and $address_pipe).
+
+ When an ACL is running for a RCPT command, $local_part contains the local
+ part of the recipient address.
+
+ When a rewrite item is being processed (see chapter 31), $local_part
+ contains the local part of the address that is being rewritten; it can be
+ used in the expansion of the replacement address, for example.
+
+ In all cases, all quoting is removed from the local part. For example, for
+ both the addresses
+
+ "abc:xyz"@test.example
+ abc\:xyz@test.example
+
+ the value of $local_part is
+
+ abc:xyz
+
+ If you use $local_part to create another address, you should always wrap it
+ inside a quoting operator. For example, in a redirect router you could
+ have:
+
+ data = ${quote_local_part:$local_part}@new.domain.example
+
+ Note: The value of $local_part is normally lower cased. If you want to
+ process local parts in a case-dependent manner in a router, you can set the
+ caseful_local_part option (see chapter 15).
+
+$local_part_data
+
+ When the local_parts condition on a router or ACL matches a local part list
+
+ the match value is copied to $local_part_data. This is an enhancement over
+ previous versions of Exim, when it only applied to the data read by a
+ lookup. For details on match values see section 10.5 et. al.
+
+ The check_local_user router option also sets this variable.
+
+ If a local part prefix or suffix has been recognized, it is not included in
+ the value of $local_part during routing and subsequent delivery. The values
+ of any prefix or suffix are in $local_part_prefix and $local_part_suffix,
+ respectively.
+
+ If the specification did not include a wildcard then the affix variable
+ value is not tainted.
+
+ If the affix specification included a wildcard then the portion of the
+ affix matched by the wildcard is in $local_part_prefix_v or
+ $local_part_suffix_v as appropriate, and both the whole and varying values
+ are tainted.
+
+$local_scan_data
+
+ This variable contains the text returned by the local_scan() function when
+ a message is received. See chapter 46 for more details.
+
+$local_user_gid
+
+ See $local_user_uid.
+
+$local_user_uid
+
+ This variable and $local_user_gid are set to the uid and gid after the
+ check_local_user router precondition succeeds. This means that their values
+ are available for the remaining preconditions (senders, require_files, and
+ condition), for the address_data expansion, and for any router-specific
+ expansions. At all other times, the values in these variables are "(uid_t)
+ (-1)" and "(gid_t)(-1)", respectively.
+
+$localhost_number
+
+ This contains the expanded value of the localhost_number option. The
+ expansion happens after the main options have been read.
+
+$log_inodes
+
+ The number of free inodes in the disk partition where Exim's log files are
+ being written. The value is recalculated whenever the variable is
+ referenced. If the relevant file system does not have the concept of
+ inodes, the value of is -1. See also the check_log_inodes option.
+
+$log_space
+
+ The amount of free space (as a number of kilobytes) in the disk partition
+ where Exim's log files are being written. The value is recalculated
+ whenever the variable is referenced. If the operating system does not have
+ the ability to find the amount of free space (only true for experimental
+ systems), the space value is -1. See also the check_log_space option.
+
+$lookup_dnssec_authenticated
+
+ This variable is set after a DNS lookup done by a dnsdb lookup expansion,
+ dnslookup router or smtp transport. It will be empty if DNSSEC was not
+ requested, "no" if the result was not labelled as authenticated data and
+ "yes" if it was. Results that are labelled as authoritative answer that
+ match the dns_trust_aa configuration variable count also as authenticated
+ data.
+
+$mailstore_basename
+
+ This variable is set only when doing deliveries in "mailstore" format in
+ the appendfile transport. During the expansion of the mailstore_prefix,
+ mailstore_suffix, message_prefix, and message_suffix options, it contains
+ the basename of the files that are being written, that is, the name without
+ the ".tmp", ".env", or ".msg" suffix. At all other times, this variable is
+ empty.
+
+$malware_name
+
+ This variable is available when Exim is compiled with the content-scanning
+ extension. It is set to the name of the virus that was found when the ACL
+ malware condition is true (see section 45.1).
+
+$max_received_linelength
+
+ This variable contains the number of bytes in the longest line that was
+ received as part of the message, not counting the line termination
+ character(s). It is not valid if the spool_files_wireformat option is used.
+
+$message_age
+
+ This variable is set at the start of a delivery attempt to contain the
+ number of seconds since the message was received. It does not change during
+ a single delivery attempt.
+
+$message_body
+
+ This variable contains the initial portion of a message's body while it is
+ being delivered, and is intended mainly for use in filter files. The
+ maximum number of characters of the body that are put into the variable is
+ set by the message_body_visible configuration option; the default is 500.
+
+ By default, newlines are converted into spaces in $message_body, to make it
+ easier to search for phrases that might be split over a line break.
+ However, this can be disabled by setting message_body_newlines to be true.
+ Binary zeros are always converted into spaces.
+
+$message_body_end
+
+ This variable contains the final portion of a message's body while it is
+ being delivered. The format and maximum size are as for $message_body.
+
+$message_body_size
+
+ When a message is being delivered, this variable contains the size of the
+ body in bytes. The count starts from the character after the blank line
+ that separates the body from the header. Newlines are included in the
+ count. See also $message_size, $body_linecount, and $body_zerocount.
+
+ If the spool file is wireformat (see the spool_files_wireformat main
+ option) the CRLF line-terminators are included in the count.
+
+$message_exim_id
+
+ When a message is being received or delivered, this variable contains the
+ unique message id that is generated and used by Exim to identify the
+ message. An id is not created for a message until after its header has been
+ successfully received. Note: This is not the contents of the Message-ID:
+ header line; it is the local id that Exim assigns to the message, for
+ example: "1BXTIK-0001yO-VA".
+
+$message_headers
+
+ This variable contains a concatenation of all the header lines when a
+ message is being processed, except for lines added by routers or
+ transports. The header lines are separated by newline characters. Their
+ contents are decoded in the same way as a header line that is inserted by
+ bheader.
+
+$message_headers_raw
+
+ This variable is like $message_headers except that no processing of the
+ contents of header lines is done.
+
+$message_id
+
+ This is an old name for $message_exim_id. It is now deprecated.
+
+$message_linecount
+
+ This variable contains the total number of lines in the header and body of
+ the message. Compare $body_linecount, which is the count for the body only.
+ During the DATA and content-scanning ACLs, $message_linecount contains the
+ number of lines received. Before delivery happens (that is, before filters,
+ routers, and transports run) the count is increased to include the
+ Received: header line that Exim standardly adds, and also any other header
+ lines that are added by ACLs. The blank line that separates the message
+ header from the body is not counted.
+
+ As with the special case of $message_size, during the expansion of the
+ appendfile transport's maildir_tag option in maildir format, the value of
+ $message_linecount is the precise size of the number of newlines in the
+ file that has been written (minus one for the blank line between the header
+ and the body).
+
+ Here is an example of the use of this variable in a DATA ACL:
+
+ deny condition = \
+ ${if <{250}{${eval:$message_linecount - $body_linecount}}}
+ message = Too many lines in message header
+
+ In the MAIL and RCPT ACLs, the value is zero because at that stage the
+ message has not yet been received.
+
+ This variable is not valid if the spool_files_wireformat option is used.
+
+$message_size
+
+ When a message is being processed, this variable contains its size in
+ bytes. In most cases, the size includes those headers that were received
+ with the message, but not those (such as Envelope-to:) that are added to
+ individual deliveries as they are written. However, there is one special
+ case: during the expansion of the maildir_tag option in the appendfile
+ transport while doing a delivery in maildir format, the value of
+ $message_size is the precise size of the file that has been written. See
+ also $message_body_size, $body_linecount, and $body_zerocount.
+
+ While running a per message ACL (mail/rcpt/predata), $message_size contains
+ the size supplied on the MAIL command, or -1 if no size was given. The
+ value may not, of course, be truthful.
+
+$mime_xxx
+
+ A number of variables whose names start with $mime are available when Exim
+ is compiled with the content-scanning extension. For details, see section
+ 45.4.
+
+$n0 - $n9
+
+ These variables are counters that can be incremented by means of the add
+ command in filter files.
+
+$original_domain
+
+ When a top-level address is being processed for delivery, this contains the
+ same value as $domain. However, if a "child" address (for example,
+ generated by an alias, forward, or filter file) is being processed, this
+ variable contains the domain of the original address (lower cased). This
+ differs from $parent_domain only when there is more than one level of
+ aliasing or forwarding. When more than one address is being delivered in a
+ single transport run, $original_domain is not set.
+
+ If a new address is created by means of a deliver command in a system
+ filter, it is set up with an artificial "parent" address. This has the
+ local part system-filter and the default qualify domain.
+
+$original_local_part
+
+ When a top-level address is being processed for delivery, this contains the
+ same value as $local_part, unless a prefix or suffix was removed from the
+ local part, because $original_local_part always contains the full local
+ part. When a "child" address (for example, generated by an alias, forward,
+ or filter file) is being processed, this variable contains the full local
+ part of the original address.
+
+ If the router that did the redirection processed the local part
+ case-insensitively, the value in $original_local_part is in lower case.
+ This variable differs from $parent_local_part only when there is more than
+ one level of aliasing or forwarding. When more than one address is being
+ delivered in a single transport run, $original_local_part is not set.
+
+ If a new address is created by means of a deliver command in a system
+ filter, it is set up with an artificial "parent" address. This has the
+ local part system-filter and the default qualify domain.
+
+$originator_gid
+
+ This variable contains the value of $caller_gid that was set when the
+ message was received. For messages received via the command line, this is
+ the gid of the sending user. For messages received by SMTP over TCP/IP,
+ this is normally the gid of the Exim user.
+
+$originator_uid
+
+ The value of $caller_uid that was set when the message was received. For
+ messages received via the command line, this is the uid of the sending
+ user. For messages received by SMTP over TCP/IP, this is normally the uid
+ of the Exim user.
+
+$parent_domain
+
+ This variable is similar to $original_domain (see above), except that it
+ refers to the immediately preceding parent address.
+
+$parent_local_part
+
+ This variable is similar to $original_local_part (see above), except that
+ it refers to the immediately preceding parent address.
+
+$pid
+
+ This variable contains the current process id.
+
+$pipe_addresses
+
+ This is not an expansion variable, but is mentioned here because the string
+ "$pipe_addresses" is handled specially in the command specification for the
+ pipe transport (chapter 29) and in transport filters (described under
+ transport_filter in chapter 24). It cannot be used in general expansion
+ strings, and provokes an "unknown variable" error if encountered.
+
+$primary_hostname
+
+ This variable contains the value set by primary_hostname in the
+ configuration file, or read by the uname() function. If uname() returns a
+ single-component name, Exim calls gethostbyname() (or getipnodebyname()
+ where available) in an attempt to acquire a fully qualified host name. See
+ also $smtp_active_hostname.
+
+$proxy_external_address, $proxy_external_port, $proxy_local_address,
+ $proxy_local_port, $proxy_session
+
+ These variables are only available when built with Proxy Protocol or SOCKS5
+ support. For details see chapter 59.1.
+
+$prdr_requested
+
+ This variable is set to "yes" if PRDR was requested by the client for the
+ current message, otherwise "no".
+
+$prvscheck_address
+
+ This variable is used in conjunction with the prvscheck expansion item,
+ which is described in sections 11.5 and 44.51.
+
+$prvscheck_keynum
+
+ This variable is used in conjunction with the prvscheck expansion item,
+ which is described in sections 11.5 and 44.51.
+
+$prvscheck_result
+
+ This variable is used in conjunction with the prvscheck expansion item,
+ which is described in sections 11.5 and 44.51.
+
+$qualify_domain
+
+ The value set for the qualify_domain option in the configuration file.
+
+$qualify_recipient
+
+ The value set for the qualify_recipient option in the configuration file,
+ or if not set, the value of $qualify_domain.
+
+$queue_name
+
+ The name of the spool queue in use; empty for the default queue.
+
+$queue_size
+
+ This variable contains the number of messages queued. It is evaluated on
+ demand, but no more often than once every minute.
+
+$r_...
+
+ Values can be placed in these variables by the set option of a router. They
+ can be given any name that starts with $r_. The values persist for the
+ address being handled through subsequent routers and the eventual
+ transport.
+
+$rcpt_count
+
+ When a message is being received by SMTP, this variable contains the number
+ of RCPT commands received for the current message. If this variable is used
+ in a RCPT ACL, its value includes the current command.
+
+$rcpt_defer_count
+
+ When a message is being received by SMTP, this variable contains the number
+ of RCPT commands in the current message that have previously been rejected
+ with a temporary (4xx) response.
+
+$rcpt_fail_count
+
+ When a message is being received by SMTP, this variable contains the number
+ of RCPT commands in the current message that have previously been rejected
+ with a permanent (5xx) response.
+
+$received_count
+
+ This variable contains the number of Received: header lines in the message,
+ including the one added by Exim (so its value is always greater than zero).
+ It is available in the DATA ACL, the non-SMTP ACL, and while routing and
+ delivering.
+
+$received_for
+
+ If there is only a single recipient address in an incoming message, this
+ variable contains that address when the Received: header line is being
+ built. The value is copied after recipient rewriting has happened, but
+ before the local_scan() function is run.
+
+$received_ip_address
+
+ As soon as an Exim server starts processing an incoming TCP/IP connection,
+ this variable is set to the address of the local IP interface, and
+ $received_port is set to the local port number. (The remote IP address and
+ port are in $sender_host_address and $sender_host_port.) When testing with
+ -bh, the port value is -1 unless it has been set using the -oMi command
+ line option.
+
+ As well as being useful in ACLs (including the "connect" ACL), these
+ variable could be used, for example, to make the filename for a TLS
+ certificate depend on which interface and/or port is being used for the
+ incoming connection. The values of $received_ip_address and $received_port
+ are saved with any messages that are received, thus making these variables
+ available at delivery time. For outbound connections see
+ $sending_ip_address.
+
+$received_port
+
+ See $received_ip_address.
+
+$received_protocol
+
+ When a message is being processed, this variable contains the name of the
+ protocol by which it was received. Most of the names used by Exim are
+ defined by RFCs 821, 2821, and 3848. They start with "smtp" (the client
+ used HELO) or "esmtp" (the client used EHLO). This can be followed by "s"
+ for secure (encrypted) and/or "a" for authenticated. Thus, for example, if
+ the protocol is set to "esmtpsa", the message was received over an
+ encrypted SMTP connection and the client was successfully authenticated.
+
+ Exim uses the protocol name "smtps" for the case when encryption is
+ automatically set up on connection without the use of STARTTLS (see
+ tls_on_connect_ports), and the client uses HELO to initiate the encrypted
+ SMTP session. The name "smtps" is also used for the rare situation where
+ the client initially uses EHLO, sets up an encrypted connection using
+ STARTTLS, and then uses HELO afterwards.
+
+ The -oMr option provides a way of specifying a custom protocol name for
+ messages that are injected locally by trusted callers. This is commonly
+ used to identify messages that are being re-injected after some kind of
+ scanning.
+
+$received_time
+
+ This variable contains the date and time when the current message was
+ received, as a number of seconds since the start of the Unix epoch.
+
+$recipient_data
+
+ This variable is set after an indexing lookup success in an ACL recipients
+ condition. It contains the data from the lookup, and the value remains set
+ until the next recipients test. Thus, you can do things like this:
+
+ require recipients = cdb*@;/some/file
+ deny some further test involving $recipient_data
+
+ Warning: This variable is set only when a lookup is used as an indexing
+ method in the address list, using the semicolon syntax as in the example
+ above. The variable is not set for a lookup that is used as part of the
+ string expansion that all such lists undergo before being interpreted.
+
+$recipient_verify_failure
+
+ In an ACL, when a recipient verification fails, this variable contains
+ information about the failure. It is set to one of the following words:
+
+ + "qualify": The address was unqualified (no domain), and the message was
+ neither local nor came from an exempted host.
+
+ + "route": Routing failed.
+
+ + "mail": Routing succeeded, and a callout was attempted; rejection
+ occurred at or before the MAIL command (that is, on initial connection,
+ HELO, or MAIL).
+
+ + "recipient": The RCPT command in a callout was rejected.
+
+ + "postmaster": The postmaster check in a callout was rejected.
+
+ The main use of this variable is expected to be to distinguish between
+ rejections of MAIL and rejections of RCPT.
+
+$recipients
+
+ This variable contains a list of envelope recipients for a message. A comma
+ and a space separate the addresses in the replacement text. However, the
+ variable is not generally available, to prevent exposure of Bcc recipients
+ in unprivileged users' filter files. You can use $recipients only in these
+ cases:
+
+ 1. In a system filter file.
+
+ 2. In the ACLs associated with the DATA command and with non-SMTP
+ messages, that is, the ACLs defined by acl_smtp_predata, acl_smtp_data,
+ acl_smtp_mime, acl_not_smtp_start, acl_not_smtp, and acl_not_smtp_mime.
+
+ 3. From within a local_scan() function.
+
+$recipients_count
+
+ When a message is being processed, this variable contains the number of
+ envelope recipients that came with the message. Duplicates are not excluded
+ from the count. While a message is being received over SMTP, the number
+ increases for each accepted recipient. It can be referenced in an ACL.
+
+$regex_match_string
+
+ This variable is set to contain the matching regular expression after a
+ regex ACL condition has matched (see section 45.5).
+
+$regex1, $regex2, etc
+
+ When a regex or mime_regex ACL condition succeeds, these variables contain
+ the captured substrings identified by the regular expression.
+
+$reply_address
+
+ When a message is being processed, this variable contains the contents of
+ the Reply-To: header line if one exists and it is not empty, or otherwise
+ the contents of the From: header line. Apart from the removal of leading
+ white space, the value is not processed in any way. In particular, no RFC
+ 2047 decoding or character code translation takes place.
+
+$return_path
+
+ When a message is being delivered, this variable contains the return path -
+ the sender field that will be sent as part of the envelope. It is not
+ enclosed in <> characters. At the start of routing an address, $return_path
+ has the same value as $sender_address, but if, for example, an incoming
+ message to a mailing list has been expanded by a router which specifies a
+ different address for bounce messages, $return_path subsequently contains
+ the new bounce address, whereas $sender_address always contains the
+ original sender address that was received with the message. In other words,
+ $sender_address contains the incoming envelope sender, and $return_path
+ contains the outgoing envelope sender.
+
+$return_size_limit
+
+ This is an obsolete name for $bounce_return_size_limit.
+
+$router_name
+
+ During the running of a router this variable contains its name.
+
+$runrc
+
+ This variable contains the return code from a command that is run by the $
+ {run...} expansion item. Warning: In a router or transport, you cannot
+ assume the order in which option values are expanded, except for those
+ preconditions whose order of testing is documented. Therefore, you cannot
+ reliably expect to set $runrc by the expansion of one option, and use it in
+ another.
+
+$self_hostname
+
+ When an address is routed to a supposedly remote host that turns out to be
+ the local host, what happens is controlled by the self generic router
+ option. One of its values causes the address to be passed to another
+ router. When this happens, $self_hostname is set to the name of the local
+ host that the original router encountered. In other circumstances its
+ contents are null.
+
+$sender_address
+
+ When a message is being processed, this variable contains the sender's
+ address that was received in the message's envelope. The case of letters in
+ the address is retained, in both the local part and the domain. For bounce
+ messages, the value of this variable is the empty string. See also
+ $return_path.
+
+$sender_address_data
+
+ If $address_data is set when the routers are called from an ACL to verify a
+ sender address, the final value is preserved in $sender_address_data, to
+ distinguish it from data from a recipient address. The value does not
+ persist after the end of the current ACL statement. If you want to preserve
+ it for longer, you can save it in an ACL variable.
+
+$sender_address_domain
+
+ The domain portion of $sender_address.
+
+$sender_address_local_part
+
+ The local part portion of $sender_address.
+
+$sender_data
+
+ This variable is set after a lookup success in an ACL senders condition or
+ in a router senders option. It contains the data from the lookup, and the
+ value remains set until the next senders test. Thus, you can do things like
+ this:
+
+ require senders = cdb*@;/some/file
+ deny some further test involving $sender_data
+
+ Warning: This variable is set only when a lookup is used as an indexing
+ method in the address list, using the semicolon syntax as in the example
+ above. The variable is not set for a lookup that is used as part of the
+ string expansion that all such lists undergo before being interpreted.
+
+$sender_fullhost
+
+ When a message is received from a remote host, this variable contains the
+ host name and IP address in a single string. It ends with the IP address in
+ square brackets, followed by a colon and a port number if the logging of
+ ports is enabled. The format of the rest of the string depends on whether
+ the host issued a HELO or EHLO SMTP command, and whether the host name was
+ verified by looking up its IP address. (Looking up the IP address can be
+ forced by the host_lookup option, independent of verification.) A plain
+ host name at the start of the string is a verified host name; if this is
+ not present, verification either failed or was not requested. A host name
+ in parentheses is the argument of a HELO or EHLO command. This is omitted
+ if it is identical to the verified host name or to the host's IP address in
+ square brackets.
+
+$sender_helo_dnssec
+
+ This boolean variable is true if a successful HELO verification was done
+ using DNS information the resolver library stated was authenticated data.
+
+$sender_helo_name
+
+ When a message is received from a remote host that has issued a HELO or
+ EHLO command, the argument of that command is placed in this variable. It
+ is also set if HELO or EHLO is used when a message is received using SMTP
+ locally via the -bs or -bS options.
+
+$sender_host_address
+
+ When a message is received from a remote host using SMTP, this variable
+ contains that host's IP address. For locally non-SMTP submitted messages,
+ it is empty.
+
+$sender_host_authenticated
+
+ This variable contains the name (not the public name) of the authenticator
+ driver that successfully authenticated the client from which the message
+ was received. It is empty if there was no successful authentication. See
+ also $authenticated_id.
+
+$sender_host_dnssec
+
+ If an attempt to populate $sender_host_name has been made (by reference,
+ hosts_lookup or otherwise) then this boolean will have been set true if,
+ and only if, the resolver library states that both the reverse and forward
+ DNS were authenticated data. At all other times, this variable is false.
+
+ It is likely that you will need to coerce DNSSEC support on in the resolver
+ library, by setting:
+
+ dns_dnssec_ok = 1
+
+ In addition, on Linux with glibc 2.31 or newer the resolver library will
+ default to stripping out a successful validation status. This will break a
+ previously working Exim installation. Provided that you do trust the
+ resolver (ie, is on localhost) you can tell glibc to pass through any
+ successful validation with a new option in /etc/resolv.conf:
+
+ options trust-ad
+
+ Exim does not perform DNSSEC validation itself, instead leaving that to a
+ validating resolver (e.g. unbound, or bind with suitable configuration).
+
+ If you have changed host_lookup_order so that "bydns" is not the first
+ mechanism in the list, then this variable will be false.
+
+ This requires that your system resolver library support EDNS0 (and that
+ DNSSEC flags exist in the system headers). If the resolver silently drops
+ all EDNS0 options, then this will have no effect. OpenBSD's asr resolver is
+ known to currently ignore EDNS0, documented in CAVEATS of asr_run(3).
+
+$sender_host_name
+
+ When a message is received from a remote host, this variable contains the
+ host's name as obtained by looking up its IP address. For messages received
+ by other means, this variable is empty.
+
+ If the host name has not previously been looked up, a reference to
+ $sender_host_name triggers a lookup (for messages from remote hosts). A
+ looked up name is accepted only if it leads back to the original IP address
+ via a forward lookup. If either the reverse or the forward lookup fails to
+ find any data, or if the forward lookup does not yield the original IP
+ address, $sender_host_name remains empty, and $host_lookup_failed is set to
+ "1".
+
+ However, if either of the lookups cannot be completed (for example, there
+ is a DNS timeout), $host_lookup_deferred is set to "1", and
+ $host_lookup_failed remains set to "0".
+
+ Once $host_lookup_failed is set to "1", Exim does not try to look up the
+ host name again if there is a subsequent reference to $sender_host_name in
+ the same Exim process, but it does try again if $host_lookup_deferred is
+ set to "1".
+
+ Exim does not automatically look up every calling host's name. If you want
+ maximum efficiency, you should arrange your configuration so that it avoids
+ these lookups altogether. The lookup happens only if one or more of the
+ following are true:
+
+ + A string containing $sender_host_name is expanded.
+
+ + The calling host matches the list in host_lookup. In the default
+ configuration, this option is set to *, so it must be changed if
+ lookups are to be avoided. (In the code, the default for host_lookup is
+ unset.)
+
+ + Exim needs the host name in order to test an item in a host list. The
+ items that require this are described in sections 10.14 and 10.18.
+
+ + The calling host matches helo_try_verify_hosts or helo_verify_hosts. In
+ this case, the host name is required to compare with the name quoted in
+ any EHLO or HELO commands that the client issues.
+
+ + The remote host issues a EHLO or HELO command that quotes one of the
+ domains in helo_lookup_domains. The default value of this option is
+
+ helo_lookup_domains = @ : @[]
+
+ which causes a lookup if a remote host (incorrectly) gives the server's
+ name or IP address in an EHLO or HELO command.
+
+$sender_host_port
+
+ When a message is received from a remote host, this variable contains the
+ port number that was used on the remote host.
+
+$sender_ident
+
+ When a message is received from a remote host, this variable contains the
+ identification received in response to an RFC 1413 request. When a message
+ has been received locally, this variable contains the login name of the
+ user that called Exim.
+
+$sender_rate_xxx
+
+ A number of variables whose names begin $sender_rate_ are set as part of
+ the ratelimit ACL condition. Details are given in section 44.38.
+
+$sender_rcvhost
+
+ This is provided specifically for use in Received: headers. It starts with
+ either the verified host name (as obtained from a reverse DNS lookup) or,
+ if there is no verified host name, the IP address in square brackets. After
+ that there may be text in parentheses. When the first item is a verified
+ host name, the first thing in the parentheses is the IP address in square
+ brackets, followed by a colon and a port number if port logging is enabled.
+ When the first item is an IP address, the port is recorded as "port=xxxx"
+ inside the parentheses.
+
+ There may also be items of the form "helo=xxxx" if HELO or EHLO was used
+ and its argument was not identical to the real host name or IP address, and
+ "ident=xxxx" if an RFC 1413 ident string is available. If all three items
+ are present in the parentheses, a newline and tab are inserted into the
+ string, to improve the formatting of the Received: header.
+
+$sender_verify_failure
+
+ In an ACL, when a sender verification fails, this variable contains
+ information about the failure. The details are the same as for
+ $recipient_verify_failure.
+
+$sending_ip_address
+
+ This variable is set whenever an outgoing SMTP connection to another host
+ has been set up. It contains the IP address of the local interface that is
+ being used. This is useful if a host that has more than one IP address
+ wants to take on different personalities depending on which one is being
+ used. For incoming connections, see $received_ip_address.
+
+$sending_port
+
+ This variable is set whenever an outgoing SMTP connection to another host
+ has been set up. It contains the local port that is being used. For
+ incoming connections, see $received_port.
+
+$smtp_active_hostname
+
+ During an incoming SMTP session, this variable contains the value of the
+ active host name, as specified by the smtp_active_hostname option. The
+ value of $smtp_active_hostname is saved with any message that is received,
+ so its value can be consulted during routing and delivery.
+
+$smtp_command
+
+ During the processing of an incoming SMTP command, this variable contains
+ the entire command. This makes it possible to distinguish between HELO and
+ EHLO in the HELO ACL, and also to distinguish between commands such as
+ these:
+
+ MAIL FROM:<>
+ MAIL FROM: <>
+
+ For a MAIL command, extra parameters such as SIZE can be inspected. For a
+ RCPT command, the address in $smtp_command is the original address before
+ any rewriting, whereas the values in $local_part and $domain are taken from
+ the address after SMTP-time rewriting.
+
+$smtp_command_argument
+
+ While an ACL is running to check an SMTP command, this variable contains
+ the argument, that is, the text that follows the command name, with leading
+ white space removed. Following the introduction of $smtp_command, this
+ variable is somewhat redundant, but is retained for backwards
+ compatibility.
+
+$smtp_command_history
+
+ A comma-separated list (with no whitespace) of the most-recent SMTP
+ commands received, in time-order left to right. Only a limited number of
+ commands are remembered.
+
+$smtp_count_at_connection_start
+
+ This variable is set greater than zero only in processes spawned by the
+ Exim daemon for handling incoming SMTP connections. The name is
+ deliberately long, in order to emphasize what the contents are. When the
+ daemon accepts a new connection, it increments this variable. A copy of the
+ variable is passed to the child process that handles the connection, but
+ its value is fixed, and never changes. It is only an approximation of how
+ many incoming connections there actually are, because many other
+ connections may come and go while a single connection is being processed.
+ When a child process terminates, the daemon decrements its copy of the
+ variable.
+
+$sn0 - $sn9
+
+ These variables are copies of the values of the $n0 - $n9 accumulators that
+ were current at the end of the system filter file. This allows a system
+ filter file to set values that can be tested in users' filter files. For
+ example, a system filter could set a value indicating how likely it is that
+ a message is junk mail.
+
+$spam_xxx
+
+ A number of variables whose names start with $spam are available when Exim
+ is compiled with the content-scanning extension. For details, see section
+ 45.2.
+
+$spf_header_comment, $spf_received, $spf_result, $spf_result_guessed,
+ $spf_smtp_comment
+
+ These variables are only available if Exim is built with SPF support. For
+ details see section 58.4.
+
+$spool_directory
+
+ The name of Exim's spool directory.
+
+$spool_inodes
+
+ The number of free inodes in the disk partition where Exim's spool files
+ are being written. The value is recalculated whenever the variable is
+ referenced. If the relevant file system does not have the concept of
+ inodes, the value of is -1. See also the check_spool_inodes option.
+
+$spool_space
+
+ The amount of free space (as a number of kilobytes) in the disk partition
+ where Exim's spool files are being written. The value is recalculated
+ whenever the variable is referenced. If the operating system does not have
+ the ability to find the amount of free space (only true for experimental
+ systems), the space value is -1. For example, to check in an ACL that there
+ is at least 50 megabytes free on the spool, you could write:
+
+ condition = ${if > {$spool_space}{50000}}
+
+ See also the check_spool_space option.
+
+$thisaddress
+
+ This variable is set only during the processing of the foranyaddress
+ command in a filter file. Its use is explained in the description of that
+ command, which can be found in the separate document entitled Exim's
+ interfaces to mail filtering.
+
+$tls_in_bits
+
+ Contains an approximation of the TLS cipher's bit-strength on the inbound
+ connection; the meaning of this depends upon the TLS implementation used.
+ If TLS has not been negotiated, the value will be 0. The value of this is
+ automatically fed into the Cyrus SASL authenticator when acting as a
+ server, to specify the "external SSF" (a SASL term).
+
+ The deprecated $tls_bits variable refers to the inbound side except when
+ used in the context of an outbound SMTP delivery, when it refers to the
+ outbound.
+
+$tls_out_bits
+
+ Contains an approximation of the TLS cipher's bit-strength on an outbound
+ SMTP connection; the meaning of this depends upon the TLS implementation
+ used. If TLS has not been negotiated, the value will be 0.
+
+$tls_in_ourcert
+
+ This variable refers to the certificate presented to the peer of an inbound
+ connection when the message was received. It is only useful as the argument
+ of a certextract expansion item, md5, sha1 or sha256 operator, or a def
+ condition.
+
+ Note: Under versions of OpenSSL preceding 1.1.1, when a list of more than
+ one file is used for tls_certificate, this variable is not reliable. The
+ macro "_TLS_BAD_MULTICERT_IN_OURCERT" will be defined for those versions.
+
+$tls_in_peercert
+
+ This variable refers to the certificate presented by the peer of an inbound
+ connection when the message was received. It is only useful as the argument
+ of a certextract expansion item, md5, sha1 or sha256 operator, or a def
+ condition. If certificate verification fails it may refer to a failing
+ chain element which is not the leaf.
+
+$tls_out_ourcert
+
+ This variable refers to the certificate presented to the peer of an
+ outbound connection. It is only useful as the argument of a certextract
+ expansion item, md5, sha1 or sha256 operator, or a def condition.
+
+$tls_out_peercert
+
+ This variable refers to the certificate presented by the peer of an
+ outbound connection. It is only useful as the argument of a certextract
+ expansion item, md5, sha1 or sha256 operator, or a def condition. If
+ certificate verification fails it may refer to a failing chain element
+ which is not the leaf.
+
+$tls_in_certificate_verified
+
+ This variable is set to "1" if a TLS certificate was verified when the
+ message was received, and "0" otherwise.
+
+ The deprecated $tls_certificate_verified variable refers to the inbound
+ side except when used in the context of an outbound SMTP delivery, when it
+ refers to the outbound.
+
+$tls_out_certificate_verified
+
+ This variable is set to "1" if a TLS certificate was verified when an
+ outbound SMTP connection was made, and "0" otherwise.
+
+$tls_in_cipher
+
+ When a message is received from a remote host over an encrypted SMTP
+ connection, this variable is set to the cipher suite that was negotiated,
+ for example DES-CBC3-SHA. In other circumstances, in particular, for
+ message received over unencrypted connections, the variable is empty.
+ Testing $tls_in_cipher for emptiness is one way of distinguishing between
+ encrypted and non-encrypted connections during ACL processing.
+
+ The deprecated $tls_cipher variable is the same as $tls_in_cipher during
+ message reception, but in the context of an outward SMTP delivery taking
+ place via the smtp transport becomes the same as $tls_out_cipher.
+
+$tls_in_cipher_std
+
+ As above, but returning the RFC standard name for the cipher suite.
+
+$tls_out_cipher
+
+ This variable is cleared before any outgoing SMTP connection is made, and
+ then set to the outgoing cipher suite if one is negotiated. See chapter 43
+ for details of TLS support and chapter 30 for details of the smtp
+ transport.
+
+$tls_out_cipher_std
+
+ As above, but returning the RFC standard name for the cipher suite.
+
+$tls_out_dane
+
+ DANE active status. See section 43.15.
+
+$tls_in_ocsp
+
+ When a message is received from a remote client connection the result of
+ any OCSP request from the client is encoded in this variable:
+
+ 0 OCSP proof was not requested (default value)
+ 1 No response to request
+ 2 Response not verified
+ 3 Verification failed
+ 4 Verification succeeded
+
+$tls_out_ocsp
+
+ When a message is sent to a remote host connection the result of any OCSP
+ request made is encoded in this variable. See $tls_in_ocsp for values.
+
+$tls_in_peerdn
+
+ When a message is received from a remote host over an encrypted SMTP
+ connection, and Exim is configured to request a certificate from the
+ client, the value of the Distinguished Name of the certificate is made
+ available in the $tls_in_peerdn during subsequent processing. If
+ certificate verification fails it may refer to a failing chain element
+ which is not the leaf.
+
+ The deprecated $tls_peerdn variable refers to the inbound side except when
+ used in the context of an outbound SMTP delivery, when it refers to the
+ outbound.
+
+$tls_out_peerdn
+
+ When a message is being delivered to a remote host over an encrypted SMTP
+ connection, and Exim is configured to request a certificate from the
+ server, the value of the Distinguished Name of the certificate is made
+ available in the $tls_out_peerdn during subsequent processing. If
+ certificate verification fails it may refer to a failing chain element
+ which is not the leaf.
+
+$tls_in_sni
+
+ When a TLS session is being established, if the client sends the Server
+ Name Indication extension, the value will be placed in this variable. If
+ the variable appears in tls_certificate then this option and some others,
+ described in 43.10, will be re-expanded early in the TLS session, to permit
+ a different certificate to be presented (and optionally a different key to
+ be used) to the client, based upon the value of the SNI extension.
+
+ The deprecated $tls_sni variable refers to the inbound side except when
+ used in the context of an outbound SMTP delivery, when it refers to the
+ outbound.
+
+$tls_out_sni
+
+ During outbound SMTP deliveries, this variable reflects the value of the
+ tls_sni option on the transport.
+
+$tls_out_tlsa_usage
+
+ Bitfield of TLSA record types found. See section 43.15.
+
+$tls_in_ver
+
+ When a message is received from a remote host over an encrypted SMTP
+ connection this variable is set to the protocol version, eg TLS1.2.
+
+$tls_out_ver
+
+ When a message is being delivered to a remote host over an encrypted SMTP
+ connection this variable is set to the protocol version.
+
+$tod_bsdinbox
+
+ The time of day and the date, in the format required for BSD-style mailbox
+ files, for example: Thu Oct 17 17:14:09 1995.
+
+$tod_epoch
+
+ The time and date as a number of seconds since the start of the Unix epoch.
+
+$tod_epoch_l
+
+ The time and date as a number of microseconds since the start of the Unix
+ epoch.
+
+$tod_full
+
+ A full version of the time and date, for example: Wed, 16 Oct 1995 09:51:40
+ +0100. The timezone is always given as a numerical offset from UTC, with
+ positive values used for timezones that are ahead (east) of UTC, and
+ negative values for those that are behind (west).
+
+$tod_log
+
+ The time and date in the format used for writing Exim's log files, for
+ example: 1995-10-12 15:32:29, but without a timezone.
+
+$tod_logfile
+
+ This variable contains the date in the format yyyymmdd. This is the format
+ that is used for datestamping log files when log_file_path contains the
+ "%D" flag.
+
+$tod_zone
+
+ This variable contains the numerical value of the local timezone, for
+ example: -0500.
+
+$tod_zulu
+
+ This variable contains the UTC date and time in "Zulu" format, as specified
+ by ISO 8601, for example: 20030221154023Z.
+
+$transport_name
+
+ During the running of a transport, this variable contains its name.
+
+$value
+
+ This variable contains the result of an expansion lookup, extraction
+ operation, or external command, as described above. It is also used during
+ a reduce expansion.
+
+$verify_mode
+
+ While a router or transport is being run in verify mode or for cutthrough
+ delivery, contains "S" for sender-verification or "R" for
+ recipient-verification. Otherwise, empty.
+
+$version_number
+
+ The version number of Exim. Same as $exim_version, may be overridden by the
+ exim_version main config option.
+
+$warn_message_delay
+
+ This variable is set only during the creation of a message warning about a
+ delivery delay. Details of its use are explained in section 50.2.
+
+$warn_message_recipients
+
+ This variable is set only during the creation of a message warning about a
+ delivery delay. Details of its use are explained in section 50.2.
+
+
+
+===============================================================================
+12. EMBEDDED PERL
+
+Exim can be built to include an embedded Perl interpreter. When this is done,
+Perl subroutines can be called as part of the string expansion process. To make
+use of the Perl support, you need version 5.004 or later of Perl installed on
+your system. To include the embedded interpreter in the Exim binary, include
+the line
+
+EXIM_PERL = perl.o
+
+in your Local/Makefile and then build Exim in the normal way.
+
+
+12.1 Setting up so Perl can be used
+-----------------------------------
+
+Access to Perl subroutines is via a global configuration option called
+perl_startup and an expansion string operator ${perl ...}. If there is no
+perl_startup option in the Exim configuration file then no Perl interpreter is
+started and there is almost no overhead for Exim (since none of the Perl
+library will be paged in unless used). If there is a perl_startup option then
+the associated value is taken to be Perl code which is executed in a newly
+created Perl interpreter.
+
+The value of perl_startup is not expanded in the Exim sense, so you do not need
+backslashes before any characters to escape special meanings. The option should
+usually be something like
+
+perl_startup = do '/etc/exim.pl'
+
+where /etc/exim.pl is Perl code which defines any subroutines you want to use
+from Exim. Exim can be configured either to start up a Perl interpreter as soon
+as it is entered, or to wait until the first time it is needed. Starting the
+interpreter at the beginning ensures that it is done while Exim still has its
+setuid privilege, but can impose an unnecessary overhead if Perl is not in fact
+used in a particular run. Also, note that this does not mean that Exim is
+necessarily running as root when Perl is called at a later time. By default,
+the interpreter is started only when it is needed, but this can be changed in
+two ways:
+
+ * Setting perl_at_start (a boolean option) in the configuration requests a
+ startup when Exim is entered.
+
+ * The command line option -ps also requests a startup when Exim is entered,
+ overriding the setting of perl_at_start.
+
+There is also a command line option -pd (for delay) which suppresses the
+initial startup, even if perl_at_start is set.
+
+ * To provide more security executing Perl code via the embedded Perl
+ interpreter, the perl_taintmode option can be set. This enables the taint
+ mode of the Perl interpreter. You are encouraged to set this option to a
+ true value. To avoid breaking existing installations, it defaults to false.
+
+
+12.2 Calling Perl subroutines
+-----------------------------
+
+When the configuration file includes a perl_startup option you can make use of
+the string expansion item to call the Perl subroutines that are defined by the
+perl_startup code. The operator is used in any of the following forms:
+
+${perl{foo}}
+${perl{foo}{argument}}
+${perl{foo}{argument1}{argument2} ... }
+
+which calls the subroutine foo with the given arguments. A maximum of eight
+arguments may be passed. Passing more than this results in an expansion failure
+with an error message of the form
+
+Too many arguments passed to Perl subroutine "foo" (max is 8)
+
+The return value of the Perl subroutine is evaluated in a scalar context before
+it is passed back to Exim to be inserted into the expanded string. If the
+return value is undef, the expansion is forced to fail in the same way as an
+explicit "fail" on an if or lookup item. If the subroutine aborts by obeying
+Perl's die function, the expansion fails with the error message that was passed
+to die.
+
+
+12.3 Calling Exim functions from Perl
+-------------------------------------
+
+Within any Perl code called from Exim, the function Exim::expand_string() is
+available to call back into Exim's string expansion function. For example, the
+Perl code
+
+my $lp = Exim::expand_string('$local_part');
+
+makes the current Exim $local_part available in the Perl variable $lp. Note
+those are single quotes and not double quotes to protect against $local_part
+being interpolated as a Perl variable.
+
+If the string expansion is forced to fail by a "fail" item, the result of
+Exim::expand_string() is undef. If there is a syntax error in the expansion
+string, the Perl call from the original expansion string fails with an
+appropriate error message, in the same way as if die were used.
+
+Two other Exim functions are available for use from within Perl code.
+Exim::debug_write() writes a string to the standard error stream if Exim's
+debugging is enabled. If you want a newline at the end, you must supply it.
+Exim::log_write() writes a string to Exim's main log, adding a leading
+timestamp. In this case, you should not supply a terminating newline.
+
+
+12.4 Use of standard output and error by Perl
+---------------------------------------------
+
+You should not write to the standard error or output streams from within your
+Perl code, as it is not defined how these are set up. In versions of Exim
+before 4.50, it is possible for the standard output or error to refer to the
+SMTP connection during message reception via the daemon. Writing to this stream
+is certain to cause chaos. From Exim 4.50 onwards, the standard output and
+error streams are connected to /dev/null in the daemon. The chaos is avoided,
+but the output is lost.
+
+The Perl warn statement writes to the standard error stream by default. Calls
+to warn may be embedded in Perl modules that you use, but over which you have
+no control. When Exim starts up the Perl interpreter, it arranges for output
+from the warn statement to be written to the Exim main log. You can change this
+by including appropriate Perl magic somewhere in your Perl code. For example,
+to discard warn output completely, you need this:
+
+$SIG{__WARN__} = sub { };
+
+Whenever a warn is obeyed, the anonymous subroutine is called. In this example,
+the code for the subroutine is empty, so it does nothing, but you can include
+any Perl code that you like. The text of the warn message is passed as the
+first subroutine argument.
+
+
+
+===============================================================================
+13. STARTING THE DAEMON AND THE USE OF NETWORK INTERFACES
+
+A host that is connected to a TCP/IP network may have one or more physical
+hardware network interfaces. Each of these interfaces may be configured as one
+or more "logical" interfaces, which are the entities that a program actually
+works with. Each of these logical interfaces is associated with an IP address.
+In addition, TCP/IP software supports "loopback" interfaces (127.0.0.1 in IPv4
+and ::1 in IPv6), which do not use any physical hardware. Exim requires
+knowledge about the host's interfaces for use in three different circumstances:
+
+ 1. When a listening daemon is started, Exim needs to know which interfaces and
+ ports to listen on.
+
+ 2. When Exim is routing an address, it needs to know which IP addresses are
+ associated with local interfaces. This is required for the correct
+ processing of MX lists by removing the local host and others with the same
+ or higher priority values. Also, Exim needs to detect cases when an address
+ is routed to an IP address that in fact belongs to the local host. Unless
+ the self router option or the allow_localhost option of the smtp transport
+ is set (as appropriate), this is treated as an error situation.
+
+ 3. When Exim connects to a remote host, it may need to know which interface to
+ use for the outgoing connection.
+
+Exim's default behaviour is likely to be appropriate in the vast majority of
+cases. If your host has only one interface, and you want all its IP addresses
+to be treated in the same way, and you are using only the standard SMTP port,
+you should not need to take any special action. The rest of this chapter does
+not apply to you.
+
+In a more complicated situation you may want to listen only on certain
+interfaces, or on different ports, and for this reason there are a number of
+options that can be used to influence Exim's behaviour. The rest of this
+chapter describes how they operate.
+
+When a message is received over TCP/IP, the interface and port that were
+actually used are set in $received_ip_address and $received_port.
+
+
+13.1 Starting a listening daemon
+--------------------------------
+
+When a listening daemon is started (by means of the -bd command line option),
+the interfaces and ports on which it listens are controlled by the following
+options:
+
+ * daemon_smtp_ports contains a list of default ports or service names. (For
+ backward compatibility, this option can also be specified in the singular.)
+
+ * local_interfaces contains list of interface IP addresses on which to
+ listen. Each item may optionally also specify a port.
+
+The default list separator in both cases is a colon, but this can be changed as
+described in section 6.21. When IPv6 addresses are involved, it is usually best
+to change the separator to avoid having to double all the colons. For example:
+
+local_interfaces = <; 127.0.0.1 ; \
+ 192.168.23.65 ; \
+ ::1 ; \
+ 3ffe:ffff:836f::fe86:a061
+
+There are two different formats for specifying a port along with an IP address
+in local_interfaces:
+
+ 1. The port is added onto the address with a dot separator. For example, to
+ listen on port 1234 on two different IP addresses:
+
+ local_interfaces = <; 192.168.23.65.1234 ; \
+ 3ffe:ffff:836f::fe86:a061.1234
+
+ 2. The IP address is enclosed in square brackets, and the port is added with a
+ colon separator, for example:
+
+ local_interfaces = <; [192.168.23.65]:1234 ; \
+ [3ffe:ffff:836f::fe86:a061]:1234
+
+When a port is not specified, the value of daemon_smtp_ports is used. The
+default setting contains just one port:
+
+daemon_smtp_ports = smtp
+
+If more than one port is listed, each interface that does not have its own port
+specified listens on all of them. Ports that are listed in daemon_smtp_ports
+can be identified either by name (defined in /etc/services) or by number.
+However, when ports are given with individual IP addresses in local_interfaces,
+only numbers (not names) can be used.
+
+
+13.2 Special IP listening addresses
+-----------------------------------
+
+The addresses 0.0.0.0 and ::0 are treated specially. They are interpreted as
+"all IPv4 interfaces" and "all IPv6 interfaces", respectively. In each case,
+Exim tells the TCP/IP stack to "listen on all IPvx interfaces" instead of
+setting up separate listening sockets for each interface. The default value of
+local_interfaces is
+
+local_interfaces = 0.0.0.0
+
+when Exim is built without IPv6 support; otherwise it is:
+
+local_interfaces = <; ::0 ; 0.0.0.0
+
+Thus, by default, Exim listens on all available interfaces, on the SMTP port.
+
+
+13.3 Overriding local_interfaces and daemon_smtp_ports
+------------------------------------------------------
+
+The -oX command line option can be used to override the values of
+daemon_smtp_ports and/or local_interfaces for a particular daemon instance.
+Another way of doing this would be to use macros and the -D option. However,
+-oX can be used by any admin user, whereas modification of the runtime
+configuration by -D is allowed only when the caller is root or exim.
+
+The value of -oX is a list of items. The default colon separator can be changed
+in the usual way (6.21) if required. If there are any items that do not contain
+dots or colons (that is, are not IP addresses), the value of daemon_smtp_ports
+is replaced by the list of those items. If there are any items that do contain
+dots or colons, the value of local_interfaces is replaced by those items. Thus,
+for example,
+
+-oX 1225
+
+overrides daemon_smtp_ports, but leaves local_interfaces unchanged, whereas
+
+-oX 192.168.34.5.1125
+
+overrides local_interfaces, leaving daemon_smtp_ports unchanged. (However,
+since local_interfaces now contains no items without ports, the value of
+daemon_smtp_ports is no longer relevant in this example.)
+
+
+13.4 Support for the submissions (aka SSMTP or SMTPS) protocol
+--------------------------------------------------------------
+
+Exim supports the use of TLS-on-connect, used by mail clients in the
+"submissions" protocol, historically also known as SMTPS or SSMTP. For some
+years, IETF Standards Track documents only blessed the STARTTLS-based
+Submission service (port 587) while common practice was to support the same
+feature set on port 465, but using TLS-on-connect. If your installation needs
+to provide service to mail clients (Mail User Agents, MUAs) then you should
+provide service on both the 587 and the 465 TCP ports.
+
+If the tls_on_connect_ports option is set to a list of port numbers or service
+names, connections to those ports must first establish TLS, before proceeding
+to the application layer use of the SMTP protocol.
+
+The common use of this option is expected to be
+
+tls_on_connect_ports = 465
+
+per RFC 8314. There is also a command line option -tls-on-connect, which forces
+all ports to behave in this way when a daemon is started.
+
+Warning: Setting tls_on_connect_ports does not of itself cause the daemon to
+listen on those ports. You must still specify them in daemon_smtp_ports,
+local_interfaces, or the -oX option. (This is because tls_on_connect_ports
+applies to inetd connections as well as to connections via the daemon.)
+
+
+13.5 IPv6 address scopes
+------------------------
+
+IPv6 addresses have "scopes", and a host with multiple hardware interfaces can,
+in principle, have the same link-local IPv6 address on different interfaces.
+Thus, additional information is needed, over and above the IP address, to
+distinguish individual interfaces. A convention of using a percent sign
+followed by something (often the interface name) has been adopted in some
+cases, leading to addresses like this:
+
+fe80::202:b3ff:fe03:45c1%eth0
+
+To accommodate this usage, a percent sign followed by an arbitrary string is
+allowed at the end of an IPv6 address. By default, Exim calls getaddrinfo() to
+convert a textual IPv6 address for actual use. This function recognizes the
+percent convention in operating systems that support it, and it processes the
+address appropriately. Unfortunately, some older libraries have problems with
+getaddrinfo(). If
+
+IPV6_USE_INET_PTON=yes
+
+is set in Local/Makefile (or an OS-dependent Makefile) when Exim is built, Exim
+uses inet_pton() to convert a textual IPv6 address for actual use, instead of
+getaddrinfo(). (Before version 4.14, it always used this function.) Of course,
+this means that the additional functionality of getaddrinfo() - recognizing
+scoped addresses - is lost.
+
+
+13.6 Disabling IPv6
+-------------------
+
+Sometimes it happens that an Exim binary that was compiled with IPv6 support is
+run on a host whose kernel does not support IPv6. The binary will fall back to
+using IPv4, but it may waste resources looking up AAAA records, and trying to
+connect to IPv6 addresses, causing delays to mail delivery. If you set the
+disable_ipv6 option true, even if the Exim binary has IPv6 support, no IPv6
+activities take place. AAAA records are never looked up, and any IPv6 addresses
+that are listed in local_interfaces, data for the manualroute router, etc. are
+ignored. If IP literals are enabled, the ipliteral router declines to handle
+IPv6 literal addresses.
+
+On the other hand, when IPv6 is in use, there may be times when you want to
+disable it for certain hosts or domains. You can use the dns_ipv4_lookup option
+to globally suppress the lookup of AAAA records for specified domains, and you
+can use the ignore_target_hosts generic router option to ignore IPv6 addresses
+in an individual router.
+
+
+13.7 Examples of starting a listening daemon
+--------------------------------------------
+
+The default case in an IPv6 environment is
+
+daemon_smtp_ports = smtp
+local_interfaces = <; ::0 ; 0.0.0.0
+
+This specifies listening on the smtp port on all IPv6 and IPv4 interfaces.
+Either one or two sockets may be used, depending on the characteristics of the
+TCP/IP stack. (This is complicated and messy; for more information, read the
+comments in the daemon.c source file.)
+
+To specify listening on ports 25 and 26 on all interfaces:
+
+daemon_smtp_ports = 25 : 26
+
+(leaving local_interfaces at the default setting) or, more explicitly:
+
+local_interfaces = <; ::0.25 ; ::0.26 \
+ 0.0.0.0.25 ; 0.0.0.0.26
+
+To listen on the default port on all IPv4 interfaces, and on port 26 on the
+IPv4 loopback address only:
+
+local_interfaces = 0.0.0.0 : 127.0.0.1.26
+
+To specify listening on the default port on specific interfaces only:
+
+local_interfaces = 10.0.0.67 : 192.168.34.67
+
+Warning: Such a setting excludes listening on the loopback interfaces.
+
+
+13.8 Recognizing the local host
+-------------------------------
+
+The local_interfaces option is also used when Exim needs to determine whether
+or not an IP address refers to the local host. That is, the IP addresses of all
+the interfaces on which a daemon is listening are always treated as local.
+
+For this usage, port numbers in local_interfaces are ignored. If either of the
+items 0.0.0.0 or ::0 are encountered, Exim gets a complete list of available
+interfaces from the operating system, and extracts the relevant (that is, IPv4
+or IPv6) addresses to use for checking.
+
+Some systems set up large numbers of virtual interfaces in order to provide
+many virtual web servers. In this situation, you may want to listen for email
+on only a few of the available interfaces, but nevertheless treat all
+interfaces as local when routing. You can do this by setting
+extra_local_interfaces to a list of IP addresses, possibly including the "all"
+wildcard values. These addresses are recognized as local, but are not used for
+listening. Consider this example:
+
+local_interfaces = <; 127.0.0.1 ; ::1 ; \
+ 192.168.53.235 ; \
+ 3ffe:2101:12:1:a00:20ff:fe86:a061
+
+extra_local_interfaces = <; ::0 ; 0.0.0.0
+
+The daemon listens on the loopback interfaces and just one IPv4 and one IPv6
+address, but all available interface addresses are treated as local when Exim
+is routing.
+
+In some environments the local host name may be in an MX list, but with an IP
+address that is not assigned to any local interface. In other cases it may be
+desirable to treat other host names as if they referred to the local host. Both
+these cases can be handled by setting the hosts_treat_as_local option. This
+contains host names rather than IP addresses. When a host is referenced during
+routing, either via an MX record or directly, it is treated as the local host
+if its name matches hosts_treat_as_local, or if any of its IP addresses match
+local_interfaces or extra_local_interfaces.
+
+
+13.9 Delivering to a remote host
+--------------------------------
+
+Delivery to a remote host is handled by the smtp transport. By default, it
+allows the system's TCP/IP functions to choose which interface to use (if there
+is more than one) when connecting to a remote host. However, the interface
+option can be set to specify which interface is used. See the description of
+the smtp transport in chapter 30 for more details.
+
+
+
+===============================================================================
+14. MAIN CONFIGURATION
+
+The first part of the runtime configuration file contains three types of item:
+
+ * Macro definitions: These lines start with an upper case letter. See section
+ 6.4 for details of macro processing.
+
+ * Named list definitions: These lines start with one of the words
+ "domainlist", "hostlist", "addresslist", or "localpartlist". Their use is
+ described in section 10.6.
+
+ * Main configuration settings: Each setting occupies one line of the file
+ (with possible continuations). If any setting is preceded by the word
+ "hide", the -bP command line option displays its value to admin users only.
+ See section 6.11 for a description of the syntax of these option settings.
+
+This chapter specifies all the main configuration options, along with their
+types and default values. For ease of finding a particular option, they appear
+in alphabetical order in section 14.23 below. However, because there are now so
+many options, they are first listed briefly in functional groups, as an aid to
+finding the name of the option you are looking for. Some options are listed in
+more than one group.
+
+
+14.1 Miscellaneous
+------------------
+
+bi_command to run for -bi command line option
+debug_store do extra internal checks
+disable_ipv6 do no IPv6 processing
+keep_malformed for broken files - should not happen
+localhost_number for unique message ids in clusters
+message_body_newlines retain newlines in $message_body
+message_body_visible how much to show in $message_body
+mua_wrapper run in "MUA wrapper" mode
+print_topbitchars top-bit characters are printing
+spool_wireformat use wire-format spool data files when possible
+timezone force time zone
+
+
+14.2 Exim parameters
+--------------------
+
+exim_group override compiled-in value
+exim_path override compiled-in value
+exim_user override compiled-in value
+primary_hostname default from uname()
+split_spool_directory use multiple directories
+spool_directory override compiled-in value
+
+
+14.3 Privilege controls
+-----------------------
+
+admin_groups groups that are Exim admin users
+commandline_checks_require_admin require admin for various checks
+deliver_drop_privilege drop root for delivery processes
+local_from_check insert Sender: if necessary
+local_from_prefix for testing From: for local sender
+local_from_suffix for testing From: for local sender
+local_sender_retain keep Sender: from untrusted user
+never_users do not run deliveries as these
+prod_requires_admin forced delivery requires admin user
+queue_list_requires_admin queue listing requires admin user
+trusted_groups groups that are trusted
+trusted_users users that are trusted
+
+
+14.4 Logging
+------------
+
+event_action custom logging
+hosts_connection_nolog exemption from connect logging
+log_file_path override compiled-in value
+log_selector set/unset optional logging
+log_timezone add timezone to log lines
+message_logs create per-message logs
+preserve_message_logs after message completion
+process_log_path for SIGUSR1 and exiwhat
+slow_lookup_log control logging of slow DNS lookups
+syslog_duplication controls duplicate log lines on syslog
+syslog_facility set syslog "facility" field
+syslog_pid pid in syslog lines
+syslog_processname set syslog "ident" field
+syslog_timestamp timestamp syslog lines
+write_rejectlog control use of message log
+
+
+14.5 Frozen messages
+--------------------
+
+auto_thaw sets time for retrying frozen messages
+freeze_tell send message when freezing
+move_frozen_messages to another directory
+timeout_frozen_after keep frozen messages only so long
+
+
+14.6 Data lookups
+-----------------
+
+ibase_servers InterBase servers
+ldap_ca_cert_dir dir of CA certs to verify LDAP server's
+ldap_ca_cert_file file of CA certs to verify LDAP server's
+ldap_cert_file client cert file for LDAP
+ldap_cert_key client key file for LDAP
+ldap_cipher_suite TLS negotiation preference control
+ldap_default_servers used if no server in query
+ldap_require_cert action to take without LDAP server cert
+ldap_start_tls require TLS within LDAP
+ldap_version set protocol version
+lookup_open_max lookup files held open
+mysql_servers default MySQL servers
+oracle_servers Oracle servers
+pgsql_servers default PostgreSQL servers
+sqlite_lock_timeout as it says
+
+
+14.7 Message ids
+----------------
+
+message_id_header_domain used to build Message-ID: header
+message_id_header_text ditto
+
+
+14.8 Embedded Perl Startup
+--------------------------
+
+perl_at_start always start the interpreter
+perl_startup code to obey when starting Perl
+perl_taintmode enable taint mode in Perl
+
+
+14.9 Daemon
+-----------
+
+daemon_smtp_ports default ports
+daemon_startup_retries number of times to retry
+daemon_startup_sleep time to sleep between tries
+extra_local_interfaces not necessarily listened on
+local_interfaces on which to listen, with optional ports
+notifier_socket override compiled-in value
+pid_file_path override compiled-in value
+queue_run_max maximum simultaneous queue runners
+
+
+14.10 Resource control
+----------------------
+
+check_log_inodes before accepting a message
+check_log_space before accepting a message
+check_spool_inodes before accepting a message
+check_spool_space before accepting a message
+deliver_queue_load_max no queue deliveries if load high
+queue_only_load queue incoming if load high
+queue_only_load_latch don't re-evaluate load for each message
+queue_run_max maximum simultaneous queue runners
+remote_max_parallel parallel SMTP delivery per message
+smtp_accept_max simultaneous incoming connections
+smtp_accept_max_nonmail non-mail commands
+smtp_accept_max_nonmail_hosts hosts to which the limit applies
+smtp_accept_max_per_connection messages per connection
+smtp_accept_max_per_host connections from one host
+smtp_accept_queue queue mail if more connections
+smtp_accept_queue_per_connection queue if more messages per connection
+smtp_accept_reserve only reserve hosts if more connections
+smtp_check_spool_space from SIZE on MAIL command
+smtp_connect_backlog passed to TCP/IP stack
+smtp_load_reserve SMTP from reserved hosts if load high
+smtp_reserve_hosts these are the reserve hosts
+
+
+14.11 Policy controls
+---------------------
+
+acl_not_smtp ACL for non-SMTP messages
+acl_not_smtp_mime ACL for non-SMTP MIME parts
+acl_not_smtp_start ACL for start of non-SMTP message
+acl_smtp_auth ACL for AUTH
+acl_smtp_connect ACL for connection
+acl_smtp_data ACL for DATA
+acl_smtp_data_prdr ACL for DATA, per-recipient
+acl_smtp_dkim ACL for DKIM verification
+acl_smtp_etrn ACL for ETRN
+acl_smtp_expn ACL for EXPN
+acl_smtp_helo ACL for EHLO or HELO
+acl_smtp_mail ACL for MAIL
+acl_smtp_mailauth ACL for AUTH on MAIL command
+acl_smtp_mime ACL for MIME parts
+acl_smtp_notquit ACL for non-QUIT terminations
+acl_smtp_predata ACL for start of data
+acl_smtp_quit ACL for QUIT
+acl_smtp_rcpt ACL for RCPT
+acl_smtp_starttls ACL for STARTTLS
+acl_smtp_vrfy ACL for VRFY
+av_scanner specify virus scanner
+check_rfc2047_length check length of RFC 2047 "encoded words"
+dns_cname_loops follow CNAMEs returned by resolver
+dns_csa_search_limit control CSA parent search depth
+dns_csa_use_reverse en/disable CSA IP reverse search
+header_maxsize total size of message header
+header_line_maxsize individual header line limit
+helo_accept_junk_hosts allow syntactic junk from these hosts
+helo_allow_chars allow illegal chars in HELO names
+helo_lookup_domains lookup hostname for these HELO names
+helo_try_verify_hosts HELO soft-checked for these hosts
+helo_verify_hosts HELO hard-checked for these hosts
+host_lookup host name looked up for these hosts
+host_lookup_order order of DNS and local name lookups
+hosts_proxy use proxy protocol for these hosts
+host_reject_connection reject connection from these hosts
+hosts_treat_as_local useful in some cluster configurations
+local_scan_timeout timeout for local_scan()
+message_size_limit for all messages
+percent_hack_domains recognize %-hack for these domains
+spamd_address set interface to SpamAssassin
+strict_acl_vars object to unset ACL variables
+spf_smtp_comment_template template for $spf_smtp_comment
+
+
+14.12 Callout cache
+-------------------
+
+callout_domain_negative_expire timeout for negative domain cache item
+callout_domain_positive_expire timeout for positive domain cache item
+callout_negative_expire timeout for negative address cache item
+callout_positive_expire timeout for positive address cache item
+callout_random_local_part string to use for "random" testing
+
+
+14.13 TLS
+---------
+
+gnutls_compat_mode use GnuTLS compatibility mode
+gnutls_allow_auto_pkcs11 allow GnuTLS to autoload PKCS11 modules
+openssl_options adjust OpenSSL compatibility options
+tls_advertise_hosts advertise TLS to these hosts
+tls_certificate location of server certificate
+tls_crl certificate revocation list
+tls_dh_max_bits clamp D-H bit count suggestion
+tls_dhparam DH parameters for server
+tls_eccurve EC curve selection for server
+tls_ocsp_file location of server certificate status proof
+tls_on_connect_ports specify SSMTP (SMTPS) ports
+tls_privatekey location of server private key
+tls_remember_esmtp don't reset after starting TLS
+tls_require_ciphers specify acceptable ciphers
+tls_try_verify_hosts try to verify client certificate
+tls_verify_certificates expected client certificates
+tls_verify_hosts insist on client certificate verify
+
+
+14.14 Local user handling
+-------------------------
+
+finduser_retries useful in NIS environments
+gecos_name used when creating Sender:
+gecos_pattern ditto
+max_username_length for systems that truncate
+unknown_login used when no login name found
+unknown_username ditto
+uucp_from_pattern for recognizing "From " lines
+uucp_from_sender ditto
+
+
+14.15 All incoming messages (SMTP and non-SMTP)
+-----------------------------------------------
+
+header_maxsize total size of message header
+header_line_maxsize individual header line limit
+message_size_limit applies to all messages
+percent_hack_domains recognize %-hack for these domains
+received_header_text expanded to make Received:
+received_headers_max for mail loop detection
+recipients_max limit per message
+recipients_max_reject permanently reject excess recipients
+
+
+14.16 Non-SMTP incoming messages
+--------------------------------
+
+receive_timeout for non-SMTP messages
+
+
+14.17 Incoming SMTP messages
+----------------------------
+
+See also the Policy controls section above.
+
+dkim_verify_hashes DKIM hash methods accepted for signatures
+dkim_verify_keytypes DKIM key types accepted for signatures
+dkim_verify_min_keysizes DKIM key sizes accepted for signatures
+dkim_verify_signers DKIM domains for which DKIM ACL is run
+dmarc_forensic_sender DMARC sender for report messages
+dmarc_history_file DMARC results log
+dmarc_tld_file DMARC toplevel domains file
+host_lookup host name looked up for these hosts
+host_lookup_order order of DNS and local name lookups
+recipient_unqualified_hosts may send unqualified recipients
+rfc1413_hosts make ident calls to these hosts
+rfc1413_query_timeout zero disables ident calls
+sender_unqualified_hosts may send unqualified senders
+smtp_accept_keepalive some TCP/IP magic
+smtp_accept_max simultaneous incoming connections
+smtp_accept_max_nonmail non-mail commands
+smtp_accept_max_nonmail_hosts hosts to which the limit applies
+smtp_accept_max_per_connection messages per connection
+smtp_accept_max_per_host connections from one host
+smtp_accept_queue queue mail if more connections
+smtp_accept_queue_per_connection queue if more messages per connection
+smtp_accept_reserve only reserve hosts if more connections
+smtp_active_hostname host name to use in messages
+smtp_banner text for welcome banner
+smtp_check_spool_space from SIZE on MAIL command
+smtp_connect_backlog passed to TCP/IP stack
+smtp_enforce_sync of SMTP command/responses
+smtp_etrn_command what to run for ETRN
+smtp_etrn_serialize only one at once
+smtp_load_reserve only reserve hosts if this load
+smtp_max_unknown_commands before dropping connection
+smtp_ratelimit_hosts apply ratelimiting to these hosts
+smtp_ratelimit_mail ratelimit for MAIL commands
+smtp_ratelimit_rcpt ratelimit for RCPT commands
+smtp_receive_timeout per command or data line
+smtp_reserve_hosts these are the reserve hosts
+smtp_return_error_details give detail on rejections
+
+
+14.18 SMTP extensions
+---------------------
+
+accept_8bitmime advertise 8BITMIME
+auth_advertise_hosts advertise AUTH to these hosts
+chunking_advertise_hosts advertise CHUNKING to these hosts
+dsn_advertise_hosts advertise DSN extensions to these hosts
+ignore_fromline_hosts allow "From " from these hosts
+ignore_fromline_local allow "From " from local SMTP
+pipelining_advertise_hosts advertise pipelining to these hosts
+pipelining_connect_advertise_hosts advertise pipelining to these hosts
+prdr_enable advertise PRDR to all hosts
+smtputf8_advertise_hosts advertise SMTPUTF8 to these hosts
+tls_advertise_hosts advertise TLS to these hosts
+
+
+14.19 Processing messages
+-------------------------
+
+allow_domain_literals recognize domain literal syntax
+allow_mx_to_ip allow MX to point to IP address
+allow_utf8_domains in addresses
+check_rfc2047_length check length of RFC 2047 "encoded words"
+delivery_date_remove from incoming messages
+envelope_to_remove from incoming messages
+extract_addresses_remove_arguments affects -t processing
+headers_charset default for translations
+qualify_domain default for senders
+qualify_recipient default for recipients
+return_path_remove from incoming messages
+strip_excess_angle_brackets in addresses
+strip_trailing_dot at end of addresses
+untrusted_set_sender untrusted can set envelope sender
+
+
+14.20 System filter
+-------------------
+
+system_filter locate system filter
+system_filter_directory_transport transport for delivery to a directory
+system_filter_file_transport transport for delivery to a file
+system_filter_group group for filter running
+system_filter_pipe_transport transport for delivery to a pipe
+system_filter_reply_transport transport for autoreply delivery
+system_filter_user user for filter running
+
+
+14.21 Routing and delivery
+--------------------------
+
+disable_ipv6 do no IPv6 processing
+dns_again_means_nonexist for broken domains
+dns_check_names_pattern pre-DNS syntax check
+dns_dnssec_ok parameter for resolver
+dns_ipv4_lookup only v4 lookup for these domains
+dns_retrans parameter for resolver
+dns_retry parameter for resolver
+dns_trust_aa DNS zones trusted as authentic
+dns_use_edns0 parameter for resolver
+hold_domains hold delivery for these domains
+local_interfaces for routing checks
+queue_domains no immediate delivery for these
+queue_only no immediate delivery at all
+queue_only_file no immediate delivery if file exists
+queue_only_load no immediate delivery if load is high
+queue_only_load_latch don't re-evaluate load for each message
+queue_only_override allow command line to override
+queue_run_in_order order of arrival
+queue_run_max of simultaneous queue runners
+queue_smtp_domains no immediate SMTP delivery for these
+remote_max_parallel parallel SMTP delivery per message
+remote_sort_domains order of remote deliveries
+retry_data_expire timeout for retry data
+retry_interval_max safety net for retry rules
+
+
+14.22 Bounce and warning messages
+---------------------------------
+
+bounce_message_file content of bounce
+bounce_message_text content of bounce
+bounce_return_body include body if returning message
+bounce_return_linesize_limit limit on returned message line length
+bounce_return_message include original message in bounce
+bounce_return_size_limit limit on returned message
+bounce_sender_authentication send authenticated sender with bounce
+dsn_from set From: contents in bounces
+errors_copy copy bounce messages
+errors_reply_to Reply-to: in bounces
+delay_warning time schedule
+delay_warning_condition condition for warning messages
+ignore_bounce_errors_after discard undeliverable bounces
+smtp_return_error_details give detail on rejections
+warn_message_file content of warning message
+
+
+14.23 Alphabetical list of main options
+---------------------------------------
+
+Those options that undergo string expansion before use are marked with *.
+
++-----------------------------------------------------+
+|accept_8bitmime|Use: main|Type: boolean|Default: true|
++-----------------------------------------------------+
+
+This option causes Exim to send 8BITMIME in its response to an SMTP EHLO
+command, and to accept the BODY= parameter on MAIL commands. However, though
+Exim is 8-bit clean, it is not a protocol converter, and it takes no steps to
+do anything special with messages received by this route.
+
+Historically Exim kept this option off by default, but the maintainers feel
+that in today's Internet, this causes more problems than it solves. It now
+defaults to true. A more detailed analysis of the issues is provided by Dan
+Bernstein:
+
+https://cr.yp.to/smtp/8bitmime.html
+
+To log received 8BITMIME status use
+
+log_selector = +8bitmime
+
++---------------------------------------------------+
+|acl_not_smtp|Use: main|Type: string*|Default: unset|
++---------------------------------------------------+
+
+This option defines the ACL that is run when a non-SMTP message has been read
+and is on the point of being accepted. See chapter 44 for further details.
+
++--------------------------------------------------------+
+|acl_not_smtp_mime|Use: main|Type: string*|Default: unset|
++--------------------------------------------------------+
+
+This option defines the ACL that is run for individual MIME parts of non-SMTP
+messages. It operates in exactly the same way as acl_smtp_mime operates for
+SMTP messages.
+
++---------------------------------------------------------+
+|acl_not_smtp_start|Use: main|Type: string*|Default: unset|
++---------------------------------------------------------+
+
+This option defines the ACL that is run before Exim starts reading a non-SMTP
+message. See chapter 44 for further details.
+
++----------------------------------------------------+
+|acl_smtp_auth|Use: main|Type: string*|Default: unset|
++----------------------------------------------------+
+
+This option defines the ACL that is run when an SMTP AUTH command is received.
+See chapter 44 for further details.
+
++-------------------------------------------------------+
+|acl_smtp_connect|Use: main|Type: string*|Default: unset|
++-------------------------------------------------------+
+
+This option defines the ACL that is run when an SMTP connection is received.
+See chapter 44 for further details.
+
++----------------------------------------------------+
+|acl_smtp_data|Use: main|Type: string*|Default: unset|
++----------------------------------------------------+
+
+This option defines the ACL that is run after an SMTP DATA command has been
+processed and the message itself has been received, but before the final
+acknowledgment is sent. See chapter 44 for further details.
+
++----------------------------------------------------------+
+|acl_smtp_data_prdr|Use: main|Type: string*|Default: accept|
++----------------------------------------------------------+
+
+This option defines the ACL that, if the PRDR feature has been negotiated, is
+run for each recipient after an SMTP DATA command has been processed and the
+message itself has been received, but before the acknowledgment is sent. See
+chapter 44 for further details.
+
++----------------------------------------------------+
+|acl_smtp_dkim|Use: main|Type: string*|Default: unset|
++----------------------------------------------------+
+
+This option defines the ACL that is run for each DKIM signature (by default, or
+as specified in the dkim_verify_signers option) of a received message. See
+section 58.3 for further details.
+
++----------------------------------------------------+
+|acl_smtp_etrn|Use: main|Type: string*|Default: unset|
++----------------------------------------------------+
+
+This option defines the ACL that is run when an SMTP ETRN command is received.
+See chapter 44 for further details.
+
++----------------------------------------------------+
+|acl_smtp_expn|Use: main|Type: string*|Default: unset|
++----------------------------------------------------+
+
+This option defines the ACL that is run when an SMTP EXPN command is received.
+See chapter 44 for further details.
+
++----------------------------------------------------+
+|acl_smtp_helo|Use: main|Type: string*|Default: unset|
++----------------------------------------------------+
+
+This option defines the ACL that is run when an SMTP EHLO or HELO command is
+received. See chapter 44 for further details.
+
++----------------------------------------------------+
+|acl_smtp_mail|Use: main|Type: string*|Default: unset|
++----------------------------------------------------+
+
+This option defines the ACL that is run when an SMTP MAIL command is received.
+See chapter 44 for further details.
+
++--------------------------------------------------------+
+|acl_smtp_mailauth|Use: main|Type: string*|Default: unset|
++--------------------------------------------------------+
+
+This option defines the ACL that is run when there is an AUTH parameter on a
+MAIL command. See chapter 44 for details of ACLs, and chapter 33 for details of
+authentication.
+
++----------------------------------------------------+
+|acl_smtp_mime|Use: main|Type: string*|Default: unset|
++----------------------------------------------------+
+
+This option is available when Exim is built with the content-scanning
+extension. It defines the ACL that is run for each MIME part in a message. See
+section 45.4 for details.
+
++-------------------------------------------------------+
+|acl_smtp_notquit|Use: main|Type: string*|Default: unset|
++-------------------------------------------------------+
+
+This option defines the ACL that is run when an SMTP session ends without a
+QUIT command being received. See chapter 44 for further details.
+
++-------------------------------------------------------+
+|acl_smtp_predata|Use: main|Type: string*|Default: unset|
++-------------------------------------------------------+
+
+This option defines the ACL that is run when an SMTP DATA command is received,
+before the message itself is received. See chapter 44 for further details.
+
++----------------------------------------------------+
+|acl_smtp_quit|Use: main|Type: string*|Default: unset|
++----------------------------------------------------+
+
+This option defines the ACL that is run when an SMTP QUIT command is received.
+See chapter 44 for further details.
+
++----------------------------------------------------+
+|acl_smtp_rcpt|Use: main|Type: string*|Default: unset|
++----------------------------------------------------+
+
+This option defines the ACL that is run when an SMTP RCPT command is received.
+See chapter 44 for further details.
+
++--------------------------------------------------------+
+|acl_smtp_starttls|Use: main|Type: string*|Default: unset|
++--------------------------------------------------------+
+
+This option defines the ACL that is run when an SMTP STARTTLS command is
+received. See chapter 44 for further details.
+
++----------------------------------------------------+
+|acl_smtp_vrfy|Use: main|Type: string*|Default: unset|
++----------------------------------------------------+
+
+This option defines the ACL that is run when an SMTP VRFY command is received.
+See chapter 44 for further details.
+
++----------------------------------------------------------+
+|add_environment|Use: main|Type: string list|Default: empty|
++----------------------------------------------------------+
+
+This option adds individual environment variables that the currently linked
+libraries and programs in child processes may use. Each list element should be
+of the form "name=value".
+
+See 29.4 for the environment of pipe transports.
+
++--------------------------------------------------------+
+|admin_groups|Use: main|Type: string list*|Default: unset|
++--------------------------------------------------------+
+
+This option is expanded just once, at the start of Exim's processing. If the
+current group or any of the supplementary groups of an Exim caller is in this
+colon-separated list, the caller has admin privileges. If all your system
+programmers are in a specific group, for example, you can give them all Exim
+admin privileges by putting that group in admin_groups. However, this does not
+permit them to read Exim's spool files (whose group owner is the Exim gid). To
+permit this, you have to add individuals to the Exim group.
+
++------------------------------------------------------------+
+|allow_domain_literals|Use: main|Type: boolean|Default: false|
++------------------------------------------------------------+
+
+If this option is set, the RFC 2822 domain literal format is permitted in email
+addresses. The option is not set by default, because the domain literal format
+is not normally required these days, and few people know about it. It has,
+however, been exploited by mail abusers.
+
+Unfortunately, it seems that some DNS black list maintainers are using this
+format to report black listing to postmasters. If you want to accept messages
+addressed to your hosts by IP address, you need to set allow_domain_literals
+true, and also to add "@[]" to the list of local domains (defined in the named
+domain list local_domains in the default configuration). This "magic string"
+matches the domain literal form of all the local host's IP addresses.
+
++-----------------------------------------------------+
+|allow_mx_to_ip|Use: main|Type: boolean|Default: false|
++-----------------------------------------------------+
+
+It appears that more and more DNS zone administrators are breaking the rules
+and putting domain names that look like IP addresses on the right hand side of
+MX records. Exim follows the rules and rejects this, giving an error message
+that explains the misconfiguration. However, some other MTAs support this
+practice, so to avoid "Why can't Exim do this?" complaints, allow_mx_to_ip
+exists, in order to enable this heinous activity. It is not recommended, except
+when you have no other choice.
+
++---------------------------------------------------------+
+|allow_utf8_domains|Use: main|Type: boolean|Default: false|
++---------------------------------------------------------+
+
+Lots of discussion is going on about internationalized domain names. One camp
+is strongly in favour of just using UTF-8 characters, and it seems that at
+least two other MTAs permit this. This option allows Exim users to experiment
+if they wish.
+
+If it is set true, Exim's domain parsing function allows valid UTF-8
+multicharacters to appear in domain name components, in addition to letters,
+digits, and hyphens.
+
+If Exim is built with internationalization support and the SMTPUTF8 ESMTP
+option is in use (see chapter 60) this option can be left as default. Without
+that, if you want to look up such domain names in the DNS, you must also adjust
+the value of dns_check_names_pattern to match the extended form. A suitable
+setting is:
+
+dns_check_names_pattern = (?i)^(?>(?(1)\.|())[a-z0-9\xc0-\xff]\
+ (?>[-a-z0-9\x80-\xff]*[a-z0-9\x80-\xbf])?)+$
+
+Alternatively, you can just disable this feature by setting
+
+dns_check_names_pattern =
+
+That is, set the option to an empty string so that no check is done.
+
++----------------------------------------------------------+
+|auth_advertise_hosts|Use: main|Type: host list*|Default: *|
++----------------------------------------------------------+
+
+If any server authentication mechanisms are configured, Exim advertises them in
+response to an EHLO command only if the calling host matches this list.
+Otherwise, Exim does not advertise AUTH. Exim does not accept AUTH commands
+from clients to which it has not advertised the availability of AUTH. The
+advertising of individual authentication mechanisms can be controlled by the
+use of the server_advertise_condition generic authenticator option on the
+individual authenticators. See chapter 33 for further details.
+
+Certain mail clients (for example, Netscape) require the user to provide a name
+and password for authentication if AUTH is advertised, even though it may not
+be needed (the host may accept messages from hosts on its local LAN without
+authentication, for example). The auth_advertise_hosts option can be used to
+make these clients more friendly by excluding them from the set of hosts to
+which Exim advertises AUTH.
+
+If you want to advertise the availability of AUTH only when the connection is
+encrypted using TLS, you can make use of the fact that the value of this option
+is expanded, with a setting like this:
+
+auth_advertise_hosts = ${if eq{$tls_in_cipher}{}{}{*}}
+
+If $tls_in_cipher is empty, the session is not encrypted, and the result of the
+expansion is empty, thus matching no hosts. Otherwise, the result of the
+expansion is *, which matches all hosts.
+
++------------------------------------------+
+|auto_thaw|Use: main|Type: time|Default: 0s|
++------------------------------------------+
+
+If this option is set to a time greater than zero, a queue runner will try a
+new delivery attempt on any frozen message, other than a bounce message, if
+this much time has passed since it was frozen. This may result in the message
+being re-frozen if nothing has changed since the last attempt. It is a way of
+saying "keep on trying, even though there are big problems".
+
+Note: This is an old option, which predates timeout_frozen_after and
+ignore_bounce_errors_after. It is retained for compatibility, but it is not
+thought to be very useful any more, and its use should probably be avoided.
+
++----------------------------------------------------+
+|av_scanner|Use: main|Type: string|Default: see below|
++----------------------------------------------------+
+
+This option is available if Exim is built with the content-scanning extension.
+It specifies which anti-virus scanner to use. The default value is:
+
+sophie:/var/run/sophie
+
+If the value of av_scanner starts with a dollar character, it is expanded
+before use. See section 45.1 for further details.
+
++------------------------------------------------+
+|bi_command|Use: main|Type: string|Default: unset|
++------------------------------------------------+
+
+This option supplies the name of a command that is run when Exim is called with
+the -bi option (see chapter 5). The string value is just the command name, it
+is not a complete command line. If an argument is required, it must come from
+the -oA command line option.
+
++----------------------------------------------------------+
+|bounce_message_file|Use: main|Type: string*|Default: unset|
++----------------------------------------------------------+
+
+This option defines a template file containing paragraphs of text to be used
+for constructing bounce messages. Details of the file's contents are given in
+chapter 50.
+
+The option is expanded to give the file path, which must be absolute and
+untainted.
+
+See also warn_message_file.
+
++---------------------------------------------------------+
+|bounce_message_text|Use: main|Type: string|Default: unset|
++---------------------------------------------------------+
+
+When this option is set, its contents are included in the default bounce
+message immediately after "This message was created automatically by mail
+delivery software." It is not used if bounce_message_file is set.
+
++--------------------------------------------------------+
+|bounce_return_body|Use: main|Type: boolean|Default: true|
++--------------------------------------------------------+
+
+This option controls whether the body of an incoming message is included in a
+bounce message when bounce_return_message is true. The default setting causes
+the entire message, both header and body, to be returned (subject to the value
+of bounce_return_size_limit). If this option is false, only the message header
+is included. In the case of a non-SMTP message containing an error that is
+detected during reception, only those header lines preceding the point at which
+the error was detected are returned.
+
++-----------------------------------------------------------------+
+|bounce_return_linesize_limit|Use: main|Type: integer|Default: 998|
++-----------------------------------------------------------------+
+
+This option sets a limit in bytes on the line length of messages that are
+returned to senders due to delivery problems, when bounce_return_message is
+true. The default value corresponds to RFC limits. If the message being
+returned has lines longer than this value it is treated as if the
+bounce_return_size_limit (below) restriction was exceeded.
+
+The option also applies to bounces returned when an error is detected during
+reception of a message. In this case lines from the original are truncated.
+
+The option does not apply to messages generated by an autoreply transport.
+
++-----------------------------------------------------------+
+|bounce_return_message|Use: main|Type: boolean|Default: true|
++-----------------------------------------------------------+
+
+If this option is set false, none of the original message is included in bounce
+messages generated by Exim. See also bounce_return_size_limit and
+bounce_return_body.
+
++--------------------------------------------------------------+
+|bounce_return_size_limit|Use: main|Type: integer|Default: 100K|
++--------------------------------------------------------------+
+
+This option sets a limit in bytes on the size of messages that are returned to
+senders as part of bounce messages when bounce_return_message is true. The
+limit should be less than the value of the global message_size_limit and of any
+message_size_limit settings on transports, to allow for the bounce text that
+Exim generates. If this option is set to zero there is no limit.
+
+When the body of any message that is to be included in a bounce message is
+greater than the limit, it is truncated, and a comment pointing this out is
+added at the top. The actual cutoff may be greater than the value given, owing
+to the use of buffering for transferring the message in chunks (typically 8K in
+size). The idea is to save bandwidth on those undeliverable 15-megabyte
+messages.
+
++------------------------------------------------------------------+
+|bounce_sender_authentication|Use: main|Type: string|Default: unset|
++------------------------------------------------------------------+
+
+This option provides an authenticated sender address that is sent with any
+bounce messages generated by Exim that are sent over an authenticated SMTP
+connection. A typical setting might be:
+
+bounce_sender_authentication = mailer-daemon@my.domain.example
+
+which would cause bounce messages to be sent using the SMTP command:
+
+MAIL FROM:<> AUTH=mailer-daemon@my.domain.example
+
+The value of bounce_sender_authentication must always be a complete email
+address.
+
++---------------------------------------------------------------+
+|callout_domain_negative_expire|Use: main|Type: time|Default: 3h|
++---------------------------------------------------------------+
+
+This option specifies the expiry time for negative callout cache data for a
+domain. See section 44.45 for details of callout verification, and section
+44.47 for details of the caching.
+
++---------------------------------------------------------------+
+|callout_domain_positive_expire|Use: main|Type: time|Default: 7d|
++---------------------------------------------------------------+
+
+This option specifies the expiry time for positive callout cache data for a
+domain. See section 44.45 for details of callout verification, and section
+44.47 for details of the caching.
+
++--------------------------------------------------------+
+|callout_negative_expire|Use: main|Type: time|Default: 2h|
++--------------------------------------------------------+
+
+This option specifies the expiry time for negative callout cache data for an
+address. See section 44.45 for details of callout verification, and section
+44.47 for details of the caching.
+
++---------------------------------------------------------+
+|callout_positive_expire|Use: main|Type: time|Default: 24h|
++---------------------------------------------------------+
+
+This option specifies the expiry time for positive callout cache data for an
+address. See section 44.45 for details of callout verification, and section
+44.47 for details of the caching.
+
++--------------------------------------------------------------------+
+|callout_random_local_part|Use: main|Type: string*|Default: see below|
++--------------------------------------------------------------------+
+
+This option defines the "random" local part that can be used as part of callout
+verification. The default value is
+
+$primary_hostname-$tod_epoch-testing
+
+See section 44.46 for details of how this value is used.
+
++-----------------------------------------------------+
+|check_log_inodes|Use: main|Type: integer|Default: 100|
++-----------------------------------------------------+
+
+See check_spool_space below.
+
++----------------------------------------------------+
+|check_log_space|Use: main|Type: integer|Default: 10M|
++----------------------------------------------------+
+
+See check_spool_space below.
+
++----------------------------------------------------------+
+|check_rfc2047_length|Use: main|Type: boolean|Default: true|
++----------------------------------------------------------+
+
+RFC 2047 defines a way of encoding non-ASCII characters in headers using a
+system of "encoded words". The RFC specifies a maximum length for an encoded
+word; strings to be encoded that exceed this length are supposed to use
+multiple encoded words. By default, Exim does not recognize encoded words that
+exceed the maximum length. However, it seems that some software, in violation
+of the RFC, generates overlong encoded words. If check_rfc2047_length is set
+false, Exim recognizes encoded words of any length.
+
++-------------------------------------------------------+
+|check_spool_inodes|Use: main|Type: integer|Default: 100|
++-------------------------------------------------------+
+
+See check_spool_space below.
+
++------------------------------------------------------+
+|check_spool_space|Use: main|Type: integer|Default: 10M|
++------------------------------------------------------+
+
+The four check_... options allow for checking of disk resources before a
+message is accepted.
+
+When any of these options are nonzero, they apply to all incoming messages. If
+you want to apply different checks to different kinds of message, you can do so
+by testing the variables $log_inodes, $log_space, $spool_inodes, and
+$spool_space in an ACL with appropriate additional conditions.
+
+check_spool_space and check_spool_inodes check the spool partition if either
+value is greater than zero, for example:
+
+check_spool_space = 100M
+check_spool_inodes = 100
+
+The spool partition is the one that contains the directory defined by
+SPOOL_DIRECTORY in Local/Makefile. It is used for holding messages in transit.
+
+check_log_space and check_log_inodes check the partition in which log files are
+written if either is greater than zero. These should be set only if
+log_file_path and spool_directory refer to different partitions.
+
+If there is less space or fewer inodes than requested, Exim refuses to accept
+incoming mail. In the case of SMTP input this is done by giving a 452 temporary
+error response to the MAIL command. If ESMTP is in use and there was a SIZE
+parameter on the MAIL command, its value is added to the check_spool_space
+value, and the check is performed even if check_spool_space is zero, unless
+no_smtp_check_spool_space is set.
+
+The values for check_spool_space and check_log_space are held as a number of
+kilobytes (though specified in bytes). If a non-multiple of 1024 is specified,
+it is rounded up.
+
+For non-SMTP input and for batched SMTP input, the test is done at start-up; on
+failure a message is written to stderr and Exim exits with a non-zero code, as
+it obviously cannot send an error message of any kind.
+
+There is a slight performance penalty for these checks. Versions of Exim
+preceding 4.88 had these disabled by default; high-rate installations confident
+they will never run out of resources may wish to deliberately disable them.
+
++--------------------------------------------------------------+
+|chunking_advertise_hosts|Use: main|Type: host list*|Default: *|
++--------------------------------------------------------------+
+
+The CHUNKING extension (RFC3030) will be advertised in the EHLO message to
+these hosts. Hosts may use the BDAT command as an alternate to DATA.
+
++-------------------------------------------------------------------------+
+|commandline_checks_require_admin|Use: main|Type: boolean|Default: "false"|
++-------------------------------------------------------------------------+
+
+This option restricts various basic checking features to require an
+administrative user. This affects most of the -b* options, such as -be.
+
++----------------------------------------------------+
+|debug_store|Use: main|Type: boolean|Default: "false"|
++----------------------------------------------------+
+
+This option, when true, enables extra checking in Exim's internal memory
+management. For use when a memory corruption issue is being investigated, it
+should normally be left as default.
+
++--------------------------------------------------------+
+|daemon_smtp_ports|Use: main|Type: string|Default: "smtp"|
++--------------------------------------------------------+
+
+This option specifies one or more default SMTP ports on which the Exim daemon
+listens. See chapter 13 for details of how it is used. For backward
+compatibility, daemon_smtp_port (singular) is a synonym.
+
++---------------------------------------------------------+
+|daemon_startup_retries|Use: main|Type: integer|Default: 9|
++---------------------------------------------------------+
+
+This option, along with daemon_startup_sleep, controls the retrying done by the
+daemon at startup when it cannot immediately bind a listening socket (typically
+because the socket is already in use): daemon_startup_retries defines the
+number of retries after the first failure, and daemon_startup_sleep defines the
+length of time to wait between retries.
+
++------------------------------------------------------+
+|daemon_startup_sleep|Use: main|Type: time|Default: 30s|
++------------------------------------------------------+
+
+See daemon_startup_retries.
+
++----------------------------------------------------+
+|delay_warning|Use: main|Type: time list|Default: 24h|
++----------------------------------------------------+
+
+When a message is delayed, Exim sends a warning message to the sender at
+intervals specified by this option. The data is a colon-separated list of times
+after which to send warning messages. If the value of the option is an empty
+string or a zero time, no warnings are sent. Up to 10 times may be given. If a
+message has been in the queue for longer than the last time, the last interval
+between the times is used to compute subsequent warning times. For example,
+with
+
+delay_warning = 4h:8h:24h
+
+the first message is sent after 4 hours, the second after 8 hours, and the
+third one after 24 hours. After that, messages are sent every 16 hours, because
+that is the interval between the last two times on the list. If you set just
+one time, it specifies the repeat interval. For example, with:
+
+delay_warning = 6h
+
+messages are repeated every six hours. To stop warnings after a given time, set
+a very large time at the end of the list. For example:
+
+delay_warning = 2h:12h:99d
+
+Note that the option is only evaluated at the time a delivery attempt fails,
+which depends on retry and queue-runner configuration. Typically retries will
+be configured more frequently than warning messages.
+
++------------------------------------------------------------------+
+|delay_warning_condition|Use: main|Type: string*|Default: see below|
++------------------------------------------------------------------+
+
+The string is expanded at the time a warning message might be sent. If all the
+deferred addresses have the same domain, it is set in $domain during the
+expansion. Otherwise $domain is empty. If the result of the expansion is a
+forced failure, an empty string, or a string matching any of "0", "no" or
+"false" (the comparison being done caselessly) then the warning message is not
+sent. The default is:
+
+delay_warning_condition = ${if or {\
+ { !eq{$h_list-id:$h_list-post:$h_list-subscribe:}{} }\
+ { match{$h_precedence:}{(?i)bulk|list|junk} }\
+ { match{$h_auto-submitted:}{(?i)auto-generated|auto-replied} }\
+ } {no}{yes}}
+
+This suppresses the sending of warnings for messages that contain List-ID:,
+List-Post:, or List-Subscribe: headers, or have "bulk", "list" or "junk" in a
+Precedence: header, or have "auto-generated" or "auto-replied" in an
+Auto-Submitted: header.
+
++-------------------------------------------------------------+
+|deliver_drop_privilege|Use: main|Type: boolean|Default: false|
++-------------------------------------------------------------+
+
+If this option is set true, Exim drops its root privilege at the start of a
+delivery process, and runs as the Exim user throughout. This severely restricts
+the kinds of local delivery that are possible, but is viable in certain types
+of configuration. There is a discussion about the use of root privilege in
+chapter 56.
+
++-----------------------------------------------------------------+
+|deliver_queue_load_max|Use: main|Type: fixed-point|Default: unset|
++-----------------------------------------------------------------+
+
+When this option is set, a queue run is abandoned if the system load average
+becomes greater than the value of the option. The option has no effect on
+ancient operating systems on which Exim cannot determine the load average. See
+also queue_only_load and smtp_load_reserve.
+
++----------------------------------------------------------+
+|delivery_date_remove|Use: main|Type: boolean|Default: true|
++----------------------------------------------------------+
+
+Exim's transports have an option for adding a Delivery-date: header to a
+message when it is delivered, in exactly the same way as Return-path: is
+handled. Delivery-date: records the actual time of delivery. Such headers
+should not be present in incoming messages, and this option causes them to be
+removed at the time the message is received, to avoid any problems that might
+occur when a delivered message is subsequently sent on to some other recipient.
+
++----------------------------------------------------+
+|disable_fsync|Use: main|Type: boolean|Default: false|
++----------------------------------------------------+
+
+This option is available only if Exim was built with the compile-time option
+ENABLE_DISABLE_FSYNC. When this is not set, a reference to disable_fsync in a
+runtime configuration generates an "unknown option" error. You should not build
+Exim with ENABLE_DISABLE_FSYNC or set disable_fsync unless you really, really,
+really understand what you are doing. No pre-compiled distributions of Exim
+should ever make this option available.
+
+When disable_fsync is set true, Exim no longer calls fsync() to force updated
+files' data to be written to disc before continuing. Unexpected events such as
+crashes and power outages may cause data to be lost or scrambled. Here be
+Dragons. Beware.
+
++---------------------------------------------------+
+|disable_ipv6|Use: main|Type: boolean|Default: false|
++---------------------------------------------------+
+
+If this option is set true, even if the Exim binary has IPv6 support, no IPv6
+activities take place. AAAA records are never looked up, and any IPv6 addresses
+that are listed in local_interfaces, data for the manualroute router, etc. are
+ignored. If IP literals are enabled, the ipliteral router declines to handle
+IPv6 literal addresses.
+
++-----------------------------------------------------------------------+
+|dkim_verify_hashes|Use: main|Type: string list|Default: sha256 : sha512|
++-----------------------------------------------------------------------+
+
+This option gives a list of hash types which are acceptable in signatures,
+
+and an order of processing. Signatures with algorithms not in the list will be
+ignored.
+
+Acceptable values include:
+
+sha1
+sha256
+sha512
+
+Note that the acceptance of sha1 violates RFC 8301.
+
++-----------------------------------------------------------------------+
+|dkim_verify_keytypes|Use: main|Type: string list|Default: ed25519 : rsa|
++-----------------------------------------------------------------------+
+
+This option gives a list of key types which are acceptable in signatures, and
+an order of processing. Signatures with algorithms not in the list will be
+ignored.
+
++-----------------------------------------------------------------------------+
+|dkim_verify_min_keysizes| Use: | Type: string |Default: rsa=1024 ed25519=|
+| | main | list | 250|
++-----------------------------------------------------------------------------+
+
+This option gives a list of key sizes which are acceptable in signatures. The
+list is keyed by the algorithm type for the key; the values are in bits.
+Signatures with keys smaller than given by this option will fail verification.
+
+The default enforces the RFC 8301 minimum key size for RSA signatures.
+
++----------------------------------------------------------+
+|dkim_verify_minimal|Use: main|Type: boolean|Default: false|
++----------------------------------------------------------+
+
+If set to true, verification of signatures will terminate after the first
+success.
+
++-----------------------------------------------------------------------+
+|dkim_verify_signers|Use: main|Type: domain list*|Default: $dkim_signers|
++-----------------------------------------------------------------------+
+
+This option gives a list of DKIM domains for which the DKIM ACL is run. It is
+expanded after the message is received; by default it runs the ACL once for
+each signature in the message. See section 58.3.
+
++------------------------------------------------------------+
+|dmarc_forensic_sender|Use: main|Type: string*|Default: unset|
++------------------------------------------------------------+
+
++--------------------------------------------------------+
+|dmarc_history_file|Use: main|Type: string|Default: unset|
++--------------------------------------------------------+
+
++----------------------------------------------------+
+|dmarc_tld_file|Use: main|Type: string|Default: unset|
++----------------------------------------------------+
+
+These options control DMARC processing. See section 58.5 for details.
+
++--------------------------------------------------------------------+
+|dns_again_means_nonexist|Use: main|Type: domain list*|Default: unset|
++--------------------------------------------------------------------+
+
+DNS lookups give a "try again" response for the DNS errors "non-authoritative
+host not found" and "SERVERFAIL". This can cause Exim to keep trying to deliver
+a message, or to give repeated temporary errors to incoming mail. Sometimes the
+effect is caused by a badly set up name server and may persist for a long time.
+If a domain which exhibits this problem matches anything in
+dns_again_means_nonexist, it is treated as if it did not exist. This option
+should be used with care. You can make it apply to reverse lookups by a setting
+such as this:
+
+dns_again_means_nonexist = *.in-addr.arpa
+
+This option applies to all DNS lookups that Exim does. It also applies when the
+gethostbyname() or getipnodebyname() functions give temporary errors, since
+these are most likely to be caused by DNS lookup problems. The dnslookup router
+has some options of its own for controlling what happens when lookups for MX or
+SRV records give temporary errors. These more specific options are applied
+after this global option.
+
++-----------------------------------------------------------------+
+|dns_check_names_pattern|Use: main|Type: string|Default: see below|
++-----------------------------------------------------------------+
+
+When this option is set to a non-empty string, it causes Exim to check domain
+names for characters that are not allowed in host names before handing them to
+the DNS resolver, because some resolvers give temporary errors for names that
+contain unusual characters. If a domain name contains any unwanted characters,
+a "not found" result is forced, and the resolver is not called. The check is
+done by matching the domain name against a regular expression, which is the
+value of this option. The default pattern is
+
+dns_check_names_pattern = \
+ (?i)^(?>(?(1)\.|())[^\W_](?>[a-z0-9/-]*[^\W_])?)+$
+
+which permits only letters, digits, slashes, and hyphens in components, but
+they must start and end with a letter or digit. Slashes are not, in fact,
+permitted in host names, but they are found in certain NS records (which can be
+accessed in Exim by using a dnsdb lookup). If you set allow_utf8_domains, you
+must modify this pattern, or set the option to an empty string.
+
++-------------------------------------------------------+
+|dns_csa_search_limit|Use: main|Type: integer|Default: 5|
++-------------------------------------------------------+
+
+This option controls the depth of parental searching for CSA SRV records in the
+DNS, as described in more detail in section 44.50.
+
++---------------------------------------------------------+
+|dns_csa_use_reverse|Use: main|Type: boolean|Default: true|
++---------------------------------------------------------+
+
+This option controls whether or not an IP address, given as a CSA domain, is
+reversed and looked up in the reverse DNS, as described in more detail in
+section 44.50.
+
++--------------------------------------------------+
+|dns_cname_loops|Use: main|Type: integer|Default: 1|
++--------------------------------------------------+
+
+This option controls the following of CNAME chains, needed if the resolver does
+not do it internally. As of 2018 most should, and the default can be left. If
+you have an ancient one, a value of 10 is likely needed.
+
+The default value of one CNAME-follow is needed thanks to the observed return
+for an MX request, given no MX presence but a CNAME to an A, of the CNAME.
+
++-------------------------------------------------+
+|dns_dnssec_ok|Use: main|Type: integer|Default: -1|
++-------------------------------------------------+
+
+If this option is set to a non-negative number then Exim will initialise the
+DNS resolver library to either use or not use DNSSEC, overriding the system
+default. A value of 0 coerces DNSSEC off, a value of 1 coerces DNSSEC on.
+
+If the resolver library does not support DNSSEC then this option has no effect.
+
+On Linux with glibc 2.31 or newer this is insufficient, the resolver library
+will default to stripping out a successful validation status. This will break a
+previously working Exim installation. Provided that you do trust the resolver
+(ie, is on localhost) you can tell glibc to pass through any successful
+validation with a new option in /etc/resolv.conf:
+
+options trust-ad
+
++-----------------------------------------------------------+
+|dns_ipv4_lookup|Use: main|Type: domain list*|Default: unset|
++-----------------------------------------------------------+
+
+When Exim is compiled with IPv6 support and disable_ipv6 is not set, it looks
+for IPv6 address records (AAAA records) as well as IPv4 address records (A
+records) when trying to find IP addresses for hosts, unless the host's domain
+matches this list.
+
+This is a fudge to help with name servers that give big delays or otherwise do
+not work for the AAAA record type. In due course, when the world's name servers
+have all been upgraded, there should be no need for this option. Note that all
+lookups, including those done for verification, are affected; this will result
+in verify failure for IPv6 connections or ones using names only valid for IPv6
+addresses.
+
++--------------------------------------------+
+|dns_retrans|Use: main|Type: time|Default: 0s|
++--------------------------------------------+
+
+The options dns_retrans and dns_retry can be used to set the retransmission and
+retry parameters for DNS lookups. Values of zero (the defaults) leave the
+system default settings unchanged. The first value is the time between retries,
+and the second is the number of retries. It isn't totally clear exactly how
+these settings affect the total time a DNS lookup may take. I haven't found any
+documentation about timeouts on DNS lookups; these parameter values are
+available in the external resolver interface structure, but nowhere does it
+seem to describe how they are used or what you might want to set in them. See
+also the slow_lookup_log option.
+
++--------------------------------------------+
+|dns_retry|Use: main|Type: integer|Default: 0|
++--------------------------------------------+
+
+See dns_retrans above.
+
++--------------------------------------------------------+
+|dns_trust_aa|Use: main|Type: domain list*|Default: unset|
++--------------------------------------------------------+
+
+If this option is set then lookup results marked with the AA bit (Authoritative
+Answer) are trusted the same way as if they were DNSSEC-verified. The authority
+section's name of the answer must match with this expanded domain list.
+
+Use this option only if you talk directly to a resolver that is authoritative
+for some zones and does not set the AD (Authentic Data) bit in the answer. Some
+DNS servers may have an configuration option to mark the answers from their own
+zones as verified (they set the AD bit). Others do not have this option. It is
+considered as poor practice using a resolver that is an authoritative server
+for some zones.
+
+Use this option only if you really have to (e.g. if you want to use DANE for
+remote delivery to a server that is listed in the DNS zones that your resolver
+is authoritative for).
+
+If the DNS answer packet has the AA bit set and contains resource record in the
+answer section, the name of the first NS record appearing in the authority
+section is compared against the list. If the answer packet is authoritative but
+the answer section is empty, the name of the first SOA record in the
+authoritative section is used instead.
+
++-------------------------------------------------+
+|dns_use_edns0|Use: main|Type: integer|Default: -1|
++-------------------------------------------------+
+
+If this option is set to a non-negative number then Exim will initialise the
+DNS resolver library to either use or not use EDNS0 extensions, overriding the
+system default. A value of 0 coerces EDNS0 off, a value of 1 coerces EDNS0 on.
+
+If the resolver library does not support EDNS0 then this option has no effect.
+
+OpenBSD's asr resolver routines are known to ignore the EDNS0 option; this
+means that DNSSEC will not work with Exim on that platform either, unless Exim
+is linked against an alternative DNS client library.
+
++----------------------------------------------+
+|drop_cr|Use: main|Type: boolean|Default: false|
++----------------------------------------------+
+
+This is an obsolete option that is now a no-op. It used to affect the way Exim
+handled CR and LF characters in incoming messages. What happens now is
+described in section 48.2.
+
++-------------------------------------------------------------+
+|dsn_advertise_hosts|Use: main|Type: host list*|Default: unset|
++-------------------------------------------------------------+
+
+DSN extensions (RFC3461) will be advertised in the EHLO message to, and
+accepted from, these hosts. Hosts may use the NOTIFY and ENVID options on RCPT
+TO commands, and RET and ORCPT options on MAIL FROM commands. A NOTIFY=SUCCESS
+option requests success-DSN messages. A NOTIFY= option with no argument
+requests that no delay or failure DSNs are sent.
+
+Note: Supplying success-DSN messages has been criticised on privacy grounds; it
+can leak details of internal forwarding.
+
++---------------------------------------------------+
+|dsn_from|Use: main|Type: string*|Default: see below|
++---------------------------------------------------+
+
+This option can be used to vary the contents of From: header lines in bounces
+and other automatically generated messages ("Delivery Status Notifications" -
+hence the name of the option). The default setting is:
+
+dsn_from = Mail Delivery System <Mailer-Daemon@$qualify_domain>
+
+The value is expanded every time it is needed. If the expansion fails, a panic
+is logged, and the default value is used.
+
++--------------------------------------------------------+
+|envelope_to_remove|Use: main|Type: boolean|Default: true|
++--------------------------------------------------------+
+
+Exim's transports have an option for adding an Envelope-to: header to a message
+when it is delivered, in exactly the same way as Return-path: is handled.
+Envelope-to: records the original recipient address from the message's envelope
+that caused the delivery to happen. Such headers should not be present in
+incoming messages, and this option causes them to be removed at the time the
+message is received, to avoid any problems that might occur when a delivered
+message is subsequently sent on to some other recipient.
+
++-------------------------------------------------------+
+|errors_copy|Use: main|Type: string list*|Default: unset|
++-------------------------------------------------------+
+
+Setting this option causes Exim to send bcc copies of bounce messages that it
+generates to other addresses. Note: This does not apply to bounce messages
+coming from elsewhere. The value of the option is a colon-separated list of
+items. Each item consists of a pattern, terminated by white space, followed by
+a comma-separated list of email addresses. If a pattern contains spaces, it
+must be enclosed in double quotes.
+
+Each pattern is processed in the same way as a single item in an address list
+(see section 10.20). When a pattern matches the recipient of the bounce
+message, the message is copied to the addresses on the list. The items are
+scanned in order, and once a matching one is found, no further items are
+examined. For example:
+
+errors_copy = spqr@mydomain postmaster@mydomain.example :\
+ rqps@mydomain hostmaster@mydomain.example,\
+ postmaster@mydomain.example
+
+The address list is expanded before use. The expansion variables $local_part
+and $domain are set from the original recipient of the error message, and if
+there was any wildcard matching in the pattern, the expansion variables $0, $1,
+etc. are set in the normal way.
+
++-----------------------------------------------------+
+|errors_reply_to|Use: main|Type: string|Default: unset|
++-----------------------------------------------------+
+
+By default, Exim's bounce and delivery warning messages contain the header line
+
+From: Mail Delivery System <Mailer-Daemon@qualify-domain>
+
+where qualify-domain is the value of the qualify_domain option. A warning
+message that is generated by the quota_warn_message option in an appendfile
+transport may contain its own From: header line that overrides the default.
+
+Experience shows that people reply to bounce messages. If the errors_reply_to
+option is set, a Reply-To: header is added to bounce and warning messages. For
+example:
+
+errors_reply_to = postmaster@my.domain.example
+
+The value of the option is not expanded. It must specify a valid RFC 2822
+address. However, if a warning message that is generated by the
+quota_warn_message option in an appendfile transport contain its own Reply-To:
+header line, the value of the errors_reply_to option is not used.
+
++---------------------------------------------------+
+|event_action|Use: main|Type: string*|Default: unset|
++---------------------------------------------------+
+
+This option declares a string to be expanded for Exim's events mechanism. For
+details see chapter 61.
+
++------------------------------------------------------------------+
+|exim_group|Use: main|Type: string|Default: compile-time configured|
++------------------------------------------------------------------+
+
+This option changes the gid under which Exim runs when it gives up root
+privilege. The default value is compiled into the binary. The value of this
+option is used only when exim_user is also set. Unless it consists entirely of
+digits, the string is looked up using getgrnam(), and failure causes a
+configuration error. See chapter 56 for a discussion of security issues.
+
++---------------------------------------------------+
+|exim_path|Use: main|Type: string|Default: see below|
++---------------------------------------------------+
+
+This option specifies the path name of the Exim binary, which is used when Exim
+needs to re-exec itself. The default is set up to point to the file exim in the
+directory configured at compile time by the BIN_DIRECTORY setting. It is
+necessary to change exim_path if, exceptionally, Exim is run from some other
+place. Warning: Do not use a macro to define the value of this option, because
+you will break those Exim utilities that scan the configuration file to find
+where the binary is. (They then use the -bP option to extract option settings
+such as the value of spool_directory.)
+
++-----------------------------------------------------------------+
+|exim_user|Use: main|Type: string|Default: compile-time configured|
++-----------------------------------------------------------------+
+
+This option changes the uid under which Exim runs when it gives up root
+privilege. The default value is compiled into the binary. Ownership of the run
+time configuration file and the use of the -C and -D command line options is
+checked against the values in the binary, not what is set here.
+
+Unless it consists entirely of digits, the string is looked up using getpwnam()
+, and failure causes a configuration error. If exim_group is not also supplied,
+the gid is taken from the result of getpwnam() if it is used. See chapter 56
+for a discussion of security issues.
+
++------------------------------------------------------------+
+|exim_version|Use: main|Type: string|Default: current version|
++------------------------------------------------------------+
+
+This option overrides the $version_number/$exim_version that Exim reports in
+various places. Use with care; this may fool stupid security scanners.
+
++-----------------------------------------------------------------+
+|extra_local_interfaces|Use: main|Type: string list|Default: unset|
++-----------------------------------------------------------------+
+
+This option defines network interfaces that are to be considered local when
+routing, but which are not used for listening by the daemon. See section 13.8
+for details.
+
++------------------------------------------------------------------------+
+|extract_addresses_remove_arguments|Use: main|Type: boolean|Default: true|
++------------------------------------------------------------------------+
+
+According to some Sendmail documentation (Sun, IRIX, HP-UX), if any addresses
+are present on the command line when the -t option is used to build an envelope
+from a message's To:, Cc: and Bcc: headers, the command line addresses are
+removed from the recipients list. This is also how Smail behaves. However,
+other Sendmail documentation (the O'Reilly book) states that command line
+addresses are added to those obtained from the header lines. When
+extract_addresses_remove_arguments is true (the default), Exim subtracts
+argument headers. If it is set false, Exim adds rather than removes argument
+addresses.
+
++---------------------------------------------------+
+|finduser_retries|Use: main|Type: integer|Default: 0|
++---------------------------------------------------+
+
+On systems running NIS or other schemes in which user and group information is
+distributed from a remote system, there can be times when getpwnam() and
+related functions fail, even when given valid data, because things time out.
+Unfortunately these failures cannot be distinguished from genuine "not found"
+errors. If finduser_retries is set greater than zero, Exim will try that many
+extra times to find a user or a group, waiting for one second between retries.
+
+You should not set this option greater than zero if your user information is in
+a traditional /etc/passwd file, because it will cause Exim needlessly to search
+the file multiple times for non-existent users, and also cause delay.
+
++-----------------------------------------------------------------------+
+|freeze_tell|Use: main|Type: string list, comma separated|Default: unset|
++-----------------------------------------------------------------------+
+
+On encountering certain errors, or when configured to do so in a system filter,
+ACL, or special router, Exim freezes a message. This means that no further
+delivery attempts take place until an administrator thaws the message, or the
+auto_thaw, ignore_bounce_errors_after, or timeout_frozen_after feature cause it
+to be processed. If freeze_tell is set, Exim generates a warning message
+whenever it freezes something, unless the message it is freezing is a
+locally-generated bounce message. (Without this exception there is the
+possibility of looping.) The warning message is sent to the addresses supplied
+as the comma-separated value of this option. If several of the message's
+addresses cause freezing, only a single message is sent. If the freezing was
+automatic, the reason(s) for freezing can be found in the message log. If you
+configure freezing in a filter or ACL, you must arrange for any logging that
+you require.
+
++-------------------------------------------------+
+|gecos_name|Use: main|Type: string*|Default: unset|
++-------------------------------------------------+
+
+Some operating systems, notably HP-UX, use the "gecos" field in the system
+password file to hold other information in addition to users' real names. Exim
+looks up this field for use when it is creating Sender: or From: headers. If
+either gecos_pattern or gecos_name are unset, the contents of the field are
+used unchanged, except that, if an ampersand is encountered, it is replaced by
+the user's login name with the first character forced to upper case, since this
+is a convention that is observed on many systems.
+
+When these options are set, gecos_pattern is treated as a regular expression
+that is to be applied to the field (again with & replaced by the login name),
+and if it matches, gecos_name is expanded and used as the user's name.
+
+Numeric variables such as $1, $2, etc. can be used in the expansion to pick up
+sub-fields that were matched by the pattern. In HP-UX, where the user's name
+terminates at the first comma, the following can be used:
+
+gecos_pattern = ([^,]*)
+gecos_name = $1
+
++---------------------------------------------------+
+|gecos_pattern|Use: main|Type: string|Default: unset|
++---------------------------------------------------+
+
+See gecos_name above.
+
++---------------------------------------------------------+
+|gnutls_compat_mode|Use: main|Type: boolean|Default: unset|
++---------------------------------------------------------+
+
+This option controls whether GnuTLS is used in compatibility mode in an Exim
+server. This reduces security slightly, but improves interworking with older
+implementations of TLS.
+
++---------------------------------------------------------------+
+|gnutls_allow_auto_pkcs11|Use: main|Type: boolean|Default: unset|
++---------------------------------------------------------------+
+
+This option will let GnuTLS (2.12.0 or later) autoload PKCS11 modules with the
+p11-kit configuration files in /etc/pkcs11/modules/.
+
+See https://www.gnutls.org/manual/gnutls.html#Smart-cards-and-HSMs for
+documentation.
+
++---------------------------------------------------------+
+|headers_charset|Use: main|Type: string|Default: see below|
++---------------------------------------------------------+
+
+This option sets a default character set for translating from encoded MIME
+"words" in header lines, when referenced by an $h_xxx expansion item. The
+default is the value of HEADERS_CHARSET in Local/Makefile. The ultimate default
+is ISO-8859-1. For more details see the description of header insertions in
+section 11.5.
+
++---------------------------------------------------------+
+|header_maxsize|Use: main|Type: integer|Default: see below|
++---------------------------------------------------------+
+
+This option controls the overall maximum size of a message's header section.
+The default is the value of HEADER_MAXSIZE in Local/Makefile; the default for
+that is 1M. Messages with larger header sections are rejected.
+
++------------------------------------------------------+
+|header_line_maxsize|Use: main|Type: integer|Default: 0|
++------------------------------------------------------+
+
+This option limits the length of any individual header line in a message, after
+all the continuations have been joined together. Messages with individual
+header lines that are longer than the limit are rejected. The default value of
+zero means "no limit".
+
++----------------------------------------------------------------+
+|helo_accept_junk_hosts|Use: main|Type: host list*|Default: unset|
++----------------------------------------------------------------+
+
+Exim checks the syntax of HELO and EHLO commands for incoming SMTP mail, and
+gives an error response for invalid data. Unfortunately, there are some SMTP
+clients that send syntactic junk. They can be accommodated by setting this
+option. Note that this is a syntax check only. See helo_verify_hosts if you
+want to do semantic checking. See also helo_allow_chars for a way of extending
+the permitted character set.
+
++------------------------------------------------------+
+|helo_allow_chars|Use: main|Type: string|Default: unset|
++------------------------------------------------------+
+
+This option can be set to a string of rogue characters that are permitted in
+all EHLO and HELO names in addition to the standard letters, digits, hyphens,
+and dots. If you really must allow underscores, you can set
+
+helo_allow_chars = _
+
+Note that the value is one string, not a list.
+
++-----------------------------------------------------------------+
+|helo_lookup_domains|Use: main|Type: domain list*|Default: "@:@[]"|
++-----------------------------------------------------------------+
+
+If the domain given by a client in a HELO or EHLO command matches this list, a
+reverse lookup is done in order to establish the host's true name. The default
+forces a lookup if the client host gives the server's name or any of its IP
+addresses (in brackets), something that broken clients have been seen to do.
+
++---------------------------------------------------------------+
+|helo_try_verify_hosts|Use: main|Type: host list*|Default: unset|
++---------------------------------------------------------------+
+
+By default, Exim just checks the syntax of HELO and EHLO commands (see
+helo_accept_junk_hosts and helo_allow_chars). However, some sites like to do
+more extensive checking of the data supplied by these commands. The ACL
+condition "verify = helo" is provided to make this possible. Formerly, it was
+necessary also to set this option (helo_try_verify_hosts) to force the check to
+occur. From release 4.53 onwards, this is no longer necessary. If the check has
+not been done before "verify = helo" is encountered, it is done at that time.
+Consequently, this option is obsolete. Its specification is retained here for
+backwards compatibility.
+
+When an EHLO or HELO command is received, if the calling host matches
+helo_try_verify_hosts, Exim checks that the host name given in the HELO or EHLO
+command either:
+
+ * is an IP literal matching the calling address of the host, or
+
+ * matches the host name that Exim obtains by doing a reverse lookup of the
+ calling host address, or
+
+ * when looked up in DNS yields the calling host address.
+
+However, the EHLO or HELO command is not rejected if any of the checks fail.
+Processing continues, but the result of the check is remembered, and can be
+detected later in an ACL by the "verify = helo" condition.
+
+If DNS was used for successful verification, the variable $helo_verify_dnssec
+records the DNSSEC status of the lookups.
+
++-----------------------------------------------------------+
+|helo_verify_hosts|Use: main|Type: host list*|Default: unset|
++-----------------------------------------------------------+
+
+Like helo_try_verify_hosts, this option is obsolete, and retained only for
+backwards compatibility. For hosts that match this option, Exim checks the host
+name given in the HELO or EHLO in the same way as for helo_try_verify_hosts. If
+the check fails, the HELO or EHLO command is rejected with a 550 error, and
+entries are written to the main and reject logs. If a MAIL command is received
+before EHLO or HELO, it is rejected with a 503 error.
+
++--------------------------------------------------------+
+|hold_domains|Use: main|Type: domain list*|Default: unset|
++--------------------------------------------------------+
+
+This option allows mail for particular domains to be held in the queue
+manually. The option is overridden if a message delivery is forced with the -M,
+-qf, -Rf or -Sf options, and also while testing or verifying addresses using
+-bt or -bv. Otherwise, if a domain matches an item in hold_domains, no routing
+or delivery for that address is done, and it is deferred every time the message
+is looked at.
+
+This option is intended as a temporary operational measure for delaying the
+delivery of mail while some problem is being sorted out, or some new
+configuration tested. If you just want to delay the processing of some domains
+until a queue run occurs, you should use queue_domains or queue_smtp_domains,
+not hold_domains.
+
+A setting of hold_domains does not override Exim's code for removing messages
+from the queue if they have been there longer than the longest retry time in
+any retry rule. If you want to hold messages for longer than the normal retry
+times, insert a dummy retry rule with a long retry time.
+
++-----------------------------------------------------+
+|host_lookup|Use: main|Type: host list*|Default: unset|
++-----------------------------------------------------+
+
+Exim does not look up the name of a calling host from its IP address unless it
+is required to compare against some host list, or the host matches
+helo_try_verify_hosts or helo_verify_hosts, or the host matches this option
+(which normally contains IP addresses rather than host names). The default
+configuration file contains
+
+host_lookup = *
+
+which causes a lookup to happen for all hosts. If the expense of these lookups
+is felt to be too great, the setting can be changed or removed.
+
+After a successful reverse lookup, Exim does a forward lookup on the name it
+has obtained, to verify that it yields the IP address that it started with. If
+this check fails, Exim behaves as if the name lookup failed.
+
+After any kind of failure, the host name (in $sender_host_name) remains unset,
+and $host_lookup_failed is set to the string "1". See also
+dns_again_means_nonexist, helo_lookup_domains, and "verify =
+reverse_host_lookup" in ACLs.
+
++---------------------------------------------------------------------+
+|host_lookup_order|Use: main|Type: string list|Default: "bydns:byaddr"|
++---------------------------------------------------------------------+
+
+This option specifies the order of different lookup methods when Exim is trying
+to find a host name from an IP address. The default is to do a DNS lookup
+first, and then to try a local lookup (using gethostbyaddr() or equivalent) if
+that fails. You can change the order of these lookups, or omit one entirely, if
+you want.
+
+Warning: The "byaddr" method does not always yield aliases when there are
+multiple PTR records in the DNS and the IP address is not listed in /etc/hosts.
+Different operating systems give different results in this case. That is why
+the default tries a DNS lookup first.
+
++----------------------------------------------------------------+
+|host_reject_connection|Use: main|Type: host list*|Default: unset|
++----------------------------------------------------------------+
+
+If this option is set, incoming SMTP calls from the hosts listed are rejected
+as soon as the connection is made. This option is obsolete, and retained only
+for backward compatibility, because nowadays the ACL specified by
+acl_smtp_connect can also reject incoming connections immediately.
+
+The ability to give an immediate rejection (either by this option or using an
+ACL) is provided for use in unusual cases. Many hosts will just try again,
+sometimes without much delay. Normally, it is better to use an ACL to reject
+incoming messages at a later stage, such as after RCPT commands. See chapter 44
+.
+
++----------------------------------------------------------------+
+|hosts_connection_nolog|Use: main|Type: host list*|Default: unset|
++----------------------------------------------------------------+
+
+This option defines a list of hosts for which connection logging does not
+happen, even though the smtp_connection log selector is set. For example, you
+might want not to log SMTP connections from local processes, or from 127.0.0.1,
+or from your local LAN. This option is consulted in the main loop of the
+daemon; you should therefore strive to restrict its value to a short inline
+list of IP addresses and networks. To disable logging SMTP connections from
+local processes, you must create a host list with an empty item. For example:
+
+hosts_connection_nolog = :
+
+If the smtp_connection log selector is not set, this option has no effect.
+
++-----------------------------------------------------+
+|hosts_proxy|Use: main|Type: host list*|Default: unset|
++-----------------------------------------------------+
+
+This option enables use of Proxy Protocol proxies for incoming connections. For
+details see section 59.1.
+
++----------------------------------------------------------------+
+|hosts_treat_as_local|Use: main|Type: domain list*|Default: unset|
++----------------------------------------------------------------+
+
+If this option is set, any host names that match the domain list are treated as
+if they were the local host when Exim is scanning host lists obtained from MX
+records or other sources. Note that the value of this option is a domain list,
+not a host list, because it is always used to check host names, not IP
+addresses.
+
+This option also applies when Exim is matching the special items "@mx_any",
+"@mx_primary", and "@mx_secondary" in a domain list (see section 10.9), and
+when checking the hosts option in the smtp transport for the local host (see
+the allow_localhost option in that transport). See also local_interfaces,
+extra_local_interfaces, and chapter 13, which contains a discussion about local
+network interfaces and recognizing the local host.
+
++--------------------------------------------------------+
+|ibase_servers|Use: main|Type: string list|Default: unset|
++--------------------------------------------------------+
+
+This option provides a list of InterBase servers and associated connection
+data, to be used in conjunction with ibase lookups (see section 9.22). The
+option is available only if Exim has been built with InterBase support.
+
++------------------------------------------------------------+
+|ignore_bounce_errors_after|Use: main|Type: time|Default: 10w|
++------------------------------------------------------------+
+
+This option affects the processing of bounce messages that cannot be delivered,
+that is, those that suffer a permanent delivery failure. (Bounce messages that
+suffer temporary delivery failures are of course retried in the usual way.)
+
+After a permanent delivery failure, bounce messages are frozen, because there
+is no sender to whom they can be returned. When a frozen bounce message has
+been in the queue for more than the given time, it is unfrozen at the next
+queue run, and a further delivery is attempted. If delivery fails again, the
+bounce message is discarded. This makes it possible to keep failed bounce
+messages around for a shorter time than the normal maximum retry time for
+frozen messages. For example,
+
+ignore_bounce_errors_after = 12h
+
+retries failed bounce message deliveries after 12 hours, discarding any further
+failures. If the value of this option is set to a zero time period, bounce
+failures are discarded immediately. Setting a very long time (as in the default
+value) has the effect of disabling this option. For ways of automatically
+dealing with other kinds of frozen message, see auto_thaw and
+timeout_frozen_after.
+
++---------------------------------------------------------------+
+|ignore_fromline_hosts|Use: main|Type: host list*|Default: unset|
++---------------------------------------------------------------+
+
+Some broken SMTP clients insist on sending a UUCP-like "From " line before the
+headers of a message. By default this is treated as the start of the message's
+body, which means that any following headers are not recognized as such. Exim
+can be made to ignore it by setting ignore_fromline_hosts to match those hosts
+that insist on sending it. If the sender is actually a local process rather
+than a remote host, and is using -bs to inject the messages,
+ignore_fromline_local must be set to achieve this effect.
+
++------------------------------------------------------------+
+|ignore_fromline_local|Use: main|Type: boolean|Default: false|
++------------------------------------------------------------+
+
+See ignore_fromline_hosts above.
+
++-----------------------------------------------------------+
+|keep_environment|Use: main|Type: string list|Default: unset|
++-----------------------------------------------------------+
+
+This option contains a string list of environment variables to keep. You have
+to trust these variables or you have to be sure that these variables do not
+impose any security risk. Keep in mind that during the startup phase Exim is
+running with an effective UID 0 in most installations. As the default value is
+an empty list, the default environment for using libraries, running embedded
+Perl code, or running external binaries is empty, and does not not even contain
+PATH or HOME.
+
+Actually the list is interpreted as a list of patterns (10.1), except that it
+is not expanded first.
+
+WARNING: Macro substitution is still done first, so having a macro FOO and
+having FOO_HOME in your keep_environment option may have unexpected results.
+You may work around this using a regular expression that does not match the
+macro name: ^[F]OO_HOME$.
+
+Current versions of Exim issue a warning during startup if you do not mention
+keep_environment in your runtime configuration file and if your current
+environment is not empty. Future versions may not issue that warning anymore.
+
+See the add_environment main config option for a way to set environment
+variables to a fixed value. The environment for pipe transports is handled
+separately, see section 29.4 for details.
+
++-----------------------------------------------+
+|keep_malformed|Use: main|Type: time|Default: 4d|
++-----------------------------------------------+
+
+This option specifies the length of time to keep messages whose spool files
+have been corrupted in some way. This should, of course, never happen. At the
+next attempt to deliver such a message, it gets removed. The incident is
+logged.
+
++------------------------------------------------------+
+|ldap_ca_cert_dir|Use: main|Type: string|Default: unset|
++------------------------------------------------------+
+
+This option indicates which directory contains CA certificates for verifying a
+TLS certificate presented by an LDAP server. While Exim does not provide a
+default value, your SSL library may. Analogous to tls_verify_certificates but
+as a client-side option for LDAP and constrained to be a directory.
+
++-------------------------------------------------------+
+|ldap_ca_cert_file|Use: main|Type: string|Default: unset|
++-------------------------------------------------------+
+
+This option indicates which file contains CA certificates for verifying a TLS
+certificate presented by an LDAP server. While Exim does not provide a default
+value, your SSL library may. Analogous to tls_verify_certificates but as a
+client-side option for LDAP and constrained to be a file.
+
++----------------------------------------------------+
+|ldap_cert_file|Use: main|Type: string|Default: unset|
++----------------------------------------------------+
+
+This option indicates which file contains an TLS client certificate which Exim
+should present to the LDAP server during TLS negotiation. Should be used
+together with ldap_cert_key.
+
++---------------------------------------------------+
+|ldap_cert_key|Use: main|Type: string|Default: unset|
++---------------------------------------------------+
+
+This option indicates which file contains the secret/private key to use to
+prove identity to the LDAP server during TLS negotiation. Should be used
+together with ldap_cert_file, which contains the identity to be proven.
+
++-------------------------------------------------------+
+|ldap_cipher_suite|Use: main|Type: string|Default: unset|
++-------------------------------------------------------+
+
+This controls the TLS cipher-suite negotiation during TLS negotiation with the
+LDAP server. See 43.4 for more details of the format of cipher-suite options
+with OpenSSL (as used by LDAP client libraries).
+
++---------------------------------------------------------------+
+|ldap_default_servers|Use: main|Type: string list|Default: unset|
++---------------------------------------------------------------+
+
+This option provides a list of LDAP servers which are tried in turn when an
+LDAP query does not contain a server. See section 9.15 for details of LDAP
+queries. This option is available only when Exim has been built with LDAP
+support.
+
++--------------------------------------------------------+
+|ldap_require_cert|Use: main|Type: string|Default: unset.|
++--------------------------------------------------------+
+
+This should be one of the values "hard", "demand", "allow", "try" or "never". A
+value other than one of these is interpreted as "never". See the entry
+"TLS_REQCERT" in your system man page for ldap.conf(5). Although Exim does not
+set a default, the LDAP library probably defaults to hard/demand.
+
++-----------------------------------------------------+
+|ldap_start_tls|Use: main|Type: boolean|Default: false|
++-----------------------------------------------------+
+
+If set, Exim will attempt to negotiate TLS with the LDAP server when connecting
+on a regular LDAP port. This is the LDAP equivalent of SMTP's "STARTTLS". This
+is distinct from using "ldaps", which is the LDAP form of SSL-on-connect. In
+the event of failure to negotiate TLS, the action taken is controlled by
+ldap_require_cert. This option is ignored for "ldapi" connections.
+
++---------------------------------------------------+
+|ldap_version|Use: main|Type: integer|Default: unset|
++---------------------------------------------------+
+
+This option can be used to force Exim to set a specific protocol version for
+LDAP. If it option is unset, it is shown by the -bP command line option as -1.
+When this is the case, the default is 3 if LDAP_VERSION3 is defined in the LDAP
+headers; otherwise it is 2. This option is available only when Exim has been
+built with LDAP support.
+
++------------------------------------------------------+
+|local_from_check|Use: main|Type: boolean|Default: true|
++------------------------------------------------------+
+
+When a message is submitted locally (that is, not over a TCP/IP connection) by
+an untrusted user, Exim removes any existing Sender: header line, and checks
+that the From: header line matches the login of the calling user and the domain
+specified by qualify_domain.
+
+Note: An unqualified address (no domain) in the From: header in a locally
+submitted message is automatically qualified by Exim, unless the -bnq command
+line option is used.
+
+You can use local_from_prefix and local_from_suffix to permit affixes on the
+local part. If the From: header line does not match, Exim adds a Sender: header
+with an address constructed from the calling user's login and the default
+qualify domain.
+
+If local_from_check is set false, the From: header check is disabled, and no
+Sender: header is ever added. If, in addition, you want to retain Sender:
+header lines supplied by untrusted users, you must also set local_sender_retain
+to be true.
+
+These options affect only the header lines in the message. The envelope sender
+is still forced to be the login id at the qualify domain unless
+untrusted_set_sender permits the user to supply an envelope sender.
+
+For messages received over TCP/IP, an ACL can specify "submission mode" to
+request similar header line checking. See section 48.16, which has more details
+about Sender: processing.
+
++-------------------------------------------------------+
+|local_from_prefix|Use: main|Type: string|Default: unset|
++-------------------------------------------------------+
+
+When Exim checks the From: header line of locally submitted messages for
+matching the login id (see local_from_check above), it can be configured to
+ignore certain prefixes and suffixes in the local part of the address. This is
+done by setting local_from_prefix and/or local_from_suffix to appropriate
+lists, in the same form as the local_part_prefix and local_part_suffix router
+options (see chapter 15). For example, if
+
+local_from_prefix = *-
+
+is set, a From: line containing
+
+From: anything-user@your.domain.example
+
+will not cause a Sender: header to be added if user@your.domain.example matches
+the actual sender address that is constructed from the login name and qualify
+domain.
+
++-------------------------------------------------------+
+|local_from_suffix|Use: main|Type: string|Default: unset|
++-------------------------------------------------------+
+
+See local_from_prefix above.
+
++---------------------------------------------------------------+
+|local_interfaces|Use: main|Type: string list|Default: see below|
++---------------------------------------------------------------+
+
+This option controls which network interfaces are used by the daemon for
+listening; they are also used to identify the local host when routing. Chapter
+13 contains a full description of this option and the related options
+daemon_smtp_ports, extra_local_interfaces, hosts_treat_as_local, and
+tls_on_connect_ports. The default value for local_interfaces is
+
+local_interfaces = 0.0.0.0
+
+when Exim is built without IPv6 support; otherwise it is
+
+local_interfaces = <; ::0 ; 0.0.0.0
+
++---------------------------------------------------+
+|local_scan_timeout|Use: main|Type: time|Default: 5m|
++---------------------------------------------------+
+
+This timeout applies to the local_scan() function (see chapter 46). Zero means
+"no timeout". If the timeout is exceeded, the incoming message is rejected with
+a temporary error if it is an SMTP message. For a non-SMTP message, the message
+is dropped and Exim ends with a non-zero code. The incident is logged on the
+main and reject logs.
+
++----------------------------------------------------------+
+|local_sender_retain|Use: main|Type: boolean|Default: false|
++----------------------------------------------------------+
+
+When a message is submitted locally (that is, not over a TCP/IP connection) by
+an untrusted user, Exim removes any existing Sender: header line. If you do not
+want this to happen, you must set local_sender_retain, and you must also set
+local_from_check to be false (Exim will complain if you do not). See also the
+ACL modifier "control = suppress_local_fixups". Section 48.16 has more details
+about Sender: processing.
+
++-------------------------------------------------------+
+|localhost_number|Use: main|Type: string*|Default: unset|
++-------------------------------------------------------+
+
+Exim's message ids are normally unique only within the local host. If
+uniqueness among a set of hosts is required, each host must set a different
+value for the localhost_number option. The string is expanded immediately after
+reading the configuration file (so that a number can be computed from the host
+name, for example) and the result of the expansion must be a number in the
+range 0-16 (or 0-10 on operating systems with case-insensitive file systems).
+This is available in subsequent string expansions via the variable
+$localhost_number. When localhost_number is set, the final two characters of
+the message id, instead of just being a fractional part of the time, are
+computed from the time and the local host number as described in section 3.4.
+
++-----------------------------------------------------------------------+
+|log_file_path|Use: main|Type: string list*|Default: set at compile time|
++-----------------------------------------------------------------------+
+
+This option sets the path which is used to determine the names of Exim's log
+files, or indicates that logging is to be to syslog, or both. It is expanded
+when Exim is entered, so it can, for example, contain a reference to the host
+name. If no specific path is set for the log files at compile or runtime, or if
+the option is unset at runtime (i.e. "log_file_path = ") they are written in a
+sub-directory called log in Exim's spool directory. A path must start with a
+slash. To send to syslog, use the word "syslog". Chapter 53 contains further
+details about Exim's logging, and section 53.1 describes how the contents of
+log_file_path are used. If this string is fixed at your installation (contains
+no expansion variables) it is recommended that you do not set this option in
+the configuration file, but instead supply the path using LOG_FILE_PATH in
+Local/Makefile so that it is available to Exim for logging errors detected
+early on - in particular, failure to read the configuration file.
+
++--------------------------------------------------+
+|log_selector|Use: main|Type: string|Default: unset|
++--------------------------------------------------+
+
+This option can be used to reduce or increase the number of things that Exim
+writes to its log files. Its argument is made up of names preceded by plus or
+minus characters. For example:
+
+log_selector = +arguments -retry_defer
+
+A list of possible names and what they control is given in the chapter on
+logging, in section 53.15.
+
++---------------------------------------------------+
+|log_timezone|Use: main|Type: boolean|Default: false|
++---------------------------------------------------+
+
+By default, the timestamps on log lines are in local time without the timezone.
+This means that if your timezone changes twice a year, the timestamps in log
+lines are ambiguous for an hour when the clocks go back. One way of avoiding
+this problem is to set the timezone to UTC. An alternative is to set
+log_timezone true. This turns on the addition of the timezone offset to
+timestamps in log lines. Turning on this option can add quite a lot to the size
+of log files because each line is extended by 6 characters. Note that the
+$tod_log variable contains the log timestamp without the zone, but there is
+another variable called $tod_zone that contains just the timezone offset.
+
++---------------------------------------------------+
+|lookup_open_max|Use: main|Type: integer|Default: 25|
++---------------------------------------------------+
+
+This option limits the number of simultaneously open files for single-key
+lookups that use regular files (that is, lsearch, dbm, and cdb). Exim normally
+keeps these files open during routing, because often the same file is required
+several times. If the limit is reached, Exim closes the least recently used
+file. Note that if you are using the ndbm library, it actually opens two files
+for each logical DBM database, though it still counts as one for the purposes
+of lookup_open_max. If you are getting "too many open files" errors with NDBM,
+you need to reduce the value of lookup_open_max.
+
++------------------------------------------------------+
+|max_username_length|Use: main|Type: integer|Default: 0|
++------------------------------------------------------+
+
+Some operating systems are broken in that they truncate long arguments to
+getpwnam() to eight characters, instead of returning "no such user". If this
+option is set greater than zero, any attempt to call getpwnam() with an
+argument that is longer behaves as if getpwnam() failed.
+
++---------------------------------------------------------+
+|message_body_newlines|Use: main|Type: bool|Default: false|
++---------------------------------------------------------+
+
+By default, newlines in the message body are replaced by spaces when setting
+the $message_body and $message_body_end expansion variables. If this option is
+set true, this no longer happens.
+
++---------------------------------------------------------+
+|message_body_visible|Use: main|Type: integer|Default: 500|
++---------------------------------------------------------+
+
+This option specifies how much of a message's body is to be included in the
+$message_body and $message_body_end expansion variables.
+
++---------------------------------------------------------------+
+|message_id_header_domain|Use: main|Type: string*|Default: unset|
++---------------------------------------------------------------+
+
+If this option is set, the string is expanded and used as the right hand side
+(domain) of the Message-ID: header that Exim creates if a locally-originated
+incoming message does not have one. "Locally-originated" means "not received
+over TCP/IP." Otherwise, the primary host name is used. Only letters, digits,
+dot and hyphen are accepted; any other characters are replaced by hyphens. If
+the expansion is forced to fail, or if the result is an empty string, the
+option is ignored.
+
++-------------------------------------------------------------+
+|message_id_header_text|Use: main|Type: string*|Default: unset|
++-------------------------------------------------------------+
+
+If this variable is set, the string is expanded and used to augment the text of
+the Message-id: header that Exim creates if a locally-originated incoming
+message does not have one. The text of this header is required by RFC 2822 to
+take the form of an address. By default, Exim uses its internal message id as
+the local part, and the primary host name as the domain. If this option is set,
+it is expanded, and provided the expansion is not forced to fail, and does not
+yield an empty string, the result is inserted into the header immediately
+before the @, separated from the internal message id by a dot. Any characters
+that are illegal in an address are automatically converted into hyphens. This
+means that variables such as $tod_log can be used, because the spaces and
+colons will become hyphens.
+
++--------------------------------------------------+
+|message_logs|Use: main|Type: boolean|Default: true|
++--------------------------------------------------+
+
+If this option is turned off, per-message log files are not created in the
+msglog spool sub-directory. This reduces the amount of disk I/O required by
+Exim, by reducing the number of files involved in handling a message from a
+minimum of four (header spool file, body spool file, delivery journal, and
+per-message log) to three. The other major I/O activity is Exim's main log,
+which is not affected by this option.
+
++-------------------------------------------------------+
+|message_size_limit|Use: main|Type: string*|Default: 50M|
++-------------------------------------------------------+
+
+This option limits the maximum size of message that Exim will process. The
+value is expanded for each incoming connection so, for example, it can be made
+to depend on the IP address of the remote host for messages arriving via TCP/
+IP. After expansion, the value must be a sequence of decimal digits, optionally
+followed by K or M.
+
+If nonzero the value will be advertised as a parameter to the ESMTP SIZE
+service extension keyword.
+
+Note: This limit cannot be made to depend on a message's sender or any other
+properties of an individual message, because it has to be advertised in the
+server's response to EHLO. String expansion failure causes a temporary error. A
+value of zero means no limit, but its use is not recommended. See also
+bounce_return_size_limit.
+
+Incoming SMTP messages are failed with a 552 error if the limit is exceeded;
+locally-generated messages either get a stderr message or a delivery failure
+message to the sender, depending on the -oe setting. Rejection of an oversized
+message is logged in both the main and the reject logs. See also the generic
+transport option message_size_limit, which limits the size of message that an
+individual transport can process.
+
+If you use a virus-scanner and set this option to to a value larger than the
+maximum size that your virus-scanner is configured to support, you may get
+failures triggered by large mails. The right size to configure for the
+virus-scanner depends upon what data is passed and the options in use but it's
+probably safest to just set it to a little larger than this value. E.g., with a
+default Exim message size of 50M and a default ClamAV StreamMaxLength of 10M,
+some problems may result.
+
+A value of 0 will disable size limit checking; Exim will still advertise the
+SIZE extension in an EHLO response, but without a limit, so as to permit SMTP
+clients to still indicate the message size along with the MAIL verb.
+
++-----------------------------------------------------------+
+|move_frozen_messages|Use: main|Type: boolean|Default: false|
++-----------------------------------------------------------+
+
+This option, which is available only if Exim has been built with the setting
+
+SUPPORT_MOVE_FROZEN_MESSAGES=yes
+
+in Local/Makefile, causes frozen messages and their message logs to be moved
+from the input and msglog directories on the spool to Finput and Fmsglog,
+respectively. There is currently no support in Exim or the standard utilities
+for handling such moved messages, and they do not show up in lists generated by
+-bp or by the Exim monitor.
+
++--------------------------------------------------+
+|mua_wrapper|Use: main|Type: boolean|Default: false|
++--------------------------------------------------+
+
+Setting this option true causes Exim to run in a very restrictive mode in which
+it passes messages synchronously to a smart host. Chapter 52 contains a full
+description of this facility.
+
++--------------------------------------------------------+
+|mysql_servers|Use: main|Type: string list|Default: unset|
++--------------------------------------------------------+
+
+This option provides a list of MySQL servers and associated connection data, to
+be used in conjunction with mysql lookups (see section 9.22). The option is
+available only if Exim has been built with MySQL support.
+
++-------------------------------------------------------+
+|never_users|Use: main|Type: string list*|Default: unset|
++-------------------------------------------------------+
+
+This option is expanded just once, at the start of Exim's processing. Local
+message deliveries are normally run in processes that are setuid to the
+recipient, and remote deliveries are normally run under Exim's own uid and gid.
+It is usually desirable to prevent any deliveries from running as root, as a
+safety precaution.
+
+When Exim is built, an option called FIXED_NEVER_USERS can be set to a list of
+users that must not be used for local deliveries. This list is fixed in the
+binary and cannot be overridden by the configuration file. By default, it
+contains just the single user name "root". The never_users runtime option can
+be used to add more users to the fixed list.
+
+If a message is to be delivered as one of the users on the fixed list or the
+never_users list, an error occurs, and delivery is deferred. A common example
+is
+
+never_users = root:daemon:bin
+
+Including root is redundant if it is also on the fixed list, but it does no
+harm. This option overrides the pipe_as_creator option of the pipe transport
+driver.
+
++-----------------------------------------------------------------------------+
+|notifier_socket| Use: | Type: | Default: $spool_directory/|
+| | main | string | exim_daemon_notify|
++-----------------------------------------------------------------------------+
+
+This option gives the name for a unix-domain socket on which the daemon listens
+for work and information-requests. Only installations running multiple daemons
+sharing a spool directory should need to modify the default.
+
+The option is expanded before use. If the platform supports Linux-style
+abstract socket names, the result is used with a nul byte prefixed. Otherwise,
+it should be a full path name and use a directory accessible to Exim.
+
+If the Exim command line uses a -oX option and does not use -oP then a notifier
+socket is not created.
+
++-----------------------------------------------------------------------------+
+| |Use: | Type: |Default: +no_sslv2 +no_sslv3 +single_dh_use|
+|openssl_options| main | string | +no_ticket +no_renegotiation|
+| | | list | |
++-----------------------------------------------------------------------------+
+
+This option allows an administrator to adjust the SSL options applied by
+OpenSSL to connections. It is given as a space-separated list of items, each
+one to be +added or -subtracted from the current value.
+
+This option is only available if Exim is built against OpenSSL. The values
+available for this option vary according to the age of your OpenSSL install.
+The "all" value controls a subset of flags which are available, typically the
+bug workaround options. The SSL_CTX_set_options man page will list the values
+known on your system and Exim should support all the "bug workaround" options
+and many of the "modifying" options. The Exim names lose the leading "SSL_OP_"
+and are lower-cased.
+
+Note that adjusting the options can have severe impact upon the security of SSL
+as used by Exim. It is possible to disable safety checks and shoot yourself in
+the foot in various unpleasant ways. This option should not be adjusted
+lightly. An unrecognised item will be detected at startup, by invoking Exim
+with the -bV flag.
+
+The option affects Exim operating both as a server and as a client.
+
+Historical note: prior to release 4.80, Exim defaulted this value to
+"+dont_insert_empty_fragments", which may still be needed for compatibility
+with some clients, but which lowers security by increasing exposure to some now
+infamous attacks.
+
+Examples:
+
+# Make both old MS and old Eudora happy:
+openssl_options = -all +microsoft_big_sslv3_buffer \
+ +dont_insert_empty_fragments
+
+# Disable older protocol versions:
+openssl_options = +no_sslv2 +no_sslv3
+
+Possible options may include:
+
+ * "all"
+
+ * "allow_unsafe_legacy_renegotiation"
+
+ * "cipher_server_preference"
+
+ * "dont_insert_empty_fragments"
+
+ * "ephemeral_rsa"
+
+ * "legacy_server_connect"
+
+ * "microsoft_big_sslv3_buffer"
+
+ * "microsoft_sess_id_bug"
+
+ * "msie_sslv2_rsa_padding"
+
+ * "netscape_challenge_bug"
+
+ * "netscape_reuse_cipher_change_bug"
+
+ * "no_compression"
+
+ * "no_session_resumption_on_renegotiation"
+
+ * "no_sslv2"
+
+ * "no_sslv3"
+
+ * "no_ticket"
+
+ * "no_tlsv1"
+
+ * "no_tlsv1_1"
+
+ * "no_tlsv1_2"
+
+ * "safari_ecdhe_ecdsa_bug"
+
+ * "single_dh_use"
+
+ * "single_ecdh_use"
+
+ * "ssleay_080_client_dh_bug"
+
+ * "sslref2_reuse_cert_type_bug"
+
+ * "tls_block_padding_bug"
+
+ * "tls_d5_bug"
+
+ * "tls_rollback_bug"
+
+As an aside, the "safari_ecdhe_ecdsa_bug" item is a misnomer and affects all
+clients connecting using the MacOS SecureTransport TLS facility prior to MacOS
+10.8.4, including email clients. If you see old MacOS clients failing to
+negotiate TLS then this option value might help, provided that your OpenSSL
+release is new enough to contain this work-around. This may be a situation
+where you have to upgrade OpenSSL to get buggy clients working.
+
++---------------------------------------------------------+
+|oracle_servers|Use: main|Type: string list|Default: unset|
++---------------------------------------------------------+
+
+This option provides a list of Oracle servers and associated connection data,
+to be used in conjunction with oracle lookups (see section 9.22). The option is
+available only if Exim has been built with Oracle support.
+
++----------------------------------------------------------------+
+|percent_hack_domains|Use: main|Type: domain list*|Default: unset|
++----------------------------------------------------------------+
+
+The "percent hack" is the convention whereby a local part containing a percent
+sign is re-interpreted as a new email address, with the percent replaced by @.
+This is sometimes called "source routing", though that term is also applied to
+RFC 2822 addresses that begin with an @ character. If this option is set, Exim
+implements the percent facility for those domains listed, but no others. This
+happens before an incoming SMTP address is tested against an ACL.
+
+Warning: The "percent hack" has often been abused by people who are trying to
+get round relaying restrictions. For this reason, it is best avoided if at all
+possible. Unfortunately, a number of less security-conscious MTAs implement it
+unconditionally. If you are running Exim on a gateway host, and routing mail
+through to internal MTAs without processing the local parts, it is a good idea
+to reject recipient addresses with percent characters in their local parts.
+Exim's default configuration does this.
+
++----------------------------------------------------+
+|perl_at_start|Use: main|Type: boolean|Default: false|
++----------------------------------------------------+
+
+This option is available only when Exim is built with an embedded Perl
+interpreter. See chapter 12 for details of its use.
+
++--------------------------------------------------+
+|perl_startup|Use: main|Type: string|Default: unset|
++--------------------------------------------------+
+
+This option is available only when Exim is built with an embedded Perl
+interpreter. See chapter 12 for details of its use.
+
++-----------------------------------------------------+
+|perl_taintmode|Use: main|Type: boolean|Default: false|
++-----------------------------------------------------+
+
+This option enables the taint mode of the embedded Perl interpreter.
+
++--------------------------------------------------------+
+|pgsql_servers|Use: main|Type: string list|Default: unset|
++--------------------------------------------------------+
+
+This option provides a list of PostgreSQL servers and associated connection
+data, to be used in conjunction with pgsql lookups (see section 9.22). The
+option is available only if Exim has been built with PostgreSQL support.
+
++------------------------------------------------------------------+
+|pid_file_path|Use: main|Type: string*|Default: set at compile time|
++------------------------------------------------------------------+
+
+This option sets the name of the file to which the Exim daemon writes its
+process id. The string is expanded, so it can contain, for example, references
+to the host name:
+
+pid_file_path = /var/log/$primary_hostname/exim.pid
+
+If no path is set, the pid is written to the file exim-daemon.pid in Exim's
+spool directory. The value set by the option can be overridden by the -oP
+command line option. A pid file is not written if a "non-standard" daemon is
+run by means of the -oX option, unless a path is explicitly supplied by -oP.
+
++----------------------------------------------------------------+
+|pipelining_advertise_hosts|Use: main|Type: host list*|Default: *|
++----------------------------------------------------------------+
+
+This option can be used to suppress the advertisement of the SMTP PIPELINING
+extension to specific hosts. See also the no_pipelining control in section
+44.22. When PIPELINING is not advertised and smtp_enforce_sync is true, an Exim
+server enforces strict synchronization for each SMTP command and response. When
+PIPELINING is advertised, Exim assumes that clients will use it; "out of order"
+commands that are "expected" do not count as protocol errors (see
+smtp_max_synprot_errors).
+
++------------------------------------------------------------------------+
+|pipelining_connect_advertise_hosts|Use: main|Type: host list*|Default: *|
++------------------------------------------------------------------------+
+
+If Exim is built with the SUPPORT_PIPE_CONNECT build option this option
+controls which hosts the facility is advertised to and from which pipeline
+early-connection (before MAIL) SMTP commands are acceptable. When used, the
+pipelining saves on roundtrip times.
+
+See also the hosts_pipe_connect smtp transport option.
+
+The SMTP service extension keyword advertised is "PIPE_CONNECT".
+
++--------------------------------------------------+
+|prdr_enable|Use: main|Type: boolean|Default: false|
++--------------------------------------------------+
+
+This option can be used to enable the Per-Recipient Data Response extension to
+SMTP, defined by Eric Hall. If the option is set, PRDR is advertised by Exim
+when operating as a server. If the client requests PRDR, and more than one
+recipient, for a message an additional ACL is called for each recipient after
+the message content is received. See section 44.9.
+
++------------------------------------------------------------+
+|preserve_message_logs|Use: main|Type: boolean|Default: false|
++------------------------------------------------------------+
+
+If this option is set, message log files are not deleted when messages are
+completed. Instead, they are moved to a sub-directory of the spool directory
+called msglog.OLD, where they remain available for statistical or debugging
+purposes. This is a dangerous option to set on systems with any appreciable
+volume of mail. Use with care!
+
++----------------------------------------------------------+
+|primary_hostname|Use: main|Type: string|Default: see below|
++----------------------------------------------------------+
+
+This specifies the name of the current host. It is used in the default EHLO or
+HELO command for outgoing SMTP messages (changeable via the helo_data option in
+the smtp transport), and as the default for qualify_domain. The value is also
+used by default in some SMTP response messages from an Exim server. This can be
+changed dynamically by setting smtp_active_hostname.
+
+If primary_hostname is not set, Exim calls uname() to find the host name. If
+this fails, Exim panics and dies. If the name returned by uname() contains only
+one component, Exim passes it to gethostbyname() (or getipnodebyname() when
+available) in order to obtain the fully qualified version. The variable
+$primary_hostname contains the host name, whether set explicitly by this
+option, or defaulted.
+
++--------------------------------------------------------+
+|print_topbitchars|Use: main|Type: boolean|Default: false|
++--------------------------------------------------------+
+
+By default, Exim considers only those characters whose codes lie in the range
+32-126 to be printing characters. In a number of circumstances (for example,
+when writing log entries) non-printing characters are converted into escape
+sequences, primarily to avoid messing up the layout. If print_topbitchars is
+set, code values of 128 and above are also considered to be printing
+characters.
+
+This option also affects the header syntax checks performed by the autoreply
+transport, and whether Exim uses RFC 2047 encoding of the user's full name when
+constructing From: and Sender: addresses (as described in section 48.18).
+Setting this option can cause Exim to generate eight bit message headers that
+do not conform to the standards.
+
++------------------------------------------------------+
+|process_log_path|Use: main|Type: string|Default: unset|
++------------------------------------------------------+
+
+This option sets the name of the file to which an Exim process writes its
+"process log" when sent a USR1 signal. This is used by the exiwhat utility
+script. If this option is unset, the file called exim-process.info in Exim's
+spool directory is used. The ability to specify the name explicitly can be
+useful in environments where two different Exims are running, using different
+spool directories.
+
++---------------------------------------------------------+
+|prod_requires_admin|Use: main|Type: boolean|Default: true|
++---------------------------------------------------------+
+
+The -M, -R, and -q command-line options require the caller to be an admin user
+unless prod_requires_admin is set false. See also queue_list_requires_admin and
+commandline_checks_require_admin.
+
++--------------------------------------------------------+
+|qualify_domain|Use: main|Type: string|Default: see below|
++--------------------------------------------------------+
+
+This option specifies the domain name that is added to any envelope sender
+addresses that do not have a domain qualification. It also applies to recipient
+addresses if qualify_recipient is not set. Unqualified addresses are accepted
+by default only for locally-generated messages. Qualification is also applied
+to addresses in header lines such as From: and To: for locally-generated
+messages, unless the -bnq command line option is used.
+
+Messages from external sources must always contain fully qualified addresses,
+unless the sending host matches sender_unqualified_hosts or
+recipient_unqualified_hosts (as appropriate), in which case incoming addresses
+are qualified with qualify_domain or qualify_recipient as necessary.
+Internally, Exim always works with fully qualified envelope addresses. If
+qualify_domain is not set, it defaults to the primary_hostname value.
+
++-----------------------------------------------------------+
+|qualify_recipient|Use: main|Type: string|Default: see below|
++-----------------------------------------------------------+
+
+This option allows you to specify a different domain for qualifying recipient
+addresses to the one that is used for senders. See qualify_domain above.
+
++---------------------------------------------------------+
+|queue_domains|Use: main|Type: domain list*|Default: unset|
++---------------------------------------------------------+
+
+This option lists domains for which immediate delivery is not required. A
+delivery process is started whenever a message is received, but only those
+domains that do not match are processed. All other deliveries wait until the
+next queue run. See also hold_domains and queue_smtp_domains.
+
++---------------------------------------------------------------+
+|queue_list_requires_admin|Use: main|Type: boolean|Default: true|
++---------------------------------------------------------------+
+
+The -bp command-line option, which lists the messages that are on the queue,
+requires the caller to be an admin user unless queue_list_requires_admin is set
+false. See also prod_requires_admin and commandline_checks_require_admin.
+
++-------------------------------------------------+
+|queue_only|Use: main|Type: boolean|Default: false|
++-------------------------------------------------+
+
+If queue_only is set, a delivery process is not automatically started whenever
+a message is received. Instead, the message waits in the queue for the next
+queue run. Even if queue_only is false, incoming messages may not get delivered
+immediately when certain conditions (such as heavy load) occur.
+
+The -odq command line has the same effect as queue_only. The -odb and -odi
+command line options override queue_only unless queue_only_override is set
+false. See also queue_only_file, queue_only_load, and smtp_accept_queue.
+
++-----------------------------------------------------+
+|queue_only_file|Use: main|Type: string|Default: unset|
++-----------------------------------------------------+
+
+This option can be set to a colon-separated list of absolute path names, each
+one optionally preceded by "smtp". When Exim is receiving a message, it tests
+for the existence of each listed path using a call to stat(). For each path
+that exists, the corresponding queueing option is set. For paths with no
+prefix, queue_only is set; for paths prefixed by "smtp", queue_smtp_domains is
+set to match all domains. So, for example,
+
+queue_only_file = smtp/some/file
+
+causes Exim to behave as if queue_smtp_domains were set to "*" whenever /some/
+file exists.
+
++----------------------------------------------------------+
+|queue_only_load|Use: main|Type: fixed-point|Default: unset|
++----------------------------------------------------------+
+
+If the system load average is higher than this value, incoming messages from
+all sources are queued, and no automatic deliveries are started. If this
+happens during local or remote SMTP input, all subsequent messages received on
+the same SMTP connection are queued by default, whatever happens to the load in
+the meantime, but this can be changed by setting queue_only_load_latch false.
+
+Deliveries will subsequently be performed by queue runner processes. This
+option has no effect on ancient operating systems on which Exim cannot
+determine the load average. See also deliver_queue_load_max and
+smtp_load_reserve.
+
++-----------------------------------------------------------+
+|queue_only_load_latch|Use: main|Type: boolean|Default: true|
++-----------------------------------------------------------+
+
+When this option is true (the default), once one message has been queued
+because the load average is higher than the value set by queue_only_load, all
+subsequent messages received on the same SMTP connection are also queued. This
+is a deliberate choice; even though the load average may fall below the
+threshold, it doesn't seem right to deliver later messages on the same
+connection when not delivering earlier ones. However, there are special
+circumstances such as very long-lived connections from scanning appliances
+where this is not the best strategy. In such cases, queue_only_load_latch
+should be set false. This causes the value of the load average to be
+re-evaluated for each message.
+
++---------------------------------------------------------+
+|queue_only_override|Use: main|Type: boolean|Default: true|
++---------------------------------------------------------+
+
+When this option is true, the -odx command line options override the setting of
+queue_only or queue_only_file in the configuration file. If queue_only_override
+is set false, the -odx options cannot be used to override; they are accepted,
+but ignored.
+
++---------------------------------------------------------+
+|queue_run_in_order|Use: main|Type: boolean|Default: false|
++---------------------------------------------------------+
+
+If this option is set, queue runs happen in order of message arrival instead of
+in an arbitrary order. For this to happen, a complete list of the entire queue
+must be set up before the deliveries start. When the queue is all held in a
+single directory (the default), a single list is created for both the ordered
+and the non-ordered cases. However, if split_spool_directory is set, a single
+list is not created when queue_run_in_order is false. In this case, the
+sub-directories are processed one at a time (in a random order), and this
+avoids setting up one huge list for the whole queue. Thus, setting
+queue_run_in_order with split_spool_directory may degrade performance when the
+queue is large, because of the extra work in setting up the single, large list.
+In most situations, queue_run_in_order should not be set.
+
++-------------------------------------------------+
+|queue_run_max|Use: main|Type: integer*|Default: 5|
++-------------------------------------------------+
+
+This controls the maximum number of queue runner processes that an Exim daemon
+can run simultaneously. This does not mean that it starts them all at once, but
+rather that if the maximum number are still running when the time comes to
+start another one, it refrains from starting another one. This can happen with
+very large queues and/or very sluggish deliveries. This option does not,
+however, interlock with other processes, so additional queue runners can be
+started by other means, or by killing and restarting the daemon.
+
+Setting this option to zero does not suppress queue runs; rather, it disables
+the limit, allowing any number of simultaneous queue runner processes to be
+run. If you do not want queue runs to occur, omit the -qxx setting on the
+daemon's command line.
+
+To set limits for different named queues use an expansion depending on the
+$queue_name variable.
+
++--------------------------------------------------------------+
+|queue_smtp_domains|Use: main|Type: domain list*|Default: unset|
++--------------------------------------------------------------+
+
+When this option is set, a delivery process is started whenever a message is
+received, routing is performed, and local deliveries take place. However, if
+any SMTP deliveries are required for domains that match queue_smtp_domains,
+they are not immediately delivered, but instead the message waits in the queue
+for the next queue run. Since routing of the message has taken place, Exim
+knows to which remote hosts it must be delivered, and so when the queue run
+happens, multiple messages for the same host are delivered over a single SMTP
+connection. The -odqs command line option causes all SMTP deliveries to be
+queued in this way, and is equivalent to setting queue_smtp_domains to "*". See
+also hold_domains and queue_domains.
+
++------------------------------------------------+
+|receive_timeout|Use: main|Type: time|Default: 0s|
++------------------------------------------------+
+
+This option sets the timeout for accepting a non-SMTP message, that is, the
+maximum time that Exim waits when reading a message on the standard input. If
+the value is zero, it will wait forever. This setting is overridden by the -or
+command line option. The timeout for incoming SMTP messages is controlled by
+smtp_receive_timeout.
+
++---------------------------------------------------------------+
+|received_header_text|Use: main|Type: string*|Default: see below|
++---------------------------------------------------------------+
+
+This string defines the contents of the Received: message header that is added
+to each message, except for the timestamp, which is automatically added on at
+the end (preceded by a semicolon). The string is expanded each time it is used.
+If the expansion yields an empty string, no Received: header line is added to
+the message. Otherwise, the string should start with the text "Received:" and
+conform to the RFC 2822 specification for Received: header lines. The default
+setting is:
+
+received_header_text = Received: \
+ ${if def:sender_rcvhost {from $sender_rcvhost\n\t}\
+ {${if def:sender_ident \
+ {from ${quote_local_part:$sender_ident} }}\
+ ${if def:sender_helo_name {(helo=$sender_helo_name)\n\t}}}}\
+ by $primary_hostname \
+ ${if def:received_protocol {with $received_protocol }}\
+ ${if def:tls_in_ver { ($tls_in_ver)}}\
+ ${if def:tls_in_cipher_std { tls $tls_in_cipher_std\n\t}}\
+ (Exim $version_number)\n\t\
+ ${if def:sender_address \
+ {(envelope-from <$sender_address>)\n\t}}\
+ id $message_exim_id\
+ ${if def:received_for {\n\tfor $received_for}}
+
+The references to the TLS version and cipher are omitted when Exim is built
+without TLS support. The use of conditional expansions ensures that this works
+for both locally generated messages and messages received from remote hosts,
+giving header lines such as the following:
+
+Received: from scrooge.carol.example ([192.168.12.25] ident=root)
+by marley.carol.example with esmtp (Exim 4.00)
+(envelope-from <bob@carol.example>)
+id 16IOWa-00019l-00
+for chas@dickens.example; Tue, 25 Dec 2001 14:43:44 +0000
+Received: by scrooge.carol.example with local (Exim 4.00)
+id 16IOWW-000083-00; Tue, 25 Dec 2001 14:43:41 +0000
+
+Until the body of the message has been received, the timestamp is the time when
+the message started to be received. Once the body has arrived, and all policy
+checks have taken place, the timestamp is updated to the time at which the
+message was accepted.
+
++--------------------------------------------------------+
+|received_headers_max|Use: main|Type: integer|Default: 30|
++--------------------------------------------------------+
+
+When a message is to be delivered, the number of Received: headers is counted,
+and if it is greater than this parameter, a mail loop is assumed to have
+occurred, the delivery is abandoned, and an error message is generated. This
+applies to both local and remote deliveries.
+
++---------------------------------------------------------------------+
+|recipient_unqualified_hosts|Use: main|Type: host list*|Default: unset|
++---------------------------------------------------------------------+
+
+This option lists those hosts from which Exim is prepared to accept unqualified
+recipient addresses in message envelopes. The addresses are made fully
+qualified by the addition of the qualify_recipient value. This option also
+affects message header lines. Exim does not reject unqualified recipient
+addresses in headers, but it qualifies them only if the message came from a
+host that matches recipient_unqualified_hosts, or if the message was submitted
+locally (not using TCP/IP), and the -bnq option was not set.
+
++-----------------------------------------------------+
+|recipients_max|Use: main|Type: integer|Default: 50000|
++-----------------------------------------------------+
+
+If this option is set greater than zero, it specifies the maximum number of
+original recipients for any message. Additional recipients that are generated
+by aliasing or forwarding do not count. SMTP messages get a 452 response for
+all recipients over the limit; earlier recipients are delivered as normal.
+Non-SMTP messages with too many recipients are failed, and no deliveries are
+done.
+
+Note: The RFCs specify that an SMTP server should accept at least 100 RCPT
+commands in a single message.
+
++------------------------------------------------------------+
+|recipients_max_reject|Use: main|Type: boolean|Default: false|
++------------------------------------------------------------+
+
+If this option is set true, Exim rejects SMTP messages containing too many
+recipients by giving 552 errors to the surplus RCPT commands, and a 554 error
+to the eventual DATA command. Otherwise (the default) it gives a 452 error to
+the surplus RCPT commands and accepts the message on behalf of the initial set
+of recipients. The remote server should then re-send the message for the
+remaining recipients at a later time.
+
++------------------------------------------------------+
+|remote_max_parallel|Use: main|Type: integer|Default: 2|
++------------------------------------------------------+
+
+This option controls parallel delivery of one message to a number of remote
+hosts. If the value is less than 2, parallel delivery is disabled, and Exim
+does all the remote deliveries for a message one by one. Otherwise, if a single
+message has to be delivered to more than one remote host, or if several copies
+have to be sent to the same remote host, up to remote_max_parallel deliveries
+are done simultaneously. If more than remote_max_parallel deliveries are
+required, the maximum number of processes are started, and as each one
+finishes, another is begun. The order of starting processes is the same as if
+sequential delivery were being done, and can be controlled by the
+remote_sort_domains option. If parallel delivery takes place while running with
+debugging turned on, the debugging output from each delivery process is tagged
+with its process id.
+
+This option controls only the maximum number of parallel deliveries for one
+message in one Exim delivery process. Because Exim has no central queue
+manager, there is no way of controlling the total number of simultaneous
+deliveries if the configuration allows a delivery attempt as soon as a message
+is received.
+
+If you want to control the total number of deliveries on the system, you need
+to set the queue_only option. This ensures that all incoming messages are added
+to the queue without starting a delivery process. Then set up an Exim daemon to
+start queue runner processes at appropriate intervals (probably fairly often,
+for example, every minute), and limit the total number of queue runners by
+setting the queue_run_max parameter. Because each queue runner delivers only
+one message at a time, the maximum number of deliveries that can then take
+place at once is queue_run_max multiplied by remote_max_parallel.
+
+If it is purely remote deliveries you want to control, use queue_smtp_domains
+instead of queue_only. This has the added benefit of doing the SMTP routing
+before queueing, so that several messages for the same host will eventually get
+delivered down the same connection.
+
++---------------------------------------------------------------+
+|remote_sort_domains|Use: main|Type: domain list*|Default: unset|
++---------------------------------------------------------------+
+
+When there are a number of remote deliveries for a message, they are sorted by
+domain into the order given by this list. For example,
+
+remote_sort_domains = *.cam.ac.uk:*.uk
+
+would attempt to deliver to all addresses in the cam.ac.uk domain first, then
+to those in the uk domain, then to any others.
+
++--------------------------------------------------+
+|retry_data_expire|Use: main|Type: time|Default: 7d|
++--------------------------------------------------+
+
+This option sets a "use before" time on retry information in Exim's hints
+database. Any older retry data is ignored. This means that, for example, once a
+host has not been tried for 7 days, Exim behaves as if it has no knowledge of
+past failures.
+
++----------------------------------------------------+
+|retry_interval_max|Use: main|Type: time|Default: 24h|
++----------------------------------------------------+
+
+Chapter 32 describes Exim's mechanisms for controlling the intervals between
+delivery attempts for messages that cannot be delivered straight away. This
+option sets an overall limit to the length of time between retries. It cannot
+be set greater than 24 hours; any attempt to do so forces the default value.
+
++--------------------------------------------------------+
+|return_path_remove|Use: main|Type: boolean|Default: true|
++--------------------------------------------------------+
+
+RFC 2821, section 4.4, states that an SMTP server must insert a Return-path:
+header line into a message when it makes a "final delivery". The Return-path:
+header preserves the sender address as received in the MAIL command. This
+description implies that this header should not be present in an incoming
+message. If return_path_remove is true, any existing Return-path: headers are
+removed from messages at the time they are received. Exim's transports have
+options for adding Return-path: headers at the time of delivery. They are
+normally used only for final local deliveries.
+
++-------------------------------------------------------+
+|return_size_limit|Use: main|Type: integer|Default: 100K|
++-------------------------------------------------------+
+
+This option is an obsolete synonym for bounce_return_size_limit.
+
++-----------------------------------------------------+
+|rfc1413_hosts|Use: main|Type: host list*|Default: @[]|
++-----------------------------------------------------+
+
+RFC 1413 identification calls are made to any client host which matches an item
+in the list. The default value specifies just this host, being any local
+interface for the system.
+
++------------------------------------------------------+
+|rfc1413_query_timeout|Use: main|Type: time|Default: 0s|
++------------------------------------------------------+
+
+This sets the timeout on RFC 1413 identification calls. If it is set to zero,
+no RFC 1413 calls are ever made.
+
++------------------------------------------------------------------+
+|sender_unqualified_hosts|Use: main|Type: host list*|Default: unset|
++------------------------------------------------------------------+
+
+This option lists those hosts from which Exim is prepared to accept unqualified
+sender addresses. The addresses are made fully qualified by the addition of
+qualify_domain. This option also affects message header lines. Exim does not
+reject unqualified addresses in headers that contain sender addresses, but it
+qualifies them only if the message came from a host that matches
+sender_unqualified_hosts, or if the message was submitted locally (not using
+TCP/IP), and the -bnq option was not set.
+
++--------------------------------------------------+
+|slow_lookup_log|Use: main|Type: integer|Default: 0|
++--------------------------------------------------+
+
+This option controls logging of slow lookups. If the value is nonzero it is
+taken as a number of milliseconds and lookups taking longer than this are
+logged. Currently this applies only to DNS lookups.
+
++-----------------------------------------------------------+
+|smtp_accept_keepalive|Use: main|Type: boolean|Default: true|
++-----------------------------------------------------------+
+
+This option controls the setting of the SO_KEEPALIVE option on incoming TCP/IP
+socket connections. When set, it causes the kernel to probe idle connections
+periodically, by sending packets with "old" sequence numbers. The other end of
+the connection should send an acknowledgment if the connection is still okay or
+a reset if the connection has been aborted. The reason for doing this is that
+it has the beneficial effect of freeing up certain types of connection that can
+get stuck when the remote host is disconnected without tidying up the TCP/IP
+call properly. The keepalive mechanism takes several hours to detect
+unreachable hosts.
+
++---------------------------------------------------+
+|smtp_accept_max|Use: main|Type: integer|Default: 20|
++---------------------------------------------------+
+
+This option specifies the maximum number of simultaneous incoming SMTP calls
+that Exim will accept. It applies only to the listening daemon; there is no
+control (in Exim) when incoming SMTP is being handled by inetd. If the value is
+set to zero, no limit is applied. However, it is required to be non-zero if
+either smtp_accept_max_per_host or smtp_accept_queue is set. See also
+smtp_accept_reserve and smtp_load_reserve.
+
+A new SMTP connection is immediately rejected if the smtp_accept_max limit has
+been reached. If not, Exim first checks smtp_accept_max_per_host. If that limit
+has not been reached for the client host, smtp_accept_reserve and
+smtp_load_reserve are then checked before accepting the connection.
+
++-----------------------------------------------------------+
+|smtp_accept_max_nonmail|Use: main|Type: integer|Default: 10|
++-----------------------------------------------------------+
+
+Exim counts the number of "non-mail" commands in an SMTP session, and drops the
+connection if there are too many. This option defines "too many". The check
+catches some denial-of-service attacks, repeated failing AUTHs, or a mad client
+looping sending EHLO, for example. The check is applied only if the client host
+matches smtp_accept_max_nonmail_hosts.
+
+When a new message is expected, one occurrence of RSET is not counted. This
+allows a client to send one RSET between messages (this is not necessary, but
+some clients do it). Exim also allows one uncounted occurrence of HELO or EHLO,
+and one occurrence of STARTTLS between messages. After starting up a TLS
+session, another EHLO is expected, and so it too is not counted. The first
+occurrence of AUTH in a connection, or immediately following STARTTLS is not
+counted. Otherwise, all commands other than MAIL, RCPT, DATA, and QUIT are
+counted.
+
++-------------------------------------------------------------------+
+|smtp_accept_max_nonmail_hosts|Use: main|Type: host list*|Default: *|
++-------------------------------------------------------------------+
+
+You can control which hosts are subject to the smtp_accept_max_nonmail check by
+setting this option. The default value makes it apply to all hosts. By changing
+the value, you can exclude any badly-behaved hosts that you have to live with.
+
++--------------------------------------------------------------------+
+|smtp_accept_max_per_connection|Use: main|Type: integer|Default: 1000|
++--------------------------------------------------------------------+
+
+The value of this option limits the number of MAIL commands that Exim is
+prepared to accept over a single SMTP connection, whether or not each command
+results in the transfer of a message. After the limit is reached, a 421
+response is given to subsequent MAIL commands. This limit is a safety
+precaution against a client that goes mad (incidents of this type have been
+seen).
+
++---------------------------------------------------------------+
+|smtp_accept_max_per_host|Use: main|Type: string*|Default: unset|
++---------------------------------------------------------------+
+
+This option restricts the number of simultaneous IP connections from a single
+host (strictly, from a single IP address) to the Exim daemon. The option is
+expanded, to enable different limits to be applied to different hosts by
+reference to $sender_host_address. Once the limit is reached, additional
+connection attempts from the same host are rejected with error code 421. This
+is entirely independent of smtp_accept_reserve. The option's default value of
+zero imposes no limit. If this option is set greater than zero, it is required
+that smtp_accept_max be non-zero.
+
+Warning: When setting this option you should not use any expansion
+constructions that take an appreciable amount of time. The expansion and test
+happen in the main daemon loop, in order to reject additional connections
+without forking additional processes (otherwise a denial-of-service attack
+could cause a vast number or processes to be created). While the daemon is
+doing this processing, it cannot accept any other incoming connections.
+
++----------------------------------------------------+
+|smtp_accept_queue|Use: main|Type: integer|Default: 0|
++----------------------------------------------------+
+
+If the number of simultaneous incoming SMTP connections being handled via the
+listening daemon exceeds this value, messages received by SMTP are just placed
+in the queue; no delivery processes are started automatically. The count is
+fixed at the start of an SMTP connection. It cannot be updated in the
+subprocess that receives messages, and so the queueing or not queueing applies
+to all messages received in the same connection.
+
+A value of zero implies no limit, and clearly any non-zero value is useful only
+if it is less than the smtp_accept_max value (unless that is zero). See also
+queue_only, queue_only_load, queue_smtp_domains, and the various -odx command
+line options.
+
++--------------------------------------------------------------------+
+|smtp_accept_queue_per_connection|Use: main|Type: integer|Default: 10|
++--------------------------------------------------------------------+
+
+This option limits the number of delivery processes that Exim starts
+automatically when receiving messages via SMTP, whether via the daemon or by
+the use of -bs or -bS. If the value of the option is greater than zero, and the
+number of messages received in a single SMTP session exceeds this number,
+subsequent messages are placed in the queue, but no delivery processes are
+started. This helps to limit the number of Exim processes when a server
+restarts after downtime and there is a lot of mail waiting for it on other
+systems. On large systems, the default should probably be increased, and on
+dial-in client systems it should probably be set to zero (that is, disabled).
+
++------------------------------------------------------+
+|smtp_accept_reserve|Use: main|Type: integer|Default: 0|
++------------------------------------------------------+
+
+When smtp_accept_max is set greater than zero, this option specifies a number
+of SMTP connections that are reserved for connections from the hosts that are
+specified in smtp_reserve_hosts. The value set in smtp_accept_max includes this
+reserve pool. The specified hosts are not restricted to this number of
+connections; the option specifies a minimum number of connection slots for
+them, not a maximum. It is a guarantee that this group of hosts can always get
+at least smtp_accept_reserve connections. However, the limit specified by
+smtp_accept_max_per_host is still applied to each individual host.
+
+For example, if smtp_accept_max is set to 50 and smtp_accept_reserve is set to
+5, once there are 45 active connections (from any hosts), new connections are
+accepted only from hosts listed in smtp_reserve_hosts, provided the other
+criteria for acceptance are met.
+
++-----------------------------------------------------------+
+|smtp_active_hostname|Use: main|Type: string*|Default: unset|
++-----------------------------------------------------------+
+
+This option is provided for multi-homed servers that want to masquerade as
+several different hosts. At the start of an incoming SMTP connection, its value
+is expanded and used instead of the value of $primary_hostname in SMTP
+responses. For example, it is used as domain name in the response to an
+incoming HELO or EHLO command.
+
+The active hostname is placed in the $smtp_active_hostname variable, which is
+saved with any messages that are received. It is therefore available for use in
+routers and transports when the message is later delivered.
+
+If this option is unset, or if its expansion is forced to fail, or if the
+expansion results in an empty string, the value of $primary_hostname is used.
+Other expansion failures cause a message to be written to the main and panic
+logs, and the SMTP command receives a temporary error. Typically, the value of
+smtp_active_hostname depends on the incoming interface address. For example:
+
+smtp_active_hostname = ${if eq{$received_ip_address}{10.0.0.1}\
+ {cox.mydomain}{box.mydomain}}
+
+Although $smtp_active_hostname is primarily concerned with incoming messages,
+it is also used as the default for HELO commands in callout verification if
+there is no remote transport from which to obtain a helo_data value.
+
++------------------------------------------------------+
+|smtp_banner|Use: main|Type: string*|Default: see below|
++------------------------------------------------------+
+
+This string, which is expanded every time it is used, is output as the initial
+positive response to an SMTP connection. The default setting is:
+
+smtp_banner = $smtp_active_hostname ESMTP Exim \
+ $version_number $tod_full
+
+Failure to expand the string causes a panic error. If you want to create a
+multiline response to the initial SMTP connection, use "\n" in the string at
+appropriate points, but not at the end. Note that the 220 code is not included
+in this string. Exim adds it automatically (several times in the case of a
+multiline response).
+
++------------------------------------------------------------+
+|smtp_check_spool_space|Use: main|Type: boolean|Default: true|
++------------------------------------------------------------+
+
+When this option is set, if an incoming SMTP session encounters the SIZE option
+on a MAIL command, it checks that there is enough space in the spool
+directory's partition to accept a message of that size, while still leaving
+free the amount specified by check_spool_space (even if that value is zero). If
+there isn't enough space, a temporary error code is returned.
+
++--------------------------------------------------------+
+|smtp_connect_backlog|Use: main|Type: integer|Default: 20|
++--------------------------------------------------------+
+
+This option specifies a maximum number of waiting SMTP connections. Exim passes
+this value to the TCP/IP system when it sets up its listener. Once this number
+of connections are waiting for the daemon's attention, subsequent connection
+attempts are refused at the TCP/IP level. At least, that is what the manuals
+say; in some circumstances such connection attempts have been observed to time
+out instead. For large systems it is probably a good idea to increase the value
+(to 50, say). It also gives some protection against denial-of-service attacks
+by SYN flooding.
+
++-------------------------------------------------------+
+|smtp_enforce_sync|Use: main|Type: boolean|Default: true|
++-------------------------------------------------------+
+
+The SMTP protocol specification requires the client to wait for a response from
+the server at certain points in the dialogue. Without PIPELINING these
+synchronization points are after every command; with PIPELINING they are fewer,
+but they still exist.
+
+Some spamming sites send out a complete set of SMTP commands without waiting
+for any response. Exim protects against this by rejecting a message if the
+client has sent further input when it should not have. The error response "554
+SMTP synchronization error" is sent, and the connection is dropped. Testing for
+this error cannot be perfect because of transmission delays (unexpected input
+may be on its way but not yet received when Exim checks). However, it does
+detect many instances.
+
+The check can be globally disabled by setting smtp_enforce_sync false. If you
+want to disable the check selectively (for example, only for certain hosts),
+you can do so by an appropriate use of a control modifier in an ACL (see
+section 44.22). See also pipelining_advertise_hosts.
+
++--------------------------------------------------------+
+|smtp_etrn_command|Use: main|Type: string*|Default: unset|
++--------------------------------------------------------+
+
+If this option is set, the given command is run whenever an SMTP ETRN command
+is received from a host that is permitted to issue such commands (see chapter
+44). The string is split up into separate arguments which are independently
+expanded. The expansion variable $domain is set to the argument of the ETRN
+command, and no syntax checking is done on it. For example:
+
+smtp_etrn_command = /etc/etrn_command $domain \
+ $sender_host_address
+
+If the option is not set, the argument for the ETRN command must be a #
+followed by an address string. In this case an exim -R <string> command is
+used; if the ETRN ACL has set up a named-queue then -MCG <queue> is appended.
+
+A new process is created to run the command, but Exim does not wait for it to
+complete. Consequently, its status cannot be checked. If the command cannot be
+run, a line is written to the panic log, but the ETRN caller still receives a
+250 success response. Exim is normally running under its own uid when receiving
+SMTP, so it is not possible for it to change the uid before running the
+command.
+
++---------------------------------------------------------+
+|smtp_etrn_serialize|Use: main|Type: boolean|Default: true|
++---------------------------------------------------------+
+
+When this option is set, it prevents the simultaneous execution of more than
+one identical command as a result of ETRN in an SMTP connection. See section
+49.8 for details.
+
++------------------------------------------------------------+
+|smtp_load_reserve|Use: main|Type: fixed-point|Default: unset|
++------------------------------------------------------------+
+
+If the system load average ever gets higher than this, incoming SMTP calls are
+accepted only from those hosts that match an entry in smtp_reserve_hosts. If
+smtp_reserve_hosts is not set, no incoming SMTP calls are accepted when the
+load is over the limit. The option has no effect on ancient operating systems
+on which Exim cannot determine the load average. See also
+deliver_queue_load_max and queue_only_load.
+
++----------------------------------------------------------+
+|smtp_max_synprot_errors|Use: main|Type: integer|Default: 3|
++----------------------------------------------------------+
+
+Exim rejects SMTP commands that contain syntax or protocol errors. In
+particular, a syntactically invalid email address, as in this command:
+
+RCPT TO:<abc xyz@a.b.c>
+
+causes immediate rejection of the command, before any other tests are done.
+(The ACL cannot be run if there is no valid address to set up for it.) An
+example of a protocol error is receiving RCPT before MAIL. If there are too
+many syntax or protocol errors in one SMTP session, the connection is dropped.
+The limit is set by this option.
+
+When the PIPELINING extension to SMTP is in use, some protocol errors are
+"expected", for instance, a RCPT command after a rejected MAIL command. Exim
+assumes that PIPELINING will be used if it advertises it (see
+pipelining_advertise_hosts), and in this situation, "expected" errors do not
+count towards the limit.
+
++------------------------------------------------------------+
+|smtp_max_unknown_commands|Use: main|Type: integer|Default: 3|
++------------------------------------------------------------+
+
+If there are too many unrecognized commands in an incoming SMTP session, an
+Exim server drops the connection. This is a defence against some kinds of abuse
+that subvert web clients into making connections to SMTP ports; in these
+circumstances, a number of non-SMTP command lines are sent first.
+
++--------------------------------------------------------------+
+|smtp_ratelimit_hosts|Use: main|Type: host list*|Default: unset|
++--------------------------------------------------------------+
+
+Some sites find it helpful to be able to limit the rate at which certain hosts
+can send them messages, and the rate at which an individual message can specify
+recipients.
+
+Exim has two rate-limiting facilities. This section describes the older
+facility, which can limit rates within a single connection. The newer ratelimit
+ACL condition can limit rates across all connections. See section 44.38 for
+details of the newer facility.
+
+When a host matches smtp_ratelimit_hosts, the values of smtp_ratelimit_mail and
+smtp_ratelimit_rcpt are used to control the rate of acceptance of MAIL and RCPT
+commands in a single SMTP session, respectively. Each option, if set, must
+contain a set of four comma-separated values:
+
+ * A threshold, before which there is no rate limiting.
+
+ * An initial time delay. Unlike other times in Exim, numbers with decimal
+ fractional parts are allowed here.
+
+ * A factor by which to increase the delay each time.
+
+ * A maximum value for the delay. This should normally be less than 5 minutes,
+ because after that time, the client is liable to timeout the SMTP command.
+
+For example, these settings have been used successfully at the site which first
+suggested this feature, for controlling mail from their customers:
+
+smtp_ratelimit_mail = 2,0.5s,1.05,4m
+smtp_ratelimit_rcpt = 4,0.25s,1.015,4m
+
+The first setting specifies delays that are applied to MAIL commands after two
+have been received over a single connection. The initial delay is 0.5 seconds,
+increasing by a factor of 1.05 each time. The second setting applies delays to
+RCPT commands when more than four occur in a single message.
+
++---------------------------------------------------------+
+|smtp_ratelimit_mail|Use: main|Type: string|Default: unset|
++---------------------------------------------------------+
+
+See smtp_ratelimit_hosts above.
+
++---------------------------------------------------------+
+|smtp_ratelimit_rcpt|Use: main|Type: string|Default: unset|
++---------------------------------------------------------+
+
+See smtp_ratelimit_hosts above.
+
++------------------------------------------------------+
+|smtp_receive_timeout|Use: main|Type: time*|Default: 5m|
++------------------------------------------------------+
+
+This sets a timeout value for SMTP reception. It applies to all forms of SMTP
+input, including batch SMTP. If a line of input (either an SMTP command or a
+data line) is not received within this time, the SMTP connection is dropped and
+the message is abandoned. A line is written to the log containing one of the
+following messages:
+
+SMTP command timeout on connection from...
+SMTP data timeout on connection from...
+
+The former means that Exim was expecting to read an SMTP command; the latter
+means that it was in the DATA phase, reading the contents of a message.
+
+If the first character of the option is a "$" the option is expanded before use
+and may depend on $sender_host_name, $sender_host_address and $sender_host_port
+.
+
+The value set by this option can be overridden by the -os command-line option.
+A setting of zero time disables the timeout, but this should never be used for
+SMTP over TCP/IP. (It can be useful in some cases of local input using -bs or
+-bS.) For non-SMTP input, the reception timeout is controlled by
+receive_timeout and -or.
+
++------------------------------------------------------------+
+|smtp_reserve_hosts|Use: main|Type: host list*|Default: unset|
++------------------------------------------------------------+
+
+This option defines hosts for which SMTP connections are reserved; see
+smtp_accept_reserve and smtp_load_reserve above.
+
++----------------------------------------------------------------+
+|smtp_return_error_details|Use: main|Type: boolean|Default: false|
++----------------------------------------------------------------+
+
+In the default state, Exim uses bland messages such as "Administrative
+prohibition" when it rejects SMTP commands for policy reasons. Many sysadmins
+like this because it gives away little information to spammers. However, some
+other sysadmins who are applying strict checking policies want to give out much
+fuller information about failures. Setting smtp_return_error_details true
+causes Exim to be more forthcoming. For example, instead of "Administrative
+prohibition", it might give:
+
+550-Rejected after DATA: '>' missing at end of address:
+550 failing address in "From" header is: <user@dom.ain
+
++--------------------------------------------------------------+
+|smtputf8_advertise_hosts|Use: main|Type: host list*|Default: *|
++--------------------------------------------------------------+
+
+When Exim is built with support for internationalised mail names, the
+availability thereof is advertised in response to EHLO only to those client
+hosts that match this option. See chapter 60 for details of Exim's support for
+internationalisation.
+
++-----------------------------------------------------------+
+|spamd_address|Use: main|Type: string|Default: 127.0.0.1 783|
++-----------------------------------------------------------+
+
+This option is available when Exim is compiled with the content-scanning
+extension. It specifies how Exim connects to SpamAssassin's spamd daemon. See
+section 45.2 for more details.
+
++--------------------------------------------------------------------+
+|spf_guess|Use: main|Type: string|Default: v=spf1 a/24 mx/24 ptr ?all|
++--------------------------------------------------------------------+
+
+This option is available when Exim is compiled with SPF support. See section
+58.4 for more details.
+
++-----------------------------------------------------------------------------+
+|spf_smtp_comment_template|Use: | Type: | Default: Please%_see%_http://|
+| | main | string* | www.open-spf.org/Why|
++-----------------------------------------------------------------------------+
+
+This option is available when Exim is compiled with SPF support. It allows the
+customisation of the SMTP comment that the SPF library generates. You are
+strongly encouraged to link to your own explanative site. The template must not
+contain spaces. If you need spaces in the output, use the proper placeholder.
+If libspf2 can not parse the template, it uses a built-in default broken link.
+The following placeholders (along with Exim variables (but see below)) are
+allowed in the template:
+
+ * %_: A space.
+
+ * %{L}: Envelope sender's local part.
+
+ * %{S}: Envelope sender.
+
+ * %{O}: Envelope sender's domain.
+
+ * %{D}: Current(?) domain.
+
+ * %{I}: SMTP client Ip.
+
+ * %{C}: SMTP client pretty IP.
+
+ * %{T}: Epoch time (UTC).
+
+ * %{P}: SMTP client domain name.
+
+ * %{V}: IP version.
+
+ * %{H}: EHLO/HELO domain.
+
+ * %{R}: Receiving domain.
+
+The capitalized placeholders do proper URL encoding, if you use them
+lowercased, no encoding takes place. This list was compiled from the libspf2
+sources.
+
+A note on using Exim variables: As currently the SPF library is initialized
+before the SMTP EHLO phase, the variables useful for expansion are quite
+limited.
+
++------------------------------------------------------------+
+|split_spool_directory|Use: main|Type: boolean|Default: false|
++------------------------------------------------------------+
+
+If this option is set, it causes Exim to split its input directory into 62
+subdirectories, each with a single alphanumeric character as its name. The
+sixth character of the message id is used to allocate messages to
+subdirectories; this is the least significant base-62 digit of the time of
+arrival of the message.
+
+Splitting up the spool in this way may provide better performance on systems
+where there are long mail queues, by reducing the number of files in any one
+directory. The msglog directory is also split up in a similar way to the input
+directory; however, if preserve_message_logs is set, all old msglog files are
+still placed in the single directory msglog.OLD.
+
+It is not necessary to take any special action for existing messages when
+changing split_spool_directory. Exim notices messages that are in the "wrong"
+place, and continues to process them. If the option is turned off after a
+period of being on, the subdirectories will eventually empty and be
+automatically deleted.
+
+When split_spool_directory is set, the behaviour of queue runner processes
+changes. Instead of creating a list of all messages in the queue, and then
+trying to deliver each one, in turn, it constructs a list of those in one
+sub-directory and tries to deliver them, before moving on to the next
+sub-directory. The sub-directories are processed in a random order. This
+spreads out the scanning of the input directories, and uses less memory. It is
+particularly beneficial when there are lots of messages in the queue. However,
+if queue_run_in_order is set, none of this new processing happens. The entire
+queue has to be scanned and sorted before any deliveries can start.
+
++--------------------------------------------------------------------+
+|spool_directory|Use: main|Type: string*|Default: set at compile time|
++--------------------------------------------------------------------+
+
+This defines the directory in which Exim keeps its spool, that is, the messages
+it is waiting to deliver. The default value is taken from the compile-time
+configuration setting, if there is one. If not, this option must be set. The
+string is expanded, so it can contain, for example, a reference to
+$primary_hostname.
+
+If the spool directory name is fixed on your installation, it is recommended
+that you set it at build time rather than from this option, particularly if the
+log files are being written to the spool directory (see log_file_path).
+Otherwise log files cannot be used for errors that are detected early on, such
+as failures in the configuration file.
+
+By using this option to override the compiled-in path, it is possible to run
+tests of Exim without using the standard spool.
+
++-------------------------------------------------------+
+|spool_wireformat|Use: main|Type: boolean|Default: false|
++-------------------------------------------------------+
+
+If this option is set, Exim may for some messages use an alternative format for
+data-files in the spool which matches the wire format. Doing this permits more
+efficient message reception and transmission. Currently it is only done for
+messages received using the ESMTP CHUNKING option.
+
+The following variables will not have useful values:
+
+$max_received_linelength
+$body_linecount
+$body_zerocount
+
+Users of the local_scan() API (see 46), and any external programs which are
+passed a reference to a message data file (except via the "regex", "malware" or
+"spam") ACL conditions) will need to be aware of the different formats
+potentially available.
+
+Using any of the ACL conditions noted will negate the reception benefit (as a
+Unix-mbox-format file is constructed for them). The transmission benefit is
+maintained.
+
++----------------------------------------------------+
+|sqlite_lock_timeout|Use: main|Type: time|Default: 5s|
++----------------------------------------------------+
+
+This option controls the timeout that the sqlite lookup uses when trying to
+access an SQLite database. See section 9.26 for more details.
+
++------------------------------------------------------+
+|strict_acl_vars|Use: main|Type: boolean|Default: false|
++------------------------------------------------------+
+
+This option controls what happens if a syntactically valid but undefined ACL
+variable is referenced. If it is false (the default), an empty string is
+substituted; if it is true, an error is generated. See section 44.19 for
+details of ACL variables.
+
++------------------------------------------------------------------+
+|strip_excess_angle_brackets|Use: main|Type: boolean|Default: false|
++------------------------------------------------------------------+
+
+If this option is set, redundant pairs of angle brackets round "route-addr"
+items in addresses are stripped. For example, <<xxx@a.b.c.d>> is treated as
+<xxx@a.b.c.d>. If this is in the envelope and the message is passed on to
+another MTA, the excess angle brackets are not passed on. If this option is not
+set, multiple pairs of angle brackets cause a syntax error.
+
++---------------------------------------------------------+
+|strip_trailing_dot|Use: main|Type: boolean|Default: false|
++---------------------------------------------------------+
+
+If this option is set, a trailing dot at the end of a domain in an address is
+ignored. If this is in the envelope and the message is passed on to another
+MTA, the dot is not passed on. If this option is not set, a dot at the end of a
+domain causes a syntax error. However, addresses in header lines are checked
+only when an ACL requests header syntax checking.
+
++--------------------------------------------------------+
+|syslog_duplication|Use: main|Type: boolean|Default: true|
++--------------------------------------------------------+
+
+When Exim is logging to syslog, it writes the log lines for its three separate
+logs at different syslog priorities so that they can in principle be separated
+on the logging hosts. Some installations do not require this separation, and in
+those cases, the duplication of certain log lines is a nuisance. If
+syslog_duplication is set false, only one copy of any particular log line is
+written to syslog. For lines that normally go to both the main log and the
+reject log, the reject log version (possibly containing message header lines)
+is written, at LOG_NOTICE priority. Lines that normally go to both the main and
+the panic log are written at the LOG_ALERT priority.
+
++-----------------------------------------------------+
+|syslog_facility|Use: main|Type: string|Default: unset|
++-----------------------------------------------------+
+
+This option sets the syslog "facility" name, used when Exim is logging to
+syslog. The value must be one of the strings "mail", "user", "news", "uucp",
+"daemon", or "localx" where x is a digit between 0 and 7. If this option is
+unset, "mail" is used. See chapter 53 for details of Exim's logging.
+
++------------------------------------------------+
+|syslog_pid|Use: main|Type: boolean|Default: true|
++------------------------------------------------+
+
+If syslog_pid is set false, the PID on Exim's log lines are omitted when these
+lines are sent to syslog. (Syslog normally prefixes the log lines with the PID
+of the logging process automatically.) You need to enable the "+pid" log
+selector item, if you want Exim to write it's PID into the logs.) See chapter
+53 for details of Exim's logging.
+
++---------------------------------------------------------+
+|syslog_processname|Use: main|Type: string|Default: "exim"|
++---------------------------------------------------------+
+
+This option sets the syslog "ident" name, used when Exim is logging to syslog.
+The value must be no longer than 32 characters. See chapter 53 for details of
+Exim's logging.
+
++------------------------------------------------------+
+|syslog_timestamp|Use: main|Type: boolean|Default: true|
++------------------------------------------------------+
+
+If syslog_timestamp is set false, the timestamps on Exim's log lines are
+omitted when these lines are sent to syslog. See chapter 53 for details of
+Exim's logging.
+
++----------------------------------------------------+
+|system_filter|Use: main|Type: string*|Default: unset|
++----------------------------------------------------+
+
+This option specifies an Exim filter file that is applied to all messages at
+the start of each delivery attempt, before any routing is done. System filters
+must be Exim filters; they cannot be Sieve filters. If the system filter
+generates any deliveries to files or pipes, or any new mail messages, the
+appropriate system_filter_..._transport option(s) must be set, to define which
+transports are to be used. Details of this facility are given in chapter 47. A
+forced expansion failure results in no filter operation.
+
++------------------------------------------------------------------------+
+|system_filter_directory_transport|Use: main|Type: string*|Default: unset|
++------------------------------------------------------------------------+
+
+This sets the name of the transport driver that is to be used when the save
+command in a system message filter specifies a path ending in "/", implying
+delivery of each message into a separate file in some directory. During the
+delivery, the variable $address_file contains the path name.
+
++-------------------------------------------------------------------+
+|system_filter_file_transport|Use: main|Type: string*|Default: unset|
++-------------------------------------------------------------------+
+
+This sets the name of the transport driver that is to be used when the save
+command in a system message filter specifies a path not ending in "/". During
+the delivery, the variable $address_file contains the path name.
+
++---------------------------------------------------------+
+|system_filter_group|Use: main|Type: string|Default: unset|
++---------------------------------------------------------+
+
+This option is used only when system_filter_user is also set. It sets the gid
+under which the system filter is run, overriding any gid that is associated
+with the user. The value may be numerical or symbolic.
+
++-------------------------------------------------------------------+
+|system_filter_pipe_transport|Use: main|Type: string*|Default: unset|
++-------------------------------------------------------------------+
+
+This specifies the transport driver that is to be used when a pipe command is
+used in a system filter. During the delivery, the variable $address_pipe
+contains the pipe command.
+
++--------------------------------------------------------------------+
+|system_filter_reply_transport|Use: main|Type: string*|Default: unset|
++--------------------------------------------------------------------+
+
+This specifies the transport driver that is to be used when a mail command is
+used in a system filter.
+
++--------------------------------------------------------+
+|system_filter_user|Use: main|Type: string|Default: unset|
++--------------------------------------------------------+
+
+If this option is set to root, the system filter is run in the main Exim
+delivery process, as root. Otherwise, the system filter runs in a separate
+process, as the given user, defaulting to the Exim run-time user. Unless the
+string consists entirely of digits, it is looked up in the password data.
+Failure to find the named user causes a configuration error. The gid is either
+taken from the password data, or specified by system_filter_group. When the uid
+is specified numerically, system_filter_group is required to be set.
+
+If the system filter generates any pipe, file, or reply deliveries, the uid
+under which the filter is run is used when transporting them, unless a
+transport option overrides.
+
++-------------------------------------------------+
+|tcp_nodelay|Use: main|Type: boolean|Default: true|
++-------------------------------------------------+
+
+If this option is set false, it stops the Exim daemon setting the TCP_NODELAY
+option on its listening sockets. Setting TCP_NODELAY turns off the "Nagle
+algorithm", which is a way of improving network performance in interactive
+(character-by-character) situations. Turning it off should improve Exim's
+performance a bit, so that is what happens by default. However, it appears that
+some broken clients cannot cope, and time out. Hence this option. It affects
+only those sockets that are set up for listening by the daemon. Sockets created
+by the smtp transport for delivering mail always set TCP_NODELAY.
+
++-----------------------------------------------------+
+|timeout_frozen_after|Use: main|Type: time|Default: 0s|
++-----------------------------------------------------+
+
+If timeout_frozen_after is set to a time greater than zero, a frozen message of
+any kind that has been in the queue for longer than the given time is
+automatically cancelled at the next queue run. If the frozen message is a
+bounce message, it is just discarded; otherwise, a bounce is sent to the
+sender, in a similar manner to cancellation by the -Mg command line option. If
+you want to timeout frozen bounce messages earlier than other kinds of frozen
+message, see ignore_bounce_errors_after.
+
+Note: the default value of zero means no timeouts; with this setting, frozen
+messages remain in the queue forever (except for any frozen bounce messages
+that are released by ignore_bounce_errors_after).
+
++----------------------------------------------+
+|timezone|Use: main|Type: string|Default: unset|
++----------------------------------------------+
+
+The value of timezone is used to set the environment variable TZ while running
+Exim (if it is different on entry). This ensures that all timestamps created by
+Exim are in the required timezone. If you want all your timestamps to be in UTC
+(aka GMT) you should set
+
+timezone = UTC
+
+The default value is taken from TIMEZONE_DEFAULT in Local/Makefile, or, if that
+is not set, from the value of the TZ environment variable when Exim is built.
+If timezone is set to the empty string, either at build or run time, any
+existing TZ variable is removed from the environment when Exim runs. This is
+appropriate behaviour for obtaining wall-clock time on some, but unfortunately
+not all, operating systems.
+
++---------------------------------------------------------+
+|tls_advertise_hosts|Use: main|Type: host list*|Default: *|
++---------------------------------------------------------+
+
+When Exim is built with support for TLS encrypted connections, the availability
+of the STARTTLS command to set up an encrypted session is advertised in
+response to EHLO only to those client hosts that match this option. See chapter
+43 for details of Exim's support for TLS. Note that the default value requires
+that a certificate be supplied using the tls_certificate option. If TLS support
+for incoming connections is not required the tls_advertise_hosts option should
+be set empty.
+
++-----------------------------------------------------+
+|tls_certificate|Use: main|Type: string|Default: list*|
++-----------------------------------------------------+
+
+The value of this option is expanded, and must then be a list of absolute paths
+to files which contain the server's certificates (in PEM format). Commonly only
+one file is needed. The server's private key is also assumed to be in this file
+if tls_privatekey is unset. See chapter 43 for further details.
+
+Note: The certificates defined by this option are used only when Exim is
+receiving incoming messages as a server. If you want to supply certificates for
+use when sending messages as a client, you must set the tls_certificate option
+in the relevant smtp transport.
+
+Note: If you use filenames based on IP addresses, change the list separator in
+the usual way (6.21) to avoid confusion under IPv6.
+
+Note: Under versions of OpenSSL preceding 1.1.1, when a list of more than one
+file is used, the $tls_in_ourcert variable is unreliable. The macro
+"_TLS_BAD_MULTICERT_IN_OURCERT" will be defined for those versions.
+
+If the option contains $tls_out_sni and Exim is built against OpenSSL, then if
+the OpenSSL build supports TLS extensions and the TLS client sends the Server
+Name Indication extension, then this option and others documented in 43.10 will
+be re-expanded.
+
+If this option is unset or empty a fresh self-signed certificate will be
+generated for every connection.
+
++----------------------------------------------+
+|tls_crl|Use: main|Type: string*|Default: unset|
++----------------------------------------------+
+
+This option specifies a certificate revocation list. The expanded value must be
+the name of a file that contains CRLs in PEM format.
+
+Under OpenSSL the option can specify a directory with CRL files.
+
+Note: Under OpenSSL the option must, if given, supply a CRL for each signing
+element of the certificate chain (i.e. all but the leaf). For the file variant
+this can be multiple PEM blocks in the one file.
+
+See 43.10 for discussion of when this option might be re-expanded.
+
++-----------------------------------------------------+
+|tls_dh_max_bits|Use: main|Type: integer|Default: 2236|
++-----------------------------------------------------+
+
+The number of bits used for Diffie-Hellman key-exchange may be suggested by the
+chosen TLS library. That value might prove to be too high for interoperability.
+This option provides a maximum clamp on the value suggested, trading off
+security for interoperability.
+
+The value must be at least 1024.
+
+The value 2236 was chosen because, at time of adding the option, it was the
+hard-coded maximum value supported by the NSS cryptographic library, as used by
+Thunderbird, while GnuTLS was suggesting 2432 bits as normal.
+
+If you prefer more security and are willing to break some clients, raise this
+number.
+
+Note that the value passed to GnuTLS for *generating* a new prime may be a
+little less than this figure, because GnuTLS is inexact and may produce a
+larger prime than requested.
+
++--------------------------------------------------+
+|tls_dhparam|Use: main|Type: string*|Default: unset|
++--------------------------------------------------+
+
+The value of this option is expanded and indicates the source of DH parameters
+to be used by Exim.
+
+This option is ignored for GnuTLS version 3.6.0 and later. The library manages
+parameter negotiation internally.
+
+Note: The Exim Maintainers strongly recommend, for other TLS library versions,
+using a filename with site-generated local DH parameters, which has been
+supported across all versions of Exim. The other specific constants available
+are a fallback so that even when "unconfigured", Exim can offer Perfect Forward
+Secrecy in older ciphersuites in TLS.
+
+If tls_dhparam is a filename starting with a "/", then it names a file from
+which DH parameters should be loaded. If the file exists, it should hold a
+PEM-encoded PKCS#3 representation of the DH prime. If the file does not exist,
+for OpenSSL it is an error. For GnuTLS, Exim will attempt to create the file
+and fill it with a generated DH prime. For OpenSSL, if the DH bit-count from
+loading the file is greater than tls_dh_max_bits then it will be ignored, and
+treated as though the tls_dhparam were set to "none".
+
+If this option expands to the string "none", then no DH parameters will be
+loaded by Exim.
+
+If this option expands to the string "historic" and Exim is using GnuTLS, then
+Exim will attempt to load a file from inside the spool directory. If the file
+does not exist, Exim will attempt to create it. See section 43.3 for further
+details.
+
+If Exim is using OpenSSL and this option is empty or unset, then Exim will load
+a default DH prime; the default is Exim-specific but lacks verifiable
+provenance.
+
+In older versions of Exim the default was the 2048 bit prime described in
+section 2.2 of RFC 5114, "2048-bit MODP Group with 224-bit Prime Order
+Subgroup", which in IKE is assigned number 23.
+
+Otherwise, the option must expand to the name used by Exim for any of a number
+of DH primes specified in RFC 2409, RFC 3526, RFC 5114, RFC 7919, or from other
+sources. As names, Exim uses a standard specified name, else "ike" followed by
+the number used by IKE, or "default" which corresponds to
+"exim.dev.20160529.3".
+
+The available standard primes are: "ffdhe2048", "ffdhe3072", "ffdhe4096",
+"ffdhe6144", "ffdhe8192", "ike1", "ike2", "ike5", "ike14", "ike15", "ike16",
+"ike17", "ike18", "ike22", "ike23" and "ike24".
+
+The available additional primes are: "exim.dev.20160529.1",
+"exim.dev.20160529.2" and "exim.dev.20160529.3".
+
+Some of these will be too small to be accepted by clients. Some may be too
+large to be accepted by clients. The open cryptographic community has
+suspicions about the integrity of some of the later IKE values, which led into
+RFC7919 providing new fixed constants (the "ffdhe" identifiers).
+
+At this point, all of the "ike" values should be considered obsolete; they're
+still in Exim to avoid breaking unusual configurations, but are candidates for
+removal the next time we have backwards-incompatible changes.
+
+The TLS protocol does not negotiate an acceptable size for this; clients tend
+to hard-drop connections if what is offered by the server is unacceptable,
+whether too large or too small, and there's no provision for the client to tell
+the server what these constraints are. Thus, as a server operator, you need to
+make an educated guess as to what is most likely to work for your userbase.
+
+Some known size constraints suggest that a bit-size in the range 2048 to 2236
+is most likely to maximise interoperability. The upper bound comes from
+applications using the Mozilla Network Security Services (NSS) library, which
+used to set its "DH_MAX_P_BITS" upper-bound to 2236. This affects many mail
+user agents (MUAs). The lower bound comes from Debian installs of Exim4 prior
+to the 4.80 release, as Debian used to patch Exim to raise the minimum
+acceptable bound from 1024 to 2048.
+
++---------------------------------------------------+
+|tls_eccurve|Use: main|Type: string*|Default: "auto"|
++---------------------------------------------------+
+
+This option selects a EC curve for use by Exim when used with OpenSSL. It has
+no effect when Exim is used with GnuTLS.
+
+After expansion it must contain a valid EC curve parameter, such as
+"prime256v1", "secp384r1", or "P-512". Consult your OpenSSL manual for valid
+selections.
+
+For OpenSSL versions before (and not including) 1.0.2, the string "auto"
+selects "prime256v1". For more recent OpenSSL versions "auto" tells the library
+to choose.
+
+If the option expands to an empty string, no EC curves will be enabled.
+
++----------------------------------------------------+
+|tls_ocsp_file|Use: main|Type: string*|Default: unset|
++----------------------------------------------------+
+
+This option must if set expand to the absolute path to a file which contains a
+current status proof for the server's certificate, as obtained from the
+Certificate Authority.
+
+Usable for GnuTLS 3.4.4 or 3.3.17 or OpenSSL 1.1.0 (or later). The macro
+"_HAVE_TLS_OCSP" will be defined for those versions.
+
+For OpenSSL 1.1.0 or later, and for GnuTLS 3.5.6 or later the expanded value of
+this option can be a list of files, to match a list given for the
+tls_certificate option. The ordering of the two lists must match. The macro
+"_HAVE_TLS_OCSP_LIST" will be defined for those versions.
+
+The file(s) should be in DER format, except for GnuTLS 3.6.3 or later or for
+OpenSSL, when an optional filetype prefix can be used. The prefix must be one
+of "DER" or "PEM", followed by a single space. If one is used it sets the
+format for subsequent files in the list; the initial format is DER. If multiple
+proofs are wanted, for multiple chain elements (this only works under TLS1.3)
+they must be coded as a combined OCSP response.
+
+Although GnuTLS will accept PEM files with multiple separate PEM blobs (ie.
+separate OCSP responses), it sends them in the TLS Certificate record
+interleaved with the certificates of the chain; although a GnuTLS client is
+happy with that, an OpenSSL client is not.
+
++---------------------------------------------------------------+
+|tls_on_connect_ports|Use: main|Type: string list|Default: unset|
++---------------------------------------------------------------+
+
+This option specifies a list of incoming SSMTP (aka SMTPS) ports that should
+operate the SSMTP (SMTPS) protocol, where a TLS session is immediately set up
+without waiting for the client to issue a STARTTLS command. For further
+details, see section 13.4.
+
++----------------------------------------------------+
+|tls_privatekey|Use: main|Type: string|Default: list*|
++----------------------------------------------------+
+
+The value of this option is expanded, and must then be a list of absolute paths
+to files which contains the server's private keys. If this option is unset, or
+if the expansion is forced to fail, or the result is an empty string, the
+private key is assumed to be in the same file as the server's certificates. See
+chapter 43 for further details.
+
+See 43.10 for discussion of when this option might be re-expanded.
+
++---------------------------------------------------------+
+|tls_remember_esmtp|Use: main|Type: boolean|Default: false|
++---------------------------------------------------------+
+
+If this option is set true, Exim violates the RFCs by remembering that it is in
+"esmtp" state after successfully negotiating a TLS session. This provides
+support for broken clients that fail to send a new EHLO after starting a TLS
+session.
+
++----------------------------------------------------------+
+|tls_require_ciphers|Use: main|Type: string*|Default: unset|
++----------------------------------------------------------+
+
+This option controls which ciphers can be used for incoming TLS connections.
+The smtp transport has an option of the same name for controlling outgoing
+connections. This option is expanded for each connection, so can be varied for
+different clients if required. The value of this option must be a list of
+permitted cipher suites. The OpenSSL and GnuTLS libraries handle cipher control
+in somewhat different ways. If GnuTLS is being used, the client controls the
+preference order of the available ciphers. Details are given in sections 43.4
+and 43.5.
+
++--------------------------------------------------------------+
+|tls_try_verify_hosts|Use: main|Type: host list*|Default: unset|
++--------------------------------------------------------------+
+
+See tls_verify_hosts below.
+
++---------------------------------------------------------------+
+|tls_verify_certificates|Use: main|Type: string*|Default: system|
++---------------------------------------------------------------+
+
+The value of this option is expanded, and must then be either the word "system"
+or the absolute path to a file or directory containing permitted certificates
+for clients that match tls_verify_hosts or tls_try_verify_hosts.
+
+The "system" value for the option will use a system default location compiled
+into the SSL library. This is not available for GnuTLS versions preceding
+3.0.20, and will be taken as empty; an explicit location must be specified.
+
+The use of a directory for the option value is not available for GnuTLS
+versions preceding 3.3.6 and a single file must be used.
+
+With OpenSSL the certificates specified explicitly either by file or directory
+are added to those given by the system default location.
+
+These certificates should be for the certificate authorities trusted, rather
+than the public cert of individual clients. With both OpenSSL and GnuTLS, if
+the value is a file then the certificates are sent by Exim as a server to
+connecting clients, defining the list of accepted certificate authorities. Thus
+the values defined should be considered public data. To avoid this, use the
+explicit directory version.
+
+See 43.10 for discussion of when this option might be re-expanded.
+
+A forced expansion failure or setting to an empty string is equivalent to being
+unset.
+
++----------------------------------------------------------+
+|tls_verify_hosts|Use: main|Type: host list*|Default: unset|
++----------------------------------------------------------+
+
+This option, along with tls_try_verify_hosts, controls the checking of
+certificates from clients. The expected certificates are defined by
+tls_verify_certificates, which must be set. A configuration error occurs if
+either tls_verify_hosts or tls_try_verify_hosts is set and
+tls_verify_certificates is not set.
+
+Any client that matches tls_verify_hosts is constrained by
+tls_verify_certificates. When the client initiates a TLS session, it must
+present one of the listed certificates. If it does not, the connection is
+aborted. Warning: Including a host in tls_verify_hosts does not require the
+host to use TLS. It can still send SMTP commands through unencrypted
+connections. Forcing a client to use TLS has to be done separately using an ACL
+to reject inappropriate commands when the connection is not encrypted.
+
+A weaker form of checking is provided by tls_try_verify_hosts. If a client
+matches this option (but not tls_verify_hosts), Exim requests a certificate and
+checks it against tls_verify_certificates, but does not abort the connection if
+there is no certificate or if it does not match. This state can be detected in
+an ACL, which makes it possible to implement policies such as "accept for relay
+only if a verified certificate has been received, but accept for local delivery
+if encrypted, even without a verified certificate".
+
+Client hosts that match neither of these lists are not asked to present
+certificates.
+
++----------------------------------------------------------+
+|trusted_groups|Use: main|Type: string list*|Default: unset|
++----------------------------------------------------------+
+
+This option is expanded just once, at the start of Exim's processing. If this
+option is set, any process that is running in one of the listed groups, or
+which has one of them as a supplementary group, is trusted. The groups can be
+specified numerically or by name. See section 5.2 for details of what trusted
+callers are permitted to do. If neither trusted_groups nor trusted_users is
+set, only root and the Exim user are trusted.
+
++---------------------------------------------------------+
+|trusted_users|Use: main|Type: string list*|Default: unset|
++---------------------------------------------------------+
+
+This option is expanded just once, at the start of Exim's processing. If this
+option is set, any process that is running as one of the listed users is
+trusted. The users can be specified numerically or by name. See section 5.2 for
+details of what trusted callers are permitted to do. If neither trusted_groups
+nor trusted_users is set, only root and the Exim user are trusted.
+
++----------------------------------------------------+
+|unknown_login|Use: main|Type: string*|Default: unset|
++----------------------------------------------------+
+
+This is a specialized feature for use in unusual configurations. By default, if
+the uid of the caller of Exim cannot be looked up using getpwuid(), Exim gives
+up. The unknown_login option can be used to set a login name to be used in this
+circumstance. It is expanded, so values like user$caller_uid can be set. When
+unknown_login is used, the value of unknown_username is used for the user's
+real name (gecos field), unless this has been set by the -F option.
+
++------------------------------------------------------+
+|unknown_username|Use: main|Type: string|Default: unset|
++------------------------------------------------------+
+
+See unknown_login.
+
++-----------------------------------------------------------------+
+|untrusted_set_sender|Use: main|Type: address list*|Default: unset|
++-----------------------------------------------------------------+
+
+When an untrusted user submits a message to Exim using the standard input, Exim
+normally creates an envelope sender address from the user's login and the
+default qualification domain. Data from the -f option (for setting envelope
+senders on non-SMTP messages) or the SMTP MAIL command (if -bs or -bS is used)
+is ignored.
+
+However, untrusted users are permitted to set an empty envelope sender address,
+to declare that a message should never generate any bounces. For example:
+
+exim -f '<>' user@domain.example
+
+The untrusted_set_sender option allows you to permit untrusted users to set
+other envelope sender addresses in a controlled way. When it is set, untrusted
+users are allowed to set envelope sender addresses that match any of the
+patterns in the list. Like all address lists, the string is expanded. The
+identity of the user is in $sender_ident, so you can, for example, restrict
+users to setting senders that start with their login ids followed by a hyphen
+by a setting like this:
+
+untrusted_set_sender = ^$sender_ident-
+
+If you want to allow untrusted users to set envelope sender addresses without
+restriction, you can use
+
+untrusted_set_sender = *
+
+The untrusted_set_sender option applies to all forms of local input, but only
+to the setting of the envelope sender. It does not permit untrusted users to
+use the other options which trusted user can use to override message
+parameters. Furthermore, it does not stop Exim from removing an existing
+Sender: header in the message, or from adding a Sender: header if necessary.
+See local_sender_retain and local_from_check for ways of overriding these
+actions. The handling of the Sender: header is also described in section 48.16.
+
+The log line for a message's arrival shows the envelope sender following "<=".
+For local messages, the user's login always follows, after "U=". In -bp
+displays, and in the Exim monitor, if an untrusted user sets an envelope sender
+address, the user's login is shown in parentheses after the sender address.
+
++-----------------------------------------------------------+
+|uucp_from_pattern|Use: main|Type: string|Default: see below|
++-----------------------------------------------------------+
+
+Some applications that pass messages to an MTA via a command line interface use
+an initial line starting with "From " to pass the envelope sender. In
+particular, this is used by UUCP software. Exim recognizes such a line by means
+of a regular expression that is set in uucp_from_pattern. When the pattern
+matches, the sender address is constructed by expanding the contents of
+uucp_from_sender, provided that the caller of Exim is a trusted user. The
+default pattern recognizes lines in the following two forms:
+
+From ph10 Fri Jan 5 12:35 GMT 1996
+From ph10 Fri, 7 Jan 97 14:00:00 GMT
+
+The pattern can be seen by running
+
+exim -bP uucp_from_pattern
+
+It checks only up to the hours and minutes, and allows for a 2-digit or 4-digit
+year in the second case. The first word after "From " is matched in the regular
+expression by a parenthesized subpattern. The default value for
+uucp_from_sender is "$1", which therefore just uses this first word ("ph10" in
+the example above) as the message's sender. See also ignore_fromline_hosts.
+
++------------------------------------------------------+
+|uucp_from_sender|Use: main|Type: string*|Default: "$1"|
++------------------------------------------------------+
+
+See uucp_from_pattern above.
+
++--------------------------------------------------------+
+|warn_message_file|Use: main|Type: string*|Default: unset|
++--------------------------------------------------------+
+
+This option defines a template file containing paragraphs of text to be used
+for constructing the warning message which is sent by Exim when a message has
+been in the queue for a specified amount of time, as specified by delay_warning
+. Details of the file's contents are given in chapter 50.
+
+The option is expanded to give the file path, which must be absolute and
+untainted.
+
+See also bounce_message_file.
+
++-----------------------------------------------------+
+|write_rejectlog|Use: main|Type: boolean|Default: true|
++-----------------------------------------------------+
+
+If this option is set false, Exim no longer writes anything to the reject log.
+See chapter 53 for details of what Exim writes to its logs.
+
+
+
+===============================================================================
+15. GENERIC OPTIONS FOR ROUTERS
+
+This chapter describes the generic options that apply to all routers. Those
+that are preconditions are marked with ** in the "use" field.
+
+For a general description of how a router operates, see sections 3.10 and 3.12.
+The latter specifies the order in which the preconditions are tested. The order
+of expansion of the options that provide data for a transport is: errors_to,
+headers_add, headers_remove, transport.
+
+The name of a router is limited to be 64 ASCII characters long; prior to Exim
+4.95 names would be silently truncated at this length, but now it is enforced.
+
++------------------------------------------------------+
+|address_data|Use: routers|Type: string*|Default: unset|
++------------------------------------------------------+
+
+The string is expanded just before the router is run, that is, after all the
+precondition tests have succeeded. If the expansion is forced to fail, the
+router declines, the value of address_data remains unchanged, and the more
+option controls what happens next. Other expansion failures cause delivery of
+the address to be deferred.
+
+When the expansion succeeds, the value is retained with the address, and can be
+accessed using the variable $address_data in the current router, subsequent
+routers, and the eventual transport.
+
+Warning: If the current or any subsequent router is a redirect router that runs
+a user's filter file, the contents of $address_data are accessible in the
+filter. This is not normally a problem, because such data is usually either not
+confidential or it "belongs" to the current user, but if you do put
+confidential data into $address_data you need to remember this point.
+
+Even if the router declines or passes, the value of $address_data remains with
+the address, though it can be changed by another address_data setting on a
+subsequent router. If a router generates child addresses, the value of
+$address_data propagates to them. This also applies to the special kind of
+"child" that is generated by a router with the unseen option.
+
+The idea of address_data is that you can use it to look up a lot of data for
+the address once, and then pick out parts of the data later. For example, you
+could use a single LDAP lookup to return a string of the form
+
+uid=1234 gid=5678 mailbox=/mail/xyz forward=/home/xyz/.forward
+
+In the transport you could pick out the mailbox by a setting such as
+
+file = ${extract{mailbox}{$address_data}}
+
+This makes the configuration file less messy, and also reduces the number of
+lookups (though Exim does cache lookups).
+
+See also the set option below.
+
+The address_data facility is also useful as a means of passing information from
+one router to another, and from a router to a transport. In addition, if
+$address_data is set by a router when verifying a recipient address from an
+ACL, it remains available for use in the rest of the ACL statement. After
+verifying a sender, the value is transferred to $sender_address_data.
+
++-------------------------------------------------------+
+|address_test|Use: routers**|Type: boolean|Default: true|
++-------------------------------------------------------+
+
+If this option is set false, the router is skipped when routing is being tested
+by means of the -bt command line option. This can be a convenience when your
+first router sends messages to an external scanner, because it saves you having
+to set the "already scanned" indicator when testing real address routing.
+
++--------------------------------------------------------------+
+|cannot_route_message|Use: routers|Type: string*|Default: unset|
++--------------------------------------------------------------+
+
+This option specifies a text message that is used when an address cannot be
+routed because Exim has run out of routers. The default message is "Unrouteable
+address". This option is useful only on routers that have more set false, or on
+the very last router in a configuration, because the value that is used is
+taken from the last router that is considered. This includes a router that is
+skipped because its preconditions are not met, as well as a router that
+declines. For example, using the default configuration, you could put:
+
+cannot_route_message = Remote domain not found in DNS
+
+on the first router, which is a dnslookup router with more set false, and
+
+cannot_route_message = Unknown local user
+
+on the final router that checks for local users. If string expansion fails for
+this option, the default message is used. Unless the expansion failure was
+explicitly forced, a message about the failure is written to the main and panic
+logs, in addition to the normal message about the routing failure.
+
++------------------------------------------------------------+
+|caseful_local_part|Use: routers|Type: boolean|Default: false|
++------------------------------------------------------------+
+
+By default, routers handle the local parts of addresses in a case-insensitive
+manner, though the actual case is preserved for transmission with the message.
+If you want the case of letters to be significant in a router, you must set
+this option true. For individual router options that contain address or local
+part lists (for example, local_parts), case-sensitive matching can be turned on
+by "+caseful" as a list item. See section 10.21 for more details.
+
+The value of the $local_part variable is forced to lower case while a router is
+running unless caseful_local_part is set. When a router assigns an address to a
+transport, the value of $local_part when the transport runs is the same as it
+was in the router. Similarly, when a router generates child addresses by
+aliasing or forwarding, the values of $original_local_part and
+$parent_local_part are those that were used by the redirecting router.
+
+This option applies to the processing of an address by a router. When a
+recipient address is being processed in an ACL, there is a separate control
+modifier that can be used to specify case-sensitive processing within the ACL
+(see section 44.22).
+
++------------------------------------------------------------+
+|check_local_user|Use: routers**|Type: boolean|Default: false|
++------------------------------------------------------------+
+
+When this option is true, Exim checks that the local part of the recipient
+address (with affixes removed if relevant) is the name of an account on the
+local system. The check is done by calling the getpwnam() function rather than
+trying to read /etc/passwd directly. This means that other methods of holding
+password data (such as NIS) are supported. If the local part is a local user,
+$home is set from the password data, and can be tested in other preconditions
+that are evaluated after this one (the order of evaluation is given in section
+3.12). However, the value of $home can be overridden by router_home_directory.
+If the local part is not a local user, the router is skipped.
+
+If you want to check that the local part is either the name of a local user or
+matches something else, you cannot combine check_local_user with a setting of
+local_parts, because that specifies the logical and of the two conditions.
+However, you can use a passwd lookup in a local_parts setting to achieve this.
+For example:
+
+local_parts = passwd;$local_part : lsearch;/etc/other/users
+
+Note, however, that the side effects of check_local_user (such as setting up a
+home directory) do not occur when a passwd lookup is used in a local_parts (or
+any other) precondition.
+
++-----------------------------------------------------+
+|condition|Use: routers**|Type: string*|Default: unset|
++-----------------------------------------------------+
+
+This option specifies a general precondition test that has to succeed for the
+router to be called. The condition option is the last precondition to be
+evaluated (see section 3.12). The string is expanded, and if the result is a
+forced failure, or an empty string, or one of the strings "0" or "no" or
+"false" (checked without regard to the case of the letters), the router is
+skipped, and the address is offered to the next one.
+
+If the result is any other value, the router is run (as this is the last
+precondition to be evaluated, all the other preconditions must be true).
+
+This option is unusual in that multiple condition options may be present. All
+condition options must succeed.
+
+The condition option provides a means of applying custom conditions to the
+running of routers. Note that in the case of a simple conditional expansion,
+the default expansion values are exactly what is wanted. For example:
+
+condition = ${if >{$message_age}{600}}
+
+Because of the default behaviour of the string expansion, this is equivalent to
+
+condition = ${if >{$message_age}{600}{true}{}}
+
+A multiple condition example, which succeeds:
+
+condition = ${if >{$message_age}{600}}
+condition = ${if !eq{${lc:$local_part}}{postmaster}}
+condition = foobar
+
+If the expansion fails (other than forced failure) delivery is deferred. Some
+of the other precondition options are common special cases that could in fact
+be specified using condition.
+
+Historical note: We have condition on ACLs and on Routers. Routers are far
+older, and use one set of semantics. ACLs are newer and when they were created,
+the ACL condition process was given far stricter parse semantics. The bool{}
+expansion condition uses the same rules as ACLs. The bool_lax{} expansion
+condition uses the same rules as Routers. More pointedly, the bool_lax{} was
+written to match the existing Router rules processing behavior.
+
+This is best illustrated in an example:
+
+# If used in an ACL condition will fail with a syntax error, but
+# in a router condition any extra characters are treated as a string
+
+$ exim -be '${if eq {${lc:GOOGLE.com}} {google.com}} {yes} {no}}'
+true {yes} {no}}
+
+$ exim -be '${if eq {${lc:WHOIS.com}} {google.com}} {yes} {no}}'
+ {yes} {no}}
+
+In each example above, the if statement actually ends after "{google.com}}".
+Since no true or false braces were defined, the default if behavior is to
+return a boolean true or a null answer (which evaluates to false). The rest of
+the line is then treated as a string. So the first example resulted in the
+boolean answer "true" with the string " {yes} {no}}" appended to it. The second
+example resulted in the null output (indicating false) with the string " {yes}
+{no}}" appended to it.
+
+In fact you can put excess forward braces in too. In the router condition,
+Exim's parser only looks for "{" symbols when they mean something, like after a
+"$" or when required as part of a conditional. But otherwise "{" and "}" are
+treated as ordinary string characters.
+
+Thus, in a Router, the above expansion strings will both always evaluate true,
+as the result of expansion is a non-empty string which doesn't match an
+explicit false value. This can be tricky to debug. By contrast, in an ACL
+either of those strings will always result in an expansion error because the
+result doesn't look sufficiently boolean.
+
++-----------------------------------------------------+
+|debug_print|Use: routers|Type: string*|Default: unset|
++-----------------------------------------------------+
+
+If this option is set and debugging is enabled (see the -d command line option)
+or in address-testing mode (see the -bt command line option), the string is
+expanded and included in the debugging output. If expansion of the string
+fails, the error message is written to the debugging output, and Exim carries
+on processing. This option is provided to help with checking out the values of
+variables and so on when debugging router configurations. For example, if a
+condition option appears not to be working, debug_print can be used to output
+the variables it references. The output happens after checks for domains,
+local_parts, and check_local_user but before any other preconditions are
+tested. A newline is added to the text if it does not end with one. The
+variable $router_name contains the name of the router.
+
++---------------------------------------------------------+
+|disable_logging|Use: routers|Type: boolean|Default: false|
++---------------------------------------------------------+
+
+If this option is set true, nothing is logged for any routing errors or for any
+deliveries caused by this router. You should not set this option unless you
+really, really know what you are doing. See also the generic transport option
+of the same name.
+
++-----------------------------------------------------------------+
+|dnssec_request_domains|Use: routers|Type: domain list*|Default: *|
++-----------------------------------------------------------------+
+
+DNS lookups for domains matching dnssec_request_domains will be done with the
+dnssec request bit set. This applies to all of the SRV, MX, AAAA, A lookup
+sequence.
+
++---------------------------------------------------------------------+
+|dnssec_require_domains|Use: routers|Type: domain list*|Default: unset|
++---------------------------------------------------------------------+
+
+DNS lookups for domains matching dnssec_require_domains will be done with the
+dnssec request bit set. Any returns not having the Authenticated Data bit (AD
+bit) set will be ignored and logged as a host-lookup failure. This applies to
+all of the SRV, MX, AAAA, A lookup sequence.
+
++--------------------------------------------------------+
+|domains|Use: routers**|Type: domain list*|Default: unset|
++--------------------------------------------------------+
+
+If this option is set, the router is skipped unless the current domain matches
+the list. If the match is achieved by means of a file lookup, the data that the
+lookup returned for the domain is placed in $domain_data for use in string
+expansions of the driver's private options. See section 3.12 for a list of the
+order in which preconditions are evaluated.
+
++-----------------------------------------------+
+|driver|Use: routers|Type: string|Default: unset|
++-----------------------------------------------+
+
+This option must always be set. It specifies which of the available routers is
+to be used.
+
++-----------------------------------------------------+
+|dsn_lasthop|Use: routers|Type: boolean|Default: false|
++-----------------------------------------------------+
+
+If this option is set true, and extended DSN (RFC3461) processing is in effect,
+Exim will not pass on DSN requests to downstream DSN-aware hosts but will
+instead send a success DSN as if the next hop does not support DSN. Not
+effective on redirect routers.
+
++---------------------------------------------------+
+|errors_to|Use: routers|Type: string*|Default: unset|
++---------------------------------------------------+
+
+If a router successfully handles an address, it may assign the address to a
+transport for delivery or it may generate child addresses. In both cases, if
+there is a delivery problem during later processing, the resulting bounce
+message is sent to the address that results from expanding this string,
+provided that the address verifies successfully. The errors_to option is
+expanded before headers_add, headers_remove, and transport.
+
+The errors_to setting associated with an address can be overridden if it
+subsequently passes through other routers that have their own errors_to
+settings, or if the message is delivered by a transport with a return_path
+setting.
+
+If errors_to is unset, or the expansion is forced to fail, or the result of the
+expansion fails to verify, the errors address associated with the incoming
+address is used. At top level, this is the envelope sender. A non-forced
+expansion failure causes delivery to be deferred.
+
+If an address for which errors_to has been set ends up being delivered over
+SMTP, the envelope sender for that delivery is the errors_to value, so that any
+bounces that are generated by other MTAs on the delivery route are also sent
+there. You can set errors_to to the empty string by either of these settings:
+
+errors_to =
+errors_to = ""
+
+An expansion item that yields an empty string has the same effect. If you do
+this, a locally detected delivery error for addresses processed by this router
+no longer gives rise to a bounce message; the error is discarded. If the
+address is delivered to a remote host, the return path is set to "<>", unless
+overridden by the return_path option on the transport.
+
+If for some reason you want to discard local errors, but use a non-empty MAIL
+command for remote delivery, you can preserve the original return path in
+$address_data in the router, and reinstate it in the transport by setting
+return_path.
+
+The most common use of errors_to is to direct mailing list bounces to the
+manager of the list, as described in section 51.2, or to implement VERP
+(Variable Envelope Return Paths) (see section 51.6).
+
++-----------------------------------------------+
+|expn|Use: routers**|Type: boolean|Default: true|
++-----------------------------------------------+
+
+If this option is turned off, the router is skipped when testing an address as
+a result of processing an SMTP EXPN command. You might, for example, want to
+turn it off on a router for users' .forward files, while leaving it on for the
+system alias file. See section 3.12 for a list of the order in which
+preconditions are evaluated.
+
+The use of the SMTP EXPN command is controlled by an ACL (see chapter 44). When
+Exim is running an EXPN command, it is similar to testing an address with -bt.
+Compare VRFY, whose counterpart is -bv.
+
++-----------------------------------------------------+
+|fail_verify|Use: routers|Type: boolean|Default: false|
++-----------------------------------------------------+
+
+Setting this option has the effect of setting both fail_verify_sender and
+fail_verify_recipient to the same value.
+
++---------------------------------------------------------------+
+|fail_verify_recipient|Use: routers|Type: boolean|Default: false|
++---------------------------------------------------------------+
+
+If this option is true and an address is accepted by this router when verifying
+a recipient, verification fails.
+
++------------------------------------------------------------+
+|fail_verify_sender|Use: routers|Type: boolean|Default: false|
++------------------------------------------------------------+
+
+If this option is true and an address is accepted by this router when verifying
+a sender, verification fails.
+
++------------------------------------------------------------+
+|fallback_hosts|Use: routers|Type: string list|Default: unset|
++------------------------------------------------------------+
+
+String expansion is not applied to this option. The argument must be a
+colon-separated list of host names or IP addresses. The list separator can be
+changed (see section 6.21), and a port can be specified with each name or
+address. In fact, the format of each item is exactly the same as defined for
+the list of hosts in a manualroute router (see section 20.5).
+
+If a router queues an address for a remote transport, this host list is
+associated with the address, and used instead of the transport's fallback host
+list. If hosts_randomize is set on the transport, the order of the list is
+randomized for each use. See the fallback_hosts option of the smtp transport
+for further details.
+
++---------------------------------------------------+
+|group|Use: routers|Type: string*|Default: see below|
++---------------------------------------------------+
+
+When a router queues an address for a transport, and the transport does not
+specify a group, the group given here is used when running the delivery
+process. The group may be specified numerically or by name. If expansion fails,
+the error is logged and delivery is deferred. The default is unset, unless
+check_local_user is set, when the default is taken from the password
+information. See also initgroups and user and the discussion in chapter 23.
+
++---------------------------------------------------+
+|headers_add|Use: routers|Type: list*|Default: unset|
++---------------------------------------------------+
+
+This option specifies a list of text headers, newline-separated (by default,
+changeable in the usual way 6.21), that is associated with any addresses that
+are accepted by the router. Each item is separately expanded, at routing time.
+However, this option has no effect when an address is just being verified. The
+way in which the text is used to add header lines at transport time is
+described in section 48.17. New header lines are not actually added until the
+message is in the process of being transported. This means that references to
+header lines in string expansions in the transport's configuration do not "see"
+the added header lines.
+
+The headers_add option is expanded after errors_to, but before headers_remove
+and transport. If an item is empty, or if an item expansion is forced to fail,
+the item has no effect. Other expansion failures are treated as configuration
+errors.
+
+Unlike most options, headers_add can be specified multiple times for a router;
+all listed headers are added.
+
+Warning 1: The headers_add option cannot be used for a redirect router that has
+the one_time option set.
+
+Warning 2: If the unseen option is set on the router, all header additions are
+deleted when the address is passed on to subsequent routers. For a redirect
+router, if a generated address is the same as the incoming address, this can
+lead to duplicate addresses with different header modifications. Exim does not
+do duplicate deliveries (except, in certain circumstances, to pipes -- see
+section 22.7), but it is undefined which of the duplicates is discarded, so
+this ambiguous situation should be avoided. The repeat_use option of the
+redirect router may be of help.
+
++------------------------------------------------------+
+|headers_remove|Use: routers|Type: list*|Default: unset|
++------------------------------------------------------+
+
+This option specifies a list of text headers, colon-separated (by default,
+changeable in the usual way 6.21), that is associated with any addresses that
+are accepted by the router. However, the option has no effect when an address
+is just being verified. Each list item is separately expanded, at transport
+time.
+
+If an item ends in *, it will match any header with the given prefix.
+
+The way in which the text is used to remove header lines at transport time is
+described in section 48.17. Header lines are not actually removed until the
+message is in the process of being transported. This means that references to
+header lines in string expansions in the transport's configuration still "see"
+the original header lines.
+
+The headers_remove option is handled after errors_to and headers_add, but
+before transport. If an item expansion is forced to fail, the item has no
+effect. Other expansion failures are treated as configuration errors.
+
+Unlike most options, headers_remove can be specified multiple times for a
+router; all listed headers are removed.
+
+Warning 1: The headers_remove option cannot be used for a redirect router that
+has the one_time option set.
+
+Warning 2: If the unseen option is set on the router, all header removal
+requests are deleted when the address is passed on to subsequent routers, and
+this can lead to problems with duplicates -- see the similar warning for
+headers_add above.
+
+Warning 3: Because of the separate expansion of the list items, items that
+contain a list separator must have it doubled. To avoid this, change the list
+separator (6.21).
+
++----------------------------------------------------------------+
+|ignore_target_hosts|Use: routers|Type: host list*|Default: unset|
++----------------------------------------------------------------+
+
+Although this option is a host list, it should normally contain IP address
+entries rather than names. If any host that is looked up by the router has an
+IP address that matches an item in this list, Exim behaves as if that IP
+address did not exist. This option allows you to cope with rogue DNS entries
+like
+
+remote.domain.example. A 127.0.0.1
+
+by setting
+
+ignore_target_hosts = 127.0.0.1
+
+on the relevant router. If all the hosts found by a dnslookup router are
+discarded in this way, the router declines. In a conventional configuration, an
+attempt to mail to such a domain would normally provoke the "unrouteable
+domain" error, and an attempt to verify an address in the domain would fail.
+Similarly, if ignore_target_hosts is set on an ipliteral router, the router
+declines if presented with one of the listed addresses.
+
+You can use this option to disable the use of IPv4 or IPv6 for mail delivery by
+means of the first or the second of the following settings, respectively:
+
+ignore_target_hosts = 0.0.0.0/0
+ignore_target_hosts = <; 0::0/0
+
+The pattern in the first line matches all IPv4 addresses, whereas the pattern
+in the second line matches all IPv6 addresses.
+
+This option may also be useful for ignoring link-local and site-local IPv6
+addresses. Because, like all host lists, the value of ignore_target_hosts is
+expanded before use as a list, it is possible to make it dependent on the
+domain that is being routed.
+
+During its expansion, $host_address is set to the IP address that is being
+checked.
+
++----------------------------------------------------+
+|initgroups|Use: routers|Type: boolean|Default: false|
++----------------------------------------------------+
+
+If the router queues an address for a transport, and this option is true, and
+the uid supplied by the router is not overridden by the transport, the
+initgroups() function is called when running the transport to ensure that any
+additional groups associated with the uid are set up. See also group and user
+and the discussion in chapter 23.
+
++-----------------------------------------------------------------+
+|local_part_prefix|Use: routers**|Type: string list|Default: unset|
++-----------------------------------------------------------------+
+
+If this option is set, the router is skipped unless the local part starts with
+one of the given strings, or local_part_prefix_optional is true. See section
+3.12 for a list of the order in which preconditions are evaluated.
+
+The list is scanned from left to right, and the first prefix that matches is
+used. A limited form of wildcard is available; if the prefix begins with an
+asterisk, it matches the longest possible sequence of arbitrary characters at
+the start of the local part. An asterisk should therefore always be followed by
+some character that does not occur in normal local parts. Wildcarding can be
+used to set up multiple user mailboxes, as described in section 51.8.
+
+During the testing of the local_parts option, and while the router is running,
+the prefix is removed from the local part, and is available in the expansion
+variable $local_part_prefix. When a message is being delivered, if the router
+accepts the address, this remains true during subsequent delivery by a
+transport. In particular, the local part that is transmitted in the RCPT
+command for LMTP, SMTP, and BSMTP deliveries has the prefix removed by default.
+This behaviour can be overridden by setting rcpt_include_affixes true on the
+relevant transport.
+
+If wildcarding (above) was used then the part of the prefix matching the
+wildcard is available in $local_part_prefix_v.
+
+When an address is being verified, local_part_prefix affects only the behaviour
+of the router. If the callout feature of verification is in use, this means
+that the full address, including the prefix, will be used during the callout.
+
+The prefix facility is commonly used to handle local parts of the form
+owner-something. Another common use is to support local parts of the form
+real-username to bypass a user's .forward file - helpful when trying to tell a
+user their forwarding is broken - by placing a router like this one immediately
+before the router that handles .forward files:
+
+real_localuser:
+ driver = accept
+ local_part_prefix = real-
+ check_local_user
+ transport = local_delivery
+
+For security, it would probably be a good idea to restrict the use of this
+router to locally-generated messages, using a condition such as this:
+
+ condition = ${if match {$sender_host_address}\
+ {\N^(|127\.0\.0\.1)$\N}}
+
+If both local_part_prefix and local_part_suffix are set for a router, both
+conditions must be met if not optional. Care must be taken if wildcards are
+used in both a prefix and a suffix on the same router. Different separator
+characters must be used to avoid ambiguity.
+
++--------------------------------------------------------------------+
+|local_part_prefix_optional|Use: routers|Type: boolean|Default: false|
++--------------------------------------------------------------------+
+
+See local_part_prefix above.
+
++-----------------------------------------------------------------+
+|local_part_suffix|Use: routers**|Type: string list|Default: unset|
++-----------------------------------------------------------------+
+
+This option operates in the same way as local_part_prefix, except that the
+local part must end (rather than start) with the given string, the
+local_part_suffix_optional option determines whether the suffix is mandatory,
+and the wildcard * character, if present, must be the last character of the
+suffix. This option facility is commonly used to handle local parts of the form
+something-request and multiple user mailboxes of the form username-foo.
+
++--------------------------------------------------------------------+
+|local_part_suffix_optional|Use: routers|Type: boolean|Default: false|
++--------------------------------------------------------------------+
+
+See local_part_suffix above.
+
++----------------------------------------------------------------+
+|local_parts|Use: routers**|Type: local part list*|Default: unset|
++----------------------------------------------------------------+
+
+The router is run only if the local part of the address matches the list. See
+section 3.12 for a list of the order in which preconditions are evaluated, and
+section 10.22 for a discussion of local part lists. Because the string is
+expanded, it is possible to make it depend on the domain, for example:
+
+local_parts = dbm;/usr/local/specials/$domain
+
+If the match is achieved by a lookup, the data that the lookup returned for the
+local part is placed in the variable $local_part_data for use in expansions of
+the router's private options. You might use this option, for example, if you
+have a large number of local virtual domains, and you want to send all
+postmaster mail to the same place without having to set up an alias in each
+virtual domain:
+
+postmaster:
+ driver = redirect
+ local_parts = postmaster
+ data = postmaster@real.domain.example
+
++----------------------------------------------------------+
+|log_as_local|Use: routers|Type: boolean|Default: see below|
++----------------------------------------------------------+
+
+Exim has two logging styles for delivery, the idea being to make local
+deliveries stand out more visibly from remote ones. In the "local" style, the
+recipient address is given just as the local part, without a domain. The use of
+this style is controlled by this option. It defaults to true for the accept
+router, and false for all the others. This option applies only when a router
+assigns an address to a transport. It has no effect on routers that redirect
+addresses.
+
++----------------------------------------------+
+|more|Use: routers|Type: boolean*|Default: true|
++----------------------------------------------+
+
+The result of string expansion for this option must be a valid boolean value,
+that is, one of the strings "yes", "no", "true", or "false". Any other result
+causes an error, and delivery is deferred. If the expansion is forced to fail,
+the default value for the option (true) is used. Other failures cause delivery
+to be deferred.
+
+If this option is set false, and the router declines to handle the address, no
+further routers are tried, routing fails, and the address is bounced. However,
+if the router explicitly passes an address to the following router by means of
+the setting
+
+self = pass
+
+or otherwise, the setting of more is ignored. Also, the setting of more does
+not affect the behaviour if one of the precondition tests fails. In that case,
+the address is always passed to the next router.
+
+Note that address_data is not considered to be a precondition. If its expansion
+is forced to fail, the router declines, and the value of more controls what
+happens next.
+
++---------------------------------------------------------+
+|pass_on_timeout|Use: routers|Type: boolean|Default: false|
++---------------------------------------------------------+
+
+If a router times out during a host lookup, it normally causes deferral of the
+address. If pass_on_timeout is set, the address is passed on to the next
+router, overriding no_more. This may be helpful for systems that are
+intermittently connected to the Internet, or those that want to pass to a smart
+host any messages that cannot immediately be delivered.
+
+There are occasional other temporary errors that can occur while doing DNS
+lookups. They are treated in the same way as a timeout, and this option applies
+to all of them.
+
++----------------------------------------------------+
+|pass_router|Use: routers|Type: string|Default: unset|
++----------------------------------------------------+
+
+Routers that recognize the generic self option (dnslookup, ipliteral, and
+manualroute) are able to return "pass", forcing routing to continue, and
+overriding a false setting of more. When one of these routers returns "pass",
+the address is normally handed on to the next router in sequence. This can be
+changed by setting pass_router to the name of another router. However (unlike
+redirect_router) the named router must be below the current router, to avoid
+loops. Note that this option applies only to the special case of "pass". It
+does not apply when a router returns "decline" because it cannot handle an
+address.
+
++--------------------------------------------------------+
+|redirect_router|Use: routers|Type: string|Default: unset|
++--------------------------------------------------------+
+
+Sometimes an administrator knows that it is pointless to reprocess addresses
+generated from alias or forward files with the same router again. For example,
+if an alias file translates real names into login ids there is no point
+searching the alias file a second time, especially if it is a large file.
+
+The redirect_router option can be set to the name of any router instance. It
+causes the routing of any generated addresses to start at the named router
+instead of at the first router. This option has no effect if the router in
+which it is set does not generate new addresses.
+
++--------------------------------------------------------------+
+|require_files|Use: routers**|Type: string list*|Default: unset|
++--------------------------------------------------------------+
+
+This option provides a general mechanism for predicating the running of a
+router on the existence or non-existence of certain files or directories.
+Before running a router, as one of its precondition tests, Exim works its way
+through the require_files list, expanding each item separately.
+
+Because the list is split before expansion, any colons in expansion items must
+be doubled, or the facility for using a different list separator must be used (
+6.21). If any expansion is forced to fail, the item is ignored. Other expansion
+failures cause routing of the address to be deferred.
+
+If any expanded string is empty, it is ignored. Otherwise, except as described
+below, each string must be a fully qualified file path, optionally preceded by
+"!". The paths are passed to the stat() function to test for the existence of
+the files or directories. The router is skipped if any paths not preceded by "!
+" do not exist, or if any paths preceded by "!" do exist.
+
+If stat() cannot determine whether a file exists or not, delivery of the
+message is deferred. This can happen when NFS-mounted filesystems are
+unavailable.
+
+This option is checked after the domains, local_parts, and senders options, so
+you cannot use it to check for the existence of a file in which to look up a
+domain, local part, or sender. (See section 3.12 for a full list of the order
+in which preconditions are evaluated.) However, as these options are all
+expanded, you can use the exists expansion condition to make such tests. The
+require_files option is intended for checking files that the router may be
+going to use internally, or which are needed by a transport (e.g., .procmailrc
+).
+
+During delivery, the stat() function is run as root, but there is a facility
+for some checking of the accessibility of a file by another user. This is not a
+proper permissions check, but just a "rough" check that operates as follows:
+
+If an item in a require_files list does not contain any forward slash
+characters, it is taken to be the user (and optional group, separated by a
+comma) to be checked for subsequent files in the list. If no group is specified
+but the user is specified symbolically, the gid associated with the uid is
+used. For example:
+
+require_files = mail:/some/file
+require_files = $local_part_data:$home/.procmailrc
+
+If a user or group name in a require_files list does not exist, the
+require_files condition fails.
+
+Exim performs the check by scanning along the components of the file path, and
+checking the access for the given uid and gid. It checks for "x" access on
+directories, and "r" access on the final file. Note that this means that file
+access control lists, if the operating system has them, are ignored.
+
+Warning 1: When the router is being run to verify addresses for an incoming
+SMTP message, Exim is not running as root, but under its own uid. This may
+affect the result of a require_files check. In particular, stat() may yield the
+error EACCES ("Permission denied"). This means that the Exim user is not
+permitted to read one of the directories on the file's path.
+
+Warning 2: Even when Exim is running as root while delivering a message, stat()
+can yield EACCES for a file in an NFS directory that is mounted without root
+access. In this case, if a check for access by a particular user is requested,
+Exim creates a subprocess that runs as that user, and tries the check again in
+that process.
+
+The default action for handling an unresolved EACCES is to consider it to be
+caused by a configuration error, and routing is deferred because the existence
+or non-existence of the file cannot be determined. However, in some
+circumstances it may be desirable to treat this condition as if the file did
+not exist. If the filename (or the exclamation mark that precedes the filename
+for non-existence) is preceded by a plus sign, the EACCES error is treated as
+if the file did not exist. For example:
+
+require_files = +/some/file
+
+If the router is not an essential part of verification (for example, it handles
+users' .forward files), another solution is to set the verify option false so
+that the router is skipped when verifying.
+
++------------------------------------------------------------------+
+|retry_use_local_part|Use: routers|Type: boolean|Default: see below|
++------------------------------------------------------------------+
+
+When a delivery suffers a temporary routing failure, a retry record is created
+in Exim's hints database. For addresses whose routing depends only on the
+domain, the key for the retry record should not involve the local part, but for
+other addresses, both the domain and the local part should be included.
+Usually, remote routing is of the former kind, and local routing is of the
+latter kind.
+
+This option controls whether the local part is used to form the key for retry
+hints for addresses that suffer temporary errors while being handled by this
+router. The default value is true for any router that has any of
+check_local_user, local_parts, condition, local_part_prefix, local_part_suffix,
+senders or require_files set, and false otherwise. Note that this option does
+not apply to hints keys for transport delays; they are controlled by a generic
+transport option of the same name.
+
+Failing to set this option when it is needed (because a remote router handles
+only some of the local-parts for a domain) can result in incorrect error
+messages being generated.
+
+The setting of retry_use_local_part applies only to the router on which it
+appears. If the router generates child addresses, they are routed
+independently; this setting does not become attached to them.
+
++---------------------------------------------------------------+
+|router_home_directory|Use: routers|Type: string*|Default: unset|
++---------------------------------------------------------------+
+
+This option sets a home directory for use while the router is running. (Compare
+transport_home_directory, which sets a home directory for later transporting.)
+In particular, if used on a redirect router, this option sets a value for $home
+while a filter is running. The value is expanded; forced expansion failure
+causes the option to be ignored - other failures cause the router to defer.
+
+Expansion of router_home_directory happens immediately after the
+check_local_user test (if configured), before any further expansions take
+place. (See section 3.12 for a list of the order in which preconditions are
+evaluated.) While the router is running, router_home_directory overrides the
+value of $home that came from check_local_user.
+
+When a router accepts an address and assigns it to a local transport (including
+the cases when a redirect router generates a pipe, file, or autoreply
+delivery), the home directory setting for the transport is taken from the first
+of these values that is set:
+
+ * The home_directory option on the transport;
+
+ * The transport_home_directory option on the router;
+
+ * The password data if check_local_user is set on the router;
+
+ * The router_home_directory option on the router.
+
+In other words, router_home_directory overrides the password data for the
+router, but not for the transport.
+
++----------------------------------------------+
+|self|Use: routers|Type: string|Default: freeze|
++----------------------------------------------+
+
+This option applies to those routers that use a recipient address to find a
+list of remote hosts. Currently, these are the dnslookup, ipliteral, and
+manualroute routers. Certain configurations of the queryprogram router can also
+specify a list of remote hosts. Usually such routers are configured to send the
+message to a remote host via an smtp transport. The self option specifies what
+happens when the first host on the list turns out to be the local host. The way
+in which Exim checks for the local host is described in section 13.8.
+
+Normally this situation indicates either an error in Exim's configuration (for
+example, the router should be configured not to process this domain), or an
+error in the DNS (for example, the MX should not point to this host). For this
+reason, the default action is to log the incident, defer the address, and
+freeze the message. The following alternatives are provided for use in special
+cases:
+
+defer
+
+ Delivery of the message is tried again later, but the message is not
+ frozen.
+
+reroute: <domain>
+
+ The domain is changed to the given domain, and the address is passed back
+ to be reprocessed by the routers. No rewriting of headers takes place. This
+ behaviour is essentially a redirection.
+
+reroute: rewrite: <domain>
+
+ The domain is changed to the given domain, and the address is passed back
+ to be reprocessed by the routers. Any headers that contain the original
+ domain are rewritten.
+
+pass
+
+ The router passes the address to the next router, or to the router named in
+ the pass_router option if it is set. This overrides no_more. During
+ subsequent routing and delivery, the variable $self_hostname contains the
+ name of the local host that the router encountered. This can be used to
+ distinguish between different cases for hosts with multiple names. The
+ combination
+
+ self = pass
+ no_more
+
+ ensures that only those addresses that routed to the local host are passed
+ on. Without no_more, addresses that were declined for other reasons would
+ also be passed to the next router.
+
+fail
+
+ Delivery fails and an error report is generated.
+
+send
+
+ The anomaly is ignored and the address is queued for the transport. This
+ setting should be used with extreme caution. For an smtp transport, it
+ makes sense only in cases where the program that is listening on the SMTP
+ port is not this version of Exim. That is, it must be some other MTA, or
+ Exim with a different configuration file that handles the domain in another
+ way.
+
++---------------------------------------------------------+
+|senders|Use: routers**|Type: address list*|Default: unset|
++---------------------------------------------------------+
+
+If this option is set, the router is skipped unless the message's sender
+address matches something on the list. See section 3.12 for a list of the order
+in which preconditions are evaluated.
+
+There are issues concerning verification when the running of routers is
+dependent on the sender. When Exim is verifying the address in an errors_to
+setting, it sets the sender to the null string. When using the -bt option to
+check a configuration file, it is necessary also to use the -f option to set an
+appropriate sender. For incoming mail, the sender is unset when verifying the
+sender, but is available when verifying any recipients. If the SMTP VRFY
+command is enabled, it must be used after MAIL if the sender address matters.
+
++-------------------------------------------------+
+|set|Use: routers|Type: string list|Default: unset|
++-------------------------------------------------+
+
+This option may be used multiple times on a router; because of this the list
+aspect is mostly irrelevant. The list separator is a semicolon but can be
+changed in the usual way.
+
+Each list-element given must be of the form "name = value" and the names used
+must start with the string "r_". Values containing a list-separator should have
+them doubled. When a router runs, the strings are evaluated in order, to create
+variables which are added to the set associated with the address. The variable
+is set with the expansion of the value. The variables can be used by the router
+options (not including any preconditions) and by the transport. Later
+definitions of a given named variable will override former ones. Variable use
+is via the usual $r_... syntax.
+
+This is similar to the address_data option, except that many independent
+variables can be used, with choice of naming.
+
++--------------------------------------------------------------+
+|translate_ip_address|Use: routers|Type: string*|Default: unset|
++--------------------------------------------------------------+
+
+There exist some rare networking situations (for example, packet radio) where
+it is helpful to be able to translate IP addresses generated by normal routing
+mechanisms into other IP addresses, thus performing a kind of manual IP
+routing. This should be done only if the normal IP routing of the TCP/IP stack
+is inadequate or broken. Because this is an extremely uncommon requirement, the
+code to support this option is not included in the Exim binary unless
+SUPPORT_TRANSLATE_IP_ADDRESS=yes is set in Local/Makefile.
+
+The translate_ip_address string is expanded for every IP address generated by
+the router, with the generated address set in $host_address. If the expansion
+is forced to fail, no action is taken. For any other expansion error, delivery
+of the message is deferred. If the result of the expansion is an IP address,
+that replaces the original address; otherwise the result is assumed to be a
+host name - this is looked up using gethostbyname() (or getipnodebyname() when
+available) to produce one or more replacement IP addresses. For example, to
+subvert all IP addresses in some specific networks, this could be added to a
+router:
+
+translate_ip_address = \
+ ${lookup{${mask:$host_address/26}}lsearch{/some/file}\
+ {$value}fail}}
+
+The file would contain lines like
+
+10.2.3.128/26 some.host
+10.8.4.34/26 10.44.8.15
+
+You should not make use of this facility unless you really understand what you
+are doing.
+
++---------------------------------------------------+
+|transport|Use: routers|Type: string*|Default: unset|
++---------------------------------------------------+
+
+This option specifies the transport to be used when a router accepts an address
+and sets it up for delivery. A transport is never needed if a router is used
+only for verification. The value of the option is expanded at routing time,
+after the expansion of errors_to, headers_add, and headers_remove, and result
+must be the name of one of the configured transports. If it is not, delivery is
+deferred.
+
+The transport option is not used by the redirect router, but it does have some
+private options that set up transports for pipe and file deliveries (see
+chapter 22).
+
++---------------------------------------------------------------------+
+|transport_current_directory|Use: routers|Type: string*|Default: unset|
++---------------------------------------------------------------------+
+
+This option associates a current directory with any address that is routed to a
+local transport. This can happen either because a transport is explicitly
+configured for the router, or because it generates a delivery to a file or a
+pipe. During the delivery process (that is, at transport time), this option
+string is expanded and is set as the current directory, unless overridden by a
+setting on the transport. If the expansion fails for any reason, including
+forced failure, an error is logged, and delivery is deferred. See chapter 23
+for details of the local delivery environment.
+
++----------------------------------------------------------------------+
+|transport_home_directory|Use: routers|Type: string*|Default: see below|
++----------------------------------------------------------------------+
+
+This option associates a home directory with any address that is routed to a
+local transport. This can happen either because a transport is explicitly
+configured for the router, or because it generates a delivery to a file or a
+pipe. During the delivery process (that is, at transport time), the option
+string is expanded and is set as the home directory, unless overridden by a
+setting of home_directory on the transport. If the expansion fails for any
+reason, including forced failure, an error is logged, and delivery is deferred.
+
+If the transport does not specify a home directory, and
+transport_home_directory is not set for the router, the home directory for the
+transport is taken from the password data if check_local_user is set for the
+router. Otherwise it is taken from router_home_directory if that option is set;
+if not, no home directory is set for the transport.
+
+See chapter 23 for further details of the local delivery environment.
+
++-------------------------------------------------+
+|unseen|Use: routers|Type: boolean*|Default: false|
++-------------------------------------------------+
+
+The result of string expansion for this option must be a valid boolean value,
+that is, one of the strings "yes", "no", "true", or "false". Any other result
+causes an error, and delivery is deferred. If the expansion is forced to fail,
+the default value for the option (false) is used. Other failures cause delivery
+to be deferred.
+
+When this option is set true, routing does not cease if the router accepts the
+address. Instead, a copy of the incoming address is passed to the next router,
+overriding a false setting of more. There is little point in setting more false
+if unseen is always true, but it may be useful in cases when the value of
+unseen contains expansion items (and therefore, presumably, is sometimes true
+and sometimes false).
+
+Setting the unseen option has a similar effect to the unseen command qualifier
+in filter files. It can be used to cause copies of messages to be delivered to
+some other destination, while also carrying out a normal delivery. In effect,
+the current address is made into a "parent" that has two children - one that is
+delivered as specified by this router, and a clone that goes on to be routed
+further. For this reason, unseen may not be combined with the one_time option
+in a redirect router.
+
+Warning: Header lines added to the address (or specified for removal) by this
+router or by previous routers affect the "unseen" copy of the message only. The
+clone that continues to be processed by further routers starts with no added
+headers and none specified for removal. For a redirect router, if a generated
+address is the same as the incoming address, this can lead to duplicate
+addresses with different header modifications. Exim does not do duplicate
+deliveries (except, in certain circumstances, to pipes -- see section 22.7),
+but it is undefined which of the duplicates is discarded, so this ambiguous
+situation should be avoided. The repeat_use option of the redirect router may
+be of help.
+
+Unlike the handling of header modifications, any data that was set by the
+address_data option in the current or previous routers is passed on to
+subsequent routers.
+
++--------------------------------------------------+
+|user|Use: routers|Type: string*|Default: see below|
++--------------------------------------------------+
+
+When a router queues an address for a transport, and the transport does not
+specify a user, the user given here is used when running the delivery process.
+The user may be specified numerically or by name. If expansion fails, the error
+is logged and delivery is deferred. This user is also used by the redirect
+router when running a filter file. The default is unset, except when
+check_local_user is set. In this case, the default is taken from the password
+information. If the user is specified as a name, and group is not set, the
+group associated with the user is used. See also initgroups and group and the
+discussion in chapter 23.
+
++-------------------------------------------------+
+|verify|Use: routers**|Type: boolean|Default: true|
++-------------------------------------------------+
+
+Setting this option has the effect of setting verify_sender and
+verify_recipient to the same value.
+
++-------------------------------------------------------+
+|verify_only|Use: routers**|Type: boolean|Default: false|
++-------------------------------------------------------+
+
+If this option is set, the router is used only when verifying an address,
+delivering in cutthrough mode or testing with the -bv option, not when actually
+doing a delivery, testing with the -bt option, or running the SMTP EXPN
+command. It can be further restricted to verifying only senders or recipients
+by means of verify_sender and verify_recipient.
+
+Warning: When the router is being run to verify addresses for an incoming SMTP
+message, Exim is not running as root, but under its own uid. If the router
+accesses any files, you need to make sure that they are accessible to the Exim
+user or group.
+
++-----------------------------------------------------------+
+|verify_recipient|Use: routers**|Type: boolean|Default: true|
++-----------------------------------------------------------+
+
+If this option is false, the router is skipped when verifying recipient
+addresses, delivering in cutthrough mode or testing recipient verification
+using -bv. See section 3.12 for a list of the order in which preconditions are
+evaluated. See also the $verify_mode variable.
+
++--------------------------------------------------------+
+|verify_sender|Use: routers**|Type: boolean|Default: true|
++--------------------------------------------------------+
+
+If this option is false, the router is skipped when verifying sender addresses
+or testing sender verification using -bvs. See section 3.12 for a list of the
+order in which preconditions are evaluated. See also the $verify_mode variable.
+
+
+
+===============================================================================
+16. THE ACCEPT ROUTER
+
+The accept router has no private options of its own. Unless it is being used
+purely for verification (see verify_only) a transport is required to be defined
+by the generic transport option. If the preconditions that are specified by
+generic options are met, the router accepts the address and queues it for the
+given transport. The most common use of this router is for setting up
+deliveries to local mailboxes. For example:
+
+localusers:
+ driver = accept
+ domains = mydomain.example
+ check_local_user
+ transport = local_delivery
+
+The domains condition in this example checks the domain of the address, and
+check_local_user checks that the local part is the login of a local user. When
+both preconditions are met, the accept router runs, and queues the address for
+the local_delivery transport.
+
+
+
+===============================================================================
+17. THE DNSLOOKUP ROUTER
+
+The dnslookup router looks up the hosts that handle mail for the recipient's
+domain in the DNS. A transport must always be set for this router, unless
+verify_only is set.
+
+If SRV support is configured (see check_srv below), Exim first searches for SRV
+records. If none are found, or if SRV support is not configured, MX records are
+looked up. If no MX records exist, address records are sought. However,
+mx_domains can be set to disable the direct use of address records.
+
+MX records of equal priority are sorted by Exim into a random order. Exim then
+looks for address records for the host names obtained from MX or SRV records.
+When a host has more than one IP address, they are sorted into a random order,
+except that IPv6 addresses are sorted before IPv4 addresses. If all the IP
+addresses found are discarded by a setting of the ignore_target_hosts generic
+option, the router declines.
+
+Unless they have the highest priority (lowest MX value), MX records that point
+to the local host, or to any host name that matches hosts_treat_as_local, are
+discarded, together with any other MX records of equal or lower priority.
+
+If the host pointed to by the highest priority MX record, or looked up as an
+address record, is the local host, or matches hosts_treat_as_local, what
+happens is controlled by the generic self option.
+
+
+17.1 Problems with DNS lookups
+------------------------------
+
+There have been problems with DNS servers when SRV records are looked up. Some
+misbehaving servers return a DNS error or timeout when a non-existent SRV
+record is sought. Similar problems have in the past been reported for MX
+records. The global dns_again_means_nonexist option can help with this problem,
+but it is heavy-handed because it is a global option.
+
+For this reason, there are two options, srv_fail_domains and mx_fail_domains,
+that control what happens when a DNS lookup in a dnslookup router results in a
+DNS failure or a "try again" response. If an attempt to look up an SRV or MX
+record causes one of these results, and the domain matches the relevant list,
+Exim behaves as if the DNS had responded "no such record". In the case of an
+SRV lookup, this means that the router proceeds to look for MX records; in the
+case of an MX lookup, it proceeds to look for A or AAAA records, unless the
+domain matches mx_domains, in which case routing fails.
+
+
+17.2 Declining addresses by dnslookup
+-------------------------------------
+
+There are a few cases where a dnslookup router will decline to accept an
+address; if such a router is expected to handle "all remaining non-local
+domains", then it is important to set no_more.
+
+The router will defer rather than decline if the domain is found in the
+fail_defer_domains router option.
+
+Reasons for a dnslookup router to decline currently include:
+
+ * The domain does not exist in DNS
+
+ * The domain exists but the MX record's host part is just "."; this is a
+ common convention (borrowed from SRV) used to indicate that there is no
+ such service for this domain and to not fall back to trying A/AAAA records.
+
+ * Ditto, but for SRV records, when check_srv is set on this router.
+
+ * MX record points to a non-existent host.
+
+ * MX record points to an IP address and the main section option
+ allow_mx_to_ip is not set.
+
+ * MX records exist and point to valid hosts, but all hosts resolve only to
+ addresses blocked by the ignore_target_hosts generic option on this router.
+
+ * The domain is not syntactically valid (see also allow_utf8_domains and
+ dns_check_names_pattern for handling one variant of this)
+
+ * check_secondary_mx is set on this router but the local host can not be
+ found in the MX records (see below)
+
+
+17.3 Private options for dnslookup
+----------------------------------
+
+The private options for the dnslookup router are as follows:
+
++--------------------------------------------------------------+
+|check_secondary_mx|Use: dnslookup|Type: boolean|Default: false|
++--------------------------------------------------------------+
+
+If this option is set, the router declines unless the local host is found in
+(and removed from) the list of hosts obtained by MX lookup. This can be used to
+process domains for which the local host is a secondary mail exchanger
+differently to other domains. The way in which Exim decides whether a host is
+the local host is described in section 13.8.
+
++-----------------------------------------------------+
+|check_srv|Use: dnslookup|Type: string*|Default: unset|
++-----------------------------------------------------+
+
+The dnslookup router supports the use of SRV records (see RFC 2782) in addition
+to MX and address records. The support is disabled by default. To enable SRV
+support, set the check_srv option to the name of the service required. For
+example,
+
+check_srv = smtp
+
+looks for SRV records that refer to the normal smtp service. The option is
+expanded, so the service name can vary from message to message or address to
+address. This might be helpful if SRV records are being used for a submission
+service. If the expansion is forced to fail, the check_srv option is ignored,
+and the router proceeds to look for MX records in the normal way.
+
+When the expansion succeeds, the router searches first for SRV records for the
+given service (it assumes TCP protocol). A single SRV record with a host name
+that consists of just a single dot indicates "no such service for this domain";
+if this is encountered, the router declines. If other kinds of SRV record are
+found, they are used to construct a host list for delivery according to the
+rules of RFC 2782. MX records are not sought in this case.
+
+When no SRV records are found, MX records (and address records) are sought in
+the traditional way. In other words, SRV records take precedence over MX
+records, just as MX records take precedence over address records. Note that
+this behaviour is not sanctioned by RFC 2782, though a previous draft RFC
+defined it. It is apparently believed that MX records are sufficient for email
+and that SRV records should not be used for this purpose. However, SRV records
+have an additional "weight" feature which some people might find useful when
+trying to split an SMTP load between hosts of different power.
+
+See section 17.1 above for a discussion of Exim's behaviour when there is a DNS
+lookup error.
+
++-------------------------------------------------------------------+
+|fail_defer_domains|Use: dnslookup|Type: domain list*|Default: unset|
++-------------------------------------------------------------------+
+
+DNS lookups for domains matching fail_defer_domains which find no matching
+record will cause the router to defer rather than the default behaviour of
+decline. This maybe be useful for queueing messages for a newly created domain
+while the DNS configuration is not ready. However, it will result in any
+message with mistyped domains also being queued.
+
++-------------------------------------------+
+|ipv4_only|Use: string*|Type: unset|Default:|
++-------------------------------------------+
+
+The string is expanded, and if the result is anything but a forced failure, or
+an empty string, or one of the strings ?0? or ?no? or ?false? (checked without
+regard to the case of the letters), only A records are used.
+
++---------------------------------------------+
+|ipv4_prefer|Use: string*|Type: unset|Default:|
++---------------------------------------------+
+
+The string is expanded, and if the result is anything but a forced failure, or
+an empty string, or one of the strings ?0? or ?no? or ?false? (checked without
+regard to the case of the letters), A records are sorted before AAAA records
+(inverting the default).
+
++-----------------------------------------------------------+
+|mx_domains|Use: dnslookup|Type: domain list*|Default: unset|
++-----------------------------------------------------------+
+
+A domain that matches mx_domains is required to have either an MX or an SRV
+record in order to be recognized. (The name of this option could be improved.)
+For example, if all the mail hosts in fict.example are known to have MX
+records, except for those in discworld.fict.example, you could use this
+setting:
+
+mx_domains = ! *.discworld.fict.example : *.fict.example
+
+This specifies that messages addressed to a domain that matches the list but
+has no MX record should be bounced immediately instead of being routed using
+the address record.
+
++----------------------------------------------------------------+
+|mx_fail_domains|Use: dnslookup|Type: domain list*|Default: unset|
++----------------------------------------------------------------+
+
+If the DNS lookup for MX records for one of the domains in this list causes a
+DNS lookup error, Exim behaves as if no MX records were found. See section 17.1
+for more discussion.
+
++---------------------------------------------------------+
+|qualify_single|Use: dnslookup|Type: boolean|Default: true|
++---------------------------------------------------------+
+
+When this option is true, the resolver option RES_DEFNAMES is set for DNS
+lookups. Typically, but not standardly, this causes the resolver to qualify
+single-component names with the default domain. For example, on a machine
+called dictionary.ref.example, the domain thesaurus would be changed to
+thesaurus.ref.example inside the resolver. For details of what your resolver
+actually does, consult your man pages for resolver and resolv.conf.
+
++----------------------------------------------------------+
+|rewrite_headers|Use: dnslookup|Type: boolean|Default: true|
++----------------------------------------------------------+
+
+If the domain name in the address that is being processed is not fully
+qualified, it may be expanded to its full form by a DNS lookup. For example, if
+an address is specified as dormouse@teaparty, the domain might be expanded to
+teaparty.wonderland.fict.example. Domain expansion can also occur as a result
+of setting the widen_domains option. If rewrite_headers is true, all
+occurrences of the abbreviated domain name in any Bcc:, Cc:, From:, Reply-to:,
+Sender:, and To: header lines of the message are rewritten with the full domain
+name.
+
+This option should be turned off only when it is known that no message is ever
+going to be sent outside an environment where the abbreviation makes sense.
+
+When an MX record is looked up in the DNS and matches a wildcard record, name
+servers normally return a record containing the name that has been looked up,
+making it impossible to detect whether a wildcard was present or not. However,
+some name servers have recently been seen to return the wildcard entry. If the
+name returned by a DNS lookup begins with an asterisk, it is not used for
+header rewriting.
+
++--------------------------------------------------------------------+
+|same_domain_copy_routing|Use: dnslookup|Type: boolean|Default: false|
++--------------------------------------------------------------------+
+
+Addresses with the same domain are normally routed by the dnslookup router to
+the same list of hosts. However, this cannot be presumed, because the router
+options and preconditions may refer to the local part of the address. By
+default, therefore, Exim routes each address in a message independently. DNS
+servers run caches, so repeated DNS lookups are not normally expensive, and in
+any case, personal messages rarely have more than a few recipients.
+
+If you are running mailing lists with large numbers of subscribers at the same
+domain, and you are using a dnslookup router which is independent of the local
+part, you can set same_domain_copy_routing to bypass repeated DNS lookups for
+identical domains in one message. In this case, when dnslookup routes an
+address to a remote transport, any other unrouted addresses in the message that
+have the same domain are automatically given the same routing without
+processing them independently, provided the following conditions are met:
+
+ * No router that processed the address specified headers_add or
+ headers_remove.
+
+ * The router did not change the address in any way, for example, by
+ "widening" the domain.
+
++----------------------------------------------------------+
+|search_parents|Use: dnslookup|Type: boolean|Default: false|
++----------------------------------------------------------+
+
+When this option is true, the resolver option RES_DNSRCH is set for DNS
+lookups. This is different from the qualify_single option in that it applies to
+domains containing dots. Typically, but not standardly, it causes the resolver
+to search for the name in the current domain and in parent domains. For
+example, on a machine in the fict.example domain, if looking up
+teaparty.wonderland failed, the resolver would try
+teaparty.wonderland.fict.example. For details of what your resolver actually
+does, consult your man pages for resolver and resolv.conf.
+
+Setting this option true can cause problems in domains that have a wildcard MX
+record, because any domain that does not have its own MX record matches the
+local wildcard.
+
++-----------------------------------------------------------------+
+|srv_fail_domains|Use: dnslookup|Type: domain list*|Default: unset|
++-----------------------------------------------------------------+
+
+If the DNS lookup for SRV records for one of the domains in this list causes a
+DNS lookup error, Exim behaves as if no SRV records were found. See section
+17.1 for more discussion.
+
++-------------------------------------------------------------+
+|widen_domains|Use: dnslookup|Type: string list|Default: unset|
++-------------------------------------------------------------+
+
+If a DNS lookup fails and this option is set, each of its strings in turn is
+added onto the end of the domain, and the lookup is tried again. For example,
+if
+
+widen_domains = fict.example:ref.example
+
+is set and a lookup of klingon.dictionary fails,
+klingon.dictionary.fict.example is looked up, and if this fails,
+klingon.dictionary.ref.example is tried. Note that the qualify_single and
+search_parents options can cause some widening to be undertaken inside the DNS
+resolver. widen_domains is not applied to sender addresses when verifying,
+unless rewrite_headers is false (not the default).
+
+
+17.4 Effect of qualify_single and search_parents
+------------------------------------------------
+
+When a domain from an envelope recipient is changed by the resolver as a result
+of the qualify_single or search_parents options, Exim rewrites the
+corresponding address in the message's header lines unless rewrite_headers is
+set false. Exim then re-routes the address, using the full domain.
+
+These two options affect only the DNS lookup that takes place inside the router
+for the domain of the address that is being routed. They do not affect lookups
+such as that implied by
+
+domains = @mx_any
+
+that may happen while processing a router precondition before the router is
+entered. No widening ever takes place for these lookups.
+
+
+
+===============================================================================
+18. THE IPLITERAL ROUTER
+
+This router has no private options. Unless it is being used purely for
+verification (see verify_only) a transport is required to be defined by the
+generic transport option. The router accepts the address if its domain part
+takes the form of an RFC 2822 domain literal. For example, the ipliteral router
+handles the address
+
+root@[192.168.1.1]
+
+by setting up delivery to the host with that IP address. IPv4 domain literals
+consist of an IPv4 address enclosed in square brackets. IPv6 domain literals
+are similar, but the address is preceded by "ipv6:". For example:
+
+postmaster@[ipv6:fe80::a00:20ff:fe86:a061.5678]
+
+Exim allows "ipv4:" before IPv4 addresses, for consistency, and on the grounds
+that sooner or later somebody will try it.
+
+If the IP address matches something in ignore_target_hosts, the router
+declines. If an IP literal turns out to refer to the local host, the generic
+self option determines what happens.
+
+The RFCs require support for domain literals; however, their use is
+controversial in today's Internet. If you want to use this router, you must
+also set the main configuration option allow_domain_literals. Otherwise, Exim
+will not recognize the domain literal syntax in addresses.
+
+
+
+===============================================================================
+19. THE IPLOOKUP ROUTER
+
+The iplookup router was written to fulfil a specific requirement in Cambridge
+University (which in fact no longer exists). For this reason, it is not
+included in the binary of Exim by default. If you want to include it, you must
+set
+
+ROUTER_IPLOOKUP=yes
+
+in your Local/Makefile configuration file.
+
+The iplookup router routes an address by sending it over a TCP or UDP
+connection to one or more specific hosts. The host can then return the same or
+a different address - in effect rewriting the recipient address in the
+message's envelope. The new address is then passed on to subsequent routers. If
+this process fails, the address can be passed on to other routers, or delivery
+can be deferred. Since iplookup is just a rewriting router, a transport must
+not be specified for it.
+
++-----------------------------------------------+
+|hosts|Use: iplookup|Type: string|Default: unset|
++-----------------------------------------------+
+
+This option must be supplied. Its value is a colon-separated list of host
+names. The hosts are looked up using gethostbyname() (or getipnodebyname() when
+available) and are tried in order until one responds to the query. If none
+respond, what happens is controlled by optional.
+
++---------------------------------------------------+
+|optional|Use: iplookup|Type: boolean|Default: false|
++---------------------------------------------------+
+
+If optional is true, if no response is obtained from any host, the address is
+passed to the next router, overriding no_more. If optional is false, delivery
+to the address is deferred.
+
++-------------------------------------------+
+|port|Use: iplookup|Type: integer|Default: 0|
++-------------------------------------------+
+
+This option must be supplied. It specifies the port number for the TCP or UDP
+call.
+
++------------------------------------------------+
+|protocol|Use: iplookup|Type: string|Default: udp|
++------------------------------------------------+
+
+This option can be set to "udp" or "tcp" to specify which of the two protocols
+is to be used.
+
++----------------------------------------------------+
+|query|Use: iplookup|Type: string*|Default: see below|
++----------------------------------------------------+
+
+This defines the content of the query that is sent to the remote hosts. The
+default value is:
+
+$local_part@$domain $local_part@$domain
+
+The repetition serves as a way of checking that a response is to the correct
+query in the default case (see response_pattern below).
+
++--------------------------------------------------+
+|reroute|Use: iplookup|Type: string*|Default: unset|
++--------------------------------------------------+
+
+If this option is not set, the rerouted address is precisely the byte string
+returned by the remote host, up to the first white space, if any. If set, the
+string is expanded to form the rerouted address. It can include parts matched
+in the response by response_pattern by means of numeric variables such as $1,
+$2, etc. The variable $0 refers to the entire input string, whether or not a
+pattern is in use. In all cases, the rerouted address must end up in the form
+local_part@domain.
+
++----------------------------------------------------------+
+|response_pattern|Use: iplookup|Type: string|Default: unset|
++----------------------------------------------------------+
+
+This option can be set to a regular expression that is applied to the string
+returned from the remote host. If the pattern does not match the response, the
+router declines. If response_pattern is not set, no checking of the response is
+done, unless the query was defaulted, in which case there is a check that the
+text returned after the first white space is the original address. This checks
+that the answer that has been received is in response to the correct question.
+For example, if the response is just a new domain, the following could be used:
+
+response_pattern = ^([^@]+)$
+reroute = $local_part@$1
+
++--------------------------------------------+
+|timeout|Use: iplookup|Type: time|Default: 5s|
++--------------------------------------------+
+
+This specifies the amount of time to wait for a response from the remote
+machine. The same timeout is used for the connect() function for a TCP call. It
+does not apply to UDP.
+
+
+
+===============================================================================
+20. THE MANUALROUTE ROUTER
+
+The manualroute router is so-called because it provides a way of manually
+routing an address according to its domain. It is mainly used when you want to
+route addresses to remote hosts according to your own rules, bypassing the
+normal DNS routing that looks up MX records. However, manualroute can also
+route to local transports, a facility that may be useful if you want to save
+messages for dial-in hosts in local files.
+
+The manualroute router compares a list of domain patterns with the domain it is
+trying to route. If there is no match, the router declines. Each pattern has
+associated with it a list of hosts and some other optional data, which may
+include a transport. The combination of a pattern and its data is called a
+"routing rule". For patterns that do not have an associated transport, the
+generic transport option must specify a transport, unless the router is being
+used purely for verification (see verify_only).
+
+In the case of verification, matching the domain pattern is sufficient for the
+router to accept the address. When actually routing an address for delivery, an
+address that matches a domain pattern is queued for the associated transport.
+If the transport is not a local one, a host list must be associated with the
+pattern; IP addresses are looked up for the hosts, and these are passed to the
+transport along with the mail address. For local transports, a host list is
+optional. If it is present, it is passed in $host as a single text string.
+
+The list of routing rules can be provided as an inline string in route_list, or
+the data can be obtained by looking up the domain in a file or database by
+setting route_data. Only one of these settings may appear in any one instance
+of manualroute. The format of routing rules is described below, following the
+list of private options.
+
+
+20.1 Private options for manualroute
+------------------------------------
+
+The private options for the manualroute router are as follows:
+
++-------------------------------------------------------------+
+|host_all_ignored|Use: manualroute|Type: string|Default: defer|
++-------------------------------------------------------------+
+
+See host_find_failed.
+
++--------------------------------------------------------------+
+|host_find_failed|Use: manualroute|Type: string|Default: freeze|
++--------------------------------------------------------------+
+
+This option controls what happens when manualroute tries to find an IP address
+for a host, and the host does not exist. The option can be set to one of the
+following values:
+
+decline
+defer
+fail
+freeze
+ignore
+pass
+
+The default ("freeze") assumes that this state is a serious configuration
+error. The difference between "pass" and "decline" is that the former forces
+the address to be passed to the next router (or the router defined by
+pass_router), overriding no_more, whereas the latter passes the address to the
+next router only if more is true.
+
+The value "ignore" causes Exim to completely ignore a host whose IP address
+cannot be found. If all the hosts in the list are ignored, the behaviour is
+controlled by the host_all_ignored option. This takes the same values as
+host_find_failed, except that it cannot be set to "ignore".
+
+The host_find_failed option applies only to a definite "does not exist" state;
+if a host lookup gets a temporary error, delivery is deferred unless the
+generic pass_on_timeout option is set.
+
++-------------------------------------------------------------+
+|hosts_randomize|Use: manualroute|Type: boolean|Default: false|
++-------------------------------------------------------------+
+
+If this option is set, the order of the items in a host list in a routing rule
+is randomized each time the list is used, unless an option in the routing rule
+overrides (see below). Randomizing the order of a host list can be used to do
+crude load sharing. However, if more than one mail address is routed by the
+same router to the same host list, the host lists are considered to be the same
+(even though they may be randomized into different orders) for the purpose of
+deciding whether to batch the deliveries into a single SMTP transaction.
+
+When hosts_randomize is true, a host list may be split into groups whose order
+is separately randomized. This makes it possible to set up MX-like behaviour.
+The boundaries between groups are indicated by an item that is just "+" in the
+host list. For example:
+
+route_list = * host1:host2:host3:+:host4:host5
+
+The order of the first three hosts and the order of the last two hosts is
+randomized for each use, but the first three always end up before the last two.
+If hosts_randomize is not set, a "+" item in the list is ignored. If a
+randomized host list is passed to an smtp transport that also has
+hosts_randomize set, the list is not re-randomized.
+
++--------------------------------------------------------+
+|route_data|Use: manualroute|Type: string*|Default: unset|
++--------------------------------------------------------+
+
+If this option is set, it must expand to yield the data part of a routing rule.
+Typically, the expansion string includes a lookup based on the domain. For
+example:
+
+route_data = ${lookup{$domain}dbm{/etc/routes}}
+
+If the expansion is forced to fail, or the result is an empty string, the
+router declines. Other kinds of expansion failure cause delivery to be
+deferred.
+
++------------------------------------------------------------+
+|route_list|Use: manualroute|Type: string list|Default: unset|
++------------------------------------------------------------+
+
+This string is a list of routing rules, in the form defined below. Note that,
+unlike most string lists, the items are separated by semicolons. This is so
+that they may contain colon-separated host lists.
+
++----------------------------------------------------------------------+
+|same_domain_copy_routing|Use: manualroute|Type: boolean|Default: false|
++----------------------------------------------------------------------+
+
+Addresses with the same domain are normally routed by the manualroute router to
+the same list of hosts. However, this cannot be presumed, because the router
+options and preconditions may refer to the local part of the address. By
+default, therefore, Exim routes each address in a message independently. DNS
+servers run caches, so repeated DNS lookups are not normally expensive, and in
+any case, personal messages rarely have more than a few recipients.
+
+If you are running mailing lists with large numbers of subscribers at the same
+domain, and you are using a manualroute router which is independent of the
+local part, you can set same_domain_copy_routing to bypass repeated DNS lookups
+for identical domains in one message. In this case, when manualroute routes an
+address to a remote transport, any other unrouted addresses in the message that
+have the same domain are automatically given the same routing without
+processing them independently. However, this is only done if headers_add and
+headers_remove are unset.
+
+
+20.2 Routing rules in route_list
+--------------------------------
+
+The value of route_list is a string consisting of a sequence of routing rules,
+separated by semicolons. If a semicolon is needed in a rule, it can be entered
+as two semicolons. Alternatively, the list separator can be changed as
+described (for colon-separated lists) in section 6.20. Empty rules are ignored.
+The format of each rule is
+
+<domain pattern> <list of hosts> <options>
+
+The following example contains two rules, each with a simple domain pattern and
+no options:
+
+route_list = \
+ dict.ref.example mail-1.ref.example:mail-2.ref.example ; \
+ thes.ref.example mail-3.ref.example:mail-4.ref.example
+
+The three parts of a rule are separated by white space. The pattern and the
+list of hosts can be enclosed in quotes if necessary, and if they are, the
+usual quoting rules apply. Each rule in a route_list must start with a single
+domain pattern, which is the only mandatory item in the rule. The pattern is in
+the same format as one item in a domain list (see section 10.9), except that it
+may not be the name of an interpolated file. That is, it may be wildcarded, or
+a regular expression, or a file or database lookup (with semicolons doubled,
+because of the use of semicolon as a separator in a route_list).
+
+The rules in route_list are searched in order until one of the patterns matches
+the domain that is being routed. The list of hosts and then options are then
+used as described below. If there is no match, the router declines. When
+route_list is set, route_data must not be set.
+
+
+20.3 Routing rules in route_data
+--------------------------------
+
+The use of route_list is convenient when there are only a small number of
+routing rules. For larger numbers, it is easier to use a file or database to
+hold the routing information, and use the route_data option instead. The value
+of route_data is a list of hosts, followed by (optional) options. Most
+commonly, route_data is set as a string that contains an expansion lookup. For
+example, suppose we place two routing rules in a file like this:
+
+dict.ref.example: mail-1.ref.example:mail-2.ref.example
+thes.ref.example: mail-3.ref.example:mail-4.ref.example
+
+This data can be accessed by setting
+
+route_data = ${lookup{$domain}lsearch{/the/file/name}}
+
+Failure of the lookup results in an empty string, causing the router to
+decline. However, you do not have to use a lookup in route_data. The only
+requirement is that the result of expanding the string is a list of hosts,
+possibly followed by options, separated by white space. The list of hosts must
+be enclosed in quotes if it contains white space.
+
+
+20.4 Format of the list of hosts
+--------------------------------
+
+A list of hosts, whether obtained via route_data or route_list, is always
+separately expanded before use. If the expansion fails, the router declines.
+The result of the expansion must be a colon-separated list of names and/or IP
+addresses, optionally also including ports. If the list is written with spaces,
+it must be protected with quotes. The format of each item in the list is
+described in the next section. The list separator can be changed as described
+in section 6.21.
+
+If the list of hosts was obtained from a route_list item, the following
+variables are set during its expansion:
+
+ * If the domain was matched against a regular expression, the numeric
+ variables $1, $2, etc. may be set. For example:
+
+ route_list = ^domain(\d+) host-$1.text.example
+
+ * $0 is always set to the entire domain.
+
+ * $1 is also set when partial matching is done in a file lookup.
+
+ * If the pattern that matched the domain was a lookup item, the data that was
+ looked up is available in the expansion variable $value. For example:
+
+ route_list = lsearch;;/some/file.routes $value
+
+Note the doubling of the semicolon in the pattern that is necessary because
+semicolon is the default route list separator.
+
+
+20.5 Format of one host item
+----------------------------
+
+Each item in the list of hosts can be either a host name or an IP address,
+optionally with an attached port number, or it can be a single "+" (see
+hosts_randomize). When no port is given, an IP address is not enclosed in
+brackets. When a port is specified, it overrides the port specification on the
+transport. The port is separated from the name or address by a colon. This
+leads to some complications:
+
+ * Because colon is the default separator for the list of hosts, either the
+ colon that specifies a port must be doubled, or the list separator must be
+ changed. The following two examples have the same effect:
+
+ route_list = * "host1.tld::1225 : host2.tld::1226"
+ route_list = * "<+ host1.tld:1225 + host2.tld:1226"
+
+ * When IPv6 addresses are involved, it gets worse, because they contain
+ colons of their own. To make this case easier, it is permitted to enclose
+ an IP address (either v4 or v6) in square brackets if a port number
+ follows. For example:
+
+ route_list = * "</ [10.1.1.1]:1225 / [::1]:1226"
+
+
+20.6 How the list of hosts is used
+----------------------------------
+
+When an address is routed to an smtp transport by manualroute, each of the
+hosts is tried, in the order specified, when carrying out the SMTP delivery.
+However, the order can be changed by setting the hosts_randomize option, either
+on the router (see section 20.1 above), or on the transport.
+
+Hosts may be listed by name or by IP address. An unadorned name in the list of
+hosts is interpreted as a host name. A name that is followed by "/MX" is
+interpreted as an indirection to a sublist of hosts obtained by looking up MX
+records in the DNS. For example:
+
+route_list = * x.y.z:p.q.r/MX:e.f.g
+
+If this feature is used with a port specifier, the port must come last. For
+example:
+
+route_list = * dom1.tld/mx::1225
+
+If the hosts_randomize option is set, the order of the items in the list is
+randomized before any lookups are done. Exim then scans the list; for any name
+that is not followed by "/MX" it looks up an IP address. If this turns out to
+be an interface on the local host and the item is not the first in the list,
+Exim discards it and any subsequent items. If it is the first item, what
+happens is controlled by the self option of the router.
+
+A name on the list that is followed by "/MX" is replaced with the list of hosts
+obtained by looking up MX records for the name. This is always a DNS lookup;
+the bydns and byname options (see section 20.7 below) are not relevant here.
+The order of these hosts is determined by the preference values in the MX
+records, according to the usual rules. Because randomizing happens before the
+MX lookup, it does not affect the order that is defined by MX preferences.
+
+If the local host is present in the sublist obtained from MX records, but is
+not the most preferred host in that list, it and any equally or less preferred
+hosts are removed before the sublist is inserted into the main list.
+
+If the local host is the most preferred host in the MX list, what happens
+depends on where in the original list of hosts the "/MX" item appears. If it is
+not the first item (that is, there are previous hosts in the main list), Exim
+discards this name and any subsequent items in the main list.
+
+If the MX item is first in the list of hosts, and the local host is the most
+preferred host, what happens is controlled by the self option of the router.
+
+DNS failures when lookup up the MX records are treated in the same way as DNS
+failures when looking up IP addresses: pass_on_timeout and host_find_failed are
+used when relevant.
+
+The generic ignore_target_hosts option applies to all hosts in the list,
+whether obtained from an MX lookup or not.
+
+
+20.7 How the options are used
+-----------------------------
+
+The options are a sequence of words, space-separated. One of the words can be
+the name of a transport; this overrides the transport option on the router for
+this particular routing rule only. The other words (if present) control
+randomization of the list of hosts on a per-rule basis, and how the IP
+addresses of the hosts are to be found when routing to a remote transport.
+These options are as follows:
+
+ * randomize: randomize the order of the hosts in this list, overriding the
+ setting of hosts_randomize for this routing rule only.
+
+ * no_randomize: do not randomize the order of the hosts in this list,
+ overriding the setting of hosts_randomize for this routing rule only.
+
+ * byname: use getipnodebyname() (gethostbyname() on older systems) to find IP
+ addresses. This function may ultimately cause a DNS lookup, but it may also
+ look in /etc/hosts or other sources of information.
+
+ * bydns: look up address records for the hosts directly in the DNS; fail if
+ no address records are found. If there is a temporary DNS error (such as a
+ timeout), delivery is deferred.
+
+ * ipv4_only: in direct DNS lookups, look up only A records.
+
+ * ipv4_prefer: in direct DNS lookups, sort A records before AAAA records.
+
+For example:
+
+route_list = domain1 host1:host2:host3 randomize bydns;\
+ domain2 host4:host5
+
+If neither byname nor bydns is given, Exim behaves as follows: First, a DNS
+lookup is done. If this yields anything other than HOST_NOT_FOUND, that result
+is used. Otherwise, Exim goes on to try a call to getipnodebyname() or
+gethostbyname(), and the result of the lookup is the result of that call.
+
+Warning: It has been discovered that on some systems, if a DNS lookup called
+via getipnodebyname() times out, HOST_NOT_FOUND is returned instead of
+TRY_AGAIN. That is why the default action is to try a DNS lookup first. Only if
+that gives a definite "no such host" is the local function called.
+
+Compatibility: From Exim 4.85 until fixed for 4.90, there was an inadvertent
+constraint that a transport name as an option had to be the last option
+specified.
+
+If no IP address for a host can be found, what happens is controlled by the
+host_find_failed option.
+
+When an address is routed to a local transport, IP addresses are not looked up.
+The host list is passed to the transport in the $host variable.
+
+
+20.8 Manualroute examples
+-------------------------
+
+In some of the examples that follow, the presence of the remote_smtp transport,
+as defined in the default configuration file, is assumed:
+
+ * The manualroute router can be used to forward all external mail to a smart
+ host. If you have set up, in the main part of the configuration, a named
+ domain list that contains your local domains, for example:
+
+ domainlist local_domains = my.domain.example
+
+ You can arrange for all other domains to be routed to a smart host by
+ making your first router something like this:
+
+ smart_route:
+ driver = manualroute
+ domains = !+local_domains
+ transport = remote_smtp
+ route_list = * smarthost.ref.example
+
+ This causes all non-local addresses to be sent to the single host
+ smarthost.ref.example. If a colon-separated list of smart hosts is given,
+ they are tried in order (but you can use hosts_randomize to vary the order
+ each time). Another way of configuring the same thing is this:
+
+ smart_route:
+ driver = manualroute
+ transport = remote_smtp
+ route_list = !+local_domains smarthost.ref.example
+
+ There is no difference in behaviour between these two routers as they
+ stand. However, they behave differently if no_more is added to them. In the
+ first example, the router is skipped if the domain does not match the
+ domains precondition; the following router is always tried. If the router
+ runs, it always matches the domain and so can never decline. Therefore,
+ no_more would have no effect. In the second case, the router is never
+ skipped; it always runs. However, if it doesn't match the domain, it
+ declines. In this case no_more would prevent subsequent routers from
+ running.
+
+ * A mail hub is a host which receives mail for a number of domains via MX
+ records in the DNS and delivers it via its own private routing mechanism.
+ Often the final destinations are behind a firewall, with the mail hub being
+ the one machine that can connect to machines both inside and outside the
+ firewall. The manualroute router is usually used on a mail hub to route
+ incoming messages to the correct hosts. For a small number of domains, the
+ routing can be inline, using the route_list option, but for a larger number
+ a file or database lookup is easier to manage.
+
+ If the domain names are in fact the names of the machines to which the mail
+ is to be sent by the mail hub, the configuration can be quite simple. For
+ example:
+
+ hub_route:
+ driver = manualroute
+ transport = remote_smtp
+ route_list = *.rhodes.tvs.example $domain
+
+ This configuration routes domains that match "*.rhodes.tvs.example" to
+ hosts whose names are the same as the mail domains. A similar approach can
+ be taken if the host name can be obtained from the domain name by a string
+ manipulation that the expansion facilities can handle. Otherwise, a lookup
+ based on the domain can be used to find the host:
+
+ through_firewall:
+ driver = manualroute
+ transport = remote_smtp
+ route_data = ${lookup {$domain} cdb {/internal/host/routes}}
+
+ The result of the lookup must be the name or IP address of the host (or
+ hosts) to which the address is to be routed. If the lookup fails, the route
+ data is empty, causing the router to decline. The address then passes to
+ the next router.
+
+ * You can use manualroute to deliver messages to pipes or files in batched
+ SMTP format for onward transportation by some other means. This is one way
+ of storing mail for a dial-up host when it is not connected. The route list
+ entry can be as simple as a single domain name in a configuration like
+ this:
+
+ save_in_file:
+ driver = manualroute
+ transport = batchsmtp_appendfile
+ route_list = saved.domain.example
+
+ though often a pattern is used to pick up more than one domain. If there
+ are several domains or groups of domains with different transport
+ requirements, different transports can be listed in the routing
+ information:
+
+ save_in_file:
+ driver = manualroute
+ route_list = \
+ *.saved.domain1.example $domain batch_appendfile; \
+ *.saved.domain2.example \
+ ${lookup{$domain}dbm{/domain2/hosts}{$value}fail} \
+ batch_pipe
+
+ The first of these just passes the domain in the $host variable, which
+ doesn't achieve much (since it is also in $domain), but the second does a
+ file lookup to find a value to pass, causing the router to decline to
+ handle the address if the lookup fails.
+
+ * Routing mail directly to UUCP software is a specific case of the use of
+ manualroute in a gateway to another mail environment. This is an example of
+ one way it can be done:
+
+ # Transport
+ uucp:
+ driver = pipe
+ user = nobody
+ command = /usr/local/bin/uux -r - \
+ ${substr_-5:$host}!rmail ${local_part}
+ return_fail_output = true
+
+ # Router
+ uucphost:
+ transport = uucp
+ driver = manualroute
+ route_data = \
+ ${lookup{$domain}lsearch{/usr/local/exim/uucphosts}}
+
+ The file /usr/local/exim/uucphosts contains entries like
+
+ darksite.ethereal.example: darksite.UUCP
+
+ It can be set up more simply without adding and removing ".UUCP" but this
+ way makes clear the distinction between the domain name
+ darksite.ethereal.example and the UUCP host name darksite.
+
+
+
+===============================================================================
+21. THE QUERYPROGRAM ROUTER
+
+The queryprogram router routes an address by running an external command and
+acting on its output. This is an expensive way to route, and is intended mainly
+for use in lightly-loaded systems, or for performing experiments. However, if
+it is possible to use the precondition options (domains, local_parts, etc) to
+skip this router for most addresses, it could sensibly be used in special
+cases, even on a busy host. There are the following private options:
+
++------------------------------------------------------+
+|command|Use: queryprogram|Type: string*|Default: unset|
++------------------------------------------------------+
+
+This option must be set. It specifies the command that is to be run. The
+command is split up into a command name and arguments, and then each is
+expanded separately (exactly as for a pipe transport, described in chapter 29).
+
++-----------------------------------------------------------+
+|command_group|Use: queryprogram|Type: string|Default: unset|
++-----------------------------------------------------------+
+
+This option specifies a gid to be set when running the command while routing an
+address for deliver. It must be set if command_user specifies a numerical uid.
+If it begins with a digit, it is interpreted as the numerical value of the gid.
+Otherwise it is looked up using getgrnam().
+
++----------------------------------------------------------+
+|command_user|Use: queryprogram|Type: string|Default: unset|
++----------------------------------------------------------+
+
+This option must be set. It specifies the uid which is set when running the
+command while routing an address for delivery. If the value begins with a
+digit, it is interpreted as the numerical value of the uid. Otherwise, it is
+looked up using getpwnam() to obtain a value for the uid and, if command_group
+is not set, a value for the gid also.
+
+Warning: Changing uid and gid is possible only when Exim is running as root,
+which it does during a normal delivery in a conventional configuration.
+However, when an address is being verified during message reception, Exim is
+usually running as the Exim user, not as root. If the queryprogram router is
+called from a non-root process, Exim cannot change uid or gid before running
+the command. In this circumstance the command runs under the current uid and
+gid.
+
++-----------------------------------------------------------+
+|current_directory|Use: queryprogram|Type: string|Default: /|
++-----------------------------------------------------------+
+
+This option specifies an absolute path which is made the current directory
+before running the command.
+
++------------------------------------------------+
+|timeout|Use: queryprogram|Type: time|Default: 1h|
++------------------------------------------------+
+
+If the command does not complete within the timeout period, its process group
+is killed and the message is frozen. A value of zero time specifies no timeout.
+
+The standard output of the command is connected to a pipe, which is read when
+the command terminates. It should consist of a single line of output,
+containing up to five fields, separated by white space. The maximum length of
+the line is 1023 characters. Longer lines are silently truncated. The first
+field is one of the following words (case-insensitive):
+
+ * Accept: routing succeeded; the remaining fields specify what to do (see
+ below).
+
+ * Decline: the router declines; pass the address to the next router, unless
+ no_more is set.
+
+ * Fail: routing failed; do not pass the address to any more routers. Any
+ subsequent text on the line is an error message. If the router is run as
+ part of address verification during an incoming SMTP message, the message
+ is included in the SMTP response.
+
+ * Defer: routing could not be completed at this time; try again later. Any
+ subsequent text on the line is an error message which is logged. It is not
+ included in any SMTP response.
+
+ * Freeze: the same as defer, except that the message is frozen.
+
+ * Pass: pass the address to the next router (or the router specified by
+ pass_router), overriding no_more.
+
+ * Redirect: the message is redirected. The remainder of the line is a list of
+ new addresses, which are routed independently, starting with the first
+ router, or the router specified by redirect_router, if set.
+
+When the first word is accept, the remainder of the line consists of a number
+of keyed data values, as follows (split into two lines here, to fit on the
+page):
+
+ACCEPT TRANSPORT=<transport> HOSTS=<list of hosts>
+LOOKUP=byname|bydns DATA=<text>
+
+The data items can be given in any order, and all are optional. If no transport
+is included, the transport specified by the generic transport option is used.
+The list of hosts and the lookup type are needed only if the transport is an
+smtp transport that does not itself supply a list of hosts.
+
+The format of the list of hosts is the same as for the manualroute router. As
+well as host names and IP addresses with optional port numbers, as described in
+section 20.5, it may contain names followed by "/MX" to specify sublists of
+hosts that are obtained by looking up MX records (see section 20.6).
+
+If the lookup type is not specified, Exim behaves as follows when trying to
+find an IP address for each host: First, a DNS lookup is done. If this yields
+anything other than HOST_NOT_FOUND, that result is used. Otherwise, Exim goes
+on to try a call to getipnodebyname() or gethostbyname(), and the result of the
+lookup is the result of that call.
+
+If the DATA field is set, its value is placed in the $address_data variable.
+For example, this return line
+
+accept hosts=x1.y.example:x2.y.example data="rule1"
+
+routes the address to the default transport, passing a list of two hosts. When
+the transport runs, the string "rule1" is in $address_data.
+
+
+
+===============================================================================
+22. THE REDIRECT ROUTER
+
+The redirect router handles several kinds of address redirection. Its most
+common uses are for resolving local part aliases from a central alias file
+(usually called /etc/aliases) and for handling users' personal .forward files,
+but it has many other potential uses. The incoming address can be redirected in
+several different ways:
+
+ * It can be replaced by one or more new addresses which are themselves routed
+ independently.
+
+ * It can be routed to be delivered to a given file or directory.
+
+ * It can be routed to be delivered to a specified pipe command.
+
+ * It can cause an automatic reply to be generated.
+
+ * It can be forced to fail, optionally with a custom error message.
+
+ * It can be temporarily deferred, optionally with a custom message.
+
+ * It can be discarded.
+
+The generic transport option must not be set for redirect routers. However,
+there are some private options which define transports for delivery to files
+and pipes, and for generating autoreplies. See the file_transport,
+pipe_transport and reply_transport descriptions below.
+
+If success DSNs have been requested redirection triggers one and the DSN
+options are not passed any further.
+
+
+22.1 Redirection data
+---------------------
+
+The router operates by interpreting a text string which it obtains either by
+expanding the contents of the data option, or by reading the entire contents of
+a file whose name is given in the file option. These two options are mutually
+exclusive. The first is commonly used for handling system aliases, in a
+configuration like this:
+
+system_aliases:
+ driver = redirect
+ data = ${lookup{$local_part}lsearch{/etc/aliases}}
+
+If the lookup fails, the expanded string in this example is empty. When the
+expansion of data results in an empty string, the router declines. A forced
+expansion failure also causes the router to decline; other expansion failures
+cause delivery to be deferred.
+
+A configuration using file is commonly used for handling users' .forward files,
+like this:
+
+userforward:
+ driver = redirect
+ check_local_user
+ file = $home/.forward
+ no_verify
+
+If the file does not exist, or causes no action to be taken (for example, it is
+empty or consists only of comments), the router declines. Warning: This is not
+the case when the file contains syntactically valid items that happen to yield
+empty addresses, for example, items containing only RFC 2822 address comments.
+
+Tainted data may not be used for a filename.
+
+Warning: It is unwise to use $local_part or $domain directly for redirection,
+as they are provided by a potential attacker. In the examples above,
+$local_part is used for looking up data held locally on the system, and not
+used directly (the second example derives $home via the passsword file or
+database, using $local_part).
+
+
+22.2 Forward files and address verification
+-------------------------------------------
+
+It is usual to set no_verify on redirect routers which handle users' .forward
+files, as in the example above. There are two reasons for this:
+
+ * When Exim is receiving an incoming SMTP message from a remote host, it is
+ running under the Exim uid, not as root. Exim is unable to change uid to
+ read the file as the user, and it may not be able to read it as the Exim
+ user. So in practice the router may not be able to operate.
+
+ * However, even when the router can operate, the existence of a .forward file
+ is unimportant when verifying an address. What should be checked is whether
+ the local part is a valid user name or not. Cutting out the redirection
+ processing saves some resources.
+
+
+22.3 Interpreting redirection data
+----------------------------------
+
+The contents of the data string, whether obtained from data or file, can be
+interpreted in two different ways:
+
+ * If the allow_filter option is set true, and the data begins with the text "
+ #Exim filter" or "#Sieve filter", it is interpreted as a list of filtering
+ instructions in the form of an Exim or Sieve filter file, respectively.
+ Details of the syntax and semantics of filter files are described in a
+ separate document entitled Exim's interfaces to mail filtering; this
+ document is intended for use by end users.
+
+ * Otherwise, the data must be a comma-separated list of redirection items, as
+ described in the next section.
+
+When a message is redirected to a file (a "mail folder"), the filename given in
+a non-filter redirection list must always be an absolute path. A filter may
+generate a relative path - how this is handled depends on the transport's
+configuration. See section 26.1 for a discussion of this issue for the
+appendfile transport.
+
+
+22.4 Items in a non-filter redirection list
+-------------------------------------------
+
+When the redirection data is not an Exim or Sieve filter, for example, if it
+comes from a conventional alias or forward file, it consists of a list of
+addresses, filenames, pipe commands, or certain special items (see section 22.6
+below). The special items can be individually enabled or disabled by means of
+options whose names begin with allow_ or forbid_, depending on their default
+values. The items in the list are separated by commas or newlines. If a comma
+is required in an item, the entire item must be enclosed in double quotes.
+
+Lines starting with a # character are comments, and are ignored, and # may also
+appear following a comma, in which case everything between the # and the next
+newline character is ignored.
+
+If an item is entirely enclosed in double quotes, these are removed. Otherwise
+double quotes are retained because some forms of mail address require their use
+(but never to enclose the entire address). In the following description, "item"
+refers to what remains after any surrounding double quotes have been removed.
+
+Warning: If you use an Exim expansion to construct a redirection address, and
+the expansion contains a reference to $local_part, you should make use of the
+quote_local_part expansion operator, in case the local part contains special
+characters. For example, to redirect all mail for the domain obsolete.example,
+retaining the existing local part, you could use this setting:
+
+data = ${quote_local_part:$local_part}@newdomain.example
+
+
+22.5 Redirecting to a local mailbox
+-----------------------------------
+
+A redirection item may safely be the same as the address currently under
+consideration. This does not cause a routing loop, because a router is
+automatically skipped if any ancestor of the address that is being processed is
+the same as the current address and was processed by the current router. Such
+an address is therefore passed to the following routers, so it is handled as if
+there were no redirection. When making this loop-avoidance test, the complete
+local part, including any prefix or suffix, is used.
+
+Specifying the same local part without a domain is a common usage in personal
+filter files when the user wants to have messages delivered to the local
+mailbox and also forwarded elsewhere. For example, the user whose login is cleo
+might have a .forward file containing this:
+
+cleo, cleopatra@egypt.example
+
+For compatibility with other MTAs, such unqualified local parts may be preceded
+by "\", but this is not a requirement for loop prevention. However, it does
+make a difference if more than one domain is being handled synonymously.
+
+If an item begins with "\" and the rest of the item parses as a valid RFC 2822
+address that does not include a domain, the item is qualified using the domain
+of the incoming address. In the absence of a leading "\", unqualified addresses
+are qualified using the value in qualify_recipient, but you can force the
+incoming domain to be used by setting qualify_preserve_domain.
+
+Care must be taken if there are alias names for local users. Consider an MTA
+handling a single local domain where the system alias file contains:
+
+Sam.Reman: spqr
+
+Now suppose that Sam (whose login id is spqr) wants to save copies of messages
+in the local mailbox, and also forward copies elsewhere. He creates this
+forward file:
+
+Sam.Reman, spqr@reme.elsewhere.example
+
+With these settings, an incoming message addressed to Sam.Reman fails. The
+redirect router for system aliases does not process Sam.Reman the second time
+round, because it has previously routed it, and the following routers
+presumably cannot handle the alias. The forward file should really contain
+
+spqr, spqr@reme.elsewhere.example
+
+but because this is such a common error, the check_ancestor option (see below)
+exists to provide a way to get round it. This is normally set on a redirect
+router that is handling users' .forward files.
+
+
+22.6 Special items in redirection lists
+---------------------------------------
+
+In addition to addresses, the following types of item may appear in redirection
+lists (that is, in non-filter redirection data):
+
+ * An item is treated as a pipe command if it begins with "|" and does not
+ parse as a valid RFC 2822 address that includes a domain. A transport for
+ running the command must be specified by the pipe_transport option.
+ Normally, either the router or the transport specifies a user and a group
+ under which to run the delivery. The default is to use the Exim user and
+ group.
+
+ Single or double quotes can be used for enclosing the individual arguments
+ of the pipe command; no interpretation of escapes is done for single
+ quotes. If the command contains a comma character, it is necessary to put
+ the whole item in double quotes, for example:
+
+ "|/some/command ready,steady,go"
+
+ since items in redirection lists are terminated by commas. Do not, however,
+ quote just the command. An item such as
+
+ |"/some/command ready,steady,go"
+
+ is interpreted as a pipe with a rather strange command name, and no
+ arguments.
+
+ Note that the above example assumes that the text comes from a lookup
+ source of some sort, so that the quotes are part of the data. If composing
+ a redirect router with a data option directly specifying this command, the
+ quotes will be used by the configuration parser to define the extent of one
+ string, but will not be passed down into the redirect router itself. There
+ are two main approaches to get around this: escape quotes to be part of the
+ data itself, or avoid using this mechanism and instead create a custom
+ transport with the command option set and reference that transport from an
+ accept router.
+
+ * An item is interpreted as a path name if it begins with "/" and does not
+ parse as a valid RFC 2822 address that includes a domain. For example,
+
+ /home/world/minbari
+
+ is treated as a filename, but
+
+ /s=molari/o=babylon/@x400gate.way
+
+ is treated as an address. For a filename, a transport must be specified
+ using the file_transport option. However, if the generated path name ends
+ with a forward slash character, it is interpreted as a directory name
+ rather than a filename, and directory_transport is used instead.
+
+ Normally, either the router or the transport specifies a user and a group
+ under which to run the delivery. The default is to use the Exim user and
+ group.
+
+ However, if a redirection item is the path /dev/null, delivery to it is
+ bypassed at a high level, and the log entry shows "**bypassed**" instead of
+ a transport name. In this case the user and group are not used.
+
+ * If an item is of the form
+
+ :include:<path name>
+
+ a list of further items is taken from the given file and included at that
+ point. Note: Such a file can not be a filter file; it is just an
+ out-of-line addition to the list. The items in the included list are
+ separated by commas or newlines and are not subject to expansion. If this
+ is the first item in an alias list in an lsearch file, a colon must be used
+ to terminate the alias name. This example is incorrect:
+
+ list1 :include:/opt/lists/list1
+
+ It must be given as
+
+ list1: :include:/opt/lists/list1
+
+ Tainted data may not be used for a filename.
+
+ * Sometimes you want to throw away mail to a particular local part. Making
+ the data option expand to an empty string does not work, because that
+ causes the router to decline. Instead, the alias item
+
+ :blackhole:
+
+ can be used. It does what its name implies. No delivery is done, and no
+ error message is generated. This has the same effect as specifying /dev/
+ null as a destination, but it can be independently disabled.
+
+ Warning: If :blackhole: appears anywhere in a redirection list, no delivery
+ is done for the original local part, even if other redirection items are
+ present. If you are generating a multi-item list (for example, by reading a
+ database) and need the ability to provide a no-op item, you must use /dev/
+ null.
+
+ * An attempt to deliver a particular address can be deferred or forced to
+ fail by redirection items of the form
+
+ :defer:
+ :fail:
+
+ respectively. When a redirection list contains such an item, it applies to
+ the entire redirection; any other items in the list are ignored. Any text
+ following :fail: or :defer: is placed in the error text associated with the
+ failure. For example, an alias file might contain:
+
+ X.Employee: :fail: Gone away, no forwarding address
+
+ In the case of an address that is being verified from an ACL or as the
+ subject of a VRFY command, the text is included in the SMTP error response
+ by default. The text is not included in the response to an EXPN command. In
+ non-SMTP cases the text is included in the error message that Exim
+ generates.
+
+ By default, Exim sends a 451 SMTP code for a :defer:, and 550 for :fail:.
+ However, if the message starts with three digits followed by a space,
+ optionally followed by an extended code of the form n.n.n, also followed by
+ a space, and the very first digit is the same as the default error code,
+ the code from the message is used instead. If the very first digit is
+ incorrect, a panic error is logged, and the default code is used. You can
+ suppress the use of the supplied code in a redirect router by setting the
+ forbid_smtp_code option true. In this case, any SMTP code is quietly
+ ignored.
+
+ In an ACL, an explicitly provided message overrides the default, but the
+ default message is available in the variable $acl_verify_message and can
+ therefore be included in a custom message if this is desired.
+
+ Normally the error text is the rest of the redirection list - a comma does
+ not terminate it - but a newline does act as a terminator. Newlines are not
+ normally present in alias expansions. In lsearch lookups they are removed
+ as part of the continuation process, but they may exist in other kinds of
+ lookup and in :include: files.
+
+ During routing for message delivery (as opposed to verification), a
+ redirection containing :fail: causes an immediate failure of the incoming
+ address, whereas :defer: causes the message to remain in the queue so that
+ a subsequent delivery attempt can happen at a later time. If an address is
+ deferred for too long, it will ultimately fail, because the normal retry
+ rules still apply.
+
+ * Sometimes it is useful to use a single-key search type with a default (see
+ chapter 9) to look up aliases. However, there may be a need for exceptions
+ to the default. These can be handled by aliasing them to :unknown:. This
+ differs from :fail: in that it causes the redirect router to decline,
+ whereas :fail: forces routing to fail. A lookup which results in an empty
+ redirection list has the same effect.
+
+
+22.7 Duplicate addresses
+------------------------
+
+Exim removes duplicate addresses from the list to which it is delivering, so as
+to deliver just one copy to each address. This does not apply to deliveries
+routed to pipes by different immediate parent addresses, but an indirect
+aliasing scheme of the type
+
+pipe: |/some/command $local_part
+localpart1: pipe
+localpart2: pipe
+
+does not work with a message that is addressed to both local parts, because
+when the second is aliased to the intermediate local part "pipe" it gets
+discarded as being the same as a previously handled address. However, a scheme
+such as
+
+localpart1: |/some/command $local_part
+localpart2: |/some/command $local_part
+
+does result in two different pipe deliveries, because the immediate parents of
+the pipes are distinct.
+
+
+22.8 Repeated redirection expansion
+-----------------------------------
+
+When a message cannot be delivered to all of its recipients immediately,
+leading to two or more delivery attempts, redirection expansion is carried out
+afresh each time for those addresses whose children were not all previously
+delivered. If redirection is being used as a mailing list, this can lead to new
+members of the list receiving copies of old messages. The one_time option can
+be used to avoid this.
+
+
+22.9 Errors in redirection lists
+--------------------------------
+
+If skip_syntax_errors is set, a malformed address that causes a parsing error
+is skipped, and an entry is written to the main log. This may be useful for
+mailing lists that are automatically managed. Otherwise, if an error is
+detected while generating the list of new addresses, the original address is
+deferred. See also syntax_errors_to.
+
+
+22.10 Private options for the redirect router
+---------------------------------------------
+
+The private options for the redirect router are as follows:
+
++------------------------------------------------------+
+|allow_defer|Use: redirect|Type: boolean|Default: false|
++------------------------------------------------------+
+
+Setting this option allows the use of :defer: in non-filter redirection data,
+or the defer command in an Exim filter file.
+
++-----------------------------------------------------+
+|allow_fail|Use: redirect|Type: boolean|Default: false|
++-----------------------------------------------------+
+
+If this option is true, the :fail: item can be used in a redirection list, and
+the fail command may be used in an Exim filter file.
+
++-------------------------------------------------------+
+|allow_filter|Use: redirect|Type: boolean|Default: false|
++-------------------------------------------------------+
+
+Setting this option allows Exim to interpret redirection data that starts with
+"#Exim filter" or "#Sieve filter" as a set of filtering instructions. There are
+some features of Exim filter files that some administrators may wish to lock
+out; see the forbid_filter_xxx options below.
+
+It is also possible to lock out Exim filters or Sieve filters while allowing
+the other type; see forbid_exim_filter and forbid_sieve_filter.
+
+The filter is run using the uid and gid set by the generic user and group
+options. These take their defaults from the password data if check_local_user
+is set, so in the normal case of users' personal filter files, the filter is
+run as the relevant user. When allow_filter is set true, Exim insists that
+either check_local_user or user is set.
+
++-------------------------------------------------------+
+|allow_freeze|Use: redirect|Type: boolean|Default: false|
++-------------------------------------------------------+
+
+Setting this option allows the use of the freeze command in an Exim filter.
+This command is more normally encountered in system filters, and is disabled by
+default for redirection filters because it isn't something you usually want to
+let ordinary users do.
+
++---------------------------------------------------------+
+|check_ancestor|Use: redirect|Type: boolean|Default: false|
++---------------------------------------------------------+
+
+This option is concerned with handling generated addresses that are the same as
+some address in the list of redirection ancestors of the current address.
+Although it is turned off by default in the code, it is set in the default
+configuration file for handling users' .forward files. It is recommended for
+this use of the redirect router.
+
+When check_ancestor is set, if a generated address (including the domain) is
+the same as any ancestor of the current address, it is replaced by a copy of
+the current address. This helps in the case where local part A is aliased to B,
+and B has a .forward file pointing back to A. For example, within a single
+domain, the local part "Joe.Bloggs" is aliased to "jb" and jb/.forward
+contains:
+
+\Joe.Bloggs, <other item(s)>
+
+Without the check_ancestor setting, either local part ("jb" or "joe.bloggs")
+gets processed once by each router and so ends up as it was originally. If "jb"
+is the real mailbox name, mail to "jb" gets delivered (having been turned into
+"joe.bloggs" by the .forward file and back to "jb" by the alias), but mail to
+"joe.bloggs" fails. Setting check_ancestor on the redirect router that handles
+the .forward file prevents it from turning "jb" back into "joe.bloggs" when
+that was the original address. See also the repeat_use option below.
+
++----------------------------------------------------------+
+|check_group|Use: redirect|Type: boolean|Default: see below|
++----------------------------------------------------------+
+
+When the file option is used, the group owner of the file is checked only when
+this option is set. The permitted groups are those listed in the owngroups
+option, together with the user's default group if check_local_user is set. If
+the file has the wrong group, routing is deferred. The default setting for this
+option is true if check_local_user is set and the modemask option permits the
+group write bit, or if the owngroups option is set. Otherwise it is false, and
+no group check occurs.
+
++----------------------------------------------------------+
+|check_owner|Use: redirect|Type: boolean|Default: see below|
++----------------------------------------------------------+
+
+When the file option is used, the owner of the file is checked only when this
+option is set. If check_local_user is set, the local user is permitted;
+otherwise the owner must be one of those listed in the owners option. The
+default value for this option is true if check_local_user or owners is set.
+Otherwise the default is false, and no owner check occurs.
+
++-----------------------------------------------+
+|data|Use: redirect|Type: string*|Default: unset|
++-----------------------------------------------+
+
+This option is mutually exclusive with file. One or other of them must be set,
+but not both. The contents of data are expanded, and then used as the list of
+forwarding items, or as a set of filtering instructions. If the expansion is
+forced to fail, or the result is an empty string or a string that has no effect
+(consists entirely of comments), the router declines.
+
+When filtering instructions are used, the string must begin with "#Exim
+filter", and all comments in the string, including this initial one, must be
+terminated with newline characters. For example:
+
+data = #Exim filter\n\
+ if $h_to: contains Exim then save $home/mail/exim endif
+
+If you are reading the data from a database where newlines cannot be included,
+you can use the ${sg} expansion item to turn the escape string of your choice
+into a newline.
+
++--------------------------------------------------------------+
+|directory_transport|Use: redirect|Type: string*|Default: unset|
++--------------------------------------------------------------+
+
+A redirect router sets up a direct delivery to a directory when a path name
+ending with a slash is specified as a new "address". The transport used is
+specified by this option, which, after expansion, must be the name of a
+configured transport. This should normally be an appendfile transport.
+
++-----------------------------------------------+
+|file|Use: redirect|Type: string*|Default: unset|
++-----------------------------------------------+
+
+This option specifies the name of a file that contains the redirection data. It
+is mutually exclusive with the data option. The string is expanded before use;
+if the expansion is forced to fail, the router declines. Other expansion
+failures cause delivery to be deferred. The result of a successful expansion
+must be an absolute path. The entire file is read and used as the redirection
+data. If the data is an empty string or a string that has no effect (consists
+entirely of comments), the router declines.
+
+If the attempt to open the file fails with a "does not exist" error, Exim runs
+a check on the containing directory, unless ignore_enotdir is true (see below).
+If the directory does not appear to exist, delivery is deferred. This can
+happen when users' .forward files are in NFS-mounted directories, and there is
+a mount problem. If the containing directory does exist, but the file does not,
+the router declines.
+
++---------------------------------------------------------+
+|file_transport|Use: redirect|Type: string*|Default: unset|
++---------------------------------------------------------+
+
+A redirect router sets up a direct delivery to a file when a path name not
+ending in a slash is specified as a new "address". The transport used is
+specified by this option, which, after expansion, must be the name of a
+configured transport. This should normally be an appendfile transport. When it
+is running, the filename is in $address_file.
+
++-------------------------------------------------------------+
+|filter_prepend_home|Use: redirect|Type: boolean|Default: true|
++-------------------------------------------------------------+
+
+When this option is true, if a save command in an Exim filter specifies a
+relative path, and $home is defined, it is automatically prepended to the
+relative path. If this option is set false, this action does not happen. The
+relative path is then passed to the transport unmodified.
+
++-----------------------------------------------------------+
+|forbid_blackhole|Use: redirect|Type: boolean|Default: false|
++-----------------------------------------------------------+
+
+If this option is true, the :blackhole: item may not appear in a redirection
+list.
+
++-------------------------------------------------------------+
+|forbid_exim_filter|Use: redirect|Type: boolean|Default: false|
++-------------------------------------------------------------+
+
+If this option is set true, only Sieve filters are permitted when allow_filter
+is true.
+
++------------------------------------------------------+
+|forbid_file|Use: redirect|Type: boolean|Default: false|
++------------------------------------------------------+
+
+If this option is true, this router may not generate a new address that
+specifies delivery to a local file or directory, either from a filter or from a
+conventional forward file. This option is forced to be true if one_time is set.
+It applies to Sieve filters as well as to Exim filters, but if true, it locks
+out the Sieve's "keep" facility.
+
++---------------------------------------------------------------+
+|forbid_filter_dlfunc|Use: redirect|Type: boolean|Default: false|
++---------------------------------------------------------------+
+
+If this option is true, string expansions in Exim filters are not allowed to
+make use of the dlfunc expansion facility to run dynamically loaded functions.
+
++-------------------------------------------------------------------+
+|forbid_filter_existstest|Use: redirect|Type: boolean|Default: false|
++-------------------------------------------------------------------+
+
+If this option is true, string expansions in Exim filters are not allowed to
+make use of the exists condition or the stat expansion item.
+
++-----------------------------------------------------------------+
+|forbid_filter_logwrite|Use: redirect|Type: boolean|Default: false|
++-----------------------------------------------------------------+
+
+If this option is true, use of the logging facility in Exim filters is not
+permitted. Logging is in any case available only if the filter is being run
+under some unprivileged uid (which is normally the case for ordinary users'
+.forward files).
+
++---------------------------------------------------------------+
+|forbid_filter_lookup|Use: redirect|Type: boolean|Default: false|
++---------------------------------------------------------------+
+
+If this option is true, string expansions in Exim filter files are not allowed
+to make use of lookup items.
+
++-------------------------------------------------------------+
+|forbid_filter_perl|Use: redirect|Type: boolean|Default: false|
++-------------------------------------------------------------+
+
+This option has an effect only if Exim is built with embedded Perl support. If
+it is true, string expansions in Exim filter files are not allowed to make use
+of the embedded Perl support.
+
++-----------------------------------------------------------------+
+|forbid_filter_readfile|Use: redirect|Type: boolean|Default: false|
++-----------------------------------------------------------------+
+
+If this option is true, string expansions in Exim filter files are not allowed
+to make use of readfile items.
+
++-------------------------------------------------------------------+
+|forbid_filter_readsocket|Use: redirect|Type: boolean|Default: false|
++-------------------------------------------------------------------+
+
+If this option is true, string expansions in Exim filter files are not allowed
+to make use of readsocket items.
+
++--------------------------------------------------------------+
+|forbid_filter_reply|Use: redirect|Type: boolean|Default: false|
++--------------------------------------------------------------+
+
+If this option is true, this router may not generate an automatic reply
+message. Automatic replies can be generated only from Exim or Sieve filter
+files, not from traditional forward files. This option is forced to be true if
+one_time is set.
+
++------------------------------------------------------------+
+|forbid_filter_run|Use: redirect|Type: boolean|Default: false|
++------------------------------------------------------------+
+
+If this option is true, string expansions in Exim filter files are not allowed
+to make use of run items.
+
++---------------------------------------------------------+
+|forbid_include|Use: redirect|Type: boolean|Default: false|
++---------------------------------------------------------+
+
+If this option is true, items of the form
+
+:include:<path name>
+
+are not permitted in non-filter redirection lists.
+
++------------------------------------------------------+
+|forbid_pipe|Use: redirect|Type: boolean|Default: false|
++------------------------------------------------------+
+
+If this option is true, this router may not generate a new address which
+specifies delivery to a pipe, either from an Exim filter or from a conventional
+forward file. This option is forced to be true if one_time is set.
+
++--------------------------------------------------------------+
+|forbid_sieve_filter|Use: redirect|Type: boolean|Default: false|
++--------------------------------------------------------------+
+
+If this option is set true, only Exim filters are permitted when allow_filter
+is true.
+
++-----------------------------------------------------------+
+|forbid_smtp_code|Use: redirect|Type: boolean|Default: false|
++-----------------------------------------------------------+
+
+If this option is set true, any SMTP error codes that are present at the start
+of messages specified for ":defer:" or ":fail:" are quietly ignored, and the
+default codes (451 and 550, respectively) are always used.
+
++---------------------------------------------------------------+
+|hide_child_in_errmsg|Use: redirect|Type: boolean|Default: false|
++---------------------------------------------------------------+
+
+If this option is true, it prevents Exim from quoting a child address if it
+generates a bounce or delay message for it. Instead it says "an address
+generated from <the top level address>". Of course, this applies only to
+bounces generated locally. If a message is forwarded to another host, its
+bounce may well quote the generated address.
+
++--------------------------------------------------------+
+|ignore_eacces|Use: redirect|Type: boolean|Default: false|
++--------------------------------------------------------+
+
+If this option is set and an attempt to open a redirection file yields the
+EACCES error (permission denied), the redirect router behaves as if the file
+did not exist.
+
++---------------------------------------------------------+
+|ignore_enotdir|Use: redirect|Type: boolean|Default: false|
++---------------------------------------------------------+
+
+If this option is set and an attempt to open a redirection file yields the
+ENOTDIR error (something on the path is not a directory), the redirect router
+behaves as if the file did not exist.
+
+Setting ignore_enotdir has another effect as well: When a redirect router that
+has the file option set discovers that the file does not exist (the ENOENT
+error), it tries to stat() the parent directory, as a check against unmounted
+NFS directories. If the parent can not be statted, delivery is deferred.
+However, it seems wrong to do this check when ignore_enotdir is set, because
+that option tells Exim to ignore "something on the path is not a directory"
+(the ENOTDIR error). This is a confusing area, because it seems that some
+operating systems give ENOENT where others give ENOTDIR.
+
++-----------------------------------------------------------+
+|include_directory|Use: redirect|Type: string|Default: unset|
++-----------------------------------------------------------+
+
+If this option is set, the path names of any :include: items in a redirection
+list must start with this directory.
+
++-------------------------------------------------------+
+|modemask|Use: redirect|Type: octal integer|Default: 022|
++-------------------------------------------------------+
+
+This specifies mode bits which must not be set for a file specified by the file
+option. If any of the forbidden bits are set, delivery is deferred.
+
++---------------------------------------------------+
+|one_time|Use: redirect|Type: boolean|Default: false|
++---------------------------------------------------+
+
+Sometimes the fact that Exim re-evaluates aliases and reprocesses redirection
+files each time it tries to deliver a message causes a problem when one or more
+of the generated addresses fails be delivered at the first attempt. The problem
+is not one of duplicate delivery - Exim is clever enough to handle that - but
+of what happens when the redirection list changes during the time that the
+message is on Exim's queue. This is particularly true in the case of mailing
+lists, where new subscribers might receive copies of messages that were posted
+before they subscribed.
+
+If one_time is set and any addresses generated by the router fail to deliver at
+the first attempt, the failing addresses are added to the message as "top
+level" addresses, and the parent address that generated them is marked
+"delivered". Thus, redirection does not happen again at the next delivery
+attempt.
+
+Warning 1: Any header line addition or removal that is specified by this router
+would be lost if delivery did not succeed at the first attempt. For this
+reason, the headers_add and headers_remove generic options are not permitted
+when one_time is set.
+
+Warning 2: To ensure that the router generates only addresses (as opposed to
+pipe or file deliveries or auto-replies) forbid_file, forbid_pipe, and
+forbid_filter_reply are forced to be true when one_time is set.
+
+Warning 3: The unseen generic router option may not be set with one_time.
+
+The original top-level address is remembered with each of the generated
+addresses, and is output in any log messages. However, any intermediate parent
+addresses are not recorded. This makes a difference to the log only if
+all_parents log selector is set. It is expected that one_time will typically be
+used for mailing lists, where there is normally just one level of expansion.
+
++-----------------------------------------------------+
+|owners|Use: redirect|Type: string list|Default: unset|
++-----------------------------------------------------+
+
+This specifies a list of permitted owners for the file specified by file. This
+list is in addition to the local user when check_local_user is set. See
+check_owner above.
+
++--------------------------------------------------------+
+|owngroups|Use: redirect|Type: string list|Default: unset|
++--------------------------------------------------------+
+
+This specifies a list of permitted groups for the file specified by file. The
+list is in addition to the local user's primary group when check_local_user is
+set. See check_group above.
+
++---------------------------------------------------------+
+|pipe_transport|Use: redirect|Type: string*|Default: unset|
++---------------------------------------------------------+
+
+A redirect router sets up a direct delivery to a pipe when a string starting
+with a vertical bar character is specified as a new "address". The transport
+used is specified by this option, which, after expansion, must be the name of a
+configured transport. This should normally be a pipe transport. When the
+transport is run, the pipe command is in $address_pipe.
+
++---------------------------------------------------------+
+|qualify_domain|Use: redirect|Type: string*|Default: unset|
++---------------------------------------------------------+
+
+If this option is set, and an unqualified address (one without a domain) is
+generated, and that address would normally be qualified by the global setting
+in qualify_recipient, it is instead qualified with the domain specified by
+expanding this string. If the expansion fails, the router declines. If you want
+to revert to the default, you can have the expansion generate
+$qualify_recipient.
+
+This option applies to all unqualified addresses generated by Exim filters, but
+for traditional .forward files, it applies only to addresses that are not
+preceded by a backslash. Sieve filters cannot generate unqualified addresses.
+
++------------------------------------------------------------------+
+|qualify_preserve_domain|Use: redirect|Type: boolean|Default: false|
++------------------------------------------------------------------+
+
+If this option is set, the router's local qualify_domain option must not be set
+(a configuration error occurs if it is). If an unqualified address (one without
+a domain) is generated, it is qualified with the domain of the parent address
+(the immediately preceding ancestor) instead of the global qualify_recipient
+value. In the case of a traditional .forward file, this applies whether or not
+the address is preceded by a backslash.
+
++----------------------------------------------------+
+|repeat_use|Use: redirect|Type: boolean|Default: true|
++----------------------------------------------------+
+
+If this option is set false, the router is skipped for a child address that has
+any ancestor that was routed by this router. This test happens before any of
+the other preconditions are tested. Exim's default anti-looping rules skip only
+when the ancestor is the same as the current address. See also check_ancestor
+above and the generic redirect_router option.
+
++----------------------------------------------------------+
+|reply_transport|Use: redirect|Type: string*|Default: unset|
++----------------------------------------------------------+
+
+A redirect router sets up an automatic reply when a mail or vacation command is
+used in a filter file. The transport used is specified by this option, which,
+after expansion, must be the name of a configured transport. This should
+normally be an autoreply transport. Other transports are unlikely to do
+anything sensible or useful.
+
++-------------------------------------------------+
+|rewrite|Use: redirect|Type: boolean|Default: true|
++-------------------------------------------------+
+
+If this option is set false, addresses generated by the router are not subject
+to address rewriting. Otherwise, they are treated like new addresses and are
+rewritten according to the global rewriting rules.
+
++-----------------------------------------------------------+
+|sieve_subaddress|Use: redirect|Type: string*|Default: unset|
++-----------------------------------------------------------+
+
+The value of this option is passed to a Sieve filter to specify the :subaddress
+part of an address.
+
++------------------------------------------------------------+
+|sieve_useraddress|Use: redirect|Type: string*|Default: unset|
++------------------------------------------------------------+
+
+The value of this option is passed to a Sieve filter to specify the :user part
+of an address. However, if it is unset, the entire original local part
+(including any prefix or suffix) is used for :user.
+
++-------------------------------------------------------------------+
+|sieve_vacation_directory|Use: redirect|Type: string*|Default: unset|
++-------------------------------------------------------------------+
+
+To enable the "vacation" extension for Sieve filters, you must set
+sieve_vacation_directory to the directory where vacation databases are held (do
+not put anything else in that directory), and ensure that the reply_transport
+option refers to an autoreply transport. Each user needs their own directory;
+Exim will create it if necessary.
+
++-------------------------------------------------------------+
+|skip_syntax_errors|Use: redirect|Type: boolean|Default: false|
++-------------------------------------------------------------+
+
+If skip_syntax_errors is set, syntactically malformed addresses in non-filter
+redirection data are skipped, and each failing address is logged. If
+syntax_errors_to is set, a message is sent to the address it defines, giving
+details of the failures. If syntax_errors_text is set, its contents are
+expanded and placed at the head of the error message generated by
+syntax_errors_to. Usually it is appropriate to set syntax_errors_to to be the
+same address as the generic errors_to option. The skip_syntax_errors option is
+often used when handling mailing lists.
+
+If all the addresses in a redirection list are skipped because of syntax
+errors, the router declines to handle the original address, and it is passed to
+the following routers.
+
+If skip_syntax_errors is set when an Exim filter is interpreted, any syntax
+error in the filter causes filtering to be abandoned without any action being
+taken. The incident is logged, and the router declines to handle the address,
+so it is passed to the following routers.
+
+Syntax errors in a Sieve filter file cause the "keep" action to occur. This
+action is specified by RFC 3028. The values of skip_syntax_errors,
+syntax_errors_to, and syntax_errors_text are not used.
+
+skip_syntax_errors can be used to specify that errors in users' forward lists
+or filter files should not prevent delivery. The syntax_errors_to option, used
+with an address that does not get redirected, can be used to notify users of
+these errors, by means of a router like this:
+
+userforward:
+ driver = redirect
+ allow_filter
+ check_local_user
+ file = $home/.forward
+ file_transport = address_file
+ pipe_transport = address_pipe
+ reply_transport = address_reply
+ no_verify
+ skip_syntax_errors
+ syntax_errors_to = real-$local_part@$domain
+ syntax_errors_text = \
+ This is an automatically generated message. An error has\n\
+ been found in your .forward file. Details of the error are\n\
+ reported below. While this error persists, you will receive\n\
+ a copy of this message for every message that is addressed\n\
+ to you. If your .forward file is a filter file, or if it is\n\
+ a non-filter file containing no valid forwarding addresses,\n\
+ a copy of each incoming message will be put in your normal\n\
+ mailbox. If a non-filter file contains at least one valid\n\
+ forwarding address, forwarding to the valid addresses will\n\
+ happen, and those will be the only deliveries that occur.
+
+You also need a router to ensure that local addresses that are prefixed by
+"real-" are recognized, but not forwarded or filtered. For example, you could
+put this immediately before the userforward router:
+
+real_localuser:
+ driver = accept
+ check_local_user
+ local_part_prefix = real-
+ transport = local_delivery
+
+For security, it would probably be a good idea to restrict the use of this
+router to locally-generated messages, using a condition such as this:
+
+ condition = ${if match {$sender_host_address}\
+ {\N^(|127\.0\.0\.1)$\N}}
+
++-------------------------------------------------------------+
+|syntax_errors_text|Use: redirect|Type: string*|Default: unset|
++-------------------------------------------------------------+
+
+See skip_syntax_errors above.
+
++----------------------------------------------------------+
+|syntax_errors_to|Use: redirect|Type: string|Default: unset|
++----------------------------------------------------------+
+
+See skip_syntax_errors above.
+
+
+
+===============================================================================
+23. ENVIRONMENT FOR RUNNING LOCAL TRANSPORTS
+
+Local transports handle deliveries to files and pipes. (The autoreply transport
+can be thought of as similar to a pipe.) Exim always runs transports in
+subprocesses, under specified uids and gids. Typical deliveries to local
+mailboxes run under the uid and gid of the local user.
+
+Exim also sets a specific current directory while running the transport; for
+some transports a home directory setting is also relevant. The pipe transport
+is the only one that sets up environment variables; see section 29.4 for
+details.
+
+The values used for the uid, gid, and the directories may come from several
+different places. In many cases, the router that handles the address associates
+settings with that address as a result of its check_local_user, group, or user
+options. However, values may also be given in the transport's own
+configuration, and these override anything that comes from the router.
+
+
+23.1 Concurrent deliveries
+--------------------------
+
+If two different messages for the same local recipient arrive more or less
+simultaneously, the two delivery processes are likely to run concurrently. When
+the appendfile transport is used to write to a file, Exim applies locking rules
+to stop concurrent processes from writing to the same file at the same time.
+
+However, when you use a pipe transport, it is up to you to arrange any locking
+that is needed. Here is a silly example:
+
+my_transport:
+ driver = pipe
+ command = /bin/sh -c 'cat >>/some/file'
+
+This is supposed to write the message at the end of the file. However, if two
+messages arrive at the same time, the file will be scrambled. You can use the
+exim_lock utility program (see section 54.15) to lock a file using the same
+algorithm that Exim itself uses.
+
+
+23.2 Uids and gids
+------------------
+
+All transports have the options group and user. If group is set, it overrides
+any group that the router set in the address, even if user is not set for the
+transport. This makes it possible, for example, to run local mail delivery
+under the uid of the recipient (set by the router), but in a special group (set
+by the transport). For example:
+
+# Routers ...
+# User/group are set by check_local_user in this router
+local_users:
+ driver = accept
+ check_local_user
+ transport = group_delivery
+
+# Transports ...
+# This transport overrides the group
+group_delivery:
+ driver = appendfile
+ file = /var/spool/mail/$local_part_data
+ group = mail
+
+If user is set for a transport, its value overrides what is set in the address
+by the router. If user is non-numeric and group is not set, the gid associated
+with the user is used. If user is numeric, group must be set.
+
+When the uid is taken from the transport's configuration, the initgroups()
+function is called for the groups associated with that uid if the initgroups
+option is set for the transport. When the uid is not specified by the
+transport, but is associated with the address by a router, the option for
+calling initgroups() is taken from the router configuration.
+
+The pipe transport contains the special option pipe_as_creator. If this is set
+and user is not set, the uid of the process that called Exim to receive the
+message is used, and if group is not set, the corresponding original gid is
+also used.
+
+This is the detailed preference order for obtaining a gid; the first of the
+following that is set is used:
+
+ * A group setting of the transport;
+
+ * A group setting of the router;
+
+ * A gid associated with a user setting of the router, either as a result of
+ check_local_user or an explicit non-numeric user setting;
+
+ * The group associated with a non-numeric user setting of the transport;
+
+ * In a pipe transport, the creator's gid if deliver_as_creator is set and the
+ uid is the creator's uid;
+
+ * The Exim gid if the Exim uid is being used as a default.
+
+If, for example, the user is specified numerically on the router and there are
+no group settings, no gid is available. In this situation, an error occurs.
+This is different for the uid, for which there always is an ultimate default.
+The first of the following that is set is used:
+
+ * A user setting of the transport;
+
+ * In a pipe transport, the creator's uid if deliver_as_creator is set;
+
+ * A user setting of the router;
+
+ * A check_local_user setting of the router;
+
+ * The Exim uid.
+
+Of course, an error will still occur if the uid that is chosen is on the
+never_users list.
+
+
+23.3 Current and home directories
+---------------------------------
+
+Routers may set current and home directories for local transports by means of
+the transport_current_directory and transport_home_directory options. However,
+if the transport's current_directory or home_directory options are set, they
+override the router's values. In detail, the home directory for a local
+transport is taken from the first of these values that is set:
+
+ * The home_directory option on the transport;
+
+ * The transport_home_directory option on the router;
+
+ * The password data if check_local_user is set on the router;
+
+ * The router_home_directory option on the router.
+
+The current directory is taken from the first of these values that is set:
+
+ * The current_directory option on the transport;
+
+ * The transport_current_directory option on the router.
+
+If neither the router nor the transport sets a current directory, Exim uses the
+value of the home directory, if it is set. Otherwise it sets the current
+directory to / before running a local transport.
+
+
+23.4 Expansion variables derived from the address
+-------------------------------------------------
+
+Normally a local delivery is handling a single address, and in that case the
+variables such as $domain and $local_part are set during local deliveries.
+However, in some circumstances more than one address may be handled at once
+(for example, while writing batch SMTP for onward transmission by some other
+means). In this case, the variables associated with the local part are never
+set, $domain is set only if all the addresses have the same domain, and
+$original_domain is never set.
+
+
+
+===============================================================================
+24. GENERIC OPTIONS FOR TRANSPORTS
+
+The name of a transport is limited to be 64 ASCII characters long; prior to
+Exim 4.95 names would be silently truncated at this length, but now it is
+enforced.
+
+The following generic options apply to all transports:
+
++------------------------------------------------------+
+|body_only|Use: transports|Type: boolean|Default: false|
++------------------------------------------------------+
+
+If this option is set, the message's headers are not transported. It is
+mutually exclusive with headers_only. If it is used with the appendfile or pipe
+transports, the settings of message_prefix and message_suffix should be
+checked, because this option does not automatically suppress them.
+
++--------------------------------------------------------------+
+|current_directory|Use: transports|Type: string*|Default: unset|
++--------------------------------------------------------------+
+
+This specifies the current directory that is to be set while running the
+transport, overriding any value that may have been set by the router. If the
+expansion fails for any reason, including forced failure, an error is logged,
+and delivery is deferred.
+
++------------------------------------------------------------+
+|disable_logging|Use: transports|Type: boolean|Default: false|
++------------------------------------------------------------+
+
+If this option is set true, nothing is logged for any deliveries by the
+transport or for any transport errors. You should not set this option unless
+you really, really know what you are doing.
+
++--------------------------------------------------------+
+|debug_print|Use: transports|Type: string*|Default: unset|
++--------------------------------------------------------+
+
+If this option is set and debugging is enabled (see the -d command line
+option), the string is expanded and included in the debugging output when the
+transport is run. If expansion of the string fails, the error message is
+written to the debugging output, and Exim carries on processing. This facility
+is provided to help with checking out the values of variables and so on when
+debugging driver configurations. For example, if a headers_add option is not
+working properly, debug_print could be used to output the variables it
+references. A newline is added to the text if it does not end with one. The
+variables $transport_name and $router_name contain the name of the transport
+and the router that called it.
+
++--------------------------------------------------------------+
+|delivery_date_add|Use: transports|Type: boolean|Default: false|
++--------------------------------------------------------------+
+
+If this option is true, a Delivery-date: header is added to the message. This
+gives the actual time the delivery was made. As this is not a standard header,
+Exim has a configuration option (delivery_date_remove) which requests its
+removal from incoming messages, so that delivered messages can safely be resent
+to other recipients.
+
++--------------------------------------------------+
+|driver|Use: transports|Type: string|Default: unset|
++--------------------------------------------------+
+
+This specifies which of the available transport drivers is to be used. There is
+no default, and this option must be set for every transport.
+
++------------------------------------------------------------+
+|envelope_to_add|Use: transports|Type: boolean|Default: false|
++------------------------------------------------------------+
+
+If this option is true, an Envelope-to: header is added to the message. This
+gives the original address(es) in the incoming envelope that caused this
+delivery to happen. More than one address may be present if the transport is
+configured to handle several addresses at once, or if more than one original
+address was redirected to the same final address. As this is not a standard
+header, Exim has a configuration option (envelope_to_remove) which requests its
+removal from incoming messages, so that delivered messages can safely be resent
+to other recipients.
+
++---------------------------------------------------------+
+|event_action|Use: transports|Type: string*|Default: unset|
++---------------------------------------------------------+
+
+This option declares a string to be expanded for Exim's events mechanism. For
+details see chapter 61.
+
++-------------------------------------------------------+
+|group|Use: transports|Type: string*|Default: Exim group|
++-------------------------------------------------------+
+
+This option specifies a gid for running the transport process, overriding any
+value that the router supplies, and also overriding any value associated with
+user (see below).
+
++------------------------------------------------------+
+|headers_add|Use: transports|Type: list*|Default: unset|
++------------------------------------------------------+
+
+This option specifies a list of text headers, newline-separated (by default,
+changeable in the usual way 6.21), which are (separately) expanded and added to
+the header portion of a message as it is transported, as described in section
+48.17. Additional header lines can also be specified by routers. If the result
+of the expansion is an empty string, or if the expansion is forced to fail, no
+action is taken. Other expansion failures are treated as errors and cause the
+delivery to be deferred.
+
+Unlike most options, headers_add can be specified multiple times for a
+transport; all listed headers are added.
+
++---------------------------------------------------------+
+|headers_only|Use: transports|Type: boolean|Default: false|
++---------------------------------------------------------+
+
+If this option is set, the message's body is not transported. It is mutually
+exclusive with body_only. If it is used with the appendfile or pipe transports,
+the settings of message_prefix and message_suffix should be checked, since this
+option does not automatically suppress them.
+
++---------------------------------------------------------+
+|headers_remove|Use: transports|Type: list*|Default: unset|
++---------------------------------------------------------+
+
+This option specifies a list of text headers, colon-separated (by default,
+changeable in the usual way 6.21), to be removed from the message. However, the
+option has no effect when an address is just being verified. Each list item is
+separately expanded. If the result of the expansion is an empty string, or if
+the expansion is forced to fail, no action is taken. Other expansion failures
+are treated as errors and cause the delivery to be deferred.
+
+If an item ends in *, it will match any header with the given prefix.
+
+Matching headers are omitted from the message as it is transported, as
+described in section 48.17. Header removal can also be specified by routers.
+
+Unlike most options, headers_remove can be specified multiple times for a
+transport; all listed headers are removed.
+
+Warning: Because of the separate expansion of the list items, items that
+contain a list separator must have it doubled. To avoid this, change the list
+separator (6.21).
+
++-----------------------------------------------------------+
+|headers_rewrite|Use: transports|Type: string|Default: unset|
++-----------------------------------------------------------+
+
+This option allows addresses in header lines to be rewritten at transport time,
+that is, as the message is being copied to its destination. The contents of the
+option are a colon-separated list of rewriting rules. Each rule is in exactly
+the same form as one of the general rewriting rules that are applied when a
+message is received. These are described in chapter 31. For example,
+
+headers_rewrite = a@b c@d f : \
+ x@y w@z
+
+changes a@b into c@d in From: header lines, and x@y into w@z in all
+address-bearing header lines. The rules are applied to the header lines just
+before they are written out at transport time, so they affect only those copies
+of the message that pass through the transport. However, only the message's
+original header lines, and any that were added by a system filter, are
+rewritten. If a router or transport adds header lines, they are not affected by
+this option. These rewriting rules are not applied to the envelope. You can
+change the return path using return_path, but you cannot change envelope
+recipients at this time.
+
++-----------------------------------------------------------+
+|home_directory|Use: transports|Type: string*|Default: unset|
++-----------------------------------------------------------+
+
+This option specifies a home directory setting for a local transport,
+overriding any value that may be set by the router. The home directory is
+placed in $home while expanding the transport's private options. It is also
+used as the current directory if no current directory is set by the
+current_directory option on the transport or the transport_current_directory
+option on the router. If the expansion fails for any reason, including forced
+failure, an error is logged, and delivery is deferred.
+
++-------------------------------------------------------+
+|initgroups|Use: transports|Type: boolean|Default: false|
++-------------------------------------------------------+
+
+If this option is true and the uid for the delivery process is provided by the
+transport, the initgroups() function is called when running the transport to
+ensure that any additional groups associated with the uid are set up.
+
++----------------------------------------------------------+
+|max_parallel|Use: transports|Type: integer*|Default: unset|
++----------------------------------------------------------+
+
+If this option is set and expands to an integer greater than zero it limits the
+number of concurrent runs of the transport. The control does not apply to
+shadow transports.
+
+Exim implements this control by means of a hints database in which a record is
+incremented whenever a transport process is being created. The record is
+decremented and possibly removed when the process terminates. Obviously there
+is scope for records to get left lying around if there is a system or program
+crash. To guard against this, Exim ignores any records that are more than six
+hours old.
+
+If you use this option, you should also arrange to delete the relevant hints
+database whenever your system reboots. The names of the files start with misc
+and they are kept in the spool/db directory. There may be one or two files,
+depending on the type of DBM in use. The same files are used for ETRN and smtp
+transport serialization.
+
++-----------------------------------------------------------+
+|message_size_limit|Use: transports|Type: string*|Default: 0|
++-----------------------------------------------------------+
+
+This option controls the size of messages passed through the transport. It is
+expanded before use; the result of the expansion must be a sequence of decimal
+digits, optionally followed by K or M. If the expansion fails for any reason,
+including forced failure, or if the result is not of the required form,
+delivery is deferred. If the value is greater than zero and the size of a
+message exceeds this limit, the address is failed. If there is any chance that
+the resulting bounce message could be routed to the same transport, you should
+ensure that return_size_limit is less than the transport's message_size_limit,
+as otherwise the bounce message will fail to get delivered.
+
++-----------------------------------------------------------------+
+|rcpt_include_affixes|Use: transports|Type: boolean|Default: false|
++-----------------------------------------------------------------+
+
+When this option is false (the default), and an address that has had any
+affixes (prefixes or suffixes) removed from the local part is delivered by any
+form of SMTP or LMTP, the affixes are not included. For example, if a router
+that contains
+
+local_part_prefix = *-
+
+routes the address abc-xyz@some.domain to an SMTP transport, the envelope is
+delivered with
+
+RCPT TO:<xyz@some.domain>
+
+This is also the case when an ACL-time callout is being used to verify a
+recipient address. However, if rcpt_include_affixes is set true, the whole
+local part is included in the RCPT command. This option applies to BSMTP
+deliveries by the appendfile and pipe transports as well as to the lmtp and
+smtp transports.
+
++---------------------------------------------------------------------+
+|retry_use_local_part|Use: transports|Type: boolean|Default: see below|
++---------------------------------------------------------------------+
+
+When a delivery suffers a temporary failure, a retry record is created in
+Exim's hints database. For remote deliveries, the key for the retry record is
+based on the name and/or IP address of the failing remote host. For local
+deliveries, the key is normally the entire address, including both the local
+part and the domain. This is suitable for most common cases of local delivery
+temporary failure - for example, exceeding a mailbox quota should delay only
+deliveries to that mailbox, not to the whole domain.
+
+However, in some special cases you may want to treat a temporary local delivery
+as a failure associated with the domain, and not with a particular local part.
+(For example, if you are storing all mail for some domain in files.) You can do
+this by setting retry_use_local_part false.
+
+For all the local transports, its default value is true. For remote transports,
+the default value is false for tidiness, but changing the value has no effect
+on a remote transport in the current implementation.
+
++--------------------------------------------------------+
+|return_path|Use: transports|Type: string*|Default: unset|
++--------------------------------------------------------+
+
+If this option is set, the string is expanded at transport time and replaces
+the existing return path (envelope sender) value in the copy of the message
+that is being delivered. An empty return path is permitted. This feature is
+designed for remote deliveries, where the value of this option is used in the
+SMTP MAIL command. If you set return_path for a local transport, the only
+effect is to change the address that is placed in the Return-path: header line,
+if one is added to the message (see the next option).
+
+Note: A changed return path is not logged unless you add
+return_path_on_delivery to the log selector.
+
+The expansion can refer to the existing value via $return_path. This is either
+the message's envelope sender, or an address set by the errors_to option on a
+router. If the expansion is forced to fail, no replacement occurs; if it fails
+for another reason, delivery is deferred. This option can be used to support
+VERP (Variable Envelope Return Paths) - see section 51.6.
+
+Note: If a delivery error is detected locally, including the case when a remote
+server rejects a message at SMTP time, the bounce message is not sent to the
+value of this option. It is sent to the previously set errors address. This
+defaults to the incoming sender address, but can be changed by setting
+errors_to in a router.
+
++------------------------------------------------------------+
+|return_path_add|Use: transports|Type: boolean|Default: false|
++------------------------------------------------------------+
+
+If this option is true, a Return-path: header is added to the message. Although
+the return path is normally available in the prefix line of BSD mailboxes, this
+is commonly not displayed by MUAs, and so the user does not have easy access to
+it.
+
+RFC 2821 states that the Return-path: header is added to a message "when the
+delivery SMTP server makes the final delivery". This implies that this header
+should not be present in incoming messages. Exim has a configuration option,
+return_path_remove, which requests removal of this header from incoming
+messages, so that delivered messages can safely be resent to other recipients.
+
++-------------------------------------------------------------+
+|shadow_condition|Use: transports|Type: string*|Default: unset|
++-------------------------------------------------------------+
+
+See shadow_transport below.
+
++------------------------------------------------------------+
+|shadow_transport|Use: transports|Type: string|Default: unset|
++------------------------------------------------------------+
+
+A local transport may set the shadow_transport option to the name of another
+local transport. Shadow remote transports are not supported.
+
+Whenever a delivery to the main transport succeeds, and either shadow_condition
+is unset, or its expansion does not result in the empty string or one of the
+strings "0" or "no" or "false", the message is also passed to the shadow
+transport, with the same delivery address or addresses. If expansion fails, no
+action is taken except that non-forced expansion failures cause a log line to
+be written.
+
+The result of the shadow transport is discarded and does not affect the
+subsequent processing of the message. Only a single level of shadowing is
+provided; the shadow_transport option is ignored on any transport when it is
+running as a shadow. Options concerned with output from pipes are also ignored.
+The log line for the successful delivery has an item added on the end, of the
+form
+
+ST=<shadow transport name>
+
+If the shadow transport did not succeed, the error message is put in
+parentheses afterwards. Shadow transports can be used for a number of different
+purposes, including keeping more detailed log information than Exim normally
+provides, and implementing automatic acknowledgment policies based on message
+headers that some sites insist on.
+
++-------------------------------------------------------------+
+|transport_filter|Use: transports|Type: string*|Default: unset|
++-------------------------------------------------------------+
+
+This option sets up a filtering (in the Unix shell sense) process for messages
+at transport time. It should not be confused with mail filtering as set up by
+individual users or via a system filter. If unset, or expanding to an empty
+string, no filtering is done.
+
+When the message is about to be written out, the command specified by
+transport_filter is started up in a separate, parallel process, and the entire
+message, including the header lines, is passed to it on its standard input
+(this in fact is done from a third process, to avoid deadlock). The command
+must be specified as an absolute path.
+
+The lines of the message that are written to the transport filter are
+terminated by newline ("\n"). The message is passed to the filter before any
+SMTP-specific processing, such as turning "\n" into "\r\n" and escaping lines
+beginning with a dot, and also before any processing implied by the settings of
+check_string and escape_string in the appendfile or pipe transports.
+
+The standard error for the filter process is set to the same destination as its
+standard output; this is read and written to the message's ultimate
+destination. The process that writes the message to the filter, the filter
+itself, and the original process that reads the result and delivers it are all
+run in parallel, like a shell pipeline.
+
+The filter can perform any transformations it likes, but of course should take
+care not to break RFC 2822 syntax. Exim does not check the result, except to
+test for a final newline when SMTP is in use. All messages transmitted over
+SMTP must end with a newline, so Exim supplies one if it is missing.
+
+A transport filter can be used to provide content-scanning on a per-user basis
+at delivery time if the only required effect of the scan is to modify the
+message. For example, a content scan could insert a new header line containing
+a spam score. This could be interpreted by a filter in the user's MUA. It is
+not possible to discard a message at this stage.
+
+A problem might arise if the filter increases the size of a message that is
+being sent down an SMTP connection. If the receiving SMTP server has indicated
+support for the SIZE parameter, Exim will have sent the size of the message at
+the start of the SMTP session. If what is actually sent is substantially more,
+the server might reject the message. This can be worked round by setting the
+size_addition option on the smtp transport, either to allow for additions to
+the message, or to disable the use of SIZE altogether.
+
+The value of the transport_filter option is the command string for starting the
+filter, which is run directly from Exim, not under a shell. The string is
+parsed by Exim in the same way as a command string for the pipe transport: Exim
+breaks it up into arguments and then expands each argument separately (see
+section 29.3). Any kind of expansion failure causes delivery to be deferred.
+The special argument $pipe_addresses is replaced by a number of arguments, one
+for each address that applies to this delivery. (This isn't an ideal name for
+this feature here, but as it was already implemented for the pipe transport, it
+seemed sensible not to change it.)
+
+The expansion variables $host and $host_address are available when the
+transport is a remote one. They contain the name and IP address of the host to
+which the message is being sent. For example:
+
+transport_filter = /some/directory/transport-filter.pl \
+ $host $host_address $sender_address $pipe_addresses
+
+Two problems arise if you want to use more complicated expansion items to
+generate transport filter commands, both of which due to the fact that the
+command is split up before expansion.
+
+ * If an expansion item contains white space, you must quote it, so that it is
+ all part of the same command item. If the entire option setting is one such
+ expansion item, you have to take care what kind of quoting you use. For
+ example:
+
+ transport_filter = '/bin/cmd${if eq{$host}{a.b.c}{1}{2}}'
+
+ This runs the command /bin/cmd1 if the host name is a.b.c, and /bin/cmd2
+ otherwise. If double quotes had been used, they would have been stripped by
+ Exim when it read the option's value. When the value is used, if the single
+ quotes were missing, the line would be split into two items, "/bin/cmd${if"
+ and "eq{$host}{a.b.c}{1}{2}", and an error would occur when Exim tried to
+ expand the first one.
+
+ * Except for the special case of $pipe_addresses that is mentioned above, an
+ expansion cannot generate multiple arguments, or a command name followed by
+ arguments. Consider this example:
+
+ transport_filter = ${lookup{$host}lsearch{/a/file}\
+ {$value}{/bin/cat}}
+
+ The result of the lookup is interpreted as the name of the command, even if
+ it contains white space. The simplest way round this is to use a shell:
+
+ transport_filter = /bin/sh -c ${lookup{$host}lsearch{/a/file}\
+ {$value}{/bin/cat}}
+
+The filter process is run under the same uid and gid as the normal delivery.
+For remote deliveries this is the Exim uid/gid by default. The command should
+normally yield a zero return code. Transport filters are not supposed to fail.
+A non-zero code is taken to mean that the transport filter encountered some
+serious problem. Delivery of the message is deferred; the message remains on
+the queue and is tried again later. It is not possible to cause a message to be
+bounced from a transport filter.
+
+If a transport filter is set on an autoreply transport, the original message is
+passed through the filter as it is being copied into the newly generated
+message, which happens if the return_message option is set.
+
++---------------------------------------------------------------+
+|transport_filter_timeout|Use: transports|Type: time|Default: 5m|
++---------------------------------------------------------------+
+
+When Exim is reading the output of a transport filter, it applies a timeout
+that can be set by this option. Exceeding the timeout is normally treated as a
+temporary delivery failure. However, if a transport filter is used with a pipe
+transport, a timeout in the transport filter is treated in the same way as a
+timeout in the pipe command itself. By default, a timeout is a hard error, but
+if the pipe transport's timeout_defer option is set true, it becomes a
+temporary error.
+
++-----------------------------------------------------+
+|user|Use: transports|Type: string*|Default: Exim user|
++-----------------------------------------------------+
+
+This option specifies the user under whose uid the delivery process is to be
+run, overriding any uid that may have been set by the router. If the user is
+given as a name, the uid is looked up from the password data, and the
+associated group is taken as the value of the gid to be used if the group
+option is not set.
+
+For deliveries that use local transports, a user and group are normally
+specified explicitly or implicitly (for example, as a result of
+check_local_user) by the router or transport.
+
+For remote transports, you should leave this option unset unless you really are
+sure you know what you are doing. When a remote transport is running, it needs
+to be able to access Exim's hints databases, because each host may have its own
+retry data.
+
+
+
+===============================================================================
+25. ADDRESS BATCHING IN LOCAL TRANSPORTS
+
+The only remote transport (smtp) is normally configured to handle more than one
+address at a time, so that when several addresses are routed to the same remote
+host, just one copy of the message is sent. Local transports, however, normally
+handle one address at a time. That is, a separate instance of the transport is
+run for each address that is routed to the transport. A separate copy of the
+message is delivered each time.
+
+In special cases, it may be desirable to handle several addresses at once in a
+local transport, for example:
+
+ * In an appendfile transport, when storing messages in files for later
+ delivery by some other means, a single copy of the message with multiple
+ recipients saves space.
+
+ * In an lmtp transport, when delivering over "local SMTP" to some process, a
+ single copy saves time, and is the normal way LMTP is expected to work.
+
+ * In a pipe transport, when passing the message to a scanner program or to
+ some other delivery mechanism such as UUCP, multiple recipients may be
+ acceptable.
+
+These three local transports all have the same options for controlling multiple
+("batched") deliveries, namely batch_max and batch_id. To save repeating the
+information for each transport, these options are described here.
+
+The batch_max option specifies the maximum number of addresses that can be
+delivered together in a single run of the transport. Its default value is one
+(no batching). When more than one address is routed to a transport that has a
+batch_max value greater than one, the addresses are delivered in a batch (that
+is, in a single run of the transport with multiple recipients), subject to
+certain conditions:
+
+ * If any of the transport's options contain a reference to $local_part, no
+ batching is possible.
+
+ * If any of the transport's options contain a reference to $domain, only
+ addresses with the same domain are batched.
+
+ * If batch_id is set, it is expanded for each address, and only those
+ addresses with the same expanded value are batched. This allows you to
+ specify customized batching conditions. Failure of the expansion for any
+ reason, including forced failure, disables batching, but it does not stop
+ the delivery from taking place.
+
+ * Batched addresses must also have the same errors address (where to send
+ delivery errors), the same header additions and removals, the same user and
+ group for the transport, and if a host list is present, the first host must
+ be the same.
+
+In the case of the appendfile and pipe transports, batching applies both when
+the file or pipe command is specified in the transport, and when it is
+specified by a redirect router, but all the batched addresses must of course be
+routed to the same file or pipe command. These two transports have an option
+called use_bsmtp, which causes them to deliver the message in "batched SMTP"
+format, with the envelope represented as SMTP commands. The check_string and
+escape_string options are forced to the values
+
+check_string = "."
+escape_string = ".."
+
+when batched SMTP is in use. A full description of the batch SMTP mechanism is
+given in section 49.10. The lmtp transport does not have a use_bsmtp option,
+because it always delivers using the SMTP protocol.
+
+If the generic envelope_to_add option is set for a batching transport, the
+Envelope-to: header that is added to the message contains all the addresses
+that are being processed together. If you are using a batching appendfile
+transport without use_bsmtp, the only way to preserve the recipient addresses
+is to set the envelope_to_add option.
+
+If you are using a pipe transport without BSMTP, and setting the transport's
+command option, you can include $pipe_addresses as part of the command. This is
+not a true variable; it is a bit of magic that causes each of the recipient
+addresses to be inserted into the command as a separate argument. This provides
+a way of accessing all the addresses that are being delivered in the batch.
+Note: This is not possible for pipe commands that are specified by a redirect
+router.
+
+
+
+===============================================================================
+26. THE APPENDFILE TRANSPORT
+
+The appendfile transport delivers a message by appending it to an existing
+file, or by creating an entirely new file in a specified directory. Single
+files to which messages are appended can be in the traditional Unix mailbox
+format, or optionally in the MBX format supported by the Pine MUA and
+University of Washington IMAP daemon, inter alia. When each message is being
+delivered as a separate file, "maildir" format can optionally be used to give
+added protection against failures that happen part-way through the delivery. A
+third form of separate-file delivery known as "mailstore" is also supported.
+For all file formats, Exim attempts to create as many levels of directory as
+necessary, provided that create_directory is set.
+
+The code for the optional formats is not included in the Exim binary by
+default. It is necessary to set SUPPORT_MBX, SUPPORT_MAILDIR and/or
+SUPPORT_MAILSTORE in Local/Makefile to have the appropriate code included.
+
+Exim recognizes system quota errors, and generates an appropriate message. Exim
+also supports its own quota control within the transport, for use when the
+system facility is unavailable or cannot be used for some reason.
+
+If there is an error while appending to a file (for example, quota exceeded or
+partition filled), Exim attempts to reset the file's length and last
+modification time back to what they were before. If there is an error while
+creating an entirely new file, the new file is removed.
+
+Before appending to a file, a number of security checks are made, and the file
+is locked. A detailed description is given below, after the list of private
+options.
+
+The appendfile transport is most commonly used for local deliveries to users'
+mailboxes. However, it can also be used as a pseudo-remote transport for
+putting messages into files for remote delivery by some means other than Exim.
+"Batch SMTP" format is often used in this case (see the use_bsmtp option).
+
+
+26.1 The file and directory options
+-----------------------------------
+
+The file option specifies a single file, to which the message is appended; the
+directory option specifies a directory, in which a new file containing the
+message is created. Only one of these two options can be set, and for normal
+deliveries to mailboxes, one of them must be set.
+
+However, appendfile is also used for delivering messages to files or
+directories whose names (or parts of names) are obtained from alias,
+forwarding, or filtering operations (for example, a save command in a user's
+Exim filter). When such a transport is running, $local_part contains the local
+part that was aliased or forwarded, and $address_file contains the name (or
+partial name) of the file or directory generated by the redirection operation.
+There are two cases:
+
+ * If neither file nor directory is set, the redirection operation must
+ specify an absolute path (one that begins with "/"). This is the most
+ common case when users with local accounts use filtering to sort mail into
+ different folders. See for example, the address_file transport in the
+ default configuration. If the path ends with a slash, it is assumed to be
+ the name of a directory. A delivery to a directory can also be forced by
+ setting maildir_format or mailstore_format.
+
+ * If file or directory is set for a delivery from a redirection, it is used
+ to determine the file or directory name for the delivery. Normally, the
+ contents of $address_file are used in some way in the string expansion.
+
+Tainted data may not be used for a file or directory name. This means that, for
+instance, $local_part cannot be used directly as a component of a path. It can
+however be used as the key for a lookup which returns a path (or component).
+
+As an example of the second case, consider an environment where users do not
+have home directories. They may be permitted to use Exim filter commands of the
+form:
+
+save folder23
+
+or Sieve filter commands of the form:
+
+require "fileinto";
+fileinto "folder23";
+
+In this situation, the expansion of file or directory in the transport must
+transform the relative path into an appropriate absolute filename. In the case
+of Sieve filters, the name inbox must be handled. It is the name that is used
+as a result of a "keep" action in the filter. This example shows one way of
+handling this requirement:
+
+file = ${if eq{$address_file}{inbox} \
+ {/var/mail/$local_part_data} \
+ {${if eq{${substr_0_1:$address_file}}{/} \
+ {$address_file} \
+ {$home/mail/$address_file} \
+ }} \
+ }
+
+With this setting of file, inbox refers to the standard mailbox location,
+absolute paths are used without change, and other folders are in the mail
+directory within the home directory.
+
+Note 1: While processing an Exim filter, a relative path such as folder23 is
+turned into an absolute path if a home directory is known to the router. In
+particular, this is the case if check_local_user is set. If you want to prevent
+this happening at routing time, you can set router_home_directory empty. This
+forces the router to pass the relative path to the transport.
+
+Note 2: An absolute path in $address_file is not treated specially; the file or
+directory option is still used if it is set.
+
+
+26.2 Private options for appendfile
+-----------------------------------
+
++-------------------------------------------------------+
+|allow_fifo|Use: appendfile|Type: boolean|Default: false|
++-------------------------------------------------------+
+
+Setting this option permits delivery to named pipes (FIFOs) as well as to
+regular files. If no process is reading the named pipe at delivery time, the
+delivery is deferred.
+
++----------------------------------------------------------+
+|allow_symlink|Use: appendfile|Type: boolean|Default: false|
++----------------------------------------------------------+
+
+By default, appendfile will not deliver if the path name for the file is that
+of a symbolic link. Setting this option relaxes that constraint, but there are
+security issues involved in the use of symbolic links. Be sure you know what
+you are doing if you set this. Details of exactly what this option affects are
+included in the discussion which follows this list of options.
+
++-----------------------------------------------------+
+|batch_id|Use: appendfile|Type: string*|Default: unset|
++-----------------------------------------------------+
+
+See the description of local delivery batching in chapter 25. However, batching
+is automatically disabled for appendfile deliveries that happen as a result of
+forwarding or aliasing or other redirection directly to a file.
+
++--------------------------------------------------+
+|batch_max|Use: appendfile|Type: integer|Default: 1|
++--------------------------------------------------+
+
+See the description of local delivery batching in chapter 25.
+
++--------------------------------------------------------+
+|check_group|Use: appendfile|Type: boolean|Default: false|
++--------------------------------------------------------+
+
+When this option is set, the group owner of the file defined by the file option
+is checked to see that it is the same as the group under which the delivery
+process is running. The default setting is false because the default file mode
+is 0600, which means that the group is irrelevant.
+
++-------------------------------------------------------+
+|check_owner|Use: appendfile|Type: boolean|Default: true|
++-------------------------------------------------------+
+
+When this option is set, the owner of the file defined by the file option is
+checked to ensure that it is the same as the user under which the delivery
+process is running.
+
++------------------------------------------------------------+
+|check_string|Use: appendfile|Type: string|Default: see below|
++------------------------------------------------------------+
+
+As appendfile writes the message, the start of each line is tested for matching
+check_string, and if it does, the initial matching characters are replaced by
+the contents of escape_string. The value of check_string is a literal string,
+not a regular expression, and the case of any letters it contains is
+significant.
+
+If use_bsmtp is set the values of check_string and escape_string are forced to
+"." and ".." respectively, and any settings in the configuration are ignored.
+Otherwise, they default to "From " and ">From " when the file option is set,
+and unset when any of the directory, maildir, or mailstore options are set.
+
+The default settings, along with message_prefix and message_suffix, are
+suitable for traditional "BSD" mailboxes, where a line beginning with "From "
+indicates the start of a new message. All four options need changing if another
+format is used. For example, to deliver to mailboxes in MMDF format:
+
+check_string = "\1\1\1\1\n"
+escape_string = "\1\1\1\1 \n"
+message_prefix = "\1\1\1\1\n"
+message_suffix = "\1\1\1\1\n"
+
++------------------------------------------------------------+
+|create_directory|Use: appendfile|Type: boolean|Default: true|
++------------------------------------------------------------+
+
+When this option is true, Exim attempts to create any missing superior
+directories for the file that it is about to write. A created directory's mode
+is given by the directory_mode option.
+
+The group ownership of a newly created directory is highly dependent on the
+operating system (and possibly the file system) that is being used. For
+example, in Solaris, if the parent directory has the setgid bit set, its group
+is propagated to the child; if not, the currently set group is used. However,
+in FreeBSD, the parent's group is always used.
+
++----------------------------------------------------------+
+|create_file|Use: appendfile|Type: string|Default: anywhere|
++----------------------------------------------------------+
+
+This option constrains the location of files and directories that are created
+by this transport. It applies to files defined by the file option and
+directories defined by the directory option. In the case of maildir delivery,
+it applies to the top level directory, not the maildir directories beneath.
+
+The option must be set to one of the words "anywhere", "inhome", or
+"belowhome". In the second and third cases, a home directory must have been set
+for the transport. This option is not useful when an explicit filename is given
+for normal mailbox deliveries. It is intended for the case when filenames are
+generated from users' .forward files. These are usually handled by an
+appendfile transport called address_file. See also file_must_exist.
+
++------------------------------------------------------+
+|directory|Use: appendfile|Type: string*|Default: unset|
++------------------------------------------------------+
+
+This option is mutually exclusive with the file option, but one of file or
+directory must be set, unless the delivery is the direct result of a
+redirection (see section 26.1).
+
+When directory is set, the string is expanded, and the message is delivered
+into a new file or files in or below the given directory, instead of being
+appended to a single mailbox file. A number of different formats are provided
+(see maildir_format and mailstore_format), and see section 26.4 for further
+details of this form of delivery.
+
++---------------------------------------------------------------+
+|directory_file|Use: appendfile|Type: string*|Default: see below|
++---------------------------------------------------------------+
+
+When directory is set, but neither maildir_format nor mailstore_format is set,
+appendfile delivers each message into a file whose name is obtained by
+expanding this string. The default value is:
+
+q${base62:$tod_epoch}-$inode
+
+This generates a unique name from the current time, in base 62 form, and the
+inode of the file. The variable $inode is available only when expanding this
+option.
+
++----------------------------------------------------------------+
+|directory_mode|Use: appendfile|Type: octal integer|Default: 0700|
++----------------------------------------------------------------+
+
+If appendfile creates any directories as a result of the create_directory
+option, their mode is specified by this option.
+
++-------------------------------------------------------------------+
+|escape_string|Use: appendfile|Type: string|Default: see description|
++-------------------------------------------------------------------+
+
+See check_string above.
+
++-------------------------------------------------+
+|file|Use: appendfile|Type: string*|Default: unset|
++-------------------------------------------------+
+
+This option is mutually exclusive with the directory option, but one of file or
+directory must be set, unless the delivery is the direct result of a
+redirection (see section 26.1). The file option specifies a single file, to
+which the message is appended. One or more of use_fcntl_lock, use_flock_lock,
+or use_lockfile must be set with file.
+
+If you are using more than one host to deliver over NFS into the same
+mailboxes, you should always use lock files.
+
+The string value is expanded for each delivery, and must yield an absolute
+path. The most common settings of this option are variations on one of these
+examples:
+
+file = /var/spool/mail/$local_part_data
+file = /home/$local_part_data/inbox
+file = $home/inbox
+
+In the first example, all deliveries are done into the same directory. If Exim
+is configured to use lock files (see use_lockfile below) it must be able to
+create a file in the directory, so the "sticky" bit must be turned on for
+deliveries to be possible, or alternatively the group option can be used to run
+the delivery under a group id which has write access to the directory.
+
++-------------------------------------------------------+
+|file_format|Use: appendfile|Type: string|Default: unset|
++-------------------------------------------------------+
+
+This option requests the transport to check the format of an existing file
+before adding to it. The check consists of matching a specific string at the
+start of the file. The value of the option consists of an even number of
+colon-separated strings. The first of each pair is the test string, and the
+second is the name of a transport. If the transport associated with a matched
+string is not the current transport, control is passed over to the other
+transport. For example, suppose the standard local_delivery transport has this
+added to it:
+
+file_format = "From : local_delivery :\
+ \1\1\1\1\n : local_mmdf_delivery"
+
+Mailboxes that begin with "From" are still handled by this transport, but if a
+mailbox begins with four binary ones followed by a newline, control is passed
+to a transport called local_mmdf_delivery, which presumably is configured to do
+the delivery in MMDF format. If a mailbox does not exist or is empty, it is
+assumed to match the current transport. If the start of a mailbox doesn't match
+any string, or if the transport named for a given string is not defined,
+delivery is deferred.
+
++------------------------------------------------------------+
+|file_must_exist|Use: appendfile|Type: boolean|Default: false|
++------------------------------------------------------------+
+
+If this option is true, the file specified by the file option must exist. A
+temporary error occurs if it does not, causing delivery to be deferred. If this
+option is false, the file is created if it does not exist.
+
++---------------------------------------------------------+
+|lock_fcntl_timeout|Use: appendfile|Type: time|Default: 0s|
++---------------------------------------------------------+
+
+By default, the appendfile transport uses non-blocking calls to fcntl() when
+locking an open mailbox file. If the call fails, the delivery process sleeps
+for lock_interval and tries again, up to lock_retries times. Non-blocking calls
+are used so that the file is not kept open during the wait for the lock; the
+reason for this is to make it as safe as possible for deliveries over NFS in
+the case when processes might be accessing an NFS mailbox without using a lock
+file. This should not be done, but misunderstandings and hence
+misconfigurations are not unknown.
+
+On a busy system, however, the performance of a non-blocking lock approach is
+not as good as using a blocking lock with a timeout. In this case, the waiting
+is done inside the system call, and Exim's delivery process acquires the lock
+and can proceed as soon as the previous lock holder releases it.
+
+If lock_fcntl_timeout is set to a non-zero time, blocking locks, with that
+timeout, are used. There may still be some retrying: the maximum number of
+retries is
+
+(lock_retries * lock_interval) / lock_fcntl_timeout
+
+rounded up to the next whole number. In other words, the total time during
+which appendfile is trying to get a lock is roughly the same, unless
+lock_fcntl_timeout is set very large.
+
+You should consider setting this option if you are getting a lot of delayed
+local deliveries because of errors of the form
+
+failed to lock mailbox /some/file (fcntl)
+
++---------------------------------------------------------+
+|lock_flock_timeout|Use: appendfile|Type: time|Default: 0s|
++---------------------------------------------------------+
+
+This timeout applies to file locking when using flock() (see use_flock); the
+timeout operates in a similar manner to lock_fcntl_timeout.
+
++----------------------------------------------------+
+|lock_interval|Use: appendfile|Type: time|Default: 3s|
++----------------------------------------------------+
+
+This specifies the time to wait between attempts to lock the file. See below
+for details of locking.
+
++------------------------------------------------------+
+|lock_retries|Use: appendfile|Type: integer|Default: 10|
++------------------------------------------------------+
+
+This specifies the maximum number of attempts to lock the file. A value of zero
+is treated as 1. See below for details of locking.
+
++---------------------------------------------------------------+
+|lockfile_mode|Use: appendfile|Type: octal integer|Default: 0600|
++---------------------------------------------------------------+
+
+This specifies the mode of the created lock file, when a lock file is being
+used (see use_lockfile and use_mbx_lock).
+
++--------------------------------------------------------+
+|lockfile_timeout|Use: appendfile|Type: time|Default: 30m|
++--------------------------------------------------------+
+
+When a lock file is being used (see use_lockfile), if a lock file already
+exists and is older than this value, it is assumed to have been left behind by
+accident, and Exim attempts to remove it.
+
++--------------------------------------------------------------+
+|mailbox_filecount|Use: appendfile|Type: string*|Default: unset|
++--------------------------------------------------------------+
+
+If this option is set, it is expanded, and the result is taken as the current
+number of files in the mailbox. It must be a decimal number, optionally
+followed by K or M. This provides a way of obtaining this information from an
+external source that maintains the data.
+
++---------------------------------------------------------+
+|mailbox_size|Use: appendfile|Type: string*|Default: unset|
++---------------------------------------------------------+
+
+If this option is set, it is expanded, and the result is taken as the current
+size the mailbox. It must be a decimal number, optionally followed by K or M.
+This provides a way of obtaining this information from an external source that
+maintains the data. This is likely to be helpful for maildir deliveries where
+it is computationally expensive to compute the size of a mailbox.
+
++-----------------------------------------------------------+
+|maildir_format|Use: appendfile|Type: boolean|Default: false|
++-----------------------------------------------------------+
+
+If this option is set with the directory option, the delivery is into a new
+file, in the "maildir" format that is used by other mail software. When the
+transport is activated directly from a redirect router (for example, the
+address_file transport in the default configuration), setting maildir_format
+causes the path received from the router to be treated as a directory, whether
+or not it ends with "/". This option is available only if SUPPORT_MAILDIR is
+present in Local/Makefile. See section 26.5 below for further details.
+
++-----------------------------------------------------------------------------+
+|maildir_quota_directory_regex|Use: appendfile|Type: string|Default: See below|
++-----------------------------------------------------------------------------+
+
+This option is relevant only when maildir_use_size_file is set. It defines a
+regular expression for specifying directories, relative to the quota directory
+(see quota_directory), that should be included in the quota calculation. The
+default value is:
+
+maildir_quota_directory_regex = ^(?:cur|new|\..*)$
+
+This includes the cur and new directories, and any maildir++ folders
+(directories whose names begin with a dot). If you want to exclude the Trash
+folder from the count (as some sites do), you need to change this setting to
+
+maildir_quota_directory_regex = ^(?:cur|new|\.(?!Trash).*)$
+
+This uses a negative lookahead in the regular expression to exclude the
+directory whose name is .Trash. When a directory is excluded from quota
+calculations, quota processing is bypassed for any messages that are delivered
+directly into that directory.
+
++---------------------------------------------------------+
+|maildir_retries|Use: appendfile|Type: integer|Default: 10|
++---------------------------------------------------------+
+
+This option specifies the number of times to retry when writing a file in
+"maildir" format. See section 26.5 below.
+
++--------------------------------------------------------+
+|maildir_tag|Use: appendfile|Type: string*|Default: unset|
++--------------------------------------------------------+
+
+This option applies only to deliveries in maildir format, and is described in
+section 26.5 below.
+
++-------------------------------------------------------------------+
+|maildir_use_size_file|Use: appendfile*|Type: boolean|Default: false|
++-------------------------------------------------------------------+
+
+The result of string expansion for this option must be a valid boolean value.
+If it is true, it enables support for maildirsize files. Exim creates a
+maildirsize file in a maildir if one does not exist, taking the quota from the
+quota option of the transport. If quota is unset, the value is zero. See
+maildir_quota_directory_regex above and section 26.5 below for further details.
+
++----------------------------------------------------------------------+
+|maildirfolder_create_regex|Use: appendfile|Type: string|Default: unset|
++----------------------------------------------------------------------+
+
+The value of this option is a regular expression. If it is unset, it has no
+effect. Otherwise, before a maildir delivery takes place, the pattern is
+matched against the name of the maildir directory, that is, the directory
+containing the new and tmp subdirectories that will be used for the delivery.
+If there is a match, Exim checks for the existence of a file called
+maildirfolder in the directory, and creates it if it does not exist. See
+section 26.5 for more details.
+
++-------------------------------------------------------------+
+|mailstore_format|Use: appendfile|Type: boolean|Default: false|
++-------------------------------------------------------------+
+
+If this option is set with the directory option, the delivery is into two new
+files in "mailstore" format. The option is available only if SUPPORT_MAILSTORE
+is present in Local/Makefile. See section 26.4 below for further details.
+
++-------------------------------------------------------------+
+|mailstore_prefix|Use: appendfile|Type: string*|Default: unset|
++-------------------------------------------------------------+
+
+This option applies only to deliveries in mailstore format, and is described in
+section 26.4 below.
+
++-------------------------------------------------------------+
+|mailstore_suffix|Use: appendfile|Type: string*|Default: unset|
++-------------------------------------------------------------+
+
+This option applies only to deliveries in mailstore format, and is described in
+section 26.4 below.
+
++-------------------------------------------------------+
+|mbx_format|Use: appendfile|Type: boolean|Default: false|
++-------------------------------------------------------+
+
+This option is available only if Exim has been compiled with SUPPORT_MBX set in
+Local/Makefile. If mbx_format is set with the file option, the message is
+appended to the mailbox file in MBX format instead of traditional Unix format.
+This format is supported by Pine4 and its associated IMAP and POP daemons, by
+means of the c-client library that they all use.
+
+Note: The message_prefix and message_suffix options are not automatically
+changed by the use of mbx_format. They should normally be set empty when using
+MBX format, so this option almost always appears in this combination:
+
+mbx_format = true
+message_prefix =
+message_suffix =
+
+If none of the locking options are mentioned in the configuration, use_mbx_lock
+is assumed and the other locking options default to false. It is possible to
+specify the other kinds of locking with mbx_format, but use_fcntl_lock and
+use_mbx_lock are mutually exclusive. MBX locking interworks with c-client,
+providing for shared access to the mailbox. It should not be used if any
+program that does not use this form of locking is going to access the mailbox,
+nor should it be used if the mailbox file is NFS mounted, because it works only
+when the mailbox is accessed from a single host.
+
+If you set use_fcntl_lock with an MBX-format mailbox, you cannot use the
+standard version of c-client, because as long as it has a mailbox open (this
+means for the whole of a Pine or IMAP session), Exim will not be able to append
+messages to it.
+
++---------------------------------------------------------------+
+|message_prefix|Use: appendfile|Type: string*|Default: see below|
++---------------------------------------------------------------+
+
+The string specified here is expanded and output at the start of every message.
+The default is unset unless file is specified and use_bsmtp is not set, in
+which case it is:
+
+message_prefix = "From ${if def:return_path{$return_path}\
+ {MAILER-DAEMON}} $tod_bsdinbox\n"
+
+Note: If you set use_crlf true, you must change any occurrences of "\n" to "\r\
+n" in message_prefix.
+
++---------------------------------------------------------------+
+|message_suffix|Use: appendfile|Type: string*|Default: see below|
++---------------------------------------------------------------+
+
+The string specified here is expanded and output at the end of every message.
+The default is unset unless file is specified and use_bsmtp is not set, in
+which case it is a single newline character. The suffix can be suppressed by
+setting
+
+message_suffix =
+
+Note: If you set use_crlf true, you must change any occurrences of "\n" to "\r\
+n" in message_suffix.
+
++------------------------------------------------------+
+|mode|Use: appendfile|Type: octal integer|Default: 0600|
++------------------------------------------------------+
+
+If the output file is created, it is given this mode. If it already exists and
+has wider permissions, they are reduced to this mode. If it has narrower
+permissions, an error occurs unless mode_fail_narrower is false. However, if
+the delivery is the result of a save command in a filter file specifying a
+particular mode, the mode of the output file is always forced to take that
+value, and this option is ignored.
+
++--------------------------------------------------------------+
+|mode_fail_narrower|Use: appendfile|Type: boolean|Default: true|
++--------------------------------------------------------------+
+
+This option applies in the case when an existing mailbox file has a narrower
+mode than that specified by the mode option. If mode_fail_narrower is true, the
+delivery is deferred ("mailbox has the wrong mode"); otherwise Exim continues
+with the delivery attempt, using the existing mode of the file.
+
++----------------------------------------------------------+
+|notify_comsat|Use: appendfile|Type: boolean|Default: false|
++----------------------------------------------------------+
+
+If this option is true, the comsat daemon is notified after every successful
+delivery to a user mailbox. This is the daemon that notifies logged on users
+about incoming mail.
+
++--------------------------------------------------+
+|quota|Use: appendfile|Type: string*|Default: unset|
++--------------------------------------------------+
+
+This option imposes a limit on the size of the file to which Exim is appending,
+or to the total space used in the directory tree when the directory option is
+set. In the latter case, computation of the space used is expensive, because
+all the files in the directory (and any sub-directories) have to be
+individually inspected and their sizes summed. (See quota_size_regex and
+maildir_use_size_file for ways to avoid this in environments where users have
+no shell access to their mailboxes).
+
+As there is no interlock against two simultaneous deliveries into a multi-file
+mailbox, it is possible for the quota to be overrun in this case. For
+single-file mailboxes, of course, an interlock is a necessity.
+
+A file's size is taken as its used value. Because of blocking effects, this may
+be a lot less than the actual amount of disk space allocated to the file. If
+the sizes of a number of files are being added up, the rounding effect can
+become quite noticeable, especially on systems that have large block sizes.
+Nevertheless, it seems best to stick to the used figure, because this is the
+obvious value which users understand most easily.
+
+The value of the option is expanded, and must then be a numerical value
+(decimal point allowed), optionally followed by one of the letters K, M, or G,
+for kilobytes, megabytes, or gigabytes, optionally followed by a slash and
+further option modifiers. If Exim is running on a system with large file
+support (Linux and FreeBSD have this), mailboxes larger than 2G can be handled.
+
+The option modifier no_check can be used to force delivery even if the over
+quota condition is met. The quota gets updated as usual.
+
+Note: A value of zero is interpreted as "no quota".
+
+The expansion happens while Exim is running as root, before it changes uid for
+the delivery. This means that files that are inaccessible to the end user can
+be used to hold quota values that are looked up in the expansion. When delivery
+fails because this quota is exceeded, the handling of the error is as for
+system quota failures.
+
+By default, Exim's quota checking mimics system quotas, and restricts the
+mailbox to the specified maximum size, though the value is not accurate to the
+last byte, owing to separator lines and additional headers that may get added
+during message delivery. When a mailbox is nearly full, large messages may get
+refused even though small ones are accepted, because the size of the current
+message is added to the quota when the check is made. This behaviour can be
+changed by setting quota_is_inclusive false. When this is done, the check for
+exceeding the quota does not include the current message. Thus, deliveries
+continue until the quota has been exceeded; thereafter, no further messages are
+delivered. See also quota_warn_threshold.
+
++------------------------------------------------------------+
+|quota_directory|Use: appendfile|Type: string*|Default: unset|
++------------------------------------------------------------+
+
+This option defines the directory to check for quota purposes when delivering
+into individual files. The default is the delivery directory, or, if a file
+called maildirfolder exists in a maildir directory, the parent of the delivery
+directory.
+
++--------------------------------------------------------+
+|quota_filecount|Use: appendfile|Type: string*|Default: 0|
++--------------------------------------------------------+
+
+This option applies when the directory option is set. It limits the total
+number of files in the directory (compare the inode limit in system quotas). It
+can only be used if quota is also set. The value is expanded; an expansion
+failure causes delivery to be deferred. A value of zero is interpreted as "no
+quota".
+
+The option modifier no_check can be used to force delivery even if the over
+quota condition is met. The quota gets updated as usual.
+
++--------------------------------------------------------------+
+|quota_is_inclusive|Use: appendfile|Type: boolean|Default: true|
++--------------------------------------------------------------+
+
+See quota above.
+
++------------------------------------------------------------+
+|quota_size_regex|Use: appendfile|Type: string|Default: unset|
++------------------------------------------------------------+
+
+This option applies when one of the delivery modes that writes a separate file
+for each message is being used. When Exim wants to find the size of one of
+these files in order to test the quota, it first checks quota_size_regex. If
+this is set to a regular expression that matches the filename, and it captures
+one string, that string is interpreted as a representation of the file's size.
+The value of quota_size_regex is not expanded.
+
+This feature is useful only when users have no shell access to their mailboxes
+- otherwise they could defeat the quota simply by renaming the files. This
+facility can be used with maildir deliveries, by setting maildir_tag to add the
+file length to the filename. For example:
+
+maildir_tag = ,S=$message_size
+quota_size_regex = ,S=(\d+)
+
+An alternative to $message_size is $message_linecount, which contains the
+number of lines in the message.
+
+The regular expression should not assume that the length is at the end of the
+filename (even though maildir_tag puts it there) because maildir MUAs sometimes
+add other information onto the ends of message filenames.
+
+Section 26.7 contains further information.
+
+This option should not be used when other message-handling software may
+duplicate messages by making hardlinks to the files. When that is done Exim
+will count the message size once for each filename, in contrast with the actual
+disk usage. When the option is not set, calculating total usage requires a
+system-call per file to get the size; the number of links is then available
+also as is used to adjust the effective size.
+
++-------------------------------------------------------------------+
+|quota_warn_message|Use: appendfile|Type: string*|Default: see below|
++-------------------------------------------------------------------+
+
+See below for the use of this option. If it is not set when
+quota_warn_threshold is set, it defaults to
+
+quota_warn_message = "\
+ To: $local_part@$domain\n\
+ Subject: Your mailbox\n\n\
+ This message is automatically created \
+ by mail delivery software.\n\n\
+ The size of your mailbox has exceeded \
+ a warning threshold that is\n\
+ set by the system administrator.\n"
+
++-------------------------------------------------------------+
+|quota_warn_threshold|Use: appendfile|Type: string*|Default: 0|
++-------------------------------------------------------------+
+
+This option is expanded in the same way as quota (see above). If the resulting
+value is greater than zero, and delivery of the message causes the size of the
+file or total space in the directory tree to cross the given threshold, a
+warning message is sent. If quota is also set, the threshold may be specified
+as a percentage of it by following the value with a percent sign. For example:
+
+quota = 10M
+quota_warn_threshold = 75%
+
+If quota is not set, a setting of quota_warn_threshold that ends with a percent
+sign is ignored.
+
+The warning message itself is specified by the quota_warn_message option, and
+it must start with a To: header line containing the recipient(s) of the warning
+message. These do not necessarily have to include the recipient(s) of the
+original message. A Subject: line should also normally be supplied. You can
+include any other header lines that you want. If you do not include a From:
+line, the default is:
+
+From: Mail Delivery System <mailer-daemon@$qualify_domain_sender>
+
+If you supply a Reply-To: line, it overrides the global errors_reply_to option.
+
+The quota option does not have to be set in order to use this option; they are
+independent of one another except when the threshold is specified as a
+percentage.
+
++------------------------------------------------------+
+|use_bsmtp|Use: appendfile|Type: boolean|Default: false|
++------------------------------------------------------+
+
+If this option is set true, appendfile writes messages in "batch SMTP" format,
+with the envelope sender and recipient(s) included as SMTP commands. If you
+want to include a leading HELO command with such messages, you can do so by
+setting the message_prefix option. See section 49.10 for details of batch SMTP.
+
++-----------------------------------------------------+
+|use_crlf|Use: appendfile|Type: boolean|Default: false|
++-----------------------------------------------------+
+
+This option causes lines to be terminated with the two-character CRLF sequence
+(carriage return, linefeed) instead of just a linefeed character. In the case
+of batched SMTP, the byte sequence written to the file is then an exact image
+of what would be sent down a real SMTP connection.
+
+Note: The contents of the message_prefix and message_suffix options (which are
+used to supply the traditional "From " and blank line separators in
+Berkeley-style mailboxes) are written verbatim, so must contain their own
+carriage return characters if these are needed. In cases where these options
+have non-empty defaults, the values end with a single linefeed, so they must be
+changed to end with "\r\n" if use_crlf is set.
+
++---------------------------------------------------------------+
+|use_fcntl_lock|Use: appendfile|Type: boolean|Default: see below|
++---------------------------------------------------------------+
+
+This option controls the use of the fcntl() function to lock a file for
+exclusive use when a message is being appended. It is set by default unless
+use_flock_lock is set. Otherwise, it should be turned off only if you know that
+all your MUAs use lock file locking. When both use_fcntl_lock and
+use_flock_lock are unset, use_lockfile must be set.
+
++-----------------------------------------------------------+
+|use_flock_lock|Use: appendfile|Type: boolean|Default: false|
++-----------------------------------------------------------+
+
+This option is provided to support the use of flock() for file locking, for the
+few situations where it is needed. Most modern operating systems support fcntl
+() and lockf() locking, and these two functions interwork with each other. Exim
+uses fcntl() locking by default.
+
+This option is required only if you are using an operating system where flock()
+is used by programs that access mailboxes (typically MUAs), and where flock()
+does not correctly interwork with fcntl(). You can use both fcntl() and flock()
+locking simultaneously if you want.
+
+Not all operating systems provide flock(). Some versions of Solaris do not have
+it (and some, I think, provide a not quite right version built on top of lockf
+()). If the OS does not have flock(), Exim will be built without the ability to
+use it, and any attempt to do so will cause a configuration error.
+
+Warning: flock() locks do not work on NFS files (unless flock() is just being
+mapped onto fcntl() by the OS).
+
++-------------------------------------------------------------+
+|use_lockfile|Use: appendfile|Type: boolean|Default: see below|
++-------------------------------------------------------------+
+
+If this option is turned off, Exim does not attempt to create a lock file when
+appending to a mailbox file. In this situation, the only locking is by fcntl().
+You should only turn use_lockfile off if you are absolutely sure that every MUA
+that is ever going to look at your users' mailboxes uses fcntl() rather than a
+lock file, and even then only when you are not delivering over NFS from more
+than one host.
+
+In order to append to an NFS file safely from more than one host, it is
+necessary to take out a lock before opening the file, and the lock file
+achieves this. Otherwise, even with fcntl() locking, there is a risk of file
+corruption.
+
+The use_lockfile option is set by default unless use_mbx_lock is set. It is not
+possible to turn both use_lockfile and use_fcntl_lock off, except when
+mbx_format is set.
+
++-------------------------------------------------------------+
+|use_mbx_lock|Use: appendfile|Type: boolean|Default: see below|
++-------------------------------------------------------------+
+
+This option is available only if Exim has been compiled with SUPPORT_MBX set in
+Local/Makefile. Setting the option specifies that special MBX locking rules be
+used. It is set by default if mbx_format is set and none of the locking options
+are mentioned in the configuration. The locking rules are the same as are used
+by the c-client library that underlies Pine and the IMAP4 and POP daemons that
+come with it (see the discussion below). The rules allow for shared access to
+the mailbox. However, this kind of locking does not work when the mailbox is
+NFS mounted.
+
+You can set use_mbx_lock with either (or both) of use_fcntl_lock and
+use_flock_lock to control what kind of locking is used in implementing the MBX
+locking rules. The default is to use fcntl() if use_mbx_lock is set without
+use_fcntl_lock or use_flock_lock.
+
+
+26.3 Operational details for appending
+--------------------------------------
+
+Before appending to a file, the following preparations are made:
+
+ * If the name of the file is /dev/null, no action is taken, and a success
+ return is given.
+
+ * If any directories on the file's path are missing, Exim creates them if the
+ create_directory option is set. A created directory's mode is given by the
+ directory_mode option.
+
+ * If file_format is set, the format of an existing file is checked. If this
+ indicates that a different transport should be used, control is passed to
+ that transport.
+
+ * If use_lockfile is set, a lock file is built in a way that will work
+ reliably over NFS, as follows:
+
+ 1. Create a "hitching post" file whose name is that of the lock file with
+ the current time, primary host name, and process id added, by opening
+ for writing as a new file. If this fails with an access error, delivery
+ is deferred.
+
+ 2. Close the hitching post file, and hard link it to the lock filename.
+
+ 3. If the call to link() succeeds, creation of the lock file has
+ succeeded. Unlink the hitching post name.
+
+ 4. Otherwise, use stat() to get information about the hitching post file,
+ and then unlink hitching post name. If the number of links is exactly
+ two, creation of the lock file succeeded but something (for example, an
+ NFS server crash and restart) caused this fact not to be communicated
+ to the link() call.
+
+ 5. If creation of the lock file failed, wait for lock_interval and try
+ again, up to lock_retries times. However, since any program that writes
+ to a mailbox should complete its task very quickly, it is reasonable to
+ time out old lock files that are normally the result of user agent and
+ system crashes. If an existing lock file is older than lockfile_timeout
+ Exim attempts to unlink it before trying again.
+
+ * A call is made to lstat() to discover whether the main file exists, and if
+ so, what its characteristics are. If lstat() fails for any reason other
+ than non-existence, delivery is deferred.
+
+ * If the file does exist and is a symbolic link, delivery is deferred, unless
+ the allow_symlink option is set, in which case the ownership of the link is
+ checked, and then stat() is called to find out about the real file, which
+ is then subjected to the checks below. The check on the top-level link
+ ownership prevents one user creating a link for another's mailbox in a
+ sticky directory, though allowing symbolic links in this case is definitely
+ not a good idea. If there is a chain of symbolic links, the intermediate
+ ones are not checked.
+
+ * If the file already exists but is not a regular file, or if the file's
+ owner and group (if the group is being checked - see check_group above) are
+ different from the user and group under which the delivery is running,
+ delivery is deferred.
+
+ * If the file's permissions are more generous than specified, they are
+ reduced. If they are insufficient, delivery is deferred, unless
+ mode_fail_narrower is set false, in which case the delivery is tried using
+ the existing permissions.
+
+ * The file's inode number is saved, and the file is then opened for
+ appending. If this fails because the file has vanished, appendfile behaves
+ as if it hadn't existed (see below). For any other failures, delivery is
+ deferred.
+
+ * If the file is opened successfully, check that the inode number hasn't
+ changed, that it is still a regular file, and that the owner and
+ permissions have not changed. If anything is wrong, defer delivery and
+ freeze the message.
+
+ * If the file did not exist originally, defer delivery if the file_must_exist
+ option is set. Otherwise, check that the file is being created in a
+ permitted directory if the create_file option is set (deferring on
+ failure), and then open for writing as a new file, with the O_EXCL and
+ O_CREAT options, except when dealing with a symbolic link (the
+ allow_symlink option must be set). In this case, which can happen if the
+ link points to a non-existent file, the file is opened for writing using
+ O_CREAT but not O_EXCL, because that prevents link following.
+
+ * If opening fails because the file exists, obey the tests given above for
+ existing files. However, to avoid looping in a situation where the file is
+ being continuously created and destroyed, the exists/not-exists loop is
+ broken after 10 repetitions, and the message is then frozen.
+
+ * If opening fails with any other error, defer delivery.
+
+ * Once the file is open, unless both use_fcntl_lock and use_flock_lock are
+ false, it is locked using fcntl() or flock() or both. If use_mbx_lock is
+ false, an exclusive lock is requested in each case. However, if
+ use_mbx_lock is true, Exim takes out a shared lock on the open file, and an
+ exclusive lock on the file whose name is
+
+ /tmp/.<device-number>.<inode-number>
+
+ using the device and inode numbers of the open mailbox file, in accordance
+ with the MBX locking rules. This file is created with a mode that is
+ specified by the lockfile_mode option.
+
+ If Exim fails to lock the file, there are two possible courses of action,
+ depending on the value of the locking timeout. This is obtained from
+ lock_fcntl_timeout or lock_flock_timeout, as appropriate.
+
+ If the timeout value is zero, the file is closed, Exim waits for
+ lock_interval, and then goes back and re-opens the file as above and tries
+ to lock it again. This happens up to lock_retries times, after which the
+ delivery is deferred.
+
+ If the timeout has a value greater than zero, blocking calls to fcntl() or
+ flock() are used (with the given timeout), so there has already been some
+ waiting involved by the time locking fails. Nevertheless, Exim does not
+ give up immediately. It retries up to
+
+ (lock_retries * lock_interval) / <timeout>
+
+ times (rounded up).
+
+At the end of delivery, Exim closes the file (which releases the fcntl() and/or
+flock() locks) and then deletes the lock file if one was created.
+
+
+26.4 Operational details for delivery to a new file
+---------------------------------------------------
+
+When the directory option is set instead of file, each message is delivered
+into a newly-created file or set of files. When appendfile is activated
+directly from a redirect router, neither file nor directory is normally set,
+because the path for delivery is supplied by the router. (See for example, the
+address_file transport in the default configuration.) In this case, delivery is
+to a new file if either the path name ends in "/", or the maildir_format or
+mailstore_format option is set.
+
+No locking is required while writing the message to a new file, so the various
+locking options of the transport are ignored. The "From" line that by default
+separates messages in a single file is not normally needed, nor is the escaping
+of message lines that start with "From", and there is no need to ensure a
+newline at the end of each message. Consequently, the default values for
+check_string, message_prefix, and message_suffix are all unset when any of
+directory, maildir_format, or mailstore_format is set.
+
+If Exim is required to check a quota setting, it adds up the sizes of all the
+files in the delivery directory by default. However, you can specify a
+different directory by setting quota_directory. Also, for maildir deliveries
+(see below) the maildirfolder convention is honoured.
+
+There are three different ways in which delivery to individual files can be
+done, controlled by the settings of the maildir_format and mailstore_format
+options. Note that code to support maildir or mailstore formats is not included
+in the binary unless SUPPORT_MAILDIR or SUPPORT_MAILSTORE, respectively, is set
+in Local/Makefile.
+
+In all three cases an attempt is made to create the directory and any necessary
+sub-directories if they do not exist, provided that the create_directory option
+is set (the default). The location of a created directory can be constrained by
+setting create_file. A created directory's mode is given by the directory_mode
+option. If creation fails, or if the create_directory option is not set when
+creation is required, delivery is deferred.
+
+
+26.5 Maildir delivery
+---------------------
+
+If the maildir_format option is true, Exim delivers each message by writing it
+to a file whose name is tmp/<stime>.H<mtime>P<pid>.<host> in the directory that
+is defined by the directory option (the "delivery directory"). If the delivery
+is successful, the file is renamed into the new subdirectory.
+
+In the filename, <stime> is the current time of day in seconds, and <mtime> is
+the microsecond fraction of the time. After a maildir delivery, Exim checks
+that the time-of-day clock has moved on by at least one microsecond before
+terminating the delivery process. This guarantees uniqueness for the filename.
+However, as a precaution, Exim calls stat() for the file before opening it. If
+any response other than ENOENT (does not exist) is given, Exim waits 2 seconds
+and tries again, up to maildir_retries times.
+
+Before Exim carries out a maildir delivery, it ensures that subdirectories
+called new, cur, and tmp exist in the delivery directory. If they do not exist,
+Exim tries to create them and any superior directories in their path, subject
+to the create_directory and create_file options. If the
+maildirfolder_create_regex option is set, and the regular expression it
+contains matches the delivery directory, Exim also ensures that a file called
+maildirfolder exists in the delivery directory. If a missing directory or
+maildirfolder file cannot be created, delivery is deferred.
+
+These features make it possible to use Exim to create all the necessary files
+and directories in a maildir mailbox, including subdirectories for maildir++
+folders. Consider this example:
+
+maildir_format = true
+directory = /var/mail/$local_part_data\
+ ${if eq{$local_part_suffix}{}{}\
+ {/.${substr_1:$local_part_suffix}}}
+maildirfolder_create_regex = /\.[^/]+$
+
+If $local_part_suffix is empty (there was no suffix for the local part),
+delivery is into a toplevel maildir with a name like /var/mail/pimbo (for the
+user called pimbo). The pattern in maildirfolder_create_regex does not match
+this name, so Exim will not look for or create the file /var/mail/pimbo/
+maildirfolder, though it will create /var/mail/pimbo/{cur,new,tmp} if
+necessary.
+
+However, if $local_part_suffix contains "-eximusers" (for example), delivery is
+into the maildir++ folder /var/mail/pimbo/.eximusers, which does match
+maildirfolder_create_regex. In this case, Exim will create /var/mail/pimbo
+/.eximusers/maildirfolder as well as the three maildir directories /var/mail/
+pimbo/.eximusers/{cur,new,tmp}.
+
+Warning: Take care when setting maildirfolder_create_regex that it does not
+inadvertently match the toplevel maildir directory, because a maildirfolder
+file at top level would completely break quota calculations.
+
+If Exim is required to check a quota setting before a maildir delivery, and
+quota_directory is not set, it looks for a file called maildirfolder in the
+maildir directory (alongside new, cur, tmp). If this exists, Exim assumes the
+directory is a maildir++ folder directory, which is one level down from the
+user's top level mailbox directory. This causes it to start at the parent
+directory instead of the current directory when calculating the amount of space
+used.
+
+One problem with delivering into a multi-file mailbox is that it is
+computationally expensive to compute the size of the mailbox for quota
+checking. Various approaches have been taken to reduce the amount of work
+needed. The next two sections describe two of them. A third alternative is to
+use some external process for maintaining the size data, and use the expansion
+of the mailbox_size option as a way of importing it into Exim.
+
+
+26.6 Using tags to record message sizes
+---------------------------------------
+
+If maildir_tag is set, the string is expanded for each delivery. When the
+maildir file is renamed into the new sub-directory, the tag is added to its
+name. However, if adding the tag takes the length of the name to the point
+where the test stat() call fails with ENAMETOOLONG, the tag is dropped and the
+maildir file is created with no tag.
+
+Tags can be used to encode the size of files in their names; see
+quota_size_regex above for an example. The expansion of maildir_tag happens
+after the message has been written. The value of the $message_size variable is
+set to the number of bytes actually written. If the expansion is forced to
+fail, the tag is ignored, but a non-forced failure causes delivery to be
+deferred. The expanded tag may contain any printing characters except "/".
+Non-printing characters in the string are ignored; if the resulting string is
+empty, it is ignored. If it starts with an alphanumeric character, a leading
+colon is inserted; this default has not proven to be the path that popular
+maildir implementations have chosen (but changing it in Exim would break
+backwards compatibility).
+
+For one common implementation, you might set:
+
+maildir_tag = ,S=${message_size}
+
+but you should check the documentation of the other software to be sure.
+
+It is advisable to also set quota_size_regex when setting maildir_tag as this
+allows Exim to extract the size from your tag, instead of having to stat() each
+message file.
+
+
+26.7 Using a maildirsize file
+-----------------------------
+
+If maildir_use_size_file is true, Exim implements the maildir++ rules for
+storing quota and message size information in a file called maildirsize within
+the toplevel maildir directory. If this file does not exist, Exim creates it,
+setting the quota from the quota option of the transport. If the maildir
+directory itself does not exist, it is created before any attempt to write a
+maildirsize file.
+
+The maildirsize file is used to hold information about the sizes of messages in
+the maildir, thus speeding up quota calculations. The quota value in the file
+is just a cache; if the quota is changed in the transport, the new value
+overrides the cached value when the next message is delivered. The cache is
+maintained for the benefit of other programs that access the maildir and need
+to know the quota.
+
+If the quota option in the transport is unset or zero, the maildirsize file is
+maintained (with a zero quota setting), but no quota is imposed.
+
+A regular expression is available for controlling which directories in the
+maildir participate in quota calculations when a maildirsizefile is in use. See
+the description of the maildir_quota_directory_regex option above for details.
+
+
+26.8 Mailstore delivery
+-----------------------
+
+If the mailstore_format option is true, each message is written as two files in
+the given directory. A unique base name is constructed from the message id and
+the current delivery process, and the files that are written use this base name
+plus the suffixes .env and .msg. The .env file contains the message's envelope,
+and the .msg file contains the message itself. The base name is placed in the
+variable $mailstore_basename.
+
+During delivery, the envelope is first written to a file with the suffix .tmp.
+The .msg file is then written, and when it is complete, the .tmp file is
+renamed as the .env file. Programs that access messages in mailstore format
+should wait for the presence of both a .msg and a .env file before accessing
+either of them. An alternative approach is to wait for the absence of a .tmp
+file.
+
+The envelope file starts with any text defined by the mailstore_prefix option,
+expanded and terminated by a newline if there isn't one. Then follows the
+sender address on one line, then all the recipient addresses, one per line.
+There can be more than one recipient only if the batch_max option is set
+greater than one. Finally, mailstore_suffix is expanded and the result appended
+to the file, followed by a newline if it does not end with one.
+
+If expansion of mailstore_prefix or mailstore_suffix ends with a forced
+failure, it is ignored. Other expansion errors are treated as serious
+configuration errors, and delivery is deferred. The variable
+$mailstore_basename is available for use during these expansions.
+
+
+26.9 Non-special new file delivery
+----------------------------------
+
+If neither maildir_format nor mailstore_format is set, a single new file is
+created directly in the named directory. For example, when delivering messages
+into files in batched SMTP format for later delivery to some host (see section
+49.10), a setting such as
+
+directory = /var/bsmtp/$host
+
+might be used. A message is written to a file with a temporary name, which is
+then renamed when the delivery is complete. The final name is obtained by
+expanding the contents of the directory_file option.
+
+
+
+===============================================================================
+27. THE AUTOREPLY TRANSPORT
+
+The autoreply transport is not a true transport in that it does not cause the
+message to be transmitted. Instead, it generates a new mail message as an
+automatic reply to the incoming message. References: and Auto-Submitted: header
+lines are included. These are constructed according to the rules in RFCs 2822
+and 3834, respectively.
+
+If the router that passes the message to this transport does not have the
+unseen option set, the original message (for the current recipient) is not
+delivered anywhere. However, when the unseen option is set on the router that
+passes the message to this transport, routing of the address continues, so
+another router can set up a normal message delivery.
+
+The autoreply transport is usually run as the result of mail filtering, a
+"vacation" message being the standard example. However, it can also be run
+directly from a router like any other transport. To reduce the possibility of
+message cascades, messages created by the autoreply transport always have empty
+envelope sender addresses, like bounce messages.
+
+The parameters of the message to be sent can be specified in the configuration
+by options described below. However, these are used only when the address
+passed to the transport does not contain its own reply information. When the
+transport is run as a consequence of a mail or vacation command in a filter
+file, the parameters of the message are supplied by the filter, and passed with
+the address. The transport's options that define the message are then ignored
+(so they are not usually set in this case). The message is specified entirely
+by the filter or by the transport; it is never built from a mixture of options.
+However, the file_optional, mode, and return_message options apply in all
+cases.
+
+Autoreply is implemented as a local transport. When used as a result of a
+command in a user's filter file, autoreply normally runs under the uid and gid
+of the user, and with appropriate current and home directories (see chapter 23
+).
+
+There is a subtle difference between routing a message to a pipe transport that
+generates some text to be returned to the sender, and routing it to an
+autoreply transport. This difference is noticeable only if more than one
+address from the same message is so handled. In the case of a pipe, the
+separate outputs from the different addresses are gathered up and returned to
+the sender in a single message, whereas if autoreply is used, a separate
+message is generated for each address that is passed to it.
+
+Non-printing characters are not permitted in the header lines generated for the
+message that autoreply creates, with the exception of newlines that are
+immediately followed by white space. If any non-printing characters are found,
+the transport defers. Whether characters with the top bit set count as printing
+characters or not is controlled by the print_topbitchars global option.
+
+If any of the generic options for manipulating headers (for example,
+headers_add) are set on an autoreply transport, they apply to the copy of the
+original message that is included in the generated message when return_message
+is set. They do not apply to the generated message itself.
+
+If the autoreply transport receives return code 2 from Exim when it submits the
+message, indicating that there were no recipients, it does not treat this as an
+error. This means that autoreplies sent to $sender_address when this is empty
+(because the incoming message is a bounce message) do not cause problems. They
+are just discarded.
+
+
+27.1 Private options for autoreply
+----------------------------------
+
++-----------------------------------------------+
+|bcc|Use: autoreply|Type: string*|Default: unset|
++-----------------------------------------------+
+
+This specifies the addresses that are to receive "blind carbon copies" of the
+message when the message is specified by the transport.
+
++----------------------------------------------+
+|cc|Use: autoreply|Type: string*|Default: unset|
++----------------------------------------------+
+
+This specifies recipients of the message and the contents of the Cc: header
+when the message is specified by the transport.
+
++------------------------------------------------+
+|file|Use: autoreply|Type: string*|Default: unset|
++------------------------------------------------+
+
+The contents of the file are sent as the body of the message when the message
+is specified by the transport. If both file and text are set, the text string
+comes first.
+
++-------------------------------------------------------+
+|file_expand|Use: autoreply|Type: boolean|Default: false|
++-------------------------------------------------------+
+
+If this is set, the contents of the file named by the file option are subjected
+to string expansion as they are added to the message.
+
++---------------------------------------------------------+
+|file_optional|Use: autoreply|Type: boolean|Default: false|
++---------------------------------------------------------+
+
+If this option is true, no error is generated if the file named by the file
+option or passed with the address does not exist or cannot be read.
+
++------------------------------------------------+
+|from|Use: autoreply|Type: string*|Default: unset|
++------------------------------------------------+
+
+This specifies the contents of the From: header when the message is specified
+by the transport.
+
++---------------------------------------------------+
+|headers|Use: autoreply|Type: string*|Default: unset|
++---------------------------------------------------+
+
+This specifies additional RFC 2822 headers that are to be added to the message
+when the message is specified by the transport. Several can be given by using "
+\n" to separate them. There is no check on the format.
+
++-----------------------------------------------+
+|log|Use: autoreply|Type: string*|Default: unset|
++-----------------------------------------------+
+
+This option names a file in which a record of every message sent is logged when
+the message is specified by the transport.
+
++-----------------------------------------------------+
+|mode|Use: autoreply|Type: octal integer|Default: 0600|
++-----------------------------------------------------+
+
+If either the log file or the "once" file has to be created, this mode is used.
+
++------------------------------------------------------------+
+|never_mail|Use: autoreply|Type: address list*|Default: unset|
++------------------------------------------------------------+
+
+If any run of the transport creates a message with a recipient that matches any
+item in the list, that recipient is quietly discarded. If all recipients are
+discarded, no message is created. This applies both when the recipients are
+generated by a filter and when they are specified in the transport.
+
++------------------------------------------------+
+|once|Use: autoreply|Type: string*|Default: unset|
++------------------------------------------------+
+
+This option names a file or DBM database in which a record of each To:
+recipient is kept when the message is specified by the transport. Note: This
+does not apply to Cc: or Bcc: recipients.
+
+If once is unset, or is set to an empty string, the message is always sent. By
+default, if once is set to a non-empty filename, the message is not sent if a
+potential recipient is already listed in the database. However, if the
+once_repeat option specifies a time greater than zero, the message is sent if
+that much time has elapsed since a message was last sent to this recipient. A
+setting of zero time for once_repeat (the default) prevents a message from
+being sent a second time - in this case, zero means infinity.
+
+If once_file_size is zero, a DBM database is used to remember recipients, and
+it is allowed to grow as large as necessary. If once_file_size is set greater
+than zero, it changes the way Exim implements the once option. Instead of using
+a DBM file to record every recipient it sends to, it uses a regular file, whose
+size will never get larger than the given value.
+
+In the file, Exim keeps a linear list of recipient addresses and the times at
+which they were sent messages. If the file is full when a new address needs to
+be added, the oldest address is dropped. If once_repeat is not set, this means
+that a given recipient may receive multiple messages, but at unpredictable
+intervals that depend on the rate of turnover of addresses in the file. If
+once_repeat is set, it specifies a maximum time between repeats.
+
++------------------------------------------------------+
+|once_file_size|Use: autoreply|Type: integer|Default: 0|
++------------------------------------------------------+
+
+See once above.
+
++--------------------------------------------------+
+|once_repeat|Use: autoreply|Type: time*|Default: 0s|
++--------------------------------------------------+
+
+See once above. After expansion, the value of this option must be a valid time
+value.
+
++----------------------------------------------------+
+|reply_to|Use: autoreply|Type: string*|Default: unset|
++----------------------------------------------------+
+
+This specifies the contents of the Reply-To: header when the message is
+specified by the transport.
+
++----------------------------------------------------------+
+|return_message|Use: autoreply|Type: boolean|Default: false|
++----------------------------------------------------------+
+
+If this is set, a copy of the original message is returned with the new
+message, subject to the maximum size set in the return_size_limit global
+configuration option.
+
++---------------------------------------------------+
+|subject|Use: autoreply|Type: string*|Default: unset|
++---------------------------------------------------+
+
+This specifies the contents of the Subject: header when the message is
+specified by the transport. It is tempting to quote the original subject in
+automatic responses. For example:
+
+subject = Re: $h_subject:
+
+There is a danger in doing this, however. It may allow a third party to
+subscribe your users to an opt-in mailing list, provided that the list accepts
+bounce messages as subscription confirmations. Well-managed lists require a
+non-bounce message to confirm a subscription, so the danger is relatively
+small.
+
++------------------------------------------------+
+|text|Use: autoreply|Type: string*|Default: unset|
++------------------------------------------------+
+
+This specifies a single string to be used as the body of the message when the
+message is specified by the transport. If both text and file are set, the text
+comes first.
+
++----------------------------------------------+
+|to|Use: autoreply|Type: string*|Default: unset|
++----------------------------------------------+
+
+This specifies recipients of the message and the contents of the To: header
+when the message is specified by the transport.
+
+
+
+===============================================================================
+28. THE LMTP TRANSPORT
+
+The lmtp transport runs the LMTP protocol (RFC 2033) over a pipe to a specified
+command or by interacting with a Unix domain socket. This transport is
+something of a cross between the pipe and smtp transports. Exim also has
+support for using LMTP over TCP/IP; this is implemented as an option for the
+smtp transport. Because LMTP is expected to be of minority interest, the
+default build-time configure in src/EDITME has it commented out. You need to
+ensure that
+
+TRANSPORT_LMTP=yes
+
+is present in your Local/Makefile in order to have the lmtp transport included
+in the Exim binary. The private options of the lmtp transport are as follows:
+
++-----------------------------------------------+
+|batch_id|Use: lmtp|Type: string*|Default: unset|
++-----------------------------------------------+
+
+See the description of local delivery batching in chapter 25.
+
++--------------------------------------------+
+|batch_max|Use: lmtp|Type: integer|Default: 1|
++--------------------------------------------+
+
+This limits the number of addresses that can be handled in a single delivery.
+Most LMTP servers can handle several addresses at once, so it is normally a
+good idea to increase this value. See the description of local delivery
+batching in chapter 25.
+
++----------------------------------------------+
+|command|Use: lmtp|Type: string*|Default: unset|
++----------------------------------------------+
+
+This option must be set if socket is not set. The string is a command which is
+run in a separate process. It is split up into a command name and list of
+arguments, each of which is separately expanded (so expansion cannot change the
+number of arguments). The command is run directly, not via a shell. The message
+is passed to the new process using the standard input and output to operate the
+LMTP protocol.
+
++---------------------------------------------------+
+|ignore_quota|Use: lmtp|Type: boolean|Default: false|
++---------------------------------------------------+
+
+If this option is set true, the string "IGNOREQUOTA" is added to RCPT commands,
+provided that the LMTP server has advertised support for IGNOREQUOTA in its
+response to the LHLO command.
+
++---------------------------------------------+
+|socket|Use: lmtp|Type: string*|Default: unset|
++---------------------------------------------+
+
+This option must be set if command is not set. The result of expansion must be
+the name of a Unix domain socket. The transport connects to the socket and
+delivers the message to it using the LMTP protocol.
+
++----------------------------------------+
+|timeout|Use: lmtp|Type: time|Default: 5m|
++----------------------------------------+
+
+The transport is aborted if the created process or Unix domain socket does not
+respond to LMTP commands or message input within this timeout. Delivery is
+deferred, and will be tried again later. Here is an example of a typical LMTP
+transport:
+
+lmtp:
+ driver = lmtp
+ command = /some/local/lmtp/delivery/program
+ batch_max = 20
+ user = exim
+
+This delivers up to 20 addresses at a time, in a mixture of domains if
+necessary, running as the user exim.
+
+
+
+===============================================================================
+29. THE PIPE TRANSPORT
+
+The pipe transport is used to deliver messages via a pipe to a command running
+in another process. One example is the use of pipe as a pseudo-remote transport
+for passing messages to some other delivery mechanism (such as UUCP). Another
+is the use by individual users to automatically process their incoming
+messages. The pipe transport can be used in one of the following ways:
+
+ * A router routes one address to a transport in the normal way, and the
+ transport is configured as a pipe transport. In this case, $local_part
+ contains the local part of the address (as usual), and the command that is
+ run is specified by the command option on the transport.
+
+ * If the batch_max option is set greater than 1 (the default is 1), the
+ transport can handle more than one address in a single run. In this case,
+ when more than one address is routed to the transport, $local_part is not
+ set (because it is not unique). However, the pseudo-variable
+ $pipe_addresses (described in section 29.3 below) contains all the
+ addresses that are routed to the transport.
+
+ * A router redirects an address directly to a pipe command (for example, from
+ an alias or forward file). In this case, $address_pipe contains the text of
+ the pipe command, and the command option on the transport is ignored unless
+ force_command is set. If only one address is being transported (batch_max
+ is not greater than one, or only one address was redirected to this pipe
+ command), $local_part contains the local part that was redirected.
+
+The pipe transport is a non-interactive delivery method. Exim can also deliver
+messages over pipes using the LMTP interactive protocol. This is implemented by
+the lmtp transport.
+
+In the case when pipe is run as a consequence of an entry in a local user's
+.forward file, the command runs under the uid and gid of that user. In other
+cases, the uid and gid have to be specified explicitly, either on the transport
+or on the router that handles the address. Current and "home" directories are
+also controllable. See chapter 23 for details of the local delivery environment
+and chapter 25 for a discussion of local delivery batching.
+
+Tainted data may not be used for the command name.
+
+
+29.1 Concurrent delivery
+------------------------
+
+If two messages arrive at almost the same time, and both are routed to a pipe
+delivery, the two pipe transports may be run concurrently. You must ensure that
+any pipe commands you set up are robust against this happening. If the commands
+write to a file, the exim_lock utility might be of use. Alternatively the
+max_parallel option could be used with a value of "1" to enforce serialization.
+
+
+29.2 Returned status and data
+-----------------------------
+
+If the command exits with a non-zero return code, the delivery is deemed to
+have failed, unless either the ignore_status option is set (in which case the
+return code is treated as zero), or the return code is one of those listed in
+the temp_errors option, which are interpreted as meaning "try again later". In
+this case, delivery is deferred. Details of a permanent failure are logged, but
+are not included in the bounce message, which merely contains "local delivery
+failed".
+
+If the command exits on a signal and the freeze_signal option is set then the
+message will be frozen in the queue. If that option is not set, a bounce will
+be sent as normal.
+
+If the return code is greater than 128 and the command being run is a shell
+script, it normally means that the script was terminated by a signal whose
+value is the return code minus 128. The freeze_signal option does not apply in
+this case.
+
+If Exim is unable to run the command (that is, if execve() fails), the return
+code is set to 127. This is the value that a shell returns if it is asked to
+run a non-existent command. The wording for the log line suggests that a
+non-existent command may be the problem.
+
+The return_output option can affect the result of a pipe delivery. If it is set
+and the command produces any output on its standard output or standard error
+streams, the command is considered to have failed, even if it gave a zero
+return code or if ignore_status is set. The output from the command is included
+as part of the bounce message. The return_fail_output option is similar, except
+that output is returned only when the command exits with a failure return code,
+that is, a value other than zero or a code that matches temp_errors.
+
+
+29.3 How the command is run
+---------------------------
+
+The command line is (by default) broken down into a command name and arguments
+by the pipe transport itself. The allow_commands and restrict_to_path options
+can be used to restrict the commands that may be run.
+
+Unquoted arguments are delimited by white space. If an argument appears in
+double quotes, backslash is interpreted as an escape character in the usual
+way. If an argument appears in single quotes, no escaping is done.
+
+String expansion is applied to the command line except when it comes from a
+traditional .forward file (commands from a filter file are expanded). The
+expansion is applied to each argument in turn rather than to the whole line.
+For this reason, any string expansion item that contains white space must be
+quoted so as to be contained within a single argument. A setting such as
+
+command = /some/path ${if eq{$local_part}{postmaster}{xx}{yy}}
+
+will not work, because the expansion item gets split between several arguments.
+You have to write
+
+command = /some/path "${if eq{$local_part}{postmaster}{xx}{yy}}"
+
+to ensure that it is all in one argument. The expansion is done in this way,
+argument by argument, so that the number of arguments cannot be changed as a
+result of expansion, and quotes or backslashes in inserted variables do not
+interact with external quoting. However, this leads to problems if you want to
+generate multiple arguments (or the command name plus arguments) from a single
+expansion. In this situation, the simplest solution is to use a shell. For
+example:
+
+command = /bin/sh -c ${lookup{$local_part}lsearch{/some/file}}
+
+Special handling takes place when an argument consists of precisely the text
+"$pipe_addresses" (no quotes). This is not a general expansion variable; the
+only place this string is recognized is when it appears as an argument for a
+pipe or transport filter command. It causes each address that is being handled
+to be inserted in the argument list at that point as a separate argument. This
+avoids any problems with spaces or shell metacharacters, and is of use when a
+pipe transport is handling groups of addresses in a batch.
+
+If force_command is enabled on the transport, special handling takes place for
+an argument that consists of precisely the text "$address_pipe". It is handled
+similarly to $pipe_addresses above. It is expanded and each argument is
+inserted in the argument list at that point as a separate argument. The
+"$address_pipe" item does not need to be the only item in the argument; in
+fact, if it were then force_command should behave as a no-op. Rather, it should
+be used to adjust the command run while preserving the argument vector
+separation.
+
+After splitting up into arguments and expansion, the resulting command is run
+in a subprocess directly from the transport, not under a shell. The message
+that is being delivered is supplied on the standard input, and the standard
+output and standard error are both connected to a single pipe that is read by
+Exim. The max_output option controls how much output the command may produce,
+and the return_output and return_fail_output options control what is done with
+it.
+
+Not running the command under a shell (by default) lessens the security risks
+in cases when a command from a user's filter file is built out of data that was
+taken from an incoming message. If a shell is required, it can of course be
+explicitly specified as the command to be run. However, there are circumstances
+where existing commands (for example, in .forward files) expect to be run under
+a shell and cannot easily be modified. To allow for these cases, there is an
+option called use_shell, which changes the way the pipe transport works.
+Instead of breaking up the command line as just described, it expands it as a
+single string and passes the result to /bin/sh. The restrict_to_path option and
+the $pipe_addresses facility cannot be used with use_shell, and the whole
+mechanism is inherently less secure.
+
+
+29.4 Environment variables
+--------------------------
+
+The environment variables listed below are set up when the command is invoked.
+This list is a compromise for maximum compatibility with other MTAs. Note that
+the environment option can be used to add additional variables to this
+environment. The environment for the pipe transport is not subject to the
+add_environment and keep_environment main config options.
+
+DOMAIN the domain of the address
+HOME the home directory, if set
+HOST the host name when called from a router (see below)
+LOCAL_PART see below
+LOCAL_PART_PREFIX see below
+LOCAL_PART_SUFFIX see below
+LOGNAME see below
+MESSAGE_ID Exim's local ID for the message
+PATH as specified by the path option below
+QUALIFY_DOMAIN the sender qualification domain
+RECIPIENT the complete recipient address
+SENDER the sender of the message (empty if a bounce)
+SHELL /bin/sh
+TZ the value of the timezone option, if set
+USER see below
+
+When a pipe transport is called directly from (for example) an accept router,
+LOCAL_PART is set to the local part of the address. When it is called as a
+result of a forward or alias expansion, LOCAL_PART is set to the local part of
+the address that was expanded. In both cases, any affixes are removed from the
+local part, and made available in LOCAL_PART_PREFIX and LOCAL_PART_SUFFIX,
+respectively. LOGNAME and USER are set to the same value as LOCAL_PART for
+compatibility with other MTAs.
+
+HOST is set only when a pipe transport is called from a router that associates
+hosts with an address, typically when using pipe as a pseudo-remote transport.
+HOST is set to the first host name specified by the router.
+
+If the transport's generic home_directory option is set, its value is used for
+the HOME environment variable. Otherwise, a home directory may be set by the
+router's transport_home_directory option, which defaults to the user's home
+directory if check_local_user is set.
+
+
+29.5 Private options for pipe
+-----------------------------
+
++----------------------------------------------------------+
+|allow_commands|Use: pipe|Type: string list*|Default: unset|
++----------------------------------------------------------+
+
+The string is expanded, and is then interpreted as a colon-separated list of
+permitted commands. If restrict_to_path is not set, the only commands permitted
+are those in the allow_commands list. They need not be absolute paths; the path
+option is still used for relative paths. If restrict_to_path is set with
+allow_commands, the command must either be in the allow_commands list, or a
+name without any slashes that is found on the path. In other words, if neither
+allow_commands nor restrict_to_path is set, there is no restriction on the
+command, but otherwise only commands that are permitted by one or the other are
+allowed. For example, if
+
+allow_commands = /usr/bin/vacation
+
+and restrict_to_path is not set, the only permitted command is /usr/bin/
+vacation. The allow_commands option may not be set if use_shell is set.
+
++-----------------------------------------------+
+|batch_id|Use: pipe|Type: string*|Default: unset|
++-----------------------------------------------+
+
+See the description of local delivery batching in chapter 25.
+
++--------------------------------------------+
+|batch_max|Use: pipe|Type: integer|Default: 1|
++--------------------------------------------+
+
+This limits the number of addresses that can be handled in a single delivery.
+See the description of local delivery batching in chapter 25.
+
++--------------------------------------------------+
+|check_string|Use: pipe|Type: string|Default: unset|
++--------------------------------------------------+
+
+As pipe writes the message, the start of each line is tested for matching
+check_string, and if it does, the initial matching characters are replaced by
+the contents of escape_string, provided both are set. The value of check_string
+is a literal string, not a regular expression, and the case of any letters it
+contains is significant. When use_bsmtp is set, the contents of check_string
+and escape_string are forced to values that implement the SMTP escaping
+protocol. Any settings made in the configuration file are ignored.
+
++----------------------------------------------+
+|command|Use: pipe|Type: string*|Default: unset|
++----------------------------------------------+
+
+This option need not be set when pipe is being used to deliver to pipes
+obtained directly from address redirections. In other cases, the option must be
+set, to provide a command to be run. It need not yield an absolute path (see
+the path option below). The command is split up into separate arguments by
+Exim, and each argument is separately expanded, as described in section 29.3
+above.
+
++--------------------------------------------------+
+|environment|Use: pipe|Type: string*|Default: unset|
++--------------------------------------------------+
+
+This option is used to add additional variables to the environment in which the
+command runs (see section 29.4 for the default list). Its value is a string
+which is expanded, and then interpreted as a colon-separated list of
+environment settings of the form <name>=<value>.
+
++---------------------------------------------------+
+|escape_string|Use: pipe|Type: string|Default: unset|
++---------------------------------------------------+
+
+See check_string above.
+
++-------------------------------------------------------+
+|freeze_exec_fail|Use: pipe|Type: boolean|Default: false|
++-------------------------------------------------------+
+
+Failure to exec the command in a pipe transport is by default treated like any
+other failure while running the command. However, if freeze_exec_fail is set,
+failure to exec is treated specially, and causes the message to be frozen,
+whatever the setting of ignore_status.
+
++----------------------------------------------------+
+|freeze_signal|Use: pipe|Type: boolean|Default: false|
++----------------------------------------------------+
+
+Normally if the process run by a command in a pipe transport exits on a signal,
+a bounce message is sent. If freeze_signal is set, the message will be frozen
+in Exim's queue instead.
+
++----------------------------------------------------+
+|force_command|Use: pipe|Type: boolean|Default: false|
++----------------------------------------------------+
+
+Normally when a router redirects an address directly to a pipe command the
+command option on the transport is ignored. If force_command is set, the
+command option will used. This is especially useful for forcing a wrapper or
+additional argument to be added to the command. For example:
+
+command = /usr/bin/remote_exec myhost -- $address_pipe
+force_command
+
+Note that $address_pipe is handled specially in command when force_command is
+set, expanding out to the original argument vector as separate items, similarly
+to a Unix shell ""$@"" construct.
+
++----------------------------------------------------+
+|ignore_status|Use: pipe|Type: boolean|Default: false|
++----------------------------------------------------+
+
+If this option is true, the status returned by the subprocess that is set up to
+run the command is ignored, and Exim behaves as if zero had been returned.
+Otherwise, a non-zero status or termination by signal causes an error return
+from the transport unless the status value is one of those listed in
+temp_errors; these cause the delivery to be deferred and tried again later.
+
+Note: This option does not apply to timeouts, which do not return a status. See
+the timeout_defer option for how timeouts are handled.
+
++-------------------------------------------------------+
+|log_defer_output|Use: pipe|Type: boolean|Default: false|
++-------------------------------------------------------+
+
+If this option is set, and the status returned by the command is one of the
+codes listed in temp_errors (that is, delivery was deferred), and any output
+was produced on stdout or stderr, the first line of it is written to the main
+log.
+
++------------------------------------------------------+
+|log_fail_output|Use: pipe|Type: boolean|Default: false|
++------------------------------------------------------+
+
+If this option is set, and the command returns any output on stdout or stderr,
+and also ends with a return code that is neither zero nor one of the return
+codes listed in temp_errors (that is, the delivery failed), the first line of
+output is written to the main log. This option and log_output are mutually
+exclusive. Only one of them may be set.
+
++-------------------------------------------------+
+|log_output|Use: pipe|Type: boolean|Default: false|
++-------------------------------------------------+
+
+If this option is set and the command returns any output on stdout or stderr,
+the first line of output is written to the main log, whatever the return code.
+This option and log_fail_output are mutually exclusive. Only one of them may be
+set.
+
++-----------------------------------------------+
+|max_output|Use: pipe|Type: integer|Default: 20K|
++-----------------------------------------------+
+
+This specifies the maximum amount of output that the command may produce on its
+standard output and standard error file combined. If the limit is exceeded, the
+process running the command is killed. This is intended as a safety measure to
+catch runaway processes. The limit is applied independently of the settings of
+the options that control what is done with such output (for example,
+return_output). Because of buffering effects, the amount of output may exceed
+the limit by a small amount before Exim notices.
+
++---------------------------------------------------------+
+|message_prefix|Use: pipe|Type: string*|Default: see below|
++---------------------------------------------------------+
+
+The string specified here is expanded and output at the start of every message.
+The default is unset if use_bsmtp is set. Otherwise it is
+
+message_prefix = \
+ From ${if def:return_path{$return_path}{MAILER-DAEMON}}\
+ ${tod_bsdinbox}\n
+
+This is required by the commonly used /usr/bin/vacation program. However, it
+must not be present if delivery is to the Cyrus IMAP server, or to the tmail
+local delivery agent. The prefix can be suppressed by setting
+
+message_prefix =
+
+Note: If you set use_crlf true, you must change any occurrences of "\n" to "\r\
+n" in message_prefix.
+
++---------------------------------------------------------+
+|message_suffix|Use: pipe|Type: string*|Default: see below|
++---------------------------------------------------------+
+
+The string specified here is expanded and output at the end of every message.
+The default is unset if use_bsmtp is set. Otherwise it is a single newline. The
+suffix can be suppressed by setting
+
+message_suffix =
+
+Note: If you set use_crlf true, you must change any occurrences of "\n" to "\r\
+n" in message_suffix.
+
++---------------------------------------------------+
+|path|Use: pipe|Type: string*|Default: /bin:/usr/bin|
++---------------------------------------------------+
+
+This option is expanded and specifies the string that is set up in the PATH
+environment variable of the subprocess. If the command option does not yield an
+absolute path name, the command is sought in the PATH directories, in the usual
+way. Warning: This does not apply to a command specified as a transport filter.
+
++------------------------------------------------------+
+|permit_coredump|Use: pipe|Type: boolean|Default: false|
++------------------------------------------------------+
+
+Normally Exim inhibits core-dumps during delivery. If you have a need to get a
+core-dump of a pipe command, enable this command. This enables core-dumps
+during delivery and affects both the Exim binary and the pipe command run. It
+is recommended that this option remain off unless and until you have a need for
+it and that this only be enabled when needed, as the risk of excessive resource
+consumption can be quite high. Note also that Exim is typically installed as a
+setuid binary and most operating systems will inhibit coredumps of these by
+default, so further OS-specific action may be required.
+
++------------------------------------------------------+
+|pipe_as_creator|Use: pipe|Type: boolean|Default: false|
++------------------------------------------------------+
+
+If the generic user option is not set and this option is true, the delivery
+process is run under the uid that was in force when Exim was originally called
+to accept the message. If the group id is not otherwise set (via the generic
+group option), the gid that was in force when Exim was originally called to
+accept the message is used.
+
++-------------------------------------------------------+
+|restrict_to_path|Use: pipe|Type: boolean|Default: false|
++-------------------------------------------------------+
+
+When this option is set, any command name not listed in allow_commands must
+contain no slashes. The command is searched for only in the directories listed
+in the path option. This option is intended for use in the case when a pipe
+command has been generated from a user's .forward file. This is usually handled
+by a pipe transport called address_pipe.
+
++---------------------------------------------------------+
+|return_fail_output|Use: pipe|Type: boolean|Default: false|
++---------------------------------------------------------+
+
+If this option is true, and the command produced any output and ended with a
+return code other than zero or one of the codes listed in temp_errors (that is,
+the delivery failed), the output is returned in the bounce message. However, if
+the message has a null sender (that is, it is itself a bounce message), output
+from the command is discarded. This option and return_output are mutually
+exclusive. Only one of them may be set.
+
++----------------------------------------------------+
+|return_output|Use: pipe|Type: boolean|Default: false|
++----------------------------------------------------+
+
+If this option is true, and the command produced any output, the delivery is
+deemed to have failed whatever the return code from the command, and the output
+is returned in the bounce message. Otherwise, the output is just discarded.
+However, if the message has a null sender (that is, it is a bounce message),
+output from the command is always discarded, whatever the setting of this
+option. This option and return_fail_output are mutually exclusive. Only one of
+them may be set.
+
++----------------------------------------------------------+
+|temp_errors|Use: pipe|Type: string list|Default: see below|
++----------------------------------------------------------+
+
+This option contains either a colon-separated list of numbers, or a single
+asterisk. If ignore_status is false and return_output is not set, and the
+command exits with a non-zero return code, the failure is treated as temporary
+and the delivery is deferred if the return code matches one of the numbers, or
+if the setting is a single asterisk. Otherwise, non-zero return codes are
+treated as permanent errors. The default setting contains the codes defined by
+EX_TEMPFAIL and EX_CANTCREAT in sysexits.h. If Exim is compiled on a system
+that does not define these macros, it assumes values of 75 and 73,
+respectively.
+
++----------------------------------------+
+|timeout|Use: pipe|Type: time|Default: 1h|
++----------------------------------------+
+
+If the command fails to complete within this time, it is killed. This normally
+causes the delivery to fail (but see timeout_defer). A zero time interval
+specifies no timeout. In order to ensure that any subprocesses created by the
+command are also killed, Exim makes the initial process a process group leader,
+and kills the whole process group on a timeout. However, this can be defeated
+if one of the processes starts a new process group.
+
++----------------------------------------------------+
+|timeout_defer|Use: pipe|Type: boolean|Default: false|
++----------------------------------------------------+
+
+A timeout in a pipe transport, either in the command that the transport runs,
+or in a transport filter that is associated with it, is by default treated as a
+hard error, and the delivery fails. However, if timeout_defer is set true, both
+kinds of timeout become temporary errors, causing the delivery to be deferred.
+
++------------------------------------------------+
+|umask|Use: pipe|Type: octal integer|Default: 022|
++------------------------------------------------+
+
+This specifies the umask setting for the subprocess that runs the command.
+
++------------------------------------------------+
+|use_bsmtp|Use: pipe|Type: boolean|Default: false|
++------------------------------------------------+
+
+If this option is set true, the pipe transport writes messages in "batch SMTP"
+format, with the envelope sender and recipient(s) included as SMTP commands. If
+you want to include a leading HELO command with such messages, you can do so by
+setting the message_prefix option. See section 49.10 for details of batch SMTP.
+
++---------------------------------------------------------+
+|use_classresources|Use: pipe|Type: boolean|Default: false|
++---------------------------------------------------------+
+
+This option is available only when Exim is running on FreeBSD, NetBSD, or BSD/
+OS. If it is set true, the setclassresources() function is used to set resource
+limits when a pipe transport is run to perform a delivery. The limits for the
+uid under which the pipe is to run are obtained from the login class database.
+
++-----------------------------------------------+
+|use_crlf|Use: pipe|Type: boolean|Default: false|
++-----------------------------------------------+
+
+This option causes lines to be terminated with the two-character CRLF sequence
+(carriage return, linefeed) instead of just a linefeed character. In the case
+of batched SMTP, the byte sequence written to the pipe is then an exact image
+of what would be sent down a real SMTP connection.
+
+The contents of the message_prefix and message_suffix options are written
+verbatim, so must contain their own carriage return characters if these are
+needed. When use_bsmtp is not set, the default values for both message_prefix
+and message_suffix end with a single linefeed, so their values must be changed
+to end with "\r\n" if use_crlf is set.
+
++------------------------------------------------+
+|use_shell|Use: pipe|Type: boolean|Default: false|
++------------------------------------------------+
+
+If this option is set, it causes the command to be passed to /bin/sh instead of
+being run directly from the transport, as described in section 29.3. This is
+less secure, but is needed in some situations where the command is expected to
+be run under a shell and cannot easily be modified. The allow_commands and
+restrict_to_path options, and the "$pipe_addresses" facility are incompatible
+with use_shell. The command is expanded as a single string, and handed to /bin/
+sh as data for its -c option.
+
+
+29.6 Using an external local delivery agent
+-------------------------------------------
+
+The pipe transport can be used to pass all messages that require local delivery
+to a separate local delivery agent such as procmail. When doing this, care must
+be taken to ensure that the pipe is run under an appropriate uid and gid. In
+some configurations one wants this to be a uid that is trusted by the delivery
+agent to supply the correct sender of the message. It may be necessary to
+recompile or reconfigure the delivery agent so that it trusts an appropriate
+user. The following is an example transport and router configuration for
+procmail:
+
+# transport
+procmail_pipe:
+ driver = pipe
+ command = /usr/local/bin/procmail -d $local_part_data
+ return_path_add
+ delivery_date_add
+ envelope_to_add
+ check_string = "From "
+ escape_string = ">From "
+ umask = 077
+ user = $local_part_data
+ group = mail
+
+# router
+procmail:
+ driver = accept
+ check_local_user
+ transport = procmail_pipe
+
+In this example, the pipe is run as the local user, but with the group set to
+mail. An alternative is to run the pipe as a specific user such as mail or exim
+, but in this case you must arrange for procmail to trust that user to supply a
+correct sender address. If you do not specify either a group or a user option,
+the pipe command is run as the local user. The home directory is the user's
+home directory by default.
+
+Note: The command that the pipe transport runs does not begin with
+
+IFS=" "
+
+as shown in some procmail documentation, because Exim does not by default use a
+shell to run pipe commands.
+
+The next example shows a transport and a router for a system where local
+deliveries are handled by the Cyrus IMAP server.
+
+# transport
+local_delivery_cyrus:
+ driver = pipe
+ command = /usr/cyrus/bin/deliver \
+ -m ${substr_1:$local_part_suffix} -- $local_part
+ user = cyrus
+ group = mail
+ return_output
+ log_output
+ message_prefix =
+ message_suffix =
+
+# router
+local_user_cyrus:
+ driver = accept
+ check_local_user
+ local_part_suffix = .*
+ transport = local_delivery_cyrus
+
+Note the unsetting of message_prefix and message_suffix, and the use of
+return_output to cause any text written by Cyrus to be returned to the sender.
+
+
+
+===============================================================================
+30. THE SMTP TRANSPORT
+
+The smtp transport delivers messages over TCP/IP connections using the SMTP or
+LMTP protocol. The list of hosts to try can either be taken from the address
+that is being processed (having been set up by the router), or specified
+explicitly for the transport. Timeout and retry processing (see chapter 32) is
+applied to each IP address independently.
+
+
+30.1 Multiple messages on a single connection
+---------------------------------------------
+
+The sending of multiple messages over a single TCP/IP connection can arise in
+two ways:
+
+ * If a message contains more than max_rcpt (see below) addresses that are
+ routed to the same host, more than one copy of the message has to be sent
+ to that host. In this situation, multiple copies may be sent in a single
+ run of the smtp transport over a single TCP/IP connection. (What Exim
+ actually does when it has too many addresses to send in one message also
+ depends on the value of the global remote_max_parallel option. Details are
+ given in section 49.1.)
+
+ * When a message has been successfully delivered over a TCP/IP connection,
+ Exim looks in its hints database to see if there are any other messages
+ awaiting a connection to the same host. If there are, a new delivery
+ process is started for one of them, and the current TCP/IP connection is
+ passed on to it. The new process may in turn send multiple copies and
+ possibly create yet another process.
+
+For each copy sent over the same TCP/IP connection, a sequence counter is
+incremented, and if it ever gets to the value of connection_max_messages, no
+further messages are sent over that connection.
+
+
+30.2 Use of the $host and $host_address variables
+-------------------------------------------------
+
+At the start of a run of the smtp transport, the values of $host and
+$host_address are the name and IP address of the first host on the host list
+passed by the router. However, when the transport is about to connect to a
+specific host, and while it is connected to that host, $host and $host_address
+are set to the values for that host. These are the values that are in force
+when the helo_data, hosts_try_auth, interface, serialize_hosts, and the various
+TLS options are expanded.
+
+
+30.3 Use of $tls_cipher and $tls_peerdn
+---------------------------------------
+
+At the start of a run of the smtp transport, the values of $tls_bits,
+$tls_cipher, $tls_peerdn and $tls_sni are the values that were set when the
+message was received. These are the values that are used for options that are
+expanded before any SMTP connections are made. Just before each connection is
+made, these four variables are emptied. If TLS is subsequently started, they
+are set to the appropriate values for the outgoing connection, and these are
+the values that are in force when any authenticators are run and when the
+authenticated_sender option is expanded.
+
+These variables are deprecated in favour of $tls_in_cipher et. al. and will be
+removed in a future release.
+
+
+30.4 Private options for smtp
+-----------------------------
+
+The private options of the smtp transport are as follows:
+
++------------------------------------------------------------------+
+|address_retry_include_sender|Use: smtp|Type: boolean|Default: true|
++------------------------------------------------------------------+
+
+When an address is delayed because of a 4xx response to a RCPT command, it is
+the combination of sender and recipient that is delayed in subsequent queue
+runs until the retry time is reached. You can delay the recipient without
+reference to the sender (which is what earlier versions of Exim did), by
+setting address_retry_include_sender false. However, this can lead to problems
+with servers that regularly issue 4xx responses to RCPT commands.
+
++------------------------------------------------------+
+|allow_localhost|Use: smtp|Type: boolean|Default: false|
++------------------------------------------------------+
+
+When a host specified in hosts or fallback_hosts (see below) turns out to be
+the local host, or is listed in hosts_treat_as_local, delivery is deferred by
+default. However, if allow_localhost is set, Exim goes on to do the delivery
+anyway. This should be used only in special cases when the configuration
+ensures that no looping will result (for example, a differently configured Exim
+is listening on the port to which the message is sent).
+
++-----------------------------------------------------------+
+|authenticated_sender|Use: smtp|Type: string*|Default: unset|
++-----------------------------------------------------------+
+
+When Exim has authenticated as a client, or if authenticated_sender_force is
+true, this option sets a value for the AUTH= item on outgoing MAIL commands,
+overriding any existing authenticated sender value. If the string expansion is
+forced to fail, the option is ignored. Other expansion failures cause delivery
+to be deferred. If the result of expansion is an empty string, that is also
+ignored.
+
+The expansion happens after the outgoing connection has been made and TLS
+started, if required. This means that the $host, $host_address, $tls_out_cipher
+, and $tls_out_peerdn variables are set according to the particular connection.
+
+If the SMTP session is not authenticated, the expansion of authenticated_sender
+still happens (and can cause the delivery to be deferred if it fails), but no
+AUTH= item is added to MAIL commands unless authenticated_sender_force is true.
+
+This option allows you to use the smtp transport in LMTP mode to deliver mail
+to Cyrus IMAP and provide the proper local part as the "authenticated sender",
+via a setting such as:
+
+authenticated_sender = $local_part
+
+This removes the need for IMAP subfolders to be assigned special ACLs to allow
+direct delivery to those subfolders.
+
+Because of expected uses such as that just described for Cyrus (when no domain
+is involved), there is no checking on the syntax of the provided value.
+
++-----------------------------------------------------------------+
+|authenticated_sender_force|Use: smtp|Type: boolean|Default: false|
++-----------------------------------------------------------------+
+
+If this option is set true, the authenticated_sender option's value is used for
+the AUTH= item on outgoing MAIL commands, even if Exim has not authenticated as
+a client.
+
++------------------------------------------------+
+|command_timeout|Use: smtp|Type: time|Default: 5m|
++------------------------------------------------+
+
+This sets a timeout for receiving a response to an SMTP command that has been
+sent out. It is also used when waiting for the initial banner line from the
+remote host. Its value must not be zero.
+
++------------------------------------------------+
+|connect_timeout|Use: smtp|Type: time|Default: 5m|
++------------------------------------------------+
+
+This sets a timeout for the connect() function, which sets up a TCP/IP call to
+a remote host. A setting of zero allows the system timeout (typically several
+minutes) to act. To have any effect, the value of this option must be less than
+the system timeout. However, it has been observed that on some systems there is
+no system timeout, which is why the default value for this option is 5 minutes,
+a value recommended by RFC 1123.
+
++------------------------------------------------------------+
+|connection_max_messages|Use: smtp|Type: integer|Default: 500|
++------------------------------------------------------------+
+
+This controls the maximum number of separate message deliveries that are sent
+over a single TCP/IP connection. If the value is zero, there is no limit. For
+testing purposes, this value can be overridden by the -oB command line option.
+
++---------------------------------------------------------------+
+|dane_require_tls_ciphers|Use: smtp|Type: string*|Default: unset|
++---------------------------------------------------------------+
+
+This option may be used to override tls_require_ciphers for connections where
+DANE has been determined to be in effect. If not set, then tls_require_ciphers
+will be used. Normal SMTP delivery is not able to make strong demands of TLS
+cipher configuration, because delivery will fall back to plaintext. Once DANE
+has been determined to be in effect, there is no plaintext fallback and making
+the TLS cipherlist configuration stronger will increase security, rather than
+counter-intuitively decreasing it. If the option expands to be empty or is
+forced to fail, then it will be treated as unset and tls_require_ciphers will
+be used instead.
+
++---------------------------------------------+
+|data_timeout|Use: smtp|Type: time|Default: 5m|
++---------------------------------------------+
+
+This sets a timeout for the transmission of each block in the data portion of
+the message. As a result, the overall timeout for a message depends on the size
+of the message. Its value must not be zero. See also final_timeout.
+
++-------------------------------------------------+
+|dkim_canon|Use: smtp|Type: string*|Default: unset|
++-------------------------------------------------+
+
+DKIM signing option. For details see section 58.2.
+
++-------------------------------------------------+
+|dkim_domain|Use: smtp|Type: string|Default: list*|
++-------------------------------------------------+
+
+DKIM signing option. For details see section 58.2.
+
++-------------------------------------------------+
+|dkim_hash|Use: smtp|Type: string*|Default: sha256|
++-------------------------------------------------+
+
+DKIM signing option. For details see section 58.2.
+
++----------------------------------------------------+
+|dkim_identity|Use: smtp|Type: string*|Default: unset|
++----------------------------------------------------+
+
+DKIM signing option. For details see section 58.2.
+
++-------------------------------------------------------+
+|dkim_private_key|Use: smtp|Type: string*|Default: unset|
++-------------------------------------------------------+
+
+DKIM signing option. For details see section 58.2.
+
++----------------------------------------------------+
+|dkim_selector|Use: smtp|Type: string*|Default: unset|
++----------------------------------------------------+
+
+DKIM signing option. For details see section 58.2.
+
++--------------------------------------------------+
+|dkim_strict|Use: smtp|Type: string*|Default: unset|
++--------------------------------------------------+
+
+DKIM signing option. For details see section 58.2.
+
++----------------------------------------------------------+
+|dkim_sign_headers|Use: smtp|Type: string*|Default: per RFC|
++----------------------------------------------------------+
+
+DKIM signing option. For details see section 58.2.
+
++------------------------------------------------------+
+|dkim_timestamps|Use: smtp|Type: string*|Default: unset|
++------------------------------------------------------+
+
+DKIM signing option. For details see section 58.2.
+
++--------------------------------------------------------+
+|delay_after_cutoff|Use: smtp|Type: boolean|Default: true|
++--------------------------------------------------------+
+
+This option controls what happens when all remote IP addresses for a given
+domain have been inaccessible for so long that they have passed their retry
+cutoff times.
+
+In the default state, if the next retry time has not been reached for any of
+them, the address is bounced without trying any deliveries. In other words,
+Exim delays retrying an IP address after the final cutoff time until a new
+retry time is reached, and can therefore bounce an address without ever trying
+a delivery, when machines have been down for a long time. Some people are
+unhappy at this prospect, so...
+
+If delay_after_cutoff is set false, Exim behaves differently. If all IP
+addresses are past their final cutoff time, Exim tries to deliver to those IP
+addresses that have not been tried since the message arrived. If there are
+none, of if they all fail, the address is bounced. In other words, it does not
+delay when a new message arrives, but immediately tries those expired IP
+addresses that haven't been tried since the message arrived. If there is a
+continuous stream of messages for the dead hosts, unsetting delay_after_cutoff
+means that there will be many more attempts to deliver to them.
+
++--------------------------------------------------------+
+|dns_qualify_single|Use: smtp|Type: boolean|Default: true|
++--------------------------------------------------------+
+
+If the hosts or fallback_hosts option is being used, and the gethostbyname
+option is false, the RES_DEFNAMES resolver option is set. See the
+qualify_single option in chapter 17 for more details.
+
++---------------------------------------------------------+
+|dns_search_parents|Use: smtp|Type: boolean|Default: false|
++---------------------------------------------------------+
+
+If the hosts or fallback_hosts option is being used, and the gethostbyname
+option is false, the RES_DNSRCH resolver option is set. See the search_parents
+option in chapter 17 for more details.
+
++--------------------------------------------------------------+
+|dnssec_request_domains|Use: smtp|Type: domain list*|Default: *|
++--------------------------------------------------------------+
+
+DNS lookups for domains matching dnssec_request_domains will be done with the
+dnssec request bit set. Setting this transport option is only useful if the
+transport overrides or sets the host names. See the dnssec_request_domains
+router option.
+
++------------------------------------------------------------------+
+|dnssec_require_domains|Use: smtp|Type: domain list*|Default: unset|
++------------------------------------------------------------------+
+
+DNS lookups for domains matching dnssec_require_domains will be done with the
+dnssec request bit set. Setting this transport option is only useful if the
+transport overrides or sets the host names. See the dnssec_require_domains
+router option.
+
++-------------------------------------------+
+|dscp|Use: smtp|Type: string*|Default: unset|
++-------------------------------------------+
+
+This option causes the DSCP value associated with a socket to be set to one of
+a number of fixed strings or to numeric value. The -bI:dscp option may be used
+to ask Exim which names it knows of. Common values include "throughput",
+"mincost", and on newer systems "ef", "af41", etc. Numeric values may be in the
+range 0 to 0x3F.
+
+The outbound packets from Exim will be marked with this value in the header
+(for IPv4, the TOS field; for IPv6, the TCLASS field); there is no guarantee
+that these values will have any effect, not be stripped by networking
+equipment, or do much of anything without cooperation with your Network
+Engineer and those of all network operators between the source and destination.
+
++---------------------------------------------------------+
+|fallback_hosts|Use: smtp|Type: string list|Default: unset|
++---------------------------------------------------------+
+
+String expansion is not applied to this option. The argument must be a
+colon-separated list of host names or IP addresses, optionally also including
+port numbers, though the separator can be changed, as described in section 6.20
+. Each individual item in the list is the same as an item in a route_list
+setting for the manualroute router, as described in section 20.5.
+
+Fallback hosts can also be specified on routers, which associate them with the
+addresses they process. As for the hosts option without hosts_override,
+fallback_hosts specified on the transport is used only if the address does not
+have its own associated fallback host list. Unlike hosts, a setting of
+fallback_hosts on an address is not overridden by hosts_override. However,
+hosts_randomize does apply to fallback host lists.
+
+If Exim is unable to deliver to any of the hosts for a particular address, and
+the errors are not permanent rejections, the address is put on a separate
+transport queue with its host list replaced by the fallback hosts, unless the
+address was routed via MX records and the current host was in the original MX
+list. In that situation, the fallback host list is not used.
+
+Once normal deliveries are complete, the fallback queue is delivered by
+re-running the same transports with the new host lists. If several failing
+addresses have the same fallback hosts (and max_rcpt permits it), a single copy
+of the message is sent.
+
+The resolution of the host names on the fallback list is controlled by the
+gethostbyname option, as for the hosts option. Fallback hosts apply both to
+cases when the host list comes with the address and when it is taken from hosts
+. This option provides a "use a smart host only if delivery fails" facility.
+
++-----------------------------------------------+
+|final_timeout|Use: smtp|Type: time|Default: 10m|
++-----------------------------------------------+
+
+This is the timeout that applies while waiting for the response to the final
+line containing just "." that terminates a message. Its value must not be zero.
+
++----------------------------------------------------+
+|gethostbyname|Use: smtp|Type: boolean|Default: false|
++----------------------------------------------------+
+
+If this option is true when the hosts and/or fallback_hosts options are being
+used, names are looked up using gethostbyname() (or getipnodebyname() when
+available) instead of using the DNS. Of course, that function may in fact use
+the DNS, but it may also consult other sources of information such as /etc/
+hosts.
+
++---------------------------------------------------------+
+|gnutls_compat_mode|Use: smtp|Type: boolean|Default: unset|
++---------------------------------------------------------+
+
+This option controls whether GnuTLS is used in compatibility mode in an Exim
+server. This reduces security slightly, but improves interworking with older
+implementations of TLS.
+
++----------------------------------------------------+
+|helo_data|Use: smtp|Type: string*|Default: see below|
++----------------------------------------------------+
+
+The value of this option is expanded after a connection to a another host has
+been set up. The result is used as the argument for the EHLO, HELO, or LHLO
+command that starts the outgoing SMTP or LMTP session. The default value of the
+option is:
+
+$primary_hostname
+
+During the expansion, the variables $host and $host_address are set to the
+identity of the remote host, and the variables $sending_ip_address and
+$sending_port are set to the local IP address and port number that are being
+used. These variables can be used to generate different values for different
+servers or different local IP addresses. For example, if you want the string
+that is used for helo_data to be obtained by a DNS lookup of the outgoing
+interface address, you could use this:
+
+helo_data = ${lookup dnsdb{ptr=$sending_ip_address}{$value}\
+ {$primary_hostname}}
+
+The use of helo_data applies both to sending messages and when doing callouts.
+
++-------------------------------------------------+
+|hosts|Use: smtp|Type: string list*|Default: unset|
++-------------------------------------------------+
+
+Hosts are associated with an address by a router such as dnslookup, which finds
+the hosts by looking up the address domain in the DNS, or by manualroute, which
+has lists of hosts in its configuration. However, email addresses can be passed
+to the smtp transport by any router, and not all of them can provide an
+associated list of hosts.
+
+The hosts option specifies a list of hosts to be used if the address being
+processed does not have any hosts associated with it. The hosts specified by
+hosts are also used, whether or not the address has its own hosts, if
+hosts_override is set.
+
+The string is first expanded, before being interpreted as a colon-separated
+list of host names or IP addresses, possibly including port numbers. The
+separator may be changed to something other than colon, as described in section
+6.20. Each individual item in the list is the same as an item in a route_list
+setting for the manualroute router, as described in section 20.5. However, note
+that the "/MX" facility of the manualroute router is not available here.
+
+If the expansion fails, delivery is deferred. Unless the failure was caused by
+the inability to complete a lookup, the error is logged to the panic log as
+well as the main log. Host names are looked up either by searching directly for
+address records in the DNS or by calling gethostbyname() (or getipnodebyname()
+when available), depending on the setting of the gethostbyname option. When
+Exim is compiled with IPv6 support, if a host that is looked up in the DNS has
+both IPv4 and IPv6 addresses, both types of address are used.
+
+During delivery, the hosts are tried in order, subject to their retry status,
+unless hosts_randomize is set.
+
++-----------------------------------------------------------+
+|hosts_avoid_esmtp|Use: smtp|Type: host list*|Default: unset|
++-----------------------------------------------------------+
+
+This option is for use with broken hosts that announce ESMTP facilities (for
+example, PIPELINING) and then fail to implement them properly. When a host
+matches hosts_avoid_esmtp, Exim sends HELO rather than EHLO at the start of the
+SMTP session. This means that it cannot use any of the ESMTP facilities such as
+AUTH, PIPELINING, SIZE, and STARTTLS.
+
++----------------------------------------------------------------+
+|hosts_avoid_pipelining|Use: smtp|Type: host list*|Default: unset|
++----------------------------------------------------------------+
+
+Exim will not use the ESMTP PIPELINING extension when delivering to any host
+that matches this list, even if the server host advertises PIPELINING support.
+
++------------------------------------------------------------+
+|hosts_pipe_connect|Use: smtp|Type: host list*|Default: unset|
++------------------------------------------------------------+
+
+If Exim is built with the SUPPORT_PIPE_CONNECT build option this option
+controls which to hosts the facility watched for and recorded, and used for
+subsequent connections.
+
+The retry hints database is used for the record, and records are subject to the
+retry_data_expire option. When used, the pipelining saves on roundtrip times.
+It also turns SMTP into a client-first protocol so combines well with TCP Fast
+Open.
+
+See also the pipelining_connect_advertise_hosts main option.
+
+Note: When the facility is used, the transport helo_data option will be
+expanded before the $sending_ip_address variable is filled in. A check is made
+for the use of that variable, without the presence of a "def:" test on it, but
+suitably complex coding can avoid the check and produce unexpected results. You
+have been warned.
+
++---------------------------------------------------------+
+|hosts_avoid_tls|Use: smtp|Type: host list*|Default: unset|
++---------------------------------------------------------+
+
+Exim will not try to start a TLS session when delivering to any host that
+matches this list. See chapter 43 for details of TLS.
+
++----------------------------------------------------------------+
+|hosts_verify_avoid_tls|Use: smtp|Type: host list*|Default: unset|
++----------------------------------------------------------------+
+
+Exim will not try to start a TLS session for a verify callout, or when
+delivering in cutthrough mode, to any host that matches this list.
+
++------------------------------------------------+
+|hosts_max_try|Use: smtp|Type: integer|Default: 5|
++------------------------------------------------+
+
+This option limits the number of IP addresses that are tried for any one
+delivery in cases where there are temporary delivery errors. Section 30.5
+describes in detail how the value of this option is used.
+
++-----------------------------------------------------------+
+|hosts_max_try_hardlimit|Use: smtp|Type: integer|Default: 50|
++-----------------------------------------------------------+
+
+This is an additional check on the maximum number of IP addresses that Exim
+tries for any one delivery. Section 30.5 describes its use and why it exists.
+
++----------------------------------------------------------+
+|hosts_nopass_tls|Use: smtp|Type: host list*|Default: unset|
++----------------------------------------------------------+
+
+For any host that matches this list, a connection on which a TLS session has
+been started will not be passed to a new delivery process for sending another
+message on the same connection. See section 43.11 for an explanation of when
+this might be needed.
+
++-----------------------------------------------------------+
+|hosts_noproxy_tls|Use: smtp|Type: host list*|Default: unset|
++-----------------------------------------------------------+
+
+For any host that matches this list, a TLS session which has been started will
+not be passed to a new delivery process for sending another message on the same
+session.
+
+The traditional implementation closes down TLS and re-starts it in the new
+process, on the same open TCP connection, for each successive message sent. If
+permitted by this option a pipe to to the new process is set up instead, and
+the original process maintains the TLS connection and proxies the SMTP
+connection from and to the new process and any subsequents. The new process has
+no access to TLS information, so cannot include it in logging.
+
++-----------------------------------------------------+
+|hosts_override|Use: smtp|Type: boolean|Default: false|
++-----------------------------------------------------+
+
+If this option is set and the hosts option is also set, any hosts that are
+attached to the address are ignored, and instead the hosts specified by the
+hosts option are always used. This option does not apply to fallback_hosts.
+
++------------------------------------------------------+
+|hosts_randomize|Use: smtp|Type: boolean|Default: false|
++------------------------------------------------------+
+
+If this option is set, and either the list of hosts is taken from the hosts or
+the fallback_hosts option, or the hosts supplied by the router were not
+obtained from MX records (this includes fallback hosts from the router), and
+were not randomized by the router, the order of trying the hosts is randomized
+each time the transport runs. Randomizing the order of a host list can be used
+to do crude load sharing.
+
+When hosts_randomize is true, a host list may be split into groups whose order
+is separately randomized. This makes it possible to set up MX-like behaviour.
+The boundaries between groups are indicated by an item that is just "+" in the
+host list. For example:
+
+hosts = host1:host2:host3:+:host4:host5
+
+The order of the first three hosts and the order of the last two hosts is
+randomized for each use, but the first three always end up before the last two.
+If hosts_randomize is not set, a "+" item in the list is ignored.
+
++------------------------------------------------------------+
+|hosts_require_auth|Use: smtp|Type: host list*|Default: unset|
++------------------------------------------------------------+
+
+This option provides a list of servers for which authentication must succeed
+before Exim will try to transfer a message. If authentication fails for servers
+which are not in this list, Exim tries to send unauthenticated. If
+authentication fails for one of these servers, delivery is deferred. This
+temporary error is detectable in the retry rules, so it can be turned into a
+hard failure if required. See also hosts_try_auth, and chapter 33 for details
+of authentication.
+
++--------------------------------------------------------+
+|hosts_request_ocsp|Use: smtp|Type: host list*|Default: *|
++--------------------------------------------------------+
+
+Exim will request a Certificate Status on a TLS session for any host that
+matches this list. tls_verify_certificates should also be set for the
+transport.
+
++------------------------------------------------------------+
+|hosts_require_dane|Use: smtp|Type: host list*|Default: unset|
++------------------------------------------------------------+
+
+If built with DANE support, Exim will require that a DNSSEC-validated TLSA
+record is present for any host matching the list, and that a DANE-verified TLS
+connection is made. See the dnssec_request_domains router and transport
+options. There will be no fallback to in-clear communication. See section 43.15
+.
+
++------------------------------------------------------------+
+|hosts_require_ocsp|Use: smtp|Type: host list*|Default: unset|
++------------------------------------------------------------+
+
+Exim will request, and check for a valid Certificate Status being given, on a
+TLS session for any host that matches this list. tls_verify_certificates should
+also be set for the transport.
+
++-----------------------------------------------------------+
+|hosts_require_tls|Use: smtp|Type: host list*|Default: unset|
++-----------------------------------------------------------+
+
+Exim will insist on using a TLS session when delivering to any host that
+matches this list. See chapter 43 for details of TLS. Note: This option affects
+outgoing mail only. To insist on TLS for incoming messages, use an appropriate
+ACL.
+
++--------------------------------------------------------+
+|hosts_try_auth|Use: smtp|Type: host list*|Default: unset|
++--------------------------------------------------------+
+
+This option provides a list of servers to which, provided they announce
+authentication support, Exim will attempt to authenticate as a client when it
+connects. If authentication fails, Exim will try to transfer the message
+unauthenticated. See also hosts_require_auth, and chapter 33 for details of
+authentication.
+
++--------------------------------------------------------+
+|hosts_try_chunking|Use: smtp|Type: host list*|Default: *|
++--------------------------------------------------------+
+
+This option provides a list of servers to which, provided they announce
+CHUNKING support, Exim will attempt to use BDAT commands rather than DATA.
+
+Unless DKIM signing is being done,
+
+BDAT will not be used in conjunction with a transport filter.
+
++----------------------------------------------------+
+|hosts_try_dane|Use: smtp|Type: host list*|Default: *|
++----------------------------------------------------+
+
+If built with DANE support, Exim will look up a TLSA record for any host
+matching the list, If one is found and that lookup was DNSSEC-validated, then
+Exim requires that a DANE-verified TLS connection is made for that host; there
+will be no fallback to in-clear communication.
+
+See the dnssec_request_domains router and transport options. See section 43.15.
+
++--------------------------------------------------------+
+|hosts_try_fastopen|Use: smtp|Type: host list*|Default: *|
++--------------------------------------------------------+
+
+This option provides a list of servers to which, provided the facility is
+supported by this system, Exim will attempt to perform a TCP Fast Open. No data
+is sent on the SYN segment but, if the remote server also supports the
+facility, it can send its SMTP banner immediately after the SYN,ACK segment.
+This can save up to one round-trip time.
+
+The facility is only active for previously-contacted servers, as the initiator
+must present a cookie in the SYN segment.
+
+On (at least some) current Linux distributions the facility must be enabled in
+the kernel by the sysadmin before the support is usable. There is no option for
+control of the server side; if the system supports it it is always enabled.
+Note that lengthy operations in the connect ACL, such as DNSBL lookups, will
+still delay the emission of the SMTP banner.
+
++----------------------------------------------------+
+|hosts_try_prdr|Use: smtp|Type: host list*|Default: *|
++----------------------------------------------------+
+
+This option provides a list of servers to which, provided they announce PRDR
+support, Exim will attempt to negotiate PRDR for multi-recipient messages. The
+option can usually be left as default.
+
++-----------------------------------------------------+
+|interface|Use: smtp|Type: string list*|Default: unset|
++-----------------------------------------------------+
+
+This option specifies which interface to bind to when making an outgoing SMTP
+call. The value is an IP address, not an interface name such as "eth0". Do not
+confuse this with the interface address that was used when a message was
+received, which is in $received_ip_address, formerly known as
+$interface_address. The name was changed to minimize confusion with the
+outgoing interface address. There is no variable that contains an outgoing
+interface address because, unless it is set by this option, its value is
+unknown.
+
+During the expansion of the interface option the variables $host and
+$host_address refer to the host to which a connection is about to be made
+during the expansion of the string. Forced expansion failure, or an empty
+string result causes the option to be ignored. Otherwise, after expansion, the
+string must be a list of IP addresses, colon-separated by default, but the
+separator can be changed in the usual way (6.21). For example:
+
+interface = <; 192.168.123.123 ; 3ffe:ffff:836f::fe86:a061
+
+The first interface of the correct type (IPv4 or IPv6) is used for the outgoing
+connection. If none of them are the correct type, the option is ignored. If
+interface is not set, or is ignored, the system's IP functions choose which
+interface to use if the host has more than one.
+
++-----------------------------------------------+
+|keepalive|Use: smtp|Type: boolean|Default: true|
++-----------------------------------------------+
+
+This option controls the setting of SO_KEEPALIVE on outgoing TCP/IP socket
+connections. When set, it causes the kernel to probe idle connections
+periodically, by sending packets with "old" sequence numbers. The other end of
+the connection should send a acknowledgment if the connection is still okay or
+a reset if the connection has been aborted. The reason for doing this is that
+it has the beneficial effect of freeing up certain types of connection that can
+get stuck when the remote host is disconnected without tidying up the TCP/IP
+call properly. The keepalive mechanism takes several hours to detect
+unreachable hosts.
+
++--------------------------------------------------------+
+|lmtp_ignore_quota|Use: smtp|Type: boolean|Default: false|
++--------------------------------------------------------+
+
+If this option is set true when the protocol option is set to "lmtp", the
+string "IGNOREQUOTA" is added to RCPT commands, provided that the LMTP server
+has advertised support for IGNOREQUOTA in its response to the LHLO command.
+
++---------------------------------------------+
+|max_rcpt|Use: smtp|Type: integer|Default: 100|
++---------------------------------------------+
+
+This option limits the number of RCPT commands that are sent in a single SMTP
+message transaction. Each set of addresses is treated independently, and so can
+cause parallel connections to the same host if remote_max_parallel permits
+this.
+
++---------------------------------------------------+
+|multi_domain|Use: smtp|Type: boolean*|Default: true|
++---------------------------------------------------+
+
+When this option is set, the smtp transport can handle a number of addresses
+containing a mixture of different domains provided they all resolve to the same
+list of hosts. Turning the option off restricts the transport to handling only
+one domain at a time. This is useful if you want to use $domain in an expansion
+for the transport, because it is set only when there is a single domain
+involved in a remote delivery.
+
+It is expanded per-address and can depend on any of $address_data, $domain_data
+, $local_part_data, $host, $host_address and $host_port.
+
++-----------------------------------------------+
+|port|Use: smtp|Type: string*|Default: see below|
++-----------------------------------------------+
+
+This option specifies the TCP/IP port on the server to which Exim connects.
+Note: Do not confuse this with the port that was used when a message was
+received, which is in $received_port, formerly known as $interface_port. The
+name was changed to minimize confusion with the outgoing port. There is no
+variable that contains an outgoing port.
+
+If the value of this option begins with a digit it is taken as a port number;
+otherwise it is looked up using getservbyname(). The default value is normally
+"smtp", but if protocol is set to "lmtp" the default is "lmtp" and if protocol
+is set to "smtps" the default is "smtps". If the expansion fails, or if a port
+number cannot be found, delivery is deferred.
+
+Note that at least one Linux distribution has been seen failing to put "smtps"
+in its "/etc/services" file, resulting is such deferrals.
+
++---------------------------------------------+
+|protocol|Use: smtp|Type: string|Default: smtp|
++---------------------------------------------+
+
+If this option is set to "lmtp" instead of "smtp", the default value for the
+port option changes to "lmtp", and the transport operates the LMTP protocol
+(RFC 2033) instead of SMTP. This protocol is sometimes used for local
+deliveries into closed message stores. Exim also has support for running LMTP
+over a pipe to a local process - see chapter 28.
+
+If this option is set to "smtps", the default value for the port option changes
+to "smtps", and the transport initiates TLS immediately after connecting, as an
+outbound SSL-on-connect, instead of using STARTTLS to upgrade. The Internet
+standards bodies used to strongly discourage use of this mode, but as of RFC
+8314 it is perferred over STARTTLS for message submission (as distinct from
+MTA-MTA communication).
+
++---------------------------------------------------------------+
+|retry_include_ip_address|Use: smtp|Type: boolean*|Default: true|
++---------------------------------------------------------------+
+
+Exim normally includes both the host name and the IP address in the key it
+constructs for indexing retry data after a temporary delivery failure. This
+means that when one of several IP addresses for a host is failing, it gets
+tried periodically (controlled by the retry rules), but use of the other IP
+addresses is not affected.
+
+However, in some dialup environments hosts are assigned a different IP address
+each time they connect. In this situation the use of the IP address as part of
+the retry key leads to undesirable behaviour. Setting this option false causes
+Exim to use only the host name. Since it is expanded it can be made to depend
+on the host or domain.
+
++---------------------------------------------------------+
+|serialize_hosts|Use: smtp|Type: host list*|Default: unset|
++---------------------------------------------------------+
+
+Because Exim operates in a distributed manner, if several messages for the same
+host arrive at around the same time, more than one simultaneous connection to
+the remote host can occur. This is not usually a problem except when there is a
+slow link between the hosts. In that situation it may be helpful to restrict
+Exim to one connection at a time. This can be done by setting serialize_hosts
+to match the relevant hosts.
+
+Exim implements serialization by means of a hints database in which a record is
+written whenever a process connects to one of the restricted hosts. The record
+is deleted when the connection is completed. Obviously there is scope for
+records to get left lying around if there is a system or program crash. To
+guard against this, Exim ignores any records that are more than six hours old.
+
+If you set up this kind of serialization, you should also arrange to delete the
+relevant hints database whenever your system reboots. The names of the files
+start with misc and they are kept in the spool/db directory. There may be one
+or two files, depending on the type of DBM in use. The same files are used for
+ETRN serialization.
+
+See also the max_parallel generic transport option.
+
++---------------------------------------------------+
+|size_addition|Use: smtp|Type: integer|Default: 1024|
++---------------------------------------------------+
+
+If a remote SMTP server indicates that it supports the SIZE option of the MAIL
+command, Exim uses this to pass over the message size at the start of an SMTP
+transaction. It adds the value of size_addition to the value it sends, to allow
+for headers and other text that may be added during delivery by configuration
+options or in a transport filter. It may be necessary to increase this if a lot
+of text is added to messages.
+
+Alternatively, if the value of size_addition is set negative, it disables the
+use of the SIZE option altogether.
+
++--------------------------------------------------+
+|socks_proxy|Use: smtp|Type: string*|Default: unset|
++--------------------------------------------------+
+
+This option enables use of SOCKS proxies for connections made by the transport.
+For details see section 59.2.
+
++------------------------------------------------------+
+|tls_certificate|Use: smtp|Type: string*|Default: unset|
++------------------------------------------------------+
+
+The value of this option must be the absolute path to a file which contains the
+client's certificate, for possible use when sending a message over an encrypted
+connection. The values of $host and $host_address are set to the name and
+address of the server during the expansion. See chapter 43 for details of TLS.
+
+Note: This option must be set if you want Exim to be able to use a TLS
+certificate when sending messages as a client. The global option of the same
+name specifies the certificate for Exim as a server; it is not automatically
+assumed that the same certificate should be used when Exim is operating as a
+client.
+
++----------------------------------------------+
+|tls_crl|Use: smtp|Type: string*|Default: unset|
++----------------------------------------------+
+
+This option specifies a certificate revocation list. The expanded value must be
+the name of a file that contains a CRL in PEM format.
+
++-----------------------------------------------------+
+|tls_dh_min_bits|Use: smtp|Type: integer|Default: 1024|
++-----------------------------------------------------+
+
+When establishing a TLS session, if a ciphersuite which uses Diffie-Hellman key
+agreement is negotiated, the server will provide a large prime number for use.
+This option establishes the minimum acceptable size of that number. If the
+parameter offered by the server is too small, then the TLS handshake will fail.
+
+Only supported when using GnuTLS.
+
++-----------------------------------------------------+
+|tls_privatekey|Use: smtp|Type: string*|Default: unset|
++-----------------------------------------------------+
+
+The value of this option must be the absolute path to a file which contains the
+client's private key. This is used when sending a message over an encrypted
+connection using a client certificate. The values of $host and $host_address
+are set to the name and address of the server during the expansion. If this
+option is unset, or the expansion is forced to fail, or the result is an empty
+string, the private key is assumed to be in the same file as the certificate.
+See chapter 43 for details of TLS.
+
++----------------------------------------------------------+
+|tls_require_ciphers|Use: smtp|Type: string*|Default: unset|
++----------------------------------------------------------+
+
+The value of this option must be a list of permitted cipher suites, for use
+when setting up an outgoing encrypted connection. (There is a global option of
+the same name for controlling incoming connections.) The values of $host and
+$host_address are set to the name and address of the server during the
+expansion. See chapter 43 for details of TLS; note that this option is used in
+different ways by OpenSSL and GnuTLS (see sections 43.4 and 43.5). For GnuTLS,
+the order of the ciphers is a preference order.
+
++----------------------------------------------+
+|tls_sni|Use: smtp|Type: string*|Default: unset|
++----------------------------------------------+
+
+If this option is set
+
+and the connection is not DANE-validated
+
+then it sets the $tls_out_sni variable and causes any TLS session to pass this
+value as the Server Name Indication extension to the remote side, which can be
+used by the remote side to select an appropriate certificate and private key
+for the session.
+
+See 43.10 for more information.
+
+Note that for OpenSSL, this feature requires a build of OpenSSL that supports
+TLS extensions.
+
++-----------------------------------------------------------+
+|tls_tempfail_tryclear|Use: smtp|Type: boolean|Default: true|
++-----------------------------------------------------------+
+
+When the server host is not in hosts_require_tls, and there is a problem in
+setting up a TLS session, this option determines whether or not Exim should try
+to deliver the message unencrypted. If it is set false, delivery to the current
+host is deferred; if there are other hosts, they are tried. If this option is
+set true, Exim attempts to deliver unencrypted after a 4xx response to
+STARTTLS. Also, if STARTTLS is accepted, but the subsequent TLS negotiation
+fails, Exim closes the current connection (because it is in an unknown state),
+opens a new one to the same host, and then tries the delivery in clear.
+
++----------------------------------------------------------+
+|tls_try_verify_hosts|Use: smtp|Type: host list*|Default: *|
++----------------------------------------------------------+
+
+This option gives a list of hosts for which, on encrypted connections,
+certificate verification will be tried but need not succeed. The
+tls_verify_certificates option must also be set. Note that unless the host is
+in this list TLS connections will be denied to hosts using self-signed
+certificates when tls_verify_certificates is matched. The
+$tls_out_certificate_verified variable is set when certificate verification
+succeeds.
+
++---------------------------------------------------------------+
+|tls_verify_cert_hostnames|Use: smtp|Type: host list*|Default: *|
++---------------------------------------------------------------+
+
+This option give a list of hosts for which, while verifying the server
+certificate, checks will be included on the host name (note that this will
+generally be the result of a DNS MX lookup) versus Subject and
+Subject-Alternate-Name fields. Wildcard names are permitted limited to being
+the initial component of a 3-or-more component FQDN.
+
+There is no equivalent checking on client certificates.
+
++---------------------------------------------------------------+
+|tls_verify_certificates|Use: smtp|Type: string*|Default: system|
++---------------------------------------------------------------+
+
+The value of this option must be either the word "system" or the absolute path
+to a file or directory containing permitted certificates for servers, for use
+when setting up an encrypted connection.
+
+The "system" value for the option will use a location compiled into the SSL
+library. This is not available for GnuTLS versions preceding 3.0.20; a value of
+"system" is taken as empty and an explicit location must be specified.
+
+The use of a directory for the option value is not available for GnuTLS
+versions preceding 3.3.6 and a single file must be used.
+
+With OpenSSL the certificates specified explicitly either by file or directory
+are added to those given by the system default location.
+
+The values of $host and $host_address are set to the name and address of the
+server during the expansion of this option. See chapter 43 for details of TLS.
+
+For back-compatibility, if neither tls_verify_hosts nor tls_try_verify_hosts
+are set (a single-colon empty list counts as being set) and certificate
+verification fails the TLS connection is closed.
+
++----------------------------------------------------------+
+|tls_verify_hosts|Use: smtp|Type: host list*|Default: unset|
++----------------------------------------------------------+
+
+This option gives a list of hosts for which, on encrypted connections,
+certificate verification must succeed. The tls_verify_certificates option must
+also be set. If both this option and tls_try_verify_hosts are unset operation
+is as if this option selected all hosts.
+
++-----------------------------------------------------+
+|utf8_downconvert|Use: smtp|Type: integer*|Default: -1|
++-----------------------------------------------------+
+
+If built with internationalization support, this option controls conversion of
+UTF-8 in message envelope addresses to a-label form. If, after expansion, the
+value is 1, 0, or -1 then this value overrides any value previously set for the
+message. Otherwise, any previously set value is used. To permit use of a
+previous value, set this option to an empty string. For details on the values
+see section 60.1.
+
+
+30.5 How the limits for the number of hosts to try are used
+-----------------------------------------------------------
+
+There are two options that are concerned with the number of hosts that are
+tried when an SMTP delivery takes place. They are hosts_max_try and
+hosts_max_try_hardlimit.
+
+The hosts_max_try option limits the number of hosts that are tried for a single
+delivery. However, despite the term "host" in its name, the option actually
+applies to each IP address independently. In other words, a multihomed host is
+treated as several independent hosts, just as it is for retrying.
+
+Many of the larger ISPs have multiple MX records which often point to
+multihomed hosts. As a result, a list of a dozen or more IP addresses may be
+created as a result of routing one of these domains.
+
+Trying every single IP address on such a long list does not seem sensible; if
+several at the top of the list fail, it is reasonable to assume there is some
+problem that is likely to affect all of them. Roughly speaking, the value of
+hosts_max_try is the maximum number that are tried before deferring the
+delivery. However, the logic cannot be quite that simple.
+
+Firstly, IP addresses that are skipped because their retry times have not
+arrived do not count, and in addition, addresses that are past their retry
+limits are also not counted, even when they are tried. This means that when
+some IP addresses are past their retry limits, more than the value of
+hosts_max_retry may be tried. The reason for this behaviour is to ensure that
+all IP addresses are considered before timing out an email address (but see
+below for an exception).
+
+Secondly, when the hosts_max_try limit is reached, Exim looks down the host
+list to see if there is a subsequent host with a different (higher valued) MX.
+If there is, that host is considered next, and the current IP address is used
+but not counted. This behaviour helps in the case of a domain with a retry rule
+that hardly ever delays any hosts, as is now explained:
+
+Consider the case of a long list of hosts with one MX value, and a few with a
+higher MX value. If hosts_max_try is small (the default is 5) only a few hosts
+at the top of the list are tried at first. With the default retry rule, which
+specifies increasing retry times, the higher MX hosts are eventually tried when
+those at the top of the list are skipped because they have not reached their
+retry times.
+
+However, it is common practice to put a fixed short retry time on domains for
+large ISPs, on the grounds that their servers are rarely down for very long.
+Unfortunately, these are exactly the domains that tend to resolve to long lists
+of hosts. The short retry time means that the lowest MX hosts are tried every
+time. The attempts may be in a different order because of random sorting, but
+without the special MX check, the higher MX hosts would never be tried until
+all the lower MX hosts had timed out (which might be several days), because
+there are always some lower MX hosts that have reached their retry times. With
+the special check, Exim considers at least one IP address from each MX value at
+every delivery attempt, even if the hosts_max_try limit has already been
+reached.
+
+The above logic means that hosts_max_try is not a hard limit, and in
+particular, Exim normally eventually tries all the IP addresses before timing
+out an email address. When hosts_max_try was implemented, this seemed a
+reasonable thing to do. Recently, however, some lunatic DNS configurations have
+been set up with hundreds of IP addresses for some domains. It can take a very
+long time indeed for an address to time out in these cases.
+
+The hosts_max_try_hardlimit option was added to help with this problem. Exim
+never tries more than this number of IP addresses; if it hits this limit and
+they are all timed out, the email address is bounced, even though not all
+possible IP addresses have been tried.
+
+
+
+===============================================================================
+31. ADDRESS REWRITING
+
+There are some circumstances in which Exim automatically rewrites domains in
+addresses. The two most common are when an address is given without a domain
+(referred to as an "unqualified address") or when an address contains an
+abbreviated domain that is expanded by DNS lookup.
+
+Unqualified envelope addresses are accepted only for locally submitted
+messages, or for messages that are received from hosts matching
+sender_unqualified_hosts or recipient_unqualified_hosts, as appropriate.
+Unqualified addresses in header lines are qualified if they are in locally
+submitted messages, or messages from hosts that are permitted to send
+unqualified envelope addresses. Otherwise, unqualified addresses in header
+lines are neither qualified nor rewritten.
+
+One situation in which Exim does not automatically rewrite a domain is when it
+is the name of a CNAME record in the DNS. The older RFCs suggest that such a
+domain should be rewritten using the "canonical" name, and some MTAs do this.
+The new RFCs do not contain this suggestion.
+
+
+31.1 Explicitly configured address rewriting
+--------------------------------------------
+
+This chapter describes the rewriting rules that can be used in the main rewrite
+section of the configuration file, and also in the generic headers_rewrite
+option that can be set on any transport.
+
+Some people believe that configured address rewriting is a Mortal Sin. Others
+believe that life is not possible without it. Exim provides the facility; you
+do not have to use it.
+
+The main rewriting rules that appear in the "rewrite" section of the
+configuration file are applied to addresses in incoming messages, both envelope
+addresses and addresses in header lines. Each rule specifies the types of
+address to which it applies.
+
+Whether or not addresses in header lines are rewritten depends on the origin of
+the headers and the type of rewriting. Global rewriting, that is, rewriting
+rules from the rewrite section of the configuration file, is applied only to
+those headers that were received with the message. Header lines that are added
+by ACLs or by a system filter or by individual routers or transports (which are
+specific to individual recipient addresses) are not rewritten by the global
+rules.
+
+Rewriting at transport time, by means of the headers_rewrite option, applies
+all headers except those added by routers and transports. That is, as well as
+the headers that were received with the message, it also applies to headers
+that were added by an ACL or a system filter.
+
+In general, rewriting addresses from your own system or domain has some
+legitimacy. Rewriting other addresses should be done only with great care and
+in special circumstances. The author of Exim believes that rewriting should be
+used sparingly, and mainly for "regularizing" addresses in your own domains.
+Although it can sometimes be used as a routing tool, this is very strongly
+discouraged.
+
+There are two commonly encountered circumstances where rewriting is used, as
+illustrated by these examples:
+
+ * The company whose domain is hitch.fict.example has a number of hosts that
+ exchange mail with each other behind a firewall, but there is only a single
+ gateway to the outer world. The gateway rewrites *.hitch.fict.example as
+ hitch.fict.example when sending mail off-site.
+
+ * A host rewrites the local parts of its own users so that, for example,
+ fp42@hitch.fict.example becomes Ford.Prefect@hitch.fict.example.
+
+
+31.2 When does rewriting happen?
+--------------------------------
+
+Configured address rewriting can take place at several different stages of a
+message's processing.
+
+At the start of an ACL for MAIL, the sender address may have been rewritten by
+a special SMTP-time rewrite rule (see section 31.9), but no ordinary rewrite
+rules have yet been applied. If, however, the sender address is verified in the
+ACL, it is rewritten before verification, and remains rewritten thereafter. The
+subsequent value of $sender_address is the rewritten address. This also applies
+if sender verification happens in a RCPT ACL. Otherwise, when the sender
+address is not verified, it is rewritten as soon as a message's header lines
+have been received.
+
+Similarly, at the start of an ACL for RCPT, the current recipient's address may
+have been rewritten by a special SMTP-time rewrite rule, but no ordinary
+rewrite rules have yet been applied to it. However, the behaviour is different
+from the sender address when a recipient is verified. The address is rewritten
+for the verification, but the rewriting is not remembered at this stage. The
+value of $local_part and $domain after verification are always the same as they
+were before (that is, they contain the unrewritten - except for SMTP-time
+rewriting - address).
+
+As soon as a message's header lines have been received, all the envelope
+recipient addresses are permanently rewritten, and rewriting is also applied to
+the addresses in the header lines (if configured). This happens before adding
+any header lines that were specified in MAIL or RCPT ACLs, and before the DATA
+ACL and local_scan() functions are run.
+
+When an address is being routed, either for delivery or for verification,
+rewriting is applied immediately to child addresses that are generated by
+redirection, unless no_rewrite is set on the router.
+
+At transport time, additional rewriting of addresses in header lines can be
+specified by setting the generic headers_rewrite option on a transport. This
+option contains rules that are identical in form to those in the rewrite
+section of the configuration file. They are applied to the original message
+header lines and any that were added by ACLs or a system filter. They are not
+applied to header lines that are added by routers or the transport.
+
+The outgoing envelope sender can be rewritten by means of the return_path
+transport option. However, it is not possible to rewrite envelope recipients at
+transport time.
+
+
+31.3 Testing the rewriting rules that apply on input
+----------------------------------------------------
+
+Exim's input rewriting configuration appears in a part of the runtime
+configuration file headed by "begin rewrite". It can be tested by the -brw
+command line option. This takes an address (which can be a full RFC 2822
+address) as its argument. The output is a list of how the address would be
+transformed by the rewriting rules for each of the different places it might
+appear in an incoming message, that is, for each different header and for the
+envelope sender and recipient fields. For example,
+
+exim -brw ph10@exim.workshop.example
+
+might produce the output
+
+sender: Philip.Hazel@exim.workshop.example
+from: Philip.Hazel@exim.workshop.example
+to: ph10@exim.workshop.example
+cc: ph10@exim.workshop.example
+bcc: ph10@exim.workshop.example
+reply-to: Philip.Hazel@exim.workshop.example
+env-from: Philip.Hazel@exim.workshop.example
+env-to: ph10@exim.workshop.example
+
+which shows that rewriting has been set up for that address when used in any of
+the source fields, but not when it appears as a recipient address. At the
+present time, there is no equivalent way of testing rewriting rules that are
+set for a particular transport.
+
+
+31.4 Rewriting rules
+--------------------
+
+The rewrite section of the configuration file consists of lines of rewriting
+rules in the form
+
+<source pattern> <replacement> <flags>
+
+Rewriting rules that are specified for the headers_rewrite generic transport
+option are given as a colon-separated list. Each item in the list takes the
+same form as a line in the main rewriting configuration (except that any colons
+must be doubled, of course).
+
+The formats of source patterns and replacement strings are described below.
+Each is terminated by white space, unless enclosed in double quotes, in which
+case normal quoting conventions apply inside the quotes. The flags are single
+characters which may appear in any order. Spaces and tabs between them are
+ignored.
+
+For each address that could potentially be rewritten, the rules are scanned in
+order, and replacements for the address from earlier rules can themselves be
+replaced by later rules (but see the "q" and "R" flags).
+
+The order in which addresses are rewritten is undefined, may change between
+releases, and must not be relied on, with one exception: when a message is
+received, the envelope sender is always rewritten first, before any header
+lines are rewritten. For example, the replacement string for a rewrite of an
+address in To: must not assume that the message's address in From: has (or has
+not) already been rewritten. However, a rewrite of From: may assume that the
+envelope sender has already been rewritten.
+
+The variables $local_part and $domain can be used in the replacement string to
+refer to the address that is being rewritten. Note that lookup-driven rewriting
+can be done by a rule of the form
+
+*@* ${lookup ...
+
+where the lookup key uses $1 and $2 or $local_part and $domain to refer to the
+address that is being rewritten.
+
+
+31.5 Rewriting patterns
+-----------------------
+
+The source pattern in a rewriting rule is any item which may appear in an
+address list (see section 10.20). It is in fact processed as a single-item
+address list, which means that it is expanded before being tested against the
+address. As always, if you use a regular expression as a pattern, you must take
+care to escape dollar and backslash characters, or use the "\N" facility to
+suppress string expansion within the regular expression.
+
+Domains in patterns should be given in lower case. Local parts in patterns are
+case-sensitive. If you want to do case-insensitive matching of local parts, you
+can use a regular expression that starts with "^(?i)".
+
+After matching, the numerical variables $1, $2, etc. may be set, depending on
+the type of match which occurred. These can be used in the replacement string
+to insert portions of the incoming address. $0 always refers to the complete
+incoming address. When a regular expression is used, the numerical variables
+are set from its capturing subexpressions. For other types of pattern they are
+set as follows:
+
+ * If a local part or domain starts with an asterisk, the numerical variables
+ refer to the character strings matched by asterisks, with $1 associated
+ with the first asterisk, and $2 with the second, if present. For example,
+ if the pattern
+
+ *queen@*.fict.example
+
+ is matched against the address hearts-queen@wonderland.fict.example then
+
+ $0 = hearts-queen@wonderland.fict.example
+ $1 = hearts-
+ $2 = wonderland
+
+ Note that if the local part does not start with an asterisk, but the domain
+ does, it is $1 that contains the wild part of the domain.
+
+ * If the domain part of the pattern is a partial lookup, the wild and fixed
+ parts of the domain are placed in the next available numerical variables.
+ Suppose, for example, that the address foo@bar.baz.example is processed by
+ a rewriting rule of the form
+
+ *@partial-dbm;/some/dbm/file <replacement string>
+
+ and the key in the file that matches the domain is "*.baz.example". Then
+
+ $1 = foo
+ $2 = bar
+ $3 = baz.example
+
+ If the address foo@baz.example is looked up, this matches the same wildcard
+ file entry, and in this case $2 is set to the empty string, but $3 is still
+ set to baz.example. If a non-wild key is matched in a partial lookup, $2 is
+ again set to the empty string and $3 is set to the whole domain. For
+ non-partial domain lookups, no numerical variables are set.
+
+
+31.6 Rewriting replacements
+---------------------------
+
+If the replacement string for a rule is a single asterisk, addresses that match
+the pattern and the flags are not rewritten, and no subsequent rewriting rules
+are scanned. For example,
+
+hatta@lookingglass.fict.example * f
+
+specifies that hatta@lookingglass.fict.example is never to be rewritten in
+From: headers.
+
+If the replacement string is not a single asterisk, it is expanded, and must
+yield a fully qualified address. Within the expansion, the variables
+$local_part and $domain refer to the address that is being rewritten. Any
+letters they contain retain their original case - they are not lower cased. The
+numerical variables are set up according to the type of pattern that matched
+the address, as described above. If the expansion is forced to fail by the
+presence of "fail" in a conditional or lookup item, rewriting by the current
+rule is abandoned, but subsequent rules may take effect. Any other expansion
+failure causes the entire rewriting operation to be abandoned, and an entry
+written to the panic log.
+
+
+31.7 Rewriting flags
+--------------------
+
+There are three different kinds of flag that may appear on rewriting rules:
+
+ * Flags that specify which headers and envelope addresses to rewrite: E, F,
+ T, b, c, f, h, r, s, t.
+
+ * A flag that specifies rewriting at SMTP time: S.
+
+ * Flags that control the rewriting process: Q, q, R, w.
+
+For rules that are part of the headers_rewrite generic transport option, E, F,
+T, and S are not permitted.
+
+
+31.8 Flags specifying which headers and envelope addresses to rewrite
+---------------------------------------------------------------------
+
+If none of the following flag letters, nor the "S" flag (see section 31.9) are
+present, a main rewriting rule applies to all headers and to both the sender
+and recipient fields of the envelope, whereas a transport-time rewriting rule
+just applies to all headers. Otherwise, the rewriting rule is skipped unless
+the relevant addresses are being processed.
+
+E rewrite all envelope fields
+F rewrite the envelope From field
+T rewrite the envelope To field
+b rewrite the Bcc: header
+c rewrite the Cc: header
+f rewrite the From: header
+h rewrite all headers
+r rewrite the Reply-To: header
+s rewrite the Sender: header
+t rewrite the To: header
+
+"All headers" means all of the headers listed above that can be selected
+individually, plus their Resent- versions. It does not include other headers
+such as Subject: etc.
+
+You should be particularly careful about rewriting Sender: headers, and
+restrict this to special known cases in your own domains.
+
+
+31.9 The SMTP-time rewriting flag
+---------------------------------
+
+The rewrite flag "S" specifies a rewrite of incoming envelope addresses at SMTP
+time, as soon as an address is received in a MAIL or RCPT command, and before
+any other processing; even before syntax checking. The pattern is required to
+be a regular expression, and it is matched against the whole of the data for
+the command, including any surrounding angle brackets.
+
+This form of rewrite rule allows for the handling of addresses that are not
+compliant with RFCs 2821 and 2822 (for example, "bang paths" in batched SMTP
+input). Because the input is not required to be a syntactically valid address,
+the variables $local_part and $domain are not available during the expansion of
+the replacement string. The result of rewriting replaces the original address
+in the MAIL or RCPT command.
+
+
+31.10 Flags controlling the rewriting process
+---------------------------------------------
+
+There are four flags which control the way the rewriting process works. These
+take effect only when a rule is invoked, that is, when the address is of the
+correct type (matches the flags) and matches the pattern:
+
+ * If the "Q" flag is set on a rule, the rewritten address is permitted to be
+ an unqualified local part. It is qualified with qualify_recipient. In the
+ absence of "Q" the rewritten address must always include a domain.
+
+ * If the "q" flag is set on a rule, no further rewriting rules are
+ considered, even if no rewriting actually takes place because of a "fail"
+ in the expansion. The "q" flag is not effective if the address is of the
+ wrong type (does not match the flags) or does not match the pattern.
+
+ * The "R" flag causes a successful rewriting rule to be re-applied to the new
+ address, up to ten times. It can be combined with the "q" flag, to stop
+ rewriting once it fails to match (after at least one successful rewrite).
+
+ * When an address in a header is rewritten, the rewriting normally applies
+ only to the working part of the address, with any comments and RFC 2822
+ "phrase" left unchanged. For example, rewriting might change
+
+ From: Ford Prefect <fp42@restaurant.hitch.fict.example>
+
+ into
+
+ From: Ford Prefect <prefectf@hitch.fict.example>
+
+ Sometimes there is a need to replace the whole address item, and this can
+ be done by adding the flag letter "w" to a rule. If this is set on a rule
+ that causes an address in a header line to be rewritten, the entire address
+ is replaced, not just the working part. The replacement must be a complete
+ RFC 2822 address, including the angle brackets if necessary. If text
+ outside angle brackets contains a character whose value is greater than 126
+ or less than 32 (except for tab), the text is encoded according to RFC
+ 2047. The character set is taken from headers_charset, which gets its
+ default at build time.
+
+ When the "w" flag is set on a rule that causes an envelope address to be
+ rewritten, all but the working part of the replacement address is
+ discarded.
+
+
+31.11 Rewriting examples
+------------------------
+
+Here is an example of the two common rewriting paradigms:
+
+*@*.hitch.fict.example $1@hitch.fict.example
+*@hitch.fict.example ${lookup{$1}dbm{/etc/realnames}\
+ {$value}fail}@hitch.fict.example bctfrF
+
+Note the use of "fail" in the lookup expansion in the second rule, forcing the
+string expansion to fail if the lookup does not succeed. In this context it has
+the effect of leaving the original address unchanged, but Exim goes on to
+consider subsequent rewriting rules, if any, because the "q" flag is not
+present in that rule. An alternative to "fail" would be to supply $1
+explicitly, which would cause the rewritten address to be the same as before,
+at the cost of a small bit of processing. Not supplying either of these is an
+error, since the rewritten address would then contain no local part.
+
+The first example above replaces the domain with a superior, more general
+domain. This may not be desirable for certain local parts. If the rule
+
+root@*.hitch.fict.example *
+
+were inserted before the first rule, rewriting would be suppressed for the
+local part root at any domain ending in hitch.fict.example.
+
+Rewriting can be made conditional on a number of tests, by making use of ${if
+in the expansion item. For example, to apply a rewriting rule only to messages
+that originate outside the local host:
+
+*@*.hitch.fict.example "${if !eq {$sender_host_address}{}\
+ {$1@hitch.fict.example}fail}"
+
+The replacement string is quoted in this example because it contains white
+space.
+
+Exim does not handle addresses in the form of "bang paths". If it sees such an
+address it treats it as an unqualified local part which it qualifies with the
+local qualification domain (if the source of the message is local or if the
+remote host is permitted to send unqualified addresses). Rewriting can
+sometimes be used to handle simple bang paths with a fixed number of
+components. For example, the rule
+
+\N^([^!]+)!(.*)@your.domain.example$\N $2@$1
+
+rewrites a two-component bang path host.name!user as the domain address
+user@host.name. However, there is a security implication in using this as a
+global rewriting rule for envelope addresses. It can provide a backdoor method
+for using your system as a relay, because the incoming addresses appear to be
+local. If the bang path addresses are received via SMTP, it is safer to use the
+"S" flag to rewrite them as they are received, so that relay checking can be
+done on the rewritten addresses.
+
+
+
+===============================================================================
+32. RETRY CONFIGURATION
+
+The "retry" section of the runtime configuration file contains a list of retry
+rules that control how often Exim tries to deliver messages that cannot be
+delivered at the first attempt. If there are no retry rules (the section is
+empty or not present), there are no retries. In this situation, temporary
+errors are treated as permanent. The default configuration contains a single,
+general-purpose retry rule (see section 7.6). The -brt command line option can
+be used to test which retry rule will be used for a given address, domain and
+error.
+
+The most common cause of retries is temporary failure to deliver to a remote
+host because the host is down, or inaccessible because of a network problem.
+Exim's retry processing in this case is applied on a per-host (strictly, per IP
+address) basis, not on a per-message basis. Thus, if one message has recently
+been delayed, delivery of a new message to the same host is not immediately
+tried, but waits for the host's retry time to arrive. If the retry_defer log
+selector is set, the message "retry time not reached" is written to the main
+log whenever a delivery is skipped for this reason. Section 49.2 contains more
+details of the handling of errors during remote deliveries.
+
+Retry processing applies to routing as well as to delivering, except as covered
+in the next paragraph. The retry rules do not distinguish between these
+actions. It is not possible, for example, to specify different behaviour for
+failures to route the domain snark.fict.example and failures to deliver to the
+host snark.fict.example. I didn't think anyone would ever need this added
+complication, so did not implement it. However, although they share the same
+retry rule, the actual retry times for routing and transporting a given domain
+are maintained independently.
+
+When a delivery is not part of a queue run (typically an immediate delivery on
+receipt of a message), the routers are always run, and local deliveries are
+always attempted, even if retry times are set for them. This makes for better
+behaviour if one particular message is causing problems (for example, causing
+quota overflow, or provoking an error in a filter file). If such a delivery
+suffers a temporary failure, the retry data is updated as normal, and
+subsequent delivery attempts from queue runs occur only when the retry time for
+the local address is reached.
+
+
+32.1 Changing retry rules
+-------------------------
+
+If you change the retry rules in your configuration, you should consider
+whether or not to delete the retry data that is stored in Exim's spool area in
+files with names like db/retry. Deleting any of Exim's hints files is always
+safe; that is why they are called "hints".
+
+The hints retry data contains suggested retry times based on the previous
+rules. In the case of a long-running problem with a remote host, it might
+record the fact that the host has timed out. If your new rules increase the
+timeout time for such a host, you should definitely remove the old retry data
+and let Exim recreate it, based on the new rules. Otherwise Exim might bounce
+messages that it should now be retaining.
+
+
+32.2 Format of retry rules
+--------------------------
+
+Each retry rule occupies one line and consists of three or four parts,
+separated by white space: a pattern, an error name, an optional list of sender
+addresses, and a list of retry parameters. The pattern and sender lists must be
+enclosed in double quotes if they contain white space. The rules are searched
+in order until one is found where the pattern, error name, and sender list (if
+present) match the failing host or address, the error that occurred, and the
+message's sender, respectively.
+
+The pattern is any single item that may appear in an address list (see section
+10.20). It is in fact processed as a one-item address list, which means that it
+is expanded before being tested against the address that has been delayed. A
+negated address list item is permitted. Address list processing treats a plain
+domain name as if it were preceded by "*@", which makes it possible for many
+retry rules to start with just a domain. For example,
+
+lookingglass.fict.example * F,24h,30m;
+
+provides a rule for any address in the lookingglass.fict.example domain,
+whereas
+
+alice@lookingglass.fict.example * F,24h,30m;
+
+applies only to temporary failures involving the local part alice. In practice,
+almost all rules start with a domain name pattern without a local part.
+
+Warning: If you use a regular expression in a retry rule pattern, it must match
+a complete address, not just a domain, because that is how regular expressions
+work in address lists.
+
+^\Nxyz\d+\.abc\.example$\N * G,1h,10m,2 Wrong
+^\N[^@]+@xyz\d+\.abc\.example$\N * G,1h,10m,2 Right
+
+
+32.3 Choosing which retry rule to use for address errors
+--------------------------------------------------------
+
+When Exim is looking for a retry rule after a routing attempt has failed (for
+example, after a DNS timeout), each line in the retry configuration is tested
+against the complete address only if retry_use_local_part is set for the
+router. Otherwise, only the domain is used, except when matching against a
+regular expression, when the local part of the address is replaced with "*". A
+domain on its own can match a domain pattern, or a pattern that starts with
+"*@". By default, retry_use_local_part is true for routers where
+check_local_user is true, and false for other routers.
+
+Similarly, when Exim is looking for a retry rule after a local delivery has
+failed (for example, after a mailbox full error), each line in the retry
+configuration is tested against the complete address only if
+retry_use_local_part is set for the transport (it defaults true for all local
+transports).
+
+However, when Exim is looking for a retry rule after a remote delivery attempt
+suffers an address error (a 4xx SMTP response for a recipient address), the
+whole address is always used as the key when searching the retry rules. The
+rule that is found is used to create a retry time for the combination of the
+failing address and the message's sender. It is the combination of sender and
+recipient that is delayed in subsequent queue runs until its retry time is
+reached. You can delay the recipient without regard to the sender by setting
+address_retry_include_sender false in the smtp transport but this can lead to
+problems with servers that regularly issue 4xx responses to RCPT commands.
+
+
+32.4 Choosing which retry rule to use for host and message errors
+-----------------------------------------------------------------
+
+For a temporary error that is not related to an individual address (for
+example, a connection timeout), each line in the retry configuration is checked
+twice. First, the name of the remote host is used as a domain name (preceded by
+"*@" when matching a regular expression). If this does not match the line, the
+domain from the email address is tried in a similar fashion. For example,
+suppose the MX records for a.b.c.example are
+
+a.b.c.example MX 5 x.y.z.example
+ MX 6 p.q.r.example
+ MX 7 m.n.o.example
+
+and the retry rules are
+
+p.q.r.example * F,24h,30m;
+a.b.c.example * F,4d,45m;
+
+and a delivery to the host x.y.z.example suffers a connection failure. The
+first rule matches neither the host nor the domain, so Exim looks at the second
+rule. This does not match the host, but it does match the domain, so it is used
+to calculate the retry time for the host x.y.z.example. Meanwhile, Exim tries
+to deliver to p.q.r.example. If this also suffers a host error, the first retry
+rule is used, because it matches the host.
+
+In other words, temporary failures to deliver to host p.q.r.example use the
+first rule to determine retry times, but for all the other hosts for the domain
+a.b.c.example, the second rule is used. The second rule is also used if routing
+to a.b.c.example suffers a temporary failure.
+
+Note: The host name is used when matching the patterns, not its IP address.
+However, if a message is routed directly to an IP address without the use of a
+host name, for example, if a manualroute router contains a setting such as:
+
+route_list = *.a.example 192.168.34.23
+
+then the "host name" that is used when searching for a retry rule is the
+textual form of the IP address.
+
+
+32.5 Retry rules for specific errors
+------------------------------------
+
+The second field in a retry rule is the name of a particular error, or an
+asterisk, which matches any error. The errors that can be tested for are:
+
+auth_failed
+
+ Authentication failed when trying to send to a host in the
+ hosts_require_auth list in an smtp transport.
+
+data_4xx
+
+ A 4xx error was received for an outgoing DATA command, either immediately
+ after the command, or after sending the message's data.
+
+mail_4xx
+
+ A 4xx error was received for an outgoing MAIL command.
+
+rcpt_4xx
+
+ A 4xx error was received for an outgoing RCPT command.
+
+For the three 4xx errors, either the first or both of the x's can be given as
+specific digits, for example: "mail_45x" or "rcpt_436". For example, to
+recognize 452 errors given to RCPT commands for addresses in a certain domain,
+and have retries every ten minutes with a one-hour timeout, you could set up a
+retry rule of this form:
+
+the.domain.name rcpt_452 F,1h,10m
+
+These errors apply to both outgoing SMTP (the smtp transport) and outgoing LMTP
+(either the lmtp transport, or the smtp transport in LMTP mode).
+
+lost_connection
+
+ A server unexpectedly closed the SMTP connection. There may, of course,
+ legitimate reasons for this (host died, network died), but if it repeats a
+ lot for the same host, it indicates something odd.
+
+lookup
+
+ A DNS lookup for a host failed. Note that a dnslookup router will need to
+ have matched its fail_defer_domains option for this retry type to be
+ usable. Also note that a manualroute router will probably need its
+ host_find_failed option set to defer.
+
+refused_MX
+
+ A connection to a host obtained from an MX record was refused.
+
+refused_A
+
+ A connection to a host not obtained from an MX record was refused.
+
+refused
+
+ A connection was refused.
+
+timeout_connect_MX
+
+ A connection attempt to a host obtained from an MX record timed out.
+
+timeout_connect_A
+
+ A connection attempt to a host not obtained from an MX record timed out.
+
+timeout_connect
+
+ A connection attempt timed out.
+
+timeout_MX
+
+ There was a timeout while connecting or during an SMTP session with a host
+ obtained from an MX record.
+
+timeout_A
+
+ There was a timeout while connecting or during an SMTP session with a host
+ not obtained from an MX record.
+
+timeout
+
+ There was a timeout while connecting or during an SMTP session.
+
+tls_required
+
+ The server was required to use TLS (it matched hosts_require_tls in the
+ smtp transport), but either did not offer TLS, or it responded with 4xx to
+ STARTTLS, or there was a problem setting up the TLS connection.
+
+quota
+
+ A mailbox quota was exceeded in a local delivery by the appendfile
+ transport.
+
+quota_<time>
+
+ A mailbox quota was exceeded in a local delivery by the appendfile
+ transport, and the mailbox has not been accessed for <time>. For example,
+ quota_4d applies to a quota error when the mailbox has not been accessed
+ for four days.
+
+The idea of quota_<time> is to make it possible to have shorter timeouts when
+the mailbox is full and is not being read by its owner. Ideally, it should be
+based on the last time that the user accessed the mailbox. However, it is not
+always possible to determine this. Exim uses the following heuristic rules:
+
+ * If the mailbox is a single file, the time of last access (the "atime") is
+ used. As no new messages are being delivered (because the mailbox is over
+ quota), Exim does not access the file, so this is the time of last user
+ access.
+
+ * For a maildir delivery, the time of last modification of the new
+ subdirectory is used. As the mailbox is over quota, no new files are
+ created in the new subdirectory, because no new messages are being
+ delivered. Any change to the new subdirectory is therefore assumed to be
+ the result of an MUA moving a new message to the cur directory when it is
+ first read. The time that is used is therefore the last time that the user
+ read a new message.
+
+ * For other kinds of multi-file mailbox, the time of last access cannot be
+ obtained, so a retry rule that uses this type of error field is never
+ matched.
+
+The quota errors apply both to system-enforced quotas and to Exim's own quota
+mechanism in the appendfile transport. The quota error also applies when a
+local delivery is deferred because a partition is full (the ENOSPC error).
+
+
+32.6 Retry rules for specified senders
+--------------------------------------
+
+You can specify retry rules that apply only when the failing message has a
+specific sender. In particular, this can be used to define retry rules that
+apply only to bounce messages. The third item in a retry rule can be of this
+form:
+
+senders=<address list>
+
+The retry timings themselves are then the fourth item. For example:
+
+* rcpt_4xx senders=: F,1h,30m
+
+matches recipient 4xx errors for bounce messages sent to any address at any
+host. If the address list contains white space, it must be enclosed in quotes.
+For example:
+
+a.domain rcpt_452 senders="xb.dom : yc.dom" G,8h,10m,1.5
+
+Warning: This facility can be unhelpful if it is used for host errors (which do
+not depend on the recipient). The reason is that the sender is used only to
+match the retry rule. Once the rule has been found for a host error, its
+contents are used to set a retry time for the host, and this will apply to all
+messages, not just those with specific senders.
+
+When testing retry rules using -brt, you can supply a sender using the -f
+command line option, like this:
+
+exim -f "" -brt user@dom.ain
+
+If you do not set -f with -brt, a retry rule that contains a senders list is
+never matched.
+
+
+32.7 Retry parameters
+---------------------
+
+The third (or fourth, if a senders list is present) field in a retry rule is a
+sequence of retry parameter sets, separated by semicolons. Each set consists of
+
+<letter>,<cutoff time>,<arguments>
+
+The letter identifies the algorithm for computing a new retry time; the cutoff
+time is the time beyond which this algorithm no longer applies, and the
+arguments vary the algorithm's action. The cutoff time is measured from the
+time that the first failure for the domain (combined with the local part if
+relevant) was detected, not from the time the message was received.
+
+The available algorithms are:
+
+ * F: retry at fixed intervals. There is a single time parameter specifying
+ the interval.
+
+ * G: retry at geometrically increasing intervals. The first argument
+ specifies a starting value for the interval, and the second a multiplier,
+ which is used to increase the size of the interval at each retry.
+
+ * H: retry at randomized intervals. The arguments are as for G. For each
+ retry, the previous interval is multiplied by the factor in order to get a
+ maximum for the next interval. The minimum interval is the first argument
+ of the parameter, and an actual interval is chosen randomly between them.
+ Such a rule has been found to be helpful in cluster configurations when all
+ the members of the cluster restart at once, and may therefore synchronize
+ their queue processing times.
+
+When computing the next retry time, the algorithm definitions are scanned in
+order until one whose cutoff time has not yet passed is reached. This is then
+used to compute a new retry time that is later than the current time. In the
+case of fixed interval retries, this simply means adding the interval to the
+current time. For geometrically increasing intervals, retry intervals are
+computed from the rule's parameters until one that is greater than the previous
+interval is found. The main configuration variable retry_interval_max limits
+the maximum interval between retries. It cannot be set greater than "24h",
+which is its default value.
+
+A single remote domain may have a number of hosts associated with it, and each
+host may have more than one IP address. Retry algorithms are selected on the
+basis of the domain name, but are applied to each IP address independently. If,
+for example, a host has two IP addresses and one is unusable, Exim will
+generate retry times for it and will not try to use it until its next retry
+time comes. Thus the good IP address is likely to be tried first most of the
+time.
+
+Retry times are hints rather than promises. Exim does not make any attempt to
+run deliveries exactly at the computed times. Instead, a queue runner process
+starts delivery processes for delayed messages periodically, and these attempt
+new deliveries only for those addresses that have passed their next retry time.
+If a new message arrives for a deferred address, an immediate delivery attempt
+occurs only if the address has passed its retry time. In the absence of new
+messages, the minimum time between retries is the interval between queue runner
+processes. There is not much point in setting retry times of five minutes if
+your queue runners happen only once an hour, unless there are a significant
+number of incoming messages (which might be the case on a system that is
+sending everything to a smart host, for example).
+
+The data in the retry hints database can be inspected by using the exim_dumpdb
+or exim_fixdb utility programs (see chapter 54). The latter utility can also be
+used to change the data. The exinext utility script can be used to find out
+what the next retry times are for the hosts associated with a particular mail
+domain, and also for local deliveries that have been deferred.
+
+
+32.8 Retry rule examples
+------------------------
+
+Here are some example retry rules:
+
+alice@wonderland.fict.example quota_5d F,7d,3h
+wonderland.fict.example quota_5d
+wonderland.fict.example * F,1h,15m; G,2d,1h,2;
+lookingglass.fict.example * F,24h,30m;
+* refused_A F,2h,20m;
+* * F,2h,15m; G,16h,1h,1.5; F,5d,8h
+
+The first rule sets up special handling for mail to
+alice@wonderland.fict.example when there is an over-quota error and the mailbox
+has not been read for at least 5 days. Retries continue every three hours for 7
+days. The second rule handles over-quota errors for all other local parts at
+wonderland.fict.example; the absence of a local part has the same effect as
+supplying "*@". As no retry algorithms are supplied, messages that fail are
+bounced immediately if the mailbox has not been read for at least 5 days.
+
+The third rule handles all other errors at wonderland.fict.example; retries
+happen every 15 minutes for an hour, then with geometrically increasing
+intervals until two days have passed since a delivery first failed. After the
+first hour there is a delay of one hour, then two hours, then four hours, and
+so on (this is a rather extreme example).
+
+The fourth rule controls retries for the domain lookingglass.fict.example. They
+happen every 30 minutes for 24 hours only. The remaining two rules handle all
+other domains, with special action for connection refusal from hosts that were
+not obtained from an MX record.
+
+The final rule in a retry configuration should always have asterisks in the
+first two fields so as to provide a general catch-all for any addresses that do
+not have their own special handling. This example tries every 15 minutes for 2
+hours, then with intervals starting at one hour and increasing by a factor of
+1.5 up to 16 hours, then every 8 hours up to 5 days.
+
+
+32.9 Timeout of retry data
+--------------------------
+
+Exim timestamps the data that it writes to its retry hints database. When it
+consults the data during a delivery it ignores any that is older than the value
+set in retry_data_expire (default 7 days). If, for example, a host hasn't been
+tried for 7 days, Exim will try to deliver to it immediately a message arrives,
+and if that fails, it will calculate a retry time as if it were failing for the
+first time.
+
+This improves the behaviour for messages routed to rarely-used hosts such as MX
+backups. If such a host was down at one time, and happens to be down again when
+Exim tries a month later, using the old retry data would imply that it had been
+down all the time, which is not a justified assumption.
+
+If a host really is permanently dead, this behaviour causes a burst of retries
+every now and again, but only if messages routed to it are rare. If there is a
+message at least once every 7 days the retry data never expires.
+
+
+32.10 Long-term failures
+------------------------
+
+Special processing happens when an email address has been failing for so long
+that the cutoff time for the last algorithm is reached. For example, using the
+default retry rule:
+
+* * F,2h,15m; G,16h,1h,1.5; F,4d,6h
+
+the cutoff time is four days. Reaching the retry cutoff is independent of how
+long any specific message has been failing; it is the length of continuous
+failure for the recipient address that counts.
+
+When the cutoff time is reached for a local delivery, or for all the IP
+addresses associated with a remote delivery, a subsequent delivery failure
+causes Exim to give up on the address, and a bounce message is generated. In
+order to cater for new messages that use the failing address, a next retry time
+is still computed from the final algorithm, and is used as follows:
+
+For local deliveries, one delivery attempt is always made for any subsequent
+messages. If this delivery fails, the address fails immediately. The
+post-cutoff retry time is not used.
+
+If the delivery is remote, there are two possibilities, controlled by the
+delay_after_cutoff option of the smtp transport. The option is true by default.
+Until the post-cutoff retry time for one of the IP addresses, as set by the
+retry_data_expire option, is reached, the failing email address is bounced
+immediately, without a delivery attempt taking place. After that time, one new
+delivery attempt is made to those IP addresses that are past their retry times,
+and if that still fails, the address is bounced and new retry times are
+computed.
+
+In other words, when all the hosts for a given email address have been failing
+for a long time, Exim bounces rather then defers until one of the hosts' retry
+times is reached. Then it tries once, and bounces if that attempt fails. This
+behaviour ensures that few resources are wasted in repeatedly trying to deliver
+to a broken destination, but if the host does recover, Exim will eventually
+notice.
+
+If delay_after_cutoff is set false, Exim behaves differently. If all IP
+addresses are past their final cutoff time, Exim tries to deliver to those IP
+addresses that have not been tried since the message arrived. If there are no
+suitable IP addresses, or if they all fail, the address is bounced. In other
+words, it does not delay when a new message arrives, but tries the expired
+addresses immediately, unless they have been tried since the message arrived.
+If there is a continuous stream of messages for the failing domains, setting
+delay_after_cutoff false means that there will be many more attempts to deliver
+to permanently failing IP addresses than when delay_after_cutoff is true.
+
+
+32.11 Deliveries that work intermittently
+-----------------------------------------
+
+Some additional logic is needed to cope with cases where a host is
+intermittently available, or when a message has some attribute that prevents
+its delivery when others to the same address get through. In this situation,
+because some messages are successfully delivered, the "retry clock" for the
+host or address keeps getting reset by the successful deliveries, and so
+failing messages remain in the queue for ever because the cutoff time is never
+reached.
+
+Two exceptional actions are applied to prevent this happening. The first
+applies to errors that are related to a message rather than a remote host.
+Section 49.2 has a discussion of the different kinds of error; examples of
+message-related errors are 4xx responses to MAIL or DATA commands, and quota
+failures. For this type of error, if a message's arrival time is earlier than
+the "first failed" time for the error, the earlier time is used when scanning
+the retry rules to decide when to try next and when to time out the address.
+
+The exceptional second action applies in all cases. If a message has been on
+the queue for longer than the cutoff time of any applicable retry rule for a
+given address, a delivery is attempted for that address, even if it is not yet
+time, and if this delivery fails, the address is timed out. A new retry time is
+not computed in this case, so that other messages for the same address are
+considered immediately.
+
+
+
+===============================================================================
+33. SMTP AUTHENTICATION
+
+The "authenticators" section of Exim's runtime configuration is concerned with
+SMTP authentication. This facility is an extension to the SMTP protocol,
+described in RFC 2554, which allows a client SMTP host to authenticate itself
+to a server. This is a common way for a server to recognize clients that are
+permitted to use it as a relay. SMTP authentication is not of relevance to the
+transfer of mail between servers that have no managerial connection with each
+other.
+
+The name of an authenticator is limited to be 64 ASCII characters long; prior
+to Exim 4.95 names would be silently truncated at this length, but now it is
+enforced.
+
+Very briefly, the way SMTP authentication works is as follows:
+
+ * The server advertises a number of authentication mechanisms in response to
+ the client's EHLO command.
+
+ * The client issues an AUTH command, naming a specific mechanism. The command
+ may, optionally, contain some authentication data.
+
+ * The server may issue one or more challenges, to which the client must send
+ appropriate responses. In simple authentication mechanisms, the challenges
+ are just prompts for user names and passwords. The server does not have to
+ issue any challenges - in some mechanisms the relevant data may all be
+ transmitted with the AUTH command.
+
+ * The server either accepts or denies authentication.
+
+ * If authentication succeeds, the client may optionally make use of the AUTH
+ option on the MAIL command to pass an authenticated sender in subsequent
+ mail transactions. Authentication lasts for the remainder of the SMTP
+ connection.
+
+ * If authentication fails, the client may give up, or it may try a different
+ authentication mechanism, or it may try transferring mail over the
+ unauthenticated connection.
+
+If you are setting up a client, and want to know which authentication
+mechanisms the server supports, you can use Telnet to connect to port 25 (the
+SMTP port) on the server, and issue an EHLO command. The response to this
+includes the list of supported mechanisms. For example:
+
+$ telnet server.example 25
+Trying 192.168.34.25...
+Connected to server.example.
+Escape character is '^]'.
+220 server.example ESMTP Exim 4.20 ...
+ehlo client.example
+250-server.example Hello client.example [10.8.4.5]
+250-SIZE 52428800
+250-PIPELINING
+250-AUTH PLAIN
+250 HELP
+
+The second-last line of this example output shows that the server supports
+authentication using the PLAIN mechanism. In Exim, the different authentication
+mechanisms are configured by specifying authenticator drivers. Like the routers
+and transports, which authenticators are included in the binary is controlled
+by build-time definitions. The following are currently available, included by
+setting
+
+AUTH_CRAM_MD5=yes
+AUTH_CYRUS_SASL=yes
+AUTH_DOVECOT=yes
+AUTH_EXTERNAL=yes
+AUTH_GSASL=yes
+AUTH_HEIMDAL_GSSAPI=yes
+AUTH_PLAINTEXT=yes
+AUTH_SPA=yes
+AUTH_TLS=yes
+
+in Local/Makefile, respectively. The first of these supports the CRAM-MD5
+authentication mechanism (RFC 2195), and the second provides an interface to
+the Cyrus SASL authentication library. The third is an interface to Dovecot's
+authentication system, delegating the work via a socket interface. The fourth
+provides for negotiation of authentication done via non-SMTP means, as defined
+by RFC 4422 Appendix A. The fifth provides an interface to the GNU SASL
+authentication library, which provides mechanisms but typically not data
+sources. The sixth provides direct access to Heimdal GSSAPI, geared for
+Kerberos, but supporting setting a server keytab. The seventh can be configured
+to support the PLAIN authentication mechanism (RFC 2595) or the LOGIN
+mechanism, which is not formally documented, but used by several MUAs. The
+eighth authenticator supports Microsoft's Secure Password Authentication
+mechanism. The last is an Exim authenticator but not an SMTP one; instead it
+can use information from a TLS negotiation.
+
+The authenticators are configured using the same syntax as other drivers (see
+section 6.23). If no authenticators are required, no authentication section
+need be present in the configuration file. Each authenticator can in principle
+have both server and client functions. When Exim is receiving SMTP mail, it is
+acting as a server; when it is sending out messages over SMTP, it is acting as
+a client. Authenticator configuration options are provided for use in both
+these circumstances.
+
+To make it clear which options apply to which situation, the prefixes server_
+and client_ are used on option names that are specific to either the server or
+the client function, respectively. Server and client functions are disabled if
+none of their options are set. If an authenticator is to be used for both
+server and client functions, a single definition, using both sets of options,
+is required. For example:
+
+cram:
+ driver = cram_md5
+ public_name = CRAM-MD5
+ server_secret = ${if eq{$auth1}{ph10}{secret1}fail}
+ client_name = ph10
+ client_secret = secret2
+
+The server_ option is used when Exim is acting as a server, and the client_
+options when it is acting as a client.
+
+Descriptions of the individual authenticators are given in subsequent chapters.
+The remainder of this chapter covers the generic options for the
+authenticators, followed by general discussion of the way authentication works
+in Exim.
+
+Beware: the meaning of $auth1, $auth2, ... varies on a per-driver and
+per-mechanism basis. Please read carefully to determine which variables hold
+account labels such as usercodes and which hold passwords or other
+authenticating data.
+
+Note that some mechanisms support two different identifiers for accounts: the
+authentication id and the authorization id. The contractions authn and authz
+are commonly encountered. The American spelling is standard here. Conceptually,
+authentication data such as passwords are tied to the identifier used to
+authenticate; servers may have rules to permit one user to act as a second
+user, so that after login the session is treated as though that second user had
+logged in. That second user is the authorization id. A robust configuration
+might confirm that the authz field is empty or matches the authn field. Often
+this is just ignored. The authn can be considered as verified data, the authz
+as an unverified request which the server might choose to honour.
+
+A realm is a text string, typically a domain name, presented by a server to a
+client to help it select an account and credentials to use. In some mechanisms,
+the client and server provably agree on the realm, but clients typically can
+not treat the realm as secure data to be blindly trusted.
+
+
+33.1 Generic options for authenticators
+---------------------------------------
+
++-----------------------------------------------------------------+
+|client_condition|Use: authenticators|Type: string*|Default: unset|
++-----------------------------------------------------------------+
+
+When Exim is authenticating as a client, it skips any authenticator whose
+client_condition expansion yields "0", "no", or "false". This can be used, for
+example, to skip plain text authenticators when the connection is not encrypted
+by a setting such as:
+
+client_condition = ${if !eq{$tls_out_cipher}{}}
+
++--------------------------------------------------------------+
+|client_set_id|Use: authenticators|Type: string*|Default: unset|
++--------------------------------------------------------------+
+
+When client authentication succeeds, this condition is expanded; the result is
+used in the log lines for outbound messages. Typically it will be the user name
+used for authentication.
+
++------------------------------------------------------+
+|driver|Use: authenticators|Type: string|Default: unset|
++------------------------------------------------------+
+
+This option must always be set. It specifies which of the available
+authenticators is to be used.
+
++-----------------------------------------------------------+
+|public_name|Use: authenticators|Type: string|Default: unset|
++-----------------------------------------------------------+
+
+This option specifies the name of the authentication mechanism that the driver
+implements, and by which it is known to the outside world. These names should
+contain only upper case letters, digits, underscores, and hyphens (RFC 2222),
+but Exim in fact matches them caselessly. If public_name is not set, it
+defaults to the driver's instance name.
+
++---------------------------------------------------------------------------+
+|server_advertise_condition|Use: authenticators|Type: string*|Default: unset|
++---------------------------------------------------------------------------+
+
+When a server is about to advertise an authentication mechanism, the condition
+is expanded. If it yields the empty string, "0", "no", or "false", the
+mechanism is not advertised. If the expansion fails, the mechanism is not
+advertised. If the failure was not forced, and was not caused by a lookup
+defer, the incident is logged. See section 33.3 below for further discussion.
+
++-----------------------------------------------------------------+
+|server_condition|Use: authenticators|Type: string*|Default: unset|
++-----------------------------------------------------------------+
+
+This option must be set for a plaintext server authenticator, where it is used
+directly to control authentication. See section 34.3 for details.
+
+For the gsasl authenticator, this option is required for various mechanisms;
+see chapter 38 for details.
+
+For the other authenticators, server_condition can be used as an additional
+authentication or authorization mechanism that is applied after the other
+authenticator conditions succeed. If it is set, it is expanded when the
+authenticator would otherwise return a success code. If the expansion is forced
+to fail, authentication fails. Any other expansion failure causes a temporary
+error code to be returned. If the result of a successful expansion is an empty
+string, "0", "no", or "false", authentication fails. If the result of the
+expansion is "1", "yes", or "true", authentication succeeds. For any other
+result, a temporary error code is returned, with the expanded string as the
+error text.
+
++-------------------------------------------------------------------+
+|server_debug_print|Use: authenticators|Type: string*|Default: unset|
++-------------------------------------------------------------------+
+
+If this option is set and authentication debugging is enabled (see the -d
+command line option), the string is expanded and included in the debugging
+output when the authenticator is run as a server. This can help with checking
+out the values of variables. If expansion of the string fails, the error
+message is written to the debugging output, and Exim carries on processing.
+
++--------------------------------------------------------------+
+|server_set_id|Use: authenticators|Type: string*|Default: unset|
++--------------------------------------------------------------+
+
+When an Exim server successfully authenticates a client, this string is
+expanded using data from the authentication, and preserved for any incoming
+messages in the variable $authenticated_id. It is also included in the log
+lines for incoming messages. For example, a user/password authenticator
+configuration might preserve the user name that was used to authenticate, and
+refer to it subsequently during delivery of the message. On a failing
+authentication the expansion result is instead saved in the
+$authenticated_fail_id variable. If expansion fails, the option is ignored.
+
++---------------------------------------------------------------------------+
+|server_mail_auth_condition|Use: authenticators|Type: string*|Default: unset|
++---------------------------------------------------------------------------+
+
+This option allows a server to discard authenticated sender addresses supplied
+as part of MAIL commands in SMTP connections that are authenticated by the
+driver on which server_mail_auth_condition is set. The option is not used as
+part of the authentication process; instead its (unexpanded) value is
+remembered for later use. How it is used is described in the following section.
+
+
+33.2 The AUTH parameter on MAIL commands
+----------------------------------------
+
+When a client supplied an AUTH= item on a MAIL command, Exim applies the
+following checks before accepting it as the authenticated sender of the
+message:
+
+ * If the connection is not using extended SMTP (that is, HELO was used rather
+ than EHLO), the use of AUTH= is a syntax error.
+
+ * If the value of the AUTH= parameter is "<>", it is ignored.
+
+ * If acl_smtp_mailauth is defined, the ACL it specifies is run. While it is
+ running, the value of $authenticated_sender is set to the value obtained
+ from the AUTH= parameter. If the ACL does not yield "accept", the value of
+ $authenticated_sender is deleted. The acl_smtp_mailauth ACL may not return
+ "drop" or "discard". If it defers, a temporary error code (451) is given
+ for the MAIL command.
+
+ * If acl_smtp_mailauth is not defined, the value of the AUTH= parameter is
+ accepted and placed in $authenticated_sender only if the client has
+ authenticated.
+
+ * If the AUTH= value was accepted by either of the two previous rules, and
+ the client has authenticated, and the authenticator has a setting for the
+ server_mail_auth_condition, the condition is checked at this point. The
+ valued that was saved from the authenticator is expanded. If the expansion
+ fails, or yields an empty string, "0", "no", or "false", the value of
+ $authenticated_sender is deleted. If the expansion yields any other value,
+ the value of $authenticated_sender is retained and passed on with the
+ message.
+
+When $authenticated_sender is set for a message, it is passed on to other hosts
+to which Exim authenticates as a client. Do not confuse this value with
+$authenticated_id, which is a string obtained from the authentication process,
+and which is not usually a complete email address.
+
+Whenever an AUTH= value is ignored, the incident is logged. The ACL for MAIL,
+if defined, is run after AUTH= is accepted or ignored. It can therefore make
+use of $authenticated_sender. The converse is not true: the value of
+$sender_address is not yet set up when the acl_smtp_mailauth ACL is run.
+
+
+33.3 Authentication on an Exim server
+-------------------------------------
+
+When Exim receives an EHLO command, it advertises the public names of those
+authenticators that are configured as servers, subject to the following
+conditions:
+
+ * The client host must match auth_advertise_hosts (default *).
+
+ * It the server_advertise_condition option is set, its expansion must not
+ yield the empty string, "0", "no", or "false".
+
+The order in which the authenticators are defined controls the order in which
+the mechanisms are advertised.
+
+Some mail clients (for example, some versions of Netscape) require the user to
+provide a name and password for authentication whenever AUTH is advertised,
+even though authentication may not in fact be needed (for example, Exim may be
+set up to allow unconditional relaying from the client by an IP address check).
+You can make such clients more friendly by not advertising AUTH to them. For
+example, if clients on the 10.9.8.0/24 network are permitted (by the ACL that
+runs for RCPT) to relay without authentication, you should set
+
+auth_advertise_hosts = ! 10.9.8.0/24
+
+so that no authentication mechanisms are advertised to them.
+
+The server_advertise_condition controls the advertisement of individual
+authentication mechanisms. For example, it can be used to restrict the
+advertisement of a particular mechanism to encrypted connections, by a setting
+such as:
+
+server_advertise_condition = ${if eq{$tls_in_cipher}{}{no}{yes}}
+
+If the session is encrypted, $tls_in_cipher is not empty, and so the expansion
+yields "yes", which allows the advertisement to happen.
+
+When an Exim server receives an AUTH command from a client, it rejects it
+immediately if AUTH was not advertised in response to an earlier EHLO command.
+This is the case if
+
+ * The client host does not match auth_advertise_hosts; or
+
+ * No authenticators are configured with server options; or
+
+ * Expansion of server_advertise_condition blocked the advertising of all the
+ server authenticators.
+
+Otherwise, Exim runs the ACL specified by acl_smtp_auth in order to decide
+whether to accept the command. If acl_smtp_auth is not set, AUTH is accepted
+from any client host.
+
+If AUTH is not rejected by the ACL, Exim searches its configuration for a
+server authentication mechanism that was advertised in response to EHLO and
+that matches the one named in the AUTH command. If it finds one, it runs the
+appropriate authentication protocol, and authentication either succeeds or
+fails. If there is no matching advertised mechanism, the AUTH command is
+rejected with a 504 error.
+
+When a message is received from an authenticated host, the value of
+$received_protocol is set to "esmtpa" or "esmtpsa" instead of "esmtp" or
+"esmtps", and $sender_host_authenticated contains the name (not the public
+name) of the authenticator driver that successfully authenticated the client
+from which the message was received. This variable is empty if there was no
+successful authentication.
+
+Successful authentication sets up information used by the authresults expansion
+item.
+
+
+33.4 Testing server authentication
+----------------------------------
+
+Exim's -bh option can be useful for testing server authentication
+configurations. The data for the AUTH command has to be sent using base64
+encoding. A quick way to produce such data for testing is the following Perl
+script:
+
+use MIME::Base64;
+printf ("%s", encode_base64(eval "\"$ARGV[0]\""));
+
+This interprets its argument as a Perl string, and then encodes it. The
+interpretation as a Perl string allows binary zeros, which are required for
+some kinds of authentication, to be included in the data. For example, a
+command line to run this script on such data might be
+
+encode '\0user\0password'
+
+Note the use of single quotes to prevent the shell interpreting the
+backslashes, so that they can be interpreted by Perl to specify characters
+whose code value is zero.
+
+Warning 1: If either of the user or password strings starts with an octal
+digit, you must use three zeros instead of one after the leading backslash. If
+you do not, the octal digit that starts your string will be incorrectly
+interpreted as part of the code for the first character.
+
+Warning 2: If there are characters in the strings that Perl interprets
+specially, you must use a Perl escape to prevent them being misinterpreted. For
+example, a command such as
+
+encode '\0user@domain.com\0pas$$word'
+
+gives an incorrect answer because of the unescaped "@" and "$" characters.
+
+If you have the mimencode command installed, another way to do produce
+base64-encoded strings is to run the command
+
+echo -e -n `\0user\0password' | mimencode
+
+The -e option of echo enables the interpretation of backslash escapes in the
+argument, and the -n option specifies no newline at the end of its output.
+However, not all versions of echo recognize these options, so you should check
+your version before relying on this suggestion.
+
+
+33.5 Authentication by an Exim client
+-------------------------------------
+
+The smtp transport has two options called hosts_require_auth and hosts_try_auth
+. When the smtp transport connects to a server that announces support for
+authentication, and the host matches an entry in either of these options, Exim
+(as a client) tries to authenticate as follows:
+
+ * For each authenticator that is configured as a client, in the order in
+ which they are defined in the configuration, it searches the authentication
+ mechanisms announced by the server for one whose name matches the public
+ name of the authenticator.
+
+ * When it finds one that matches, it runs the authenticator's client code.
+ The variables $host and $host_address are available for any string
+ expansions that the client might do. They are set to the server's name and
+ IP address. If any expansion is forced to fail, the authentication attempt
+ is abandoned, and Exim moves on to the next authenticator. Otherwise an
+ expansion failure causes delivery to be deferred.
+
+ * If the result of the authentication attempt is a temporary error or a
+ timeout, Exim abandons trying to send the message to the host for the
+ moment. It will try again later. If there are any backup hosts available,
+ they are tried in the usual way.
+
+ * If the response to authentication is a permanent error (5xx code), Exim
+ carries on searching the list of authenticators and tries another one if
+ possible. If all authentication attempts give permanent errors, or if there
+ are no attempts because no mechanisms match (or option expansions force
+ failure), what happens depends on whether the host matches
+ hosts_require_auth or hosts_try_auth. In the first case, a temporary error
+ is generated, and delivery is deferred. The error can be detected in the
+ retry rules, and thereby turned into a permanent error if you wish. In the
+ second case, Exim tries to deliver the message unauthenticated.
+
+Note that the hostlist test for whether to do authentication can be confused if
+name-IP lookups change between the time the peer is decided upon and the time
+that the transport runs. For example, with a manualroute router given a host
+name, and with DNS "round-robin" used by that name: if the local resolver cache
+times out between the router and the transport running, the transport may get
+an IP for the name for its authentication check which does not match the
+connection peer IP. No authentication will then be done, despite the names
+being identical.
+
+For such cases use a separate transport which always authenticates.
+
+When Exim has authenticated itself to a remote server, it adds the AUTH
+parameter to the MAIL commands it sends, if it has an authenticated sender for
+the message. If the message came from a remote host, the authenticated sender
+is the one that was receiving on an incoming MAIL command, provided that the
+incoming connection was authenticated and the server_mail_auth condition
+allowed the authenticated sender to be retained. If a local process calls Exim
+to send a message, the sender address that is built from the login name and
+qualify_domain is treated as authenticated. However, if the
+authenticated_sender option is set on the smtp transport, it overrides the
+authenticated sender that was received with the message.
+
+
+
+===============================================================================
+34. THE PLAINTEXT AUTHENTICATOR
+
+The plaintext authenticator can be configured to support the PLAIN and LOGIN
+authentication mechanisms, both of which transfer authentication data as plain
+(unencrypted) text (though base64 encoded). The use of plain text is a security
+risk; you are strongly advised to insist on the use of SMTP encryption (see
+chapter 43) if you use the PLAIN or LOGIN mechanisms. If you do use unencrypted
+plain text, you should not use the same passwords for SMTP connections as you
+do for login accounts.
+
+
+34.1 Avoiding cleartext use
+---------------------------
+
+The following generic option settings will disable plaintext authenticators
+when TLS is not being used:
+
+ server_advertise_condition = ${if def:tls_in_cipher }
+ client_condition = ${if def:tls_out_cipher}
+
+Note: a plaintext SMTP AUTH done inside TLS is not vulnerable to casual
+snooping, but is still vulnerable to a Man In The Middle attack unless
+certificates (including their names) have been properly verified.
+
+
+34.2 Plaintext server options
+-----------------------------
+
+When configured as a server, plaintext uses the following options:
+
++-----------------------------------------------------------------+
+|server_condition|Use: authenticators|Type: string*|Default: unset|
++-----------------------------------------------------------------+
+
+This is actually a global authentication option, but it must be set in order to
+configure the plaintext driver as a server. Its use is described below.
+
++---------------------------------------------------------------+
+|server_prompts|Use: plaintext|Type: string list*|Default: unset|
++---------------------------------------------------------------+
+
+The contents of this option, after expansion, must be a colon-separated list of
+prompt strings. If expansion fails, a temporary authentication rejection is
+given.
+
+
+34.3 Using plaintext in a server
+--------------------------------
+
+When running as a server, plaintext performs the authentication test by
+expanding a string. The data sent by the client with the AUTH command, or in
+response to subsequent prompts, is base64 encoded, and so may contain any byte
+values when decoded. If any data is supplied with the command, it is treated as
+a list of strings, separated by NULs (binary zeros), the first three of which
+are placed in the expansion variables $auth1, $auth2, and $auth3 (neither LOGIN
+nor PLAIN uses more than three strings).
+
+For compatibility with previous releases of Exim, the values are also placed in
+the expansion variables $1, $2, and $3. However, the use of these variables for
+this purpose is now deprecated, as it can lead to confusion in string
+expansions that also use them for other things.
+
+If there are more strings in server_prompts than the number of strings supplied
+with the AUTH command, the remaining prompts are used to obtain more data. Each
+response from the client may be a list of NUL-separated strings.
+
+Once a sufficient number of data strings have been received, server_condition
+is expanded. If the expansion is forced to fail, authentication fails. Any
+other expansion failure causes a temporary error code to be returned. If the
+result of a successful expansion is an empty string, "0", "no", or "false",
+authentication fails. If the result of the expansion is "1", "yes", or "true",
+authentication succeeds and the generic server_set_id option is expanded and
+saved in $authenticated_id. For any other result, a temporary error code is
+returned, with the expanded string as the error text.
+
+Warning: If you use a lookup in the expansion to find the user's password, be
+sure to make the authentication fail if the user is unknown. There are good and
+bad examples at the end of the next section.
+
+
+34.4 The PLAIN authentication mechanism
+---------------------------------------
+
+The PLAIN authentication mechanism (RFC 2595) specifies that three strings be
+sent as one item of data (that is, one combined string containing two NUL
+separators). The data is sent either as part of the AUTH command, or
+subsequently in response to an empty prompt from the server.
+
+The second and third strings are a user name and a corresponding password.
+Using a single fixed user name and password as an example, this could be
+configured as follows:
+
+fixed_plain:
+ driver = plaintext
+ public_name = PLAIN
+ server_prompts = :
+ server_condition = \
+ ${if and {{eq{$auth2}{username}}{eq{$auth3}{mysecret}}}}
+ server_set_id = $auth2
+
+Note that the default result strings from if ("true" or an empty string) are
+exactly what we want here, so they need not be specified. Obviously, if the
+password contains expansion-significant characters such as dollar, backslash,
+or closing brace, they have to be escaped.
+
+The server_prompts setting specifies a single, empty prompt (empty items at the
+end of a string list are ignored). If all the data comes as part of the AUTH
+command, as is commonly the case, the prompt is not used. This authenticator is
+advertised in the response to EHLO as
+
+250-AUTH PLAIN
+
+and a client host can authenticate itself by sending the command
+
+AUTH PLAIN AHVzZXJuYW1lAG15c2VjcmV0
+
+As this contains three strings (more than the number of prompts), no further
+data is required from the client. Alternatively, the client may just send
+
+AUTH PLAIN
+
+to initiate authentication, in which case the server replies with an empty
+prompt. The client must respond with the combined data string.
+
+The data string is base64 encoded, as required by the RFC. This example, when
+decoded, is <NUL>"username"<NUL>"mysecret", where <NUL> represents a zero byte.
+This is split up into three strings, the first of which is empty. The
+server_condition option in the authenticator checks that the second two are
+"username" and "mysecret" respectively.
+
+Having just one fixed user name and password, as in this example, is not very
+realistic, though for a small organization with only a handful of
+authenticating clients it could make sense.
+
+A more sophisticated instance of this authenticator could use the user name in
+$auth2 to look up a password in a file or database, and maybe do an encrypted
+comparison (see crypteq in chapter 11). Here is a example of this approach,
+where the passwords are looked up in a DBM file. Warning: This is an incorrect
+example:
+
+server_condition = \
+ ${if eq{$auth3}{${lookup{$auth2}dbm{/etc/authpwd}}}}
+
+The expansion uses the user name ($auth2) as the key to look up a password,
+which it then compares to the supplied password ($auth3). Why is this example
+incorrect? It works fine for existing users, but consider what happens if a
+non-existent user name is given. The lookup fails, but as no success/failure
+strings are given for the lookup, it yields an empty string. Thus, to defeat
+the authentication, all a client has to do is to supply a non-existent user
+name and an empty password. The correct way of writing this test is:
+
+server_condition = ${lookup{$auth2}dbm{/etc/authpwd}\
+ {${if eq{$value}{$auth3}}} {false}}
+
+In this case, if the lookup succeeds, the result is checked; if the lookup
+fails, "false" is returned and authentication fails. If crypteq is being used
+instead of eq, the first example is in fact safe, because crypteq always fails
+if its second argument is empty. However, the second way of writing the test
+makes the logic clearer.
+
+
+34.5 The LOGIN authentication mechanism
+---------------------------------------
+
+The LOGIN authentication mechanism is not documented in any RFC, but is in use
+in a number of programs. No data is sent with the AUTH command. Instead, a user
+name and password are supplied separately, in response to prompts. The
+plaintext authenticator can be configured to support this as in this example:
+
+fixed_login:
+ driver = plaintext
+ public_name = LOGIN
+ server_prompts = User Name : Password
+ server_condition = \
+ ${if and {{eq{$auth1}{username}}{eq{$auth2}{mysecret}}}}
+ server_set_id = $auth1
+
+Because of the way plaintext operates, this authenticator accepts data supplied
+with the AUTH command (in contravention of the specification of LOGIN), but if
+the client does not supply it (as is the case for LOGIN clients), the prompt
+strings are used to obtain two data items.
+
+Some clients are very particular about the precise text of the prompts. For
+example, Outlook Express is reported to recognize only "Username:" and
+"Password:". Here is an example of a LOGIN authenticator that uses those
+strings. It uses the ldapauth expansion condition to check the user name and
+password by binding to an LDAP server:
+
+login:
+ driver = plaintext
+ public_name = LOGIN
+ server_prompts = Username:: : Password::
+ server_condition = ${if and{{ \
+ !eq{}{$auth1} }{ \
+ ldapauth{\
+ user="uid=${quote_ldap_dn:$auth1},ou=people,o=example.org" \
+ pass=${quote:$auth2} \
+ ldap://ldap.example.org/} }} }
+ server_set_id = uid=$auth1,ou=people,o=example.org
+
+We have to check that the username is not empty before using it, because LDAP
+does not permit empty DN components. We must also use the quote_ldap_dn
+operator to correctly quote the DN for authentication. However, the basic quote
+operator, rather than any of the LDAP quoting operators, is the correct one to
+use for the password, because quoting is needed only to make the password
+conform to the Exim syntax. At the LDAP level, the password is an uninterpreted
+string.
+
+
+34.6 Support for different kinds of authentication
+--------------------------------------------------
+
+A number of string expansion features are provided for the purpose of
+interfacing to different ways of user authentication. These include checking
+traditionally encrypted passwords from /etc/passwd (or equivalent), PAM,
+Radius, ldapauth, pwcheck, and saslauthd. For details see section 11.7.
+
+
+34.7 Using plaintext in a client
+--------------------------------
+
+The plaintext authenticator has two client options:
+
++------------------------------------------------------------------------+
+|client_ignore_invalid_base64|Use: plaintext|Type: boolean|Default: false|
++------------------------------------------------------------------------+
+
+If the client receives a server prompt that is not a valid base64 string,
+authentication is abandoned by default. However, if this option is set true,
+the error in the challenge is ignored and the client sends the response as
+usual.
+
++-------------------------------------------------------+
+|client_send|Use: plaintext|Type: string*|Default: unset|
++-------------------------------------------------------+
+
+The string is a colon-separated list of authentication data strings. Each
+string is independently expanded before being sent to the server. The first
+string is sent with the AUTH command; any more strings are sent in response to
+prompts from the server. Before each string is expanded, the value of the most
+recent prompt is placed in the next $auth<n> variable, starting with $auth1 for
+the first prompt. Up to three prompts are stored in this way. Thus, the prompt
+that is received in response to sending the first string (with the AUTH
+command) can be used in the expansion of the second string, and so on. If an
+invalid base64 string is received when client_ignore_invalid_base64 is set, an
+empty string is put in the $auth<n> variable.
+
+Note: You cannot use expansion to create multiple strings, because splitting
+takes priority and happens first.
+
+Because the PLAIN authentication mechanism requires NUL (binary zero) bytes in
+the data, further processing is applied to each string before it is sent. If
+there are any single circumflex characters in the string, they are converted to
+NULs. Should an actual circumflex be required as data, it must be doubled in
+the string.
+
+This is an example of a client configuration that implements the PLAIN
+authentication mechanism with a fixed user name and password:
+
+fixed_plain:
+ driver = plaintext
+ public_name = PLAIN
+ client_send = ^username^mysecret
+
+The lack of colons means that the entire text is sent with the AUTH command,
+with the circumflex characters converted to NULs.
+
+Note that due to the ambiguity of parsing three consectutive circumflex
+characters there is no way to provide a password having a leading circumflex.
+
+A similar example that uses the LOGIN mechanism is:
+
+fixed_login:
+ driver = plaintext
+ public_name = LOGIN
+ client_send = : username : mysecret
+
+The initial colon means that the first string is empty, so no data is sent with
+the AUTH command itself. The remaining strings are sent in response to prompts.
+
+
+
+===============================================================================
+35. THE CRAM_MD5 AUTHENTICATOR
+
+The CRAM-MD5 authentication mechanism is described in RFC 2195. The server
+sends a challenge string to the client, and the response consists of a user
+name and the CRAM-MD5 digest of the challenge string combined with a secret
+string (password) which is known to both server and client. Thus, the secret is
+not sent over the network as plain text, which makes this authenticator more
+secure than plaintext. However, the downside is that the secret has to be
+available in plain text at either end.
+
+
+35.1 Using cram_md5 as a server
+-------------------------------
+
+This authenticator has one server option, which must be set to configure the
+authenticator as a server:
+
++--------------------------------------------------------+
+|server_secret|Use: cram_md5|Type: string*|Default: unset|
++--------------------------------------------------------+
+
+When the server receives the client's response, the user name is placed in the
+expansion variable $auth1, and server_secret is expanded to obtain the password
+for that user. The server then computes the CRAM-MD5 digest that the client
+should have sent, and checks that it received the correct string. If the
+expansion of server_secret is forced to fail, authentication fails. If the
+expansion fails for some other reason, a temporary error code is returned to
+the client.
+
+For compatibility with previous releases of Exim, the user name is also placed
+in $1. However, the use of this variables for this purpose is now deprecated,
+as it can lead to confusion in string expansions that also use numeric
+variables for other things.
+
+For example, the following authenticator checks that the user name given by the
+client is "ph10", and if so, uses "secret" as the password. For any other user
+name, authentication fails.
+
+fixed_cram:
+ driver = cram_md5
+ public_name = CRAM-MD5
+ server_secret = ${if eq{$auth1}{ph10}{secret}fail}
+ server_set_id = $auth1
+
+If authentication succeeds, the setting of server_set_id preserves the user
+name in $authenticated_id. A more typical configuration might look up the
+secret string in a file, using the user name as the key. For example:
+
+lookup_cram:
+ driver = cram_md5
+ public_name = CRAM-MD5
+ server_secret = ${lookup{$auth1}lsearch{/etc/authpwd}\
+ {$value}fail}
+ server_set_id = $auth1
+
+Note that this expansion explicitly forces failure if the lookup fails because
+$auth1 contains an unknown user name.
+
+As another example, if you wish to re-use a Cyrus SASL sasldb2 file without
+using the relevant libraries, you need to know the realm to specify in the
+lookup and then ask for the "userPassword" attribute for that user in that
+realm, with:
+
+cyrusless_crammd5:
+ driver = cram_md5
+ public_name = CRAM-MD5
+ server_secret = ${lookup{$auth1:mail.example.org:userPassword}\
+ dbmjz{/etc/sasldb2}{$value}fail}
+ server_set_id = $auth1
+
+
+35.2 Using cram_md5 as a client
+-------------------------------
+
+When used as a client, the cram_md5 authenticator has two options:
+
++----------------------------------------------------------------------+
+|client_name|Use: cram_md5|Type: string*|Default: the primary host name|
++----------------------------------------------------------------------+
+
+This string is expanded, and the result used as the user name data when
+computing the response to the server's challenge.
+
++--------------------------------------------------------+
+|client_secret|Use: cram_md5|Type: string*|Default: unset|
++--------------------------------------------------------+
+
+This option must be set for the authenticator to work as a client. Its value is
+expanded and the result used as the secret string when computing the response.
+
+Different user names and secrets can be used for different servers by referring
+to $host or $host_address in the options. Forced failure of either expansion
+string is treated as an indication that this authenticator is not prepared to
+handle this case. Exim moves on to the next configured client authenticator.
+Any other expansion failure causes Exim to give up trying to send the message
+to the current server.
+
+A simple example configuration of a cram_md5 authenticator, using fixed
+strings, is:
+
+fixed_cram:
+ driver = cram_md5
+ public_name = CRAM-MD5
+ client_name = ph10
+ client_secret = secret
+
+
+
+===============================================================================
+36. THE CYRUS_SASL AUTHENTICATOR
+
+The code for this authenticator was provided by Matthew Byng-Maddick while at A
+L Digital Ltd.
+
+The cyrus_sasl authenticator provides server support for the Cyrus SASL library
+implementation of the RFC 2222 ("Simple Authentication and Security Layer").
+This library supports a number of authentication mechanisms, including PLAIN
+and LOGIN, but also several others that Exim does not support directly. In
+particular, there is support for Kerberos authentication.
+
+The cyrus_sasl authenticator provides a gatewaying mechanism directly to the
+Cyrus interface, so if your Cyrus library can do, for example, CRAM-MD5, then
+so can the cyrus_sasl authenticator. By default it uses the public name of the
+driver to determine which mechanism to support.
+
+Where access to some kind of secret file is required, for example, in GSSAPI or
+CRAM-MD5, it is worth noting that the authenticator runs as the Exim user, and
+that the Cyrus SASL library has no way of escalating privileges by default. You
+may also find you need to set environment variables, depending on the driver
+you are using.
+
+The application name provided by Exim is "exim", so various SASL options may be
+set in exim.conf in your SASL directory. If you are using GSSAPI for Kerberos,
+note that because of limitations in the GSSAPI interface, changing the server
+keytab might need to be communicated down to the Kerberos layer independently.
+The mechanism for doing so is dependent upon the Kerberos implementation.
+
+For example, for older releases of Heimdal, the environment variable
+KRB5_KTNAME may be set to point to an alternative keytab file. Exim will pass
+this variable through from its own inherited environment when started as root
+or the Exim user. The keytab file needs to be readable by the Exim user. With
+newer releases of Heimdal, a setuid Exim may cause Heimdal to discard the
+environment variable. In practice, for those releases, the Cyrus authenticator
+is not a suitable interface for GSSAPI (Kerberos) support. Instead, consider
+the heimdal_gssapi authenticator, described in chapter 39
+
+
+36.1 Using cyrus_sasl as a server
+---------------------------------
+
+The cyrus_sasl authenticator has four private options. It puts the username (on
+a successful authentication) into $auth1. For compatibility with previous
+releases of Exim, the username is also placed in $1. However, the use of this
+variable for this purpose is now deprecated, as it can lead to confusion in
+string expansions that also use numeric variables for other things.
+
++----------------------------------------------------------------+
+|server_hostname|Use: cyrus_sasl|Type: string*|Default: see below|
++----------------------------------------------------------------+
+
+This option selects the hostname that is used when communicating with the
+library. The default value is "$primary_hostname". It is up to the underlying
+SASL plug-in what it does with this data.
+
++-----------------------------------------------------------+
+|server_mech|Use: cyrus_sasl|Type: string|Default: see below|
++-----------------------------------------------------------+
+
+This option selects the authentication mechanism this driver should use. The
+default is the value of the generic public_name option. This option allows you
+to use a different underlying mechanism from the advertised name. For example:
+
+sasl:
+ driver = cyrus_sasl
+ public_name = X-ANYTHING
+ server_mech = CRAM-MD5
+ server_set_id = $auth1
+
++---------------------------------------------------------+
+|server_realm|Use: cyrus_sasl|Type: string*|Default: unset|
++---------------------------------------------------------+
+
+This specifies the SASL realm that the server claims to be in.
+
++-----------------------------------------------------------+
+|server_service|Use: cyrus_sasl|Type: string|Default: "smtp"|
++-----------------------------------------------------------+
+
+This is the SASL service that the server claims to implement.
+
+For straightforward cases, you do not need to set any of the authenticator's
+private options. All you need to do is to specify an appropriate mechanism as
+the public name. Thus, if you have a SASL library that supports CRAM-MD5 and
+PLAIN, you could have two authenticators as follows:
+
+sasl_cram_md5:
+ driver = cyrus_sasl
+ public_name = CRAM-MD5
+ server_set_id = $auth1
+
+sasl_plain:
+ driver = cyrus_sasl
+ public_name = PLAIN
+ server_set_id = $auth2
+
+Cyrus SASL does implement the LOGIN authentication method, even though it is
+not a standard method. It is disabled by default in the source distribution,
+but it is present in many binary distributions.
+
+
+
+===============================================================================
+37. THE DOVECOT AUTHENTICATOR
+
+This authenticator is an interface to the authentication facility of the
+Dovecot 2 POP/IMAP server, which can support a number of authentication
+methods. Note that Dovecot must be configured to use auth-client not
+auth-userdb. If you are using Dovecot to authenticate POP/IMAP clients, it
+might be helpful to use the same mechanisms for SMTP authentication. This is a
+server authenticator only. There is only one option:
+
++------------------------------------------------------+
+|server_socket|Use: dovecot|Type: string|Default: unset|
++------------------------------------------------------+
+
+This option must specify the UNIX socket that is the interface to Dovecot
+authentication. The public_name option must specify an authentication mechanism
+that Dovecot is configured to support. You can have several authenticators for
+different mechanisms. For example:
+
+dovecot_plain:
+ driver = dovecot
+ public_name = PLAIN
+ server_socket = /var/run/dovecot/auth-client
+ server_set_id = $auth1
+
+dovecot_ntlm:
+ driver = dovecot
+ public_name = NTLM
+ server_socket = /var/run/dovecot/auth-client
+ server_set_id = $auth1
+
+If the SMTP connection is encrypted, or if $sender_host_address is equal to
+$received_ip_address (that is, the connection is local), the "secured" option
+is passed in the Dovecot authentication command. If, for a TLS connection, a
+client certificate has been verified, the "valid-client-cert" option is passed.
+When authentication succeeds, the identity of the user who authenticated is
+placed in $auth1.
+
+The Dovecot configuration to match the above wil look something like:
+
+conf.d/10-master.conf :-
+
+service auth {
+...
+#SASL
+ unix_listener auth-client {
+ mode = 0660
+ user = mail
+ }
+...
+}
+
+conf.d/10-auth.conf :-
+
+auth_mechanisms = plain login ntlm
+
+
+
+===============================================================================
+38. THE GSASL AUTHENTICATOR
+
+The gsasl authenticator provides integration for the GNU SASL library and the
+mechanisms it provides. This is new as of the 4.80 release and there are a few
+areas where the library does not let Exim smoothly scale to handle future
+authentication mechanisms, so no guarantee can be made that any particular new
+authentication mechanism will be supported without code changes in Exim.
+
+The library is expected to add support in an upcoming realease for the
+SCRAM-SHA-256 method. The macro _HAVE_AUTH_GSASL_SCRAM_SHA_256 will be defined
+when this happens.
+
++----------------------------------------------------+
+|client_authz|Use: gsasl|Type: string*|Default: unset|
++----------------------------------------------------+
+
+This option can be used to supply an authorization id which is different to the
+authentication_id provided by client_username option. If unset or (after
+expansion) empty it is not used, which is the common case.
+
++-------------------------------------------------------------+
+|client_channelbinding|Use: gsasl|Type: boolean|Default: false|
++-------------------------------------------------------------+
+
+See server_channelbinding below.
+
++-------------------------------------------------------+
+|client_password|Use: gsasl|Type: string*|Default: unset|
++-------------------------------------------------------+
+
+This option is exapanded before use, and should result in the password to be
+used, in clear.
+
++-------------------------------------------------------+
+|client_username|Use: gsasl|Type: string*|Default: unset|
++-------------------------------------------------------+
+
+This option is exapanded before use, and should result in the account name to
+be used.
+
++--------------------------------------------------------+
+|client_spassword|Use: gsasl|Type: string*|Default: unset|
++--------------------------------------------------------+
+
+If a SCRAM mechanism is being used and this option is set it is used in
+preference to client_password. The value after expansion should be a 40 (for
+SHA-1) or 64 (for SHA-256) character string with the PBKDF2-prepared password,
+hex-encoded. Note that this value will depend on the salt and iteration-count
+supplied by the server.
+
++-------------------------------------------------------------+
+|server_channelbinding|Use: gsasl|Type: boolean|Default: false|
++-------------------------------------------------------------+
+
+Do not set this true and rely on the properties without consulting a
+cryptographic engineer.
+
+Some authentication mechanisms are able to use external context at both ends of
+the session to bind the authentication to that context, and fail the
+authentication process if that context differs. Specifically, some TLS
+ciphersuites can provide identifying information about the cryptographic
+context.
+
+This should have meant that certificate identity and verification becomes a
+non-issue, as a man-in-the-middle attack will cause the correct client and
+server to see different identifiers and authentication will fail.
+
+This is only usable by mechanisms which support "channel binding"; at time of
+writing, that's the SCRAM family. When using this feature the "-PLUS" variants
+of the method names need to be used.
+
+This defaults off to ensure smooth upgrade across Exim releases, in case this
+option causes some clients to start failing. Some future release of Exim might
+have switched the default to be true.
+
+However, Channel Binding in TLS has proven to be vulnerable in current
+versions. Do not plan to rely upon this feature for security, ever, without
+consulting with a subject matter expert (a cryptographic engineer).
+
++-----------------------------------------------------------+
+|server_hostname|Use: gsasl|Type: string*|Default: see below|
++-----------------------------------------------------------+
+
+This option selects the hostname that is used when communicating with the
+library. The default value is "$primary_hostname". Some mechanisms will use
+this data.
+
++------------------------------------------------------+
+|server_mech|Use: gsasl|Type: string|Default: see below|
++------------------------------------------------------+
+
+This option selects the authentication mechanism this driver should use. The
+default is the value of the generic public_name option. This option allows you
+to use a different underlying mechanism from the advertised name. For example:
+
+sasl:
+ driver = gsasl
+ public_name = X-ANYTHING
+ server_mech = CRAM-MD5
+ server_set_id = $auth1
+
++-------------------------------------------------------+
+|server_password|Use: gsasl|Type: string*|Default: unset|
++-------------------------------------------------------+
+
+Various mechanisms need access to the cleartext password on the server, so that
+proof-of-possession can be demonstrated on the wire, without sending the
+password itself.
+
+The data available for lookup varies per mechanism. In all cases, $auth1 is set
+to the authentication id. The $auth2 variable will always be the authorization
+id (authz) if available, else the empty string. The $auth3 variable will always
+be the realm if available, else the empty string.
+
+A forced failure will cause authentication to defer.
+
+If using this option, it may make sense to set the server_condition option to
+be simply "true".
+
++----------------------------------------------------+
+|server_realm|Use: gsasl|Type: string*|Default: unset|
++----------------------------------------------------+
+
+This specifies the SASL realm that the server claims to be in. Some mechanisms
+will use this data.
+
++--------------------------------------------------------+
+|server_scram_iter|Use: gsasl|Type: string*|Default: 4096|
++--------------------------------------------------------+
+
+This option provides data for the SCRAM family of mechanisms.
+
+The $auth1, $auth2 and $auth3 variables are available when this option is
+expanded.
+
+The result of expansion should be a decimal number, and represents both a
+lower-bound on the security, and a compute cost factor imposed on the client
+(if it does not cache results, or the server changes either the iteration count
+or the salt). A minimum value of 4096 is required by the standards for all
+current SCRAM mechanism variants.
+
++---------------------------------------------------------+
+|server_scram_salt|Use: gsasl|Type: string*|Default: unset|
++---------------------------------------------------------+
+
+This option provides data for the SCRAM family of mechanisms.
+
+The $auth1, $auth2 and $auth3 variables are available when this option is
+expanded. The value should be a base64-encoded string, of random data typically
+4-to-16 bytes long. If unset or empty after expansion the library will provides
+a value for the protocol conversation.
+
++--------------------------------------------------+
+|server_key|Use: gsasl|Type: string*|Default: unset|
++--------------------------------------------------+
+
++---------------------------------------------------+
+|server_skey|Use: gsasl|Type: string*|Default: unset|
++---------------------------------------------------+
+
+These options can be used for the SCRAM family of mechanisms to provide stored
+information related to a password, the storage of which is preferable to
+plaintext.
+
+server_key is the value defined in the SCRAM standards as ServerKey;
+server_skey is StoredKey.
+
+They are only available for version 1.9.0 (or later) of the gsasl library. When
+this is so, the macros _OPT_AUTHENTICATOR_GSASL_SERVER_KEY and
+_HAVE_AUTH_GSASL_SCRAM_S_KEY will be defined.
+
+The $authN variables are available when these options are expanded.
+
+If set, the results of expansion should for each should be a 28 (for SHA-1) or
+44 (for SHA-256) character string of base64-coded data, and will be used in
+preference to the server_password option. If unset or not of the right length,
+server_password will be used.
+
+The libgsasl library release includes a utility gsasl which can be used to
+generate these values.
+
++------------------------------------------------------+
+|server_service|Use: gsasl|Type: string|Default: "smtp"|
++------------------------------------------------------+
+
+This is the SASL service that the server claims to implement. Some mechanisms
+will use this data.
+
+
+38.1 gsasl auth variables
+-------------------------
+
+These may be set when evaluating specific options, as detailed above. They will
+also be set when evaluating server_condition.
+
+Unless otherwise stated below, the gsasl integration will use the following
+meanings for these variables:
+
+ * $auth1: the authentication id
+
+ * $auth2: the authorization id
+
+ * $auth3: the realm
+
+On a per-mechanism basis:
+
+ * EXTERNAL: only $auth1 is set, to the possibly empty authorization id; the
+ server_condition option must be present.
+
+ * ANONYMOUS: only $auth1 is set, to the possibly empty anonymous token; the
+ server_condition option must be present.
+
+ * GSSAPI: $auth1 will be set to the GSSAPI Display Name; $auth2 will be set
+ to the authorization id, the server_condition option must be present.
+
+An anonymous token is something passed along as an unauthenticated identifier;
+this is analogous to FTP anonymous authentication passing an email address, or
+software-identifier@, as the "password".
+
+An example showing the password having the realm specified in the callback and
+demonstrating a Cyrus SASL to GSASL migration approach is:
+
+gsasl_cyrusless_crammd5:
+ driver = gsasl
+ public_name = CRAM-MD5
+ server_realm = imap.example.org
+ server_password = ${lookup{$auth1:$auth3:userPassword}\
+ dbmjz{/etc/sasldb2}{$value}fail}
+ server_set_id = ${quote:$auth1}
+ server_condition = yes
+
+
+
+===============================================================================
+39. THE HEIMDAL_GSSAPI AUTHENTICATOR
+
+The heimdal_gssapi authenticator provides server integration for the Heimdal
+GSSAPI/Kerberos library, permitting Exim to set a keytab pathname reliably.
+
++--------------------------------------------------------------------+
+|server_hostname|Use: heimdal_gssapi|Type: string*|Default: see below|
++--------------------------------------------------------------------+
+
+This option selects the hostname that is used, with server_service, for
+constructing the GSS server name, as a GSS_C_NT_HOSTBASED_SERVICE identifier.
+The default value is "$primary_hostname".
+
++--------------------------------------------------------------+
+|server_keytab|Use: heimdal_gssapi|Type: string*|Default: unset|
++--------------------------------------------------------------+
+
+If set, then Heimdal will not use the system default keytab (typically /etc/
+krb5.keytab) but instead the pathname given in this option. The value should be
+a pathname, with no "file:" prefix.
+
++--------------------------------------------------------------+
+|server_service|Use: heimdal_gssapi|Type: string*|Default: smtp|
++--------------------------------------------------------------+
+
+This option specifies the service identifier used, in conjunction with
+server_hostname, for building the identifier for finding credentials from the
+keytab.
+
+
+39.1 heimdal_gssapi auth variables
+----------------------------------
+
+Beware that these variables will typically include a realm, thus will appear to
+be roughly like an email address already. The authzid in $auth2 is not
+verified, so a malicious client can set it to anything.
+
+The $auth1 field should be safely trustable as a value from the Key
+Distribution Center. Note that these are not quite email addresses. Each
+identifier is for a role, and so the left-hand-side may include a role suffix.
+For instance, "joe/admin@EXAMPLE.ORG".
+
+ * $auth1: the authentication id, set to the GSS Display Name.
+
+ * $auth2: the authorization id, sent within SASL encapsulation after
+ authentication. If that was empty, this will also be set to the GSS Display
+ Name.
+
+
+
+===============================================================================
+40. THE SPA AUTHENTICATOR
+
+The spa authenticator provides client support for Microsoft's Secure Password
+Authentication mechanism, which is also sometimes known as NTLM (NT LanMan).
+The code for client side of this authenticator was contributed by Marc
+Prud'hommeaux, and much of it is taken from the Samba project (https://
+www.samba.org/). The code for the server side was subsequently contributed by
+Tom Kistner. The mechanism works as follows:
+
+ * After the AUTH command has been accepted, the client sends an SPA
+ authentication request based on the user name and optional domain.
+
+ * The server sends back a challenge.
+
+ * The client builds a challenge response which makes use of the user's
+ password and sends it to the server, which then accepts or rejects it.
+
+Encryption is used to protect the password in transit.
+
+
+40.1 Using spa as a server
+--------------------------
+
+The spa authenticator has just one server option:
+
++-----------------------------------------------------+
+|server_password|Use: spa|Type: string*|Default: unset|
++-----------------------------------------------------+
+
+This option is expanded, and the result must be the cleartext password for the
+authenticating user, whose name is at this point in $auth1. For compatibility
+with previous releases of Exim, the user name is also placed in $1. However,
+the use of this variable for this purpose is now deprecated, as it can lead to
+confusion in string expansions that also use numeric variables for other
+things. For example:
+
+spa:
+ driver = spa
+ public_name = NTLM
+ server_password = \
+ ${lookup{$auth1}lsearch{/etc/exim/spa_clearpass}{$value}fail}
+
+If the expansion is forced to fail, authentication fails. Any other expansion
+failure causes a temporary error code to be returned.
+
+
+40.2 Using spa as a client
+--------------------------
+
+The spa authenticator has the following client options:
+
++---------------------------------------------------+
+|client_domain|Use: spa|Type: string*|Default: unset|
++---------------------------------------------------+
+
+This option specifies an optional domain for the authentication.
+
++-----------------------------------------------------+
+|client_password|Use: spa|Type: string*|Default: unset|
++-----------------------------------------------------+
+
+This option specifies the user's password, and must be set.
+
++-----------------------------------------------------+
+|client_username|Use: spa|Type: string*|Default: unset|
++-----------------------------------------------------+
+
+This option specifies the user name, and must be set. Here is an example of a
+configuration of this authenticator for use with the mail servers at msn.com:
+
+msn:
+ driver = spa
+ public_name = MSN
+ client_username = msn/msn_username
+ client_password = msn_plaintext_password
+ client_domain = DOMAIN_OR_UNSET
+
+
+
+===============================================================================
+41. THE EXTERNAL AUTHENTICATOR
+
+The external authenticator provides support for authentication based on
+non-SMTP information. The specification is in RFC 4422 Appendix A (https://
+tools.ietf.org/html/rfc4422). It is only a transport and negotiation mechanism;
+the process of authentication is entirely controlled by the server
+configuration.
+
+The client presents an identity in-clear. It is probably wise for a server to
+only advertise, and for clients to only attempt, this authentication method on
+a secure (eg. under TLS) connection.
+
+One possible use, compatible with the K-9 Mail Andoid client (https://
+k9mail.github.io/), is for using X509 client certificates.
+
+It thus overlaps in function with the TLS authenticator (see 42) but is a full
+SMTP SASL authenticator rather than being implicit for TLS-connection carried
+client certificates only.
+
+The examples and discussion in this chapter assume that client-certificate
+authentication is being done.
+
+The client must present a certificate, for which it must have been requested
+via the tls_verify_hosts or tls_try_verify_hosts main options (see 43). For
+authentication to be effective the certificate should be verifiable against a
+trust-anchor certificate known to the server.
+
+
+41.1 External options
+---------------------
+
+The external authenticator has two server options:
+
++--------------------------------------------------------+
+|server_param2|Use: external|Type: string*|Default: unset|
++--------------------------------------------------------+
+
++--------------------------------------------------------+
+|server_param3|Use: external|Type: string*|Default: unset|
++--------------------------------------------------------+
+
+These options are expanded before the server_condition option and the result
+are placed in $auth2 and $auth3 resectively. If the expansion is forced to
+fail, authentication fails. Any other expansion failure causes a temporary
+error code to be returned.
+
+They can be used to clarify the coding of a complex server_condition.
+
+
+41.2 Using external in a server
+-------------------------------
+
+When running as a server, external performs the authentication test by
+expanding a string. The data sent by the client with the AUTH command, or in
+response to subsequent prompts, is base64 encoded, and so may contain any byte
+values when decoded. The decoded value is treated as an identity for
+authentication and placed in the expansion variable $auth1.
+
+For compatibility with previous releases of Exim, the value is also placed in
+the expansion variable $1. However, the use of this variable for this purpose
+is now deprecated, as it can lead to confusion in string expansions that also
+use them for other things.
+
+Once an identity has been received, server_condition is expanded. If the
+expansion is forced to fail, authentication fails. Any other expansion failure
+causes a temporary error code to be returned. If the result of a successful
+expansion is an empty string, "0", "no", or "false", authentication fails. If
+the result of the expansion is "1", "yes", or "true", authentication succeeds
+and the generic server_set_id option is expanded and saved in $authenticated_id
+. For any other result, a temporary error code is returned, with the expanded
+string as the error text.
+
+Example:
+
+ext_ccert_san_mail:
+ driver = external
+ public_name = EXTERNAL
+
+ server_advertise_condition = $tls_in_certificate_verified
+ server_param2 = ${certextract {subj_altname,mail,>:} \
+ {$tls_in_peercert}}
+ server_condition = ${if forany {$auth2} \
+ {eq {$item}{$auth1}}}
+ server_set_id = $auth1
+
+This accepts a client certificate that is verifiable against any of your
+configured trust-anchors (which usually means the full set of public CAs) and
+which has a mail-SAN matching the claimed identity sent by the client.
+
+Note: up to TLS1.2, the client cert is on the wire in-clear, including the SAN.
+The account name is therefore guessable by an opponent. TLS 1.3 protects both
+server and client certificates, and is not vulnerable in this way.
+
+
+41.3 Using external in a client
+-------------------------------
+
+The external authenticator has one client option:
+
++------------------------------------------------------+
+|client_send|Use: external|Type: string*|Default: unset|
++------------------------------------------------------+
+
+This option is expanded and sent with the AUTH command as the identity being
+asserted.
+
+Example:
+
+ext_ccert:
+ driver = external
+ public_name = EXTERNAL
+
+ client_condition = ${if !eq{$tls_out_cipher}{}}
+ client_send = myaccount@smarthost.example.net
+
+
+
+===============================================================================
+42. THE TLS AUTHENTICATOR
+
+The tls authenticator provides server support for authentication based on
+client certificates.
+
+It is not an SMTP authentication mechanism and is not advertised by the server
+as part of the SMTP EHLO response. It is an Exim authenticator in the sense
+that it affects the protocol element of the log line, can be tested for by the
+authenticated ACL condition, and can set the $authenticated_id variable.
+
+The client must present a verifiable certificate, for which it must have been
+requested via the tls_verify_hosts or tls_try_verify_hosts main options (see 43
+).
+
+If an authenticator of this type is configured it is run before any SMTP-level
+communication is done, and can authenticate the connection. If it does, SMTP
+authentication is not offered.
+
+A maximum of one authenticator of this type may be present.
+
+The tls authenticator has three server options:
+
++---------------------------------------------------+
+|server_param1|Use: tls|Type: string*|Default: unset|
++---------------------------------------------------+
+
+This option is expanded after the TLS negotiation and the result is placed in
+$auth1. If the expansion is forced to fail, authentication fails. Any other
+expansion failure causes a temporary error code to be returned.
+
++---------------------------------------------------+
+|server_param2|Use: tls|Type: string*|Default: unset|
++---------------------------------------------------+
+
++---------------------------------------------------+
+|server_param3|Use: tls|Type: string*|Default: unset|
++---------------------------------------------------+
+
+As above, for $auth2 and $auth3.
+
+server_param1 may also be spelled server_param.
+
+Example:
+
+tls:
+ driver = tls
+ server_param1 = ${certextract {subj_altname,mail,>:} \
+ {$tls_in_peercert}}
+ server_condition = ${if and { {eq{$tls_in_certificate_verified}{1}} \
+ {forany {$auth1} \
+ {!= {0} \
+ {${lookup ldap{ldap:///\
+ mailname=${quote_ldap_dn:${lc:$item}},\
+ ou=users,LDAP_DC?mailid} {$value}{0} \
+ } } } }}}
+ server_set_id = ${if = {1}{${listcount:$auth1}} {$auth1}{}}
+
+This accepts a client certificate that is verifiable against any of your
+configured trust-anchors (which usually means the full set of public CAs) and
+which has a SAN with a good account name.
+
+Note that, up to TLS1.2, the client cert is on the wire in-clear, including the
+SAN, The account name is therefore guessable by an opponent. TLS 1.3 protects
+both server and client certificates, and is not vulnerable in this way.
+Likewise, a traditional plaintext SMTP AUTH done inside TLS is not.
+
+Note that because authentication is traditionally an SMTP operation, the
+authenticated ACL condition cannot be used in a connect- or helo-ACL.
+
+
+
+===============================================================================
+43. ENCRYPTED SMTP CONNECTIONS USING TLS/SSL
+
+Support for TLS (Transport Layer Security), formerly known as SSL (Secure
+Sockets Layer), is implemented by making use of the OpenSSL library or the
+GnuTLS library (Exim requires GnuTLS release 1.0 or later). There is no
+cryptographic code in the Exim distribution itself for implementing TLS. In
+order to use this feature you must install OpenSSL or GnuTLS, and then build a
+version of Exim that includes TLS support (see section 4.7). You also need to
+understand the basic concepts of encryption at a managerial level, and in
+particular, the way that public keys, private keys, and certificates are used.
+
+RFC 3207 defines how SMTP connections can make use of encryption. Once a
+connection is established, the client issues a STARTTLS command. If the server
+accepts this, the client and the server negotiate an encryption mechanism. If
+the negotiation succeeds, the data that subsequently passes between them is
+encrypted.
+
+Exim's ACLs can detect whether the current SMTP session is encrypted or not,
+and if so, what cipher suite is in use, whether the client supplied a
+certificate, and whether or not that certificate was verified. This makes it
+possible for an Exim server to deny or accept certain commands based on the
+encryption state.
+
+Warning: Certain types of firewall and certain anti-virus products can disrupt
+TLS connections. You need to turn off SMTP scanning for these products in order
+to get TLS to work.
+
+
+43.1 Support for the "submissions" (aka "ssmtp" and "smtps") protocol
+---------------------------------------------------------------------
+
+The history of port numbers for TLS in SMTP is a little messy and has been
+contentious. As of RFC 8314, the common practice of using the historically
+allocated port 465 for "email submission but with TLS immediately upon connect
+instead of using STARTTLS" is officially blessed by the IETF, and recommended
+by them in preference to STARTTLS.
+
+The name originally assigned to the port was "ssmtp" or "smtps", but as clarity
+emerged over the dual roles of SMTP, for MX delivery and Email Submission,
+nomenclature has shifted. The modern name is now "submissions".
+
+This approach was, for a while, officially abandoned when encrypted SMTP was
+standardized, but many clients kept using it, even as the TCP port number was
+reassigned for other use. Thus you may encounter guidance claiming that you
+shouldn't enable use of this port. In practice, a number of mail-clients have
+only ever supported submissions, not submission with STARTTLS upgrade. Ideally,
+offer both submission (587) and submissions (465) service.
+
+Exim supports TLS-on-connect by means of the tls_on_connect_ports global
+option. Its value must be a list of port numbers; the most common use is
+expected to be:
+
+tls_on_connect_ports = 465
+
+The port numbers specified by this option apply to all SMTP connections, both
+via the daemon and via inetd. You still need to specify all the ports that the
+daemon uses (by setting daemon_smtp_ports or local_interfaces or the -oX
+command line option) because tls_on_connect_ports does not add an extra port -
+rather, it specifies different behaviour on a port that is defined elsewhere.
+
+There is also a -tls-on-connect command line option. This overrides
+tls_on_connect_ports; it forces the TLS-only behaviour for all ports.
+
+
+43.2 OpenSSL vs GnuTLS
+----------------------
+
+TLS is supported in Exim using either the OpenSSL or GnuTLS library. To build
+Exim to use OpenSSL you need to set
+
+USE_OPENSSL=yes
+
+in Local/Makefile.
+
+To build Exim to use GnuTLS, you need to set
+
+USE_GNUTLS=yes
+
+in Local/Makefile.
+
+You must also set TLS_LIBS and TLS_INCLUDE appropriately, so that the include
+files and libraries for GnuTLS can be found.
+
+There are some differences in usage when using GnuTLS instead of OpenSSL:
+
+ * The tls_verify_certificates option cannot be the path of a directory for
+ GnuTLS versions before 3.3.6 (for later versions, or OpenSSL, it can be
+ either).
+
+ * The default value for tls_dhparam differs for historical reasons.
+
+ * Distinguished Name (DN) strings reported by the OpenSSL library use a slash
+ for separating fields; GnuTLS uses commas, in accordance with RFC 2253.
+ This affects the value of the $tls_in_peerdn and $tls_out_peerdn variables.
+
+ * OpenSSL identifies cipher suites using hyphens as separators, for example:
+ DES-CBC3-SHA. GnuTLS historically used underscores, for example:
+ RSA_ARCFOUR_SHA. What is more, OpenSSL complains if underscores are present
+ in a cipher list. To make life simpler, Exim changes underscores to hyphens
+ for OpenSSL and passes the string unchanged to GnuTLS (expecting the
+ library to handle its own older variants) when processing lists of cipher
+ suites in the tls_require_ciphers options (the global option and the smtp
+ transport option).
+
+ * The tls_require_ciphers options operate differently, as described in the
+ sections 43.4 and 43.5.
+
+ * The tls_dh_min_bits SMTP transport option is only honoured by GnuTLS. When
+ using OpenSSL, this option is ignored. (If an API is found to let OpenSSL
+ be configured in this way, let the Exim Maintainers know and we'll likely
+ use it).
+
+ * With GnuTLS, if an explicit list is used for the tls_privatekey main option
+ main option, it must be ordered to match the tls_certificate list.
+
+ * Some other recently added features may only be available in one or the
+ other. This should be documented with the feature. If the documentation
+ does not explicitly state that the feature is infeasible in the other TLS
+ implementation, then patches are welcome.
+
+ * The output from "exim -bV" will show which (if any) support was included in
+ the build. Also, the macro "_HAVE_OPENSSL" or "_HAVE_GNUTLS" will be
+ defined.
+
+
+43.3 GnuTLS parameter computation
+---------------------------------
+
+This section only applies if tls_dhparam is set to "historic" or to an explicit
+path; if the latter, then the text about generation still applies, but not the
+chosen filename. By default, as of Exim 4.80 a hard-coded D-H prime is used.
+See the documentation of tls_dhparam for more information.
+
+GnuTLS uses D-H parameters that may take a substantial amount of time to
+compute. It is unreasonable to re-compute them for every TLS session.
+Therefore, Exim keeps this data in a file in its spool directory, called
+gnutls-params-NNNN for some value of NNNN, corresponding to the number of bits
+requested. The file is owned by the Exim user and is readable only by its
+owner. Every Exim process that start up GnuTLS reads the D-H parameters from
+this file. If the file does not exist, the first Exim process that needs it
+computes the data and writes it to a temporary file which is renamed once it is
+complete. It does not matter if several Exim processes do this simultaneously
+(apart from wasting a few resources). Once a file is in place, new Exim
+processes immediately start using it.
+
+For maximum security, the parameters that are stored in this file should be
+recalculated periodically, the frequency depending on your paranoia level. If
+you are avoiding using the fixed D-H primes published in RFCs, then you are
+concerned about some advanced attacks and will wish to do this; if you do not
+regenerate then you might as well stick to the standard primes.
+
+Arranging this is easy in principle; just delete the file when you want new
+values to be computed. However, there may be a problem. The calculation of new
+parameters needs random numbers, and these are obtained from /dev/random. If
+the system is not very active, /dev/random may delay returning data until
+enough randomness (entropy) is available. This may cause Exim to hang for a
+substantial amount of time, causing timeouts on incoming connections.
+
+The solution is to generate the parameters externally to Exim. They are stored
+in gnutls-params-N in PEM format, which means that they can be generated
+externally using the certtool command that is part of GnuTLS.
+
+To replace the parameters with new ones, instead of deleting the file and
+letting Exim re-create it, you can generate new parameters using certtool and,
+when this has been done, replace Exim's cache file by renaming. The relevant
+commands are something like this:
+
+# ls
+[ look for file; assume gnutls-params-2236 is the most recent ]
+# rm -f new-params
+# touch new-params
+# chown exim:exim new-params
+# chmod 0600 new-params
+# certtool --generate-dh-params --bits 2236 >>new-params
+# openssl dhparam -noout -text -in new-params | head
+[ check the first line, make sure it's not more than 2236;
+ if it is, then go back to the start ("rm") and repeat
+ until the size generated is at most the size requested ]
+# chmod 0400 new-params
+# mv new-params gnutls-params-2236
+
+If Exim never has to generate the parameters itself, the possibility of
+stalling is removed.
+
+The filename changed in Exim 4.80, to gain the -bits suffix. The value which
+Exim will choose depends upon the version of GnuTLS in use. For older GnuTLS,
+the value remains hard-coded in Exim as 1024. As of GnuTLS 2.12.x, there is a
+way for Exim to ask for the "normal" number of bits for D-H public-key usage,
+and Exim does so. This attempt to remove Exim from TLS policy decisions failed,
+as GnuTLS 2.12 returns a value higher than the current hard-coded limit of the
+NSS library. Thus Exim gains the tls_dh_max_bits global option, which applies
+to all D-H usage, client or server. If the value returned by GnuTLS is greater
+than tls_dh_max_bits then the value will be clamped down to tls_dh_max_bits.
+The default value has been set at the current NSS limit, which is still much
+higher than Exim historically used.
+
+The filename and bits used will change as the GnuTLS maintainers change the
+value for their parameter "GNUTLS_SEC_PARAM_NORMAL", as clamped by
+tls_dh_max_bits. At the time of writing (mid 2012), GnuTLS 2.12 recommends 2432
+bits, while NSS is limited to 2236 bits.
+
+In fact, the requested value will be *lower* than tls_dh_max_bits, to increase
+the chance of the generated prime actually being within acceptable bounds, as
+GnuTLS has been observed to overshoot. Note the check step in the procedure
+above. There is no sane procedure available to Exim to double-check the size of
+the generated prime, so it might still be too large.
+
+
+43.4 Requiring specific ciphers in OpenSSL
+------------------------------------------
+
+There is a function in the OpenSSL library that can be passed a list of cipher
+suites before the cipher negotiation takes place. This specifies which ciphers
+are acceptable for TLS versions prior to 1.3. The list is colon separated and
+may contain names like DES-CBC3-SHA. Exim passes the expanded value of
+tls_require_ciphers directly to this function call. Many systems will install
+the OpenSSL manual-pages, so you may have ciphers(1) available to you. The
+following quotation from the OpenSSL documentation specifies what forms of item
+are allowed in the cipher string:
+
+ * It can consist of a single cipher suite such as RC4-SHA.
+
+ * It can represent a list of cipher suites containing a certain algorithm, or
+ cipher suites of a certain type. For example SHA1 represents all ciphers
+ suites using the digest algorithm SHA1 and SSLv3 represents all SSL v3
+ algorithms.
+
+ * Lists of cipher suites can be combined in a single cipher string using the
+ + character. This is used as a logical and operation. For example SHA1+DES
+ represents all cipher suites containing the SHA1 and the DES algorithms.
+
+Each cipher string can be optionally preceded by one of the characters "!", "-"
+or "+".
+
+ * If "!" is used, the ciphers are permanently deleted from the list. The
+ ciphers deleted can never reappear in the list even if they are explicitly
+ stated.
+
+ * If "-" is used, the ciphers are deleted from the list, but some or all of
+ the ciphers can be added again by later options.
+
+ * If "+" is used, the ciphers are moved to the end of the list. This option
+ does not add any new ciphers; it just moves matching existing ones.
+
+If none of these characters is present, the string is interpreted as a list of
+ciphers to be appended to the current preference list. If the list includes any
+ciphers already present they will be ignored: that is, they will not be moved
+to the end of the list.
+
+The OpenSSL ciphers(1) command may be used to test the results of a given
+string:
+
+# note single-quotes to get ! past any shell history expansion
+$ openssl ciphers 'HIGH:!MD5:!SHA1'
+
+This example will let the library defaults be permitted on the MX port, where
+there's probably no identity verification anyway, but ups the ante on the
+submission ports where the administrator might have some influence on the
+choice of clients used:
+
+# OpenSSL variant; see man ciphers(1)
+tls_require_ciphers = ${if =={$received_port}{25}\
+ {DEFAULT}\
+ {HIGH:!MD5:!SHA1}}
+
+This example will prefer ECDSA-authenticated ciphers over RSA ones:
+
+tls_require_ciphers = ECDSA:RSA:!COMPLEMENTOFDEFAULT
+
+For TLS version 1.3 the control available is less fine-grained and Exim does
+not provide access to it at present. The value of the tls_require_ciphers
+option is ignored when TLS version 1.3 is negotiated.
+
+As of writing the library default cipher suite list for TLSv1.3 is
+
+TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:TLS_AES_128_GCM_SHA256
+
+
+43.5 Requiring specific ciphers or other parameters in GnuTLS
+-------------------------------------------------------------
+
+The GnuTLS library allows the caller to provide a "priority string", documented
+as part of the gnutls_priority_init function. This is very similar to the
+ciphersuite specification in OpenSSL.
+
+The tls_require_ciphers option is treated as the GnuTLS priority string and
+controls both protocols and ciphers.
+
+The tls_require_ciphers option is available both as an global option,
+controlling how Exim behaves as a server, and also as an option of the smtp
+transport, controlling how Exim behaves as a client. In both cases the value is
+string expanded. The resulting string is not an Exim list and the string is
+given to the GnuTLS library, so that Exim does not need to be aware of future
+feature enhancements of GnuTLS.
+
+Documentation of the strings accepted may be found in the GnuTLS manual, under
+"Priority strings". This is online as https://www.gnutls.org/manual/html_node/
+Priority-Strings.html, but beware that this relates to GnuTLS 3, which may be
+newer than the version installed on your system. If you are using GnuTLS 3,
+then the example code https://www.gnutls.org/manual/gnutls.html#
+Listing-the-ciphersuites-in-a-priority-string on that site can be used to test
+a given string.
+
+For example:
+
+# Disable older versions of protocols
+tls_require_ciphers = NORMAL:%LATEST_RECORD_VERSION:-VERS-SSL3.0
+
+Prior to Exim 4.80, an older API of GnuTLS was used, and Exim supported three
+additional options, "gnutls_require_kx", "gnutls_require_mac" and "
+gnutls_require_protocols". tls_require_ciphers was an Exim list.
+
+This example will let the library defaults be permitted on the MX port, where
+there's probably no identity verification anyway, and lowers security further
+by increasing compatibility; but this ups the ante on the submission ports
+where the administrator might have some influence on the choice of clients
+used:
+
+# GnuTLS variant
+tls_require_ciphers = ${if =={$received_port}{25}\
+ {NORMAL:%COMPAT}\
+ {SECURE128}}
+
+
+43.6 Configuring an Exim server to use TLS
+------------------------------------------
+
+When Exim has been built with TLS support, it advertises the availability of
+the STARTTLS command to client hosts that match tls_advertise_hosts, but not to
+any others. The default value of this option is *, which means that STARTTLS is
+always advertised. Set it to blank to never advertise; this is reasonable for
+systems that want to use TLS only as a client.
+
+If STARTTLS is to be used you need to set some other options in order to make
+TLS available.
+
+If a client issues a STARTTLS command and there is some configuration problem
+in the server, the command is rejected with a 454 error. If the client persists
+in trying to issue SMTP commands, all except QUIT are rejected with the error
+
+554 Security failure
+
+If a STARTTLS command is issued within an existing TLS session, it is rejected
+with a 554 error code.
+
+To enable TLS operations on a server, the tls_advertise_hosts option must be
+set to match some hosts. The default is * which matches all hosts.
+
+If this is all you do, TLS encryption will be enabled but not authentication -
+meaning that the peer has no assurance it is actually you he is talking to. You
+gain protection from a passive sniffer listening on the wire but not from
+someone able to intercept the communication.
+
+Further protection requires some further configuration at the server end.
+
+To make TLS work you need to set, in the server,
+
+tls_certificate = /some/file/name
+tls_privatekey = /some/file/name
+
+These options are, in fact, expanded strings, so you can make them depend on
+the identity of the client that is connected if you wish. The first file
+contains the server's X509 certificate, and the second contains the private key
+that goes with it. These files need to be PEM format and readable by the Exim
+user, and must always be given as full path names. The key must not be
+password-protected. They can be the same file if both the certificate and the
+key are contained within it. If tls_privatekey is not set, or if its expansion
+is forced to fail or results in an empty string, this is assumed to be the
+case. The certificate file may also contain intermediate certificates that need
+to be sent to the client to enable it to authenticate the server's certificate.
+
+For dual-stack (eg. RSA and ECDSA) configurations, these options can be
+colon-separated lists of file paths. Ciphers using given authentication
+algorithms require the presence of a suitable certificate to supply the
+public-key. The server selects among the certificates to present to the client
+depending on the selected cipher, hence the priority ordering for ciphers will
+affect which certificate is used.
+
+If you do not understand about certificates and keys, please try to find a
+source of this background information, which is not Exim-specific. (There are a
+few comments below in section 43.12.)
+
+Note: These options do not apply when Exim is operating as a client - they
+apply only in the case of a server. If you need to use a certificate in an Exim
+client, you must set the options of the same names in an smtp transport.
+
+With just these options, an Exim server will be able to use TLS. It does not
+require the client to have a certificate (but see below for how to insist on
+this). There is one other option that may be needed in other situations. If
+
+tls_dhparam = /some/file/name
+
+is set, the SSL library is initialized for the use of Diffie-Hellman ciphers
+with the parameters contained in the file. Set this to "none" to disable use of
+DH entirely, by making no prime available:
+
+tls_dhparam = none
+
+This may also be set to a string identifying a standard prime to be used for
+DH; if it is set to "default" or, for OpenSSL, is unset, then the prime used is
+"ike23". There are a few standard primes available, see the documentation for
+tls_dhparam for the complete list.
+
+See the command
+
+openssl dhparam
+
+for a way of generating file data.
+
+The strings supplied for these three options are expanded every time a client
+host connects. It is therefore possible to use different certificates and keys
+for different hosts, if you so wish, by making use of the client's IP address
+in $sender_host_address to control the expansion. If a string expansion is
+forced to fail, Exim behaves as if the option is not set.
+
+The variable $tls_in_cipher is set to the cipher suite that was negotiated for
+an incoming TLS connection. It is included in the Received: header of an
+incoming message (by default - you can, of course, change this), and it is also
+included in the log line that records a message's arrival, keyed by "X=",
+unless the tls_cipher log selector is turned off. The encrypted condition can
+be used to test for specific cipher suites in ACLs.
+
+Once TLS has been established, the ACLs that run for subsequent SMTP commands
+can check the name of the cipher suite and vary their actions accordingly. The
+cipher suite names vary, depending on which TLS library is being used. For
+example, OpenSSL uses the name DES-CBC3-SHA for the cipher suite which in other
+contexts is known as TLS_RSA_WITH_3DES_EDE_CBC_SHA. Check the OpenSSL or GnuTLS
+documentation for more details.
+
+For outgoing SMTP deliveries, $tls_out_cipher is used and logged (again
+depending on the tls_cipher log selector).
+
+
+43.7 Requesting and verifying client certificates
+-------------------------------------------------
+
+If you want an Exim server to request a certificate when negotiating a TLS
+session with a client, you must set either tls_verify_hosts or
+tls_try_verify_hosts. You can, of course, set either of them to * to apply to
+all TLS connections. For any host that matches one of these options, Exim
+requests a certificate as part of the setup of the TLS session. The contents of
+the certificate are verified by comparing it with a list of expected
+trust-anchors or certificates. These may be the system default set (depending
+on library version), an explicit file or, depending on library version, a
+directory, identified by tls_verify_certificates.
+
+A file can contain multiple certificates, concatenated end to end. If a
+directory is used (OpenSSL only), each certificate must be in a separate file,
+with a name (or a symbolic link) of the form <hash>.0, where <hash> is a hash
+value constructed from the certificate. You can compute the relevant hash by
+running the command
+
+openssl x509 -hash -noout -in /cert/file
+
+where /cert/file contains a single certificate.
+
+There is no checking of names of the client against the certificate Subject
+Name or Subject Alternate Names.
+
+The difference between tls_verify_hosts and tls_try_verify_hosts is what
+happens if the client does not supply a certificate, or if the certificate does
+not match any of the certificates in the collection named by
+tls_verify_certificates. If the client matches tls_verify_hosts, the attempt to
+set up a TLS session is aborted, and the incoming connection is dropped. If the
+client matches tls_try_verify_hosts, the (encrypted) SMTP session continues.
+ACLs that run for subsequent SMTP commands can detect the fact that no
+certificate was verified, and vary their actions accordingly. For example, you
+can insist on a certificate before accepting a message for relaying, but not
+when the message is destined for local delivery.
+
+When a client supplies a certificate (whether it verifies or not), the value of
+the Distinguished Name of the certificate is made available in the variable
+$tls_in_peerdn during subsequent processing of the message.
+
+Because it is often a long text string, it is not included in the log line or
+Received: header by default. You can arrange for it to be logged, keyed by "DN=
+", by setting the tls_peerdn log selector, and you can use received_header_text
+to change the Received: header. When no certificate is supplied, $tls_in_peerdn
+is empty.
+
+
+43.8 Revoked certificates
+-------------------------
+
+Certificate issuing authorities issue Certificate Revocation Lists (CRLs) when
+certificates are revoked. If you have such a list, you can pass it to an Exim
+server using the global option called tls_crl and to an Exim client using an
+identically named option for the smtp transport. In each case, the value of the
+option is expanded and must then be the name of a file that contains a CRL in
+PEM format. The downside is that clients have to periodically re-download a
+potentially huge file from every certificate authority they know of.
+
+The way with most moving parts at query time is Online Certificate Status
+Protocol (OCSP), where the client verifies the certificate against an OCSP
+server run by the CA. This lets the CA track all usage of the certs. It
+requires running software with access to the private key of the CA, to sign the
+responses to the OCSP queries. OCSP is based on HTTP and can be proxied
+accordingly.
+
+The only widespread OCSP server implementation (known to this writer) comes as
+part of OpenSSL and aborts on an invalid request, such as connecting to the
+port and then disconnecting. This requires re-entering the passphrase each time
+some random client does this.
+
+The third way is OCSP Stapling; in this, the server using a certificate issued
+by the CA periodically requests an OCSP proof of validity from the OCSP server,
+then serves it up inline as part of the TLS negotiation. This approach adds no
+extra round trips, does not let the CA track users, scales well with number of
+certs issued by the CA and is resilient to temporary OCSP server failures, as
+long as the server starts retrying to fetch an OCSP proof some time before its
+current proof expires. The downside is that it requires server support.
+
+Unless Exim is built with the support disabled, or with GnuTLS earlier than
+version 3.3.16 / 3.4.8 support for OCSP stapling is included.
+
+There is a global option called tls_ocsp_file. The file specified therein is
+expected to be in DER format, and contain an OCSP proof. Exim will serve it as
+part of the TLS handshake. This option will be re-expanded for SNI, if the
+tls_certificate option contains "tls_in_sni", as per other TLS options.
+
+Exim does not at this time implement any support for fetching a new OCSP proof.
+The burden is on the administrator to handle this, outside of Exim. The file
+specified should be replaced atomically, so that the contents are always valid.
+Exim will expand the tls_ocsp_file option on each connection, so a new file
+will be handled transparently on the next connection.
+
+When built with OpenSSL Exim will check for a valid next update timestamp in
+the OCSP proof; if not present, or if the proof has expired, it will be
+ignored.
+
+For the client to be able to verify the stapled OCSP the server must also
+supply, in its stapled information, any intermediate certificates for the chain
+leading to the OCSP proof from the signer of the server certificate. There may
+be zero or one such. These intermediate certificates should be added to the
+server OCSP stapling file named by tls_ocsp_file.
+
+Note that the proof only covers the terminal server certificate, not any of the
+chain from CA to it.
+
+There is no current way to staple a proof for a client certificate.
+
+ A helper script "ocsp_fetch.pl" for fetching a proof from a CA
+ OCSP server is supplied. The server URL may be included in the
+ server certificate, if the CA is helpful.
+
+ One failure mode seen was the OCSP Signer cert expiring before the end
+ of validity of the OCSP proof. The checking done by Exim/OpenSSL
+ noted this as invalid overall, but the re-fetch script did not.
+
+
+43.9 Configuring an Exim client to use TLS
+------------------------------------------
+
+The tls_cipher and tls_peerdn log selectors apply to outgoing SMTP deliveries
+as well as to incoming, the latter one causing logging of the server
+certificate's DN. The remaining client configuration for TLS is all within the
+smtp transport.
+
+It is not necessary to set any options to have TLS work in the smtp transport.
+If Exim is built with TLS support, and TLS is advertised by a server, the smtp
+transport always tries to start a TLS session. However, this can be prevented
+by setting hosts_avoid_tls (an option of the transport) to a list of server
+hosts for which TLS should not be used.
+
+If you do not want Exim to attempt to send messages unencrypted when an attempt
+to set up an encrypted connection fails in any way, you can set
+hosts_require_tls to a list of hosts for which encryption is mandatory. For
+those hosts, delivery is always deferred if an encrypted connection cannot be
+set up. If there are any other hosts for the address, they are tried in the
+usual way.
+
+When the server host is not in hosts_require_tls, Exim may try to deliver the
+message unencrypted. It always does this if the response to STARTTLS is a 5xx
+code. For a temporary error code, or for a failure to negotiate a TLS session
+after a success response code, what happens is controlled by the
+tls_tempfail_tryclear option of the smtp transport. If it is false, delivery to
+this host is deferred, and other hosts (if available) are tried. If it is true,
+Exim attempts to deliver unencrypted after a 4xx response to STARTTLS, and if
+STARTTLS is accepted, but the subsequent TLS negotiation fails, Exim closes the
+current connection (because it is in an unknown state), opens a new one to the
+same host, and then tries the delivery unencrypted.
+
+The tls_certificate and tls_privatekey options of the smtp transport provide
+the client with a certificate, which is passed to the server if it requests it.
+If the server is Exim, it will request a certificate only if tls_verify_hosts
+or tls_try_verify_hosts matches the client.
+
+Note: Do not use a certificate which has the OCSP-must-staple extension, for
+client use (they are usable for server use). As the TLS protocol has no means
+for the client to staple before TLS 1.3 it will result in failed connections.
+
+If the tls_verify_certificates option is set on the smtp transport, it
+specifies a collection of expected server certificates. These may be the system
+default set (depending on library version), a file, or (depending on library
+version) a directory. The client verifies the server's certificate against this
+collection, taking into account any revoked certificates that are in the list
+defined by tls_crl. Failure to verify fails the TLS connection unless either of
+the tls_verify_hosts or tls_try_verify_hosts options are set.
+
+The tls_verify_hosts and tls_try_verify_hosts options restrict certificate
+verification to the listed servers. Verification either must or need not
+succeed respectively.
+
+The tls_verify_cert_hostnames option lists hosts for which additional name
+checks are made on the server certificate.
+
+The match against this list is, as per other Exim usage, the IP for the host.
+That is most closely associated with the name on the DNS A (or AAAA) record for
+the host. However, the name that needs to be in the certificate is the one at
+the head of any CNAME chain leading to the A record.
+
+The option defaults to always checking.
+
+The smtp transport has two OCSP-related options: hosts_require_ocsp; a
+host-list for which a Certificate Status is requested and required for the
+connection to proceed. The default value is empty. hosts_request_ocsp; a
+host-list for which (additionally) a Certificate Status is requested (but not
+necessarily verified). The default value is "*" meaning that requests are made
+unless configured otherwise.
+
+The host(s) should also be in hosts_require_tls, and tls_verify_certificates
+configured for the transport, for OCSP to be relevant.
+
+If tls_require_ciphers is set on the smtp transport, it must contain a list of
+permitted cipher suites. If either of these checks fails, delivery to the
+current host is abandoned, and the smtp transport tries to deliver to
+alternative hosts, if any.
+
+Note: These options must be set in the smtp transport for Exim to use TLS when
+it is operating as a client. Exim does not assume that a server certificate
+(set by the global options of the same name) should also be used when operating
+as a client.
+
+All the TLS options in the smtp transport are expanded before use, with $host
+and $host_address containing the name and address of the server to which the
+client is connected. Forced failure of an expansion causes Exim to behave as if
+the relevant option were unset.
+
+Before an SMTP connection is established, the $tls_out_bits, $tls_out_cipher,
+$tls_out_peerdn and $tls_out_sni variables are emptied. (Until the first
+connection, they contain the values that were set when the message was
+received.) If STARTTLS is subsequently successfully obeyed, these variables are
+set to the relevant values for the outgoing connection.
+
+
+43.10 Use of TLS Server Name Indication
+---------------------------------------
+
+With TLS1.0 or above, there is an extension mechanism by which extra
+information can be included at various points in the protocol. One of these
+extensions, documented in RFC 6066 (and before that RFC 4366) is "Server Name
+Indication", commonly "SNI". This extension is sent by the client in the
+initial handshake, so that the server can examine the servername within and
+possibly choose to use different certificates and keys (and more) for this
+session.
+
+This is analogous to HTTP's "Host:" header, and is the main mechanism by which
+HTTPS-enabled web-sites can be virtual-hosted, many sites to one IP address.
+
+With SMTP to MX, there are the same problems here as in choosing the identity
+against which to validate a certificate: you can't rely on insecure DNS to
+provide the identity which you then cryptographically verify. So this will be
+of limited use in that environment.
+
+With SMTP to Submission, there is a well-defined hostname which clients are
+connecting to and can validate certificates against. Thus clients can choose to
+include this information in the TLS negotiation. If this becomes wide-spread,
+then hosters can choose to present different certificates to different clients.
+Or even negotiate different cipher suites.
+
+The tls_sni option on an SMTP transport is an expanded string; the result, if
+not empty, will be sent on a TLS session as part of the handshake. There's
+nothing more to it. Choosing a sensible value not derived insecurely is the
+only point of caution. The $tls_out_sni variable will be set to this string for
+the lifetime of the client connection (including during authentication).
+
+If DAVE validated the connection attempt then the value of the tls_sni option
+is forced to the domain part of the recipient address.
+
+Except during SMTP client sessions, if $tls_in_sni is set then it is a string
+received from a client. It can be logged with the log_selector item "+tls_sni".
+
+If the string "tls_in_sni" appears in the main section's tls_certificate option
+(prior to expansion) then the following options will be re-expanded during TLS
+session handshake, to permit alternative values to be chosen:
+
+ * tls_certificate
+
+ * tls_crl
+
+ * tls_privatekey
+
+ * tls_verify_certificates
+
+ * tls_ocsp_file
+
+Great care should be taken to deal with matters of case, various injection
+attacks in the string ("../" or SQL), and ensuring that a valid filename can
+always be referenced; it is important to remember that $tls_in_sni is arbitrary
+unverified data provided prior to authentication. Further, the initial
+certificate is loaded before SNI has arrived, so an expansion for
+tls_certificate must have a default which is used when $tls_in_sni is empty.
+
+The Exim developers are proceeding cautiously and so far no other TLS options
+are re-expanded.
+
+When Exim is built against OpenSSL, OpenSSL must have been built with support
+for TLS Extensions. This holds true for OpenSSL 1.0.0+ and 0.9.8+ with
+enable-tlsext in EXTRACONFIGURE. If you invoke openssl s_client -h and see
+"-servername" in the output, then OpenSSL has support.
+
+When Exim is built against GnuTLS, SNI support is available as of GnuTLS
+0.5.10. (Its presence predates the current API which Exim uses, so if Exim
+built, then you have SNI support).
+
+
+43.11 Multiple messages on the same encrypted TCP/IP connection
+---------------------------------------------------------------
+
+Exim sends multiple messages down the same TCP/IP connection by starting up an
+entirely new delivery process for each message, passing the socket from one
+process to the next. This implementation does not fit well with the use of TLS,
+because there is quite a lot of state information associated with a TLS
+connection, not just a socket identification. Passing all the state information
+to a new process is not feasible. Consequently, for sending using TLS Exim
+starts an additional proxy process for handling the encryption, piping the
+unencrypted data stream from and to the delivery processes.
+
+An older mode of operation can be enabled on a per-host basis by the
+hosts_noproxy_tls option on the smtp transport. If the host matches this list
+the proxy process described above is not used; instead Exim shuts down an
+existing TLS session being run by the delivery process before passing the
+socket to a new process. The new process may then try to start a new TLS
+session, and if successful, may try to re-authenticate if AUTH is in use,
+before sending the next message.
+
+The RFC is not clear as to whether or not an SMTP session continues in clear
+after TLS has been shut down, or whether TLS may be restarted again later, as
+just described. However, if the server is Exim, this shutdown and
+reinitialization works. It is not known which (if any) other servers operate
+successfully if the client closes a TLS session and continues with unencrypted
+SMTP, but there are certainly some that do not work. For such servers, Exim
+should not pass the socket to another process, because the failure of the
+subsequent attempt to use it would cause Exim to record a temporary host error,
+and delay other deliveries to that host.
+
+To test for this case, Exim sends an EHLO command to the server after closing
+down the TLS session. If this fails in any way, the connection is closed
+instead of being passed to a new delivery process, but no retry information is
+recorded.
+
+There is also a manual override; you can set hosts_nopass_tls on the smtp
+transport to match those hosts for which Exim should not pass connections to
+new processes if TLS has been used.
+
+
+43.12 Certificates and all that
+-------------------------------
+
+In order to understand fully how TLS works, you need to know about
+certificates, certificate signing, and certificate authorities. This is a large
+topic and an introductory guide is unsuitable for the Exim reference manual, so
+instead we provide pointers to existing documentation.
+
+The Apache web-server was for a long time the canonical guide, so their
+documentation is a good place to start; their SSL module's Introduction
+document is currently at
+
+https://httpd.apache.org/docs/current/ssl/ssl_intro.html
+
+and their FAQ is at
+
+https://httpd.apache.org/docs/current/ssl/ssl_faq.html
+
+Eric Rescorla's book, SSL and TLS, published by Addison-Wesley (ISBN
+0-201-61598-3) in 2001, contains both introductory and more in-depth
+descriptions. More recently Ivan Risti?'s book Bulletproof SSL and TLS,
+published by Feisty Duck (ISBN 978-1907117046) in 2013 is good. Ivan is the
+author of the popular TLS testing tools at https://www.ssllabs.com/.
+
+
+43.13 Certificate chains
+------------------------
+
+The file named by tls_certificate may contain more than one certificate. This
+is useful in the case where the certificate that is being sent is validated by
+an intermediate certificate which the other end does not have. Multiple
+certificates must be in the correct order in the file. First the host's
+certificate itself, then the first intermediate certificate to validate the
+issuer of the host certificate, then the next intermediate certificate to
+validate the issuer of the first intermediate certificate, and so on, until
+finally (optionally) the root certificate. The root certificate must already be
+trusted by the recipient for validation to succeed, of course, but if it's not
+preinstalled, sending the root certificate along with the rest makes it
+available for the user to install if the receiving end is a client MUA that can
+interact with a user.
+
+Note that certificates using MD5 are unlikely to work on today's Internet; even
+if your libraries allow loading them for use in Exim when acting as a server,
+increasingly clients will not accept such certificates. The error diagnostics
+in such a case can be frustratingly vague.
+
+
+43.14 Self-signed certificates
+------------------------------
+
+You can create a self-signed certificate using the req command provided with
+OpenSSL, like this:
+
+openssl req -x509 -newkey rsa:1024 -keyout file1 -out file2 \
+ -days 9999 -nodes
+
+file1 and file2 can be the same file; the key and the certificate are delimited
+and so can be identified independently. The -days option specifies a period for
+which the certificate is valid. The -nodes option is important: if you do not
+set it, the key is encrypted with a passphrase that you are prompted for, and
+any use that is made of the key causes more prompting for the passphrase. This
+is not helpful if you are going to use this certificate and key in an MTA,
+where prompting is not possible.
+
+NB: we are now past the point where 9999 days takes us past the 32-bit Unix
+epoch. If your system uses unsigned time_t (most do) and is 32-bit, then the
+above command might produce a date in the past. Think carefully about the
+lifetime of the systems you're deploying, and either reduce the duration of the
+certificate or reconsider your platform deployment. (At time of writing,
+reducing the duration is the most likely choice, but the inexorable progression
+of time takes us steadily towards an era where this will not be a sensible
+resolution).
+
+A self-signed certificate made in this way is sufficient for testing, and may
+be adequate for all your requirements if you are mainly interested in
+encrypting transfers, and not in secure identification.
+
+However, many clients require that the certificate presented by the server be a
+user (also called "leaf" or "site") certificate, and not a self-signed
+certificate. In this situation, the self-signed certificate described above
+must be installed on the client host as a trusted root certification authority
+(CA), and the certificate used by Exim must be a user certificate signed with
+that self-signed certificate.
+
+For information on creating self-signed CA certificates and using them to sign
+user certificates, see the General implementation overview chapter of the
+Open-source PKI book, available online at https://sourceforge.net/projects/
+ospkibook/.
+
+
+43.15 DANE
+----------
+
+DNS-based Authentication of Named Entities, as applied to SMTP over TLS,
+provides assurance to a client that it is actually talking to the server it
+wants to rather than some attacker operating a Man In The Middle (MITM)
+operation. The latter can terminate the TLS connection you make, and make
+another one to the server (so both you and the server still think you have an
+encrypted connection) and, if one of the "well known" set of Certificate
+Authorities has been suborned - something which *has* been seen already (2014),
+a verifiable certificate (if you're using normal root CAs, eg. the Mozilla set,
+as your trust anchors).
+
+What DANE does is replace the CAs with the DNS as the trust anchor. The
+assurance is limited to a) the possibility that the DNS has been suborned, b)
+mistakes made by the admins of the target server. The attack surface presented
+by (a) is thought to be smaller than that of the set of root CAs.
+
+It also allows the server to declare (implicitly) that connections to it should
+use TLS. An MITM could simply fail to pass on a server's STARTTLS.
+
+DANE scales better than having to maintain (and communicate via side-channel)
+copies of server certificates for every possible target server. It also scales
+(slightly) better than having to maintain on an SMTP client a copy of the
+standard CAs bundle. It also means not having to pay a CA for certificates.
+
+DANE requires a server operator to do three things: 1) run DNSSEC. This
+provides assurance to clients that DNS lookups they do for the server have not
+been tampered with. The domain MX record applying to this server, its A record,
+its TLSA record and any associated CNAME records must all be covered by DNSSEC.
+2) add TLSA DNS records. These say what the server certificate for a TLS
+connection should be. 3) offer a server certificate, or certificate chain, in
+TLS connections which is is anchored by one of the TLSA records.
+
+There are no changes to Exim specific to server-side operation of DANE. Support
+for client-side operation of DANE can be included at compile time by defining
+SUPPORT_DANE=yes in Local/Makefile. If it has been included, the macro
+"_HAVE_DANE" will be defined.
+
+A TLSA record consist of 4 fields, the "Certificate Usage", the "Selector", the
+"Matching type", and the "Certificate Association Data". For a detailed
+description of the TLSA record see RFC 7671.
+
+The TLSA record for the server may have "Certificate Usage" (1st) field of
+DANE-TA(2) or DANE-EE(3). These are the "Trust Anchor" and "End Entity"
+variants. The latter specifies the End Entity directly, i.e. the certificate
+involved is that of the server (and if only DANE-EE is used then it should be
+the sole one transmitted during the TLS handshake); this is appropriate for a
+single system, using a self-signed certificate. DANE-TA usage is effectively
+declaring a specific CA to be used; this might be a private CA or a public,
+well-known one. A private CA at simplest is just a self-signed certificate
+(with certain attributes) which is used to sign server certificates, but
+running one securely does require careful arrangement. With DANE-TA, as
+implemented in Exim and commonly in other MTAs, the server TLS handshake must
+transmit the entire certificate chain from CA to server-certificate. DANE-TA is
+commonly used for several services and/or servers, each having a TLSA
+query-domain CNAME record, all of which point to a single TLSA record. DANE-TA
+and DANE-EE can both be used together.
+
+Our recommendation is to use DANE with a certificate from a public CA, because
+this enables a variety of strategies for remote clients to verify your
+certificate. You can then publish information both via DANE and another
+technology, "MTA-STS", described below.
+
+When you use DANE-TA to publish trust anchor information, you ask entities
+outside your administrative control to trust the Certificate Authority for
+connections to you. If using a private CA then you should expect others to
+still apply the technical criteria they'd use for a public CA to your
+certificates. In particular, you should probably try to follow current best
+practices for CA operation around hash algorithms and key sizes. Do not expect
+other organizations to lower their security expectations just because a
+particular profile might be reasonable for your own internal use.
+
+When this text was last updated, this in practice means to avoid use of SHA-1
+and MD5; if using RSA to use key sizes of at least 2048 bits (and no larger
+than 4096, for interoperability); to use keyUsage fields correctly; to use
+random serial numbers. The list of requirements is subject to change as best
+practices evolve. If you're not already using a private CA, or it doesn't meet
+these requirements, then we encourage you to avoid all these issues and use a
+public CA such as Let's Encrypt instead.
+
+The TLSA record should have a "Selector" (2nd) field of SPKI(1) and a "Matching
+Type" (3rd) field of SHA2-512(2).
+
+For the "Certificate Authority Data" (4th) field, commands like
+
+ openssl x509 -pubkey -noout <certificate.pem \
+ | openssl rsa -outform der -pubin 2>/dev/null \
+ | openssl sha512 \
+ | awk '{print $2}'
+
+are workable to create a hash of the certificate's public key.
+
+An example TLSA record for DANE-EE(3), SPKI(1), and SHA-512 (2) looks like
+
+ _25._tcp.mail.example.com. TLSA 3 1 2 8BA8A336E...
+
+At the time of writing, https://www.huque.com/bin/gen_tlsa is useful for
+quickly generating TLSA records.
+
+For use with the DANE-TA model, server certificates must have a correct name
+(SubjectName or SubjectAltName).
+
+The Certificate issued by the CA published in the DANE-TA model should be
+issued using a strong hash algorithm. Exim, and importantly various other MTAs
+sending to you, will not re-enable hash algorithms which have been disabled by
+default in TLS libraries. This means no MD5 and no SHA-1. SHA2-256 is the
+minimum for reliable interoperability (and probably the maximum too, in 2018).
+
+The use of OCSP-stapling should be considered, allowing for fast revocation of
+certificates (which would otherwise be limited by the DNS TTL on the TLSA
+records). However, this is likely to only be usable with DANE-TA. NOTE: the
+default of requesting OCSP for all hosts is modified iff DANE is in use, to:
+
+ hosts_request_ocsp = ${if or { {= {0}{$tls_out_tlsa_usage}} \
+ {= {4}{$tls_out_tlsa_usage}} } \
+ {*}{}}
+
+The (new) variable $tls_out_tlsa_usage is a bitfield with numbered bits set for
+TLSA record usage codes. The zero above means DANE was not in use, the four
+means that only DANE-TA usage TLSA records were found. If the definition of
+hosts_request_ocsp includes the string "tls_out_tlsa_usage", they are
+re-expanded in time to control the OCSP request.
+
+This modification of hosts_request_ocsp is only done if it has the default
+value of "*". Admins who change it, and those who use hosts_require_ocsp,
+should consider the interaction with DANE in their OCSP settings.
+
+For client-side DANE there are three new smtp transport options, hosts_try_dane
+, hosts_require_dane and dane_require_tls_ciphers. The "require" variant will
+result in failure if the target host is not DNSSEC-secured. To get
+DNSSEC-secured hostname resolution, use the dnssec_request_domains router or
+transport option.
+
+DANE will only be usable if the target host has DNSSEC-secured MX, A and TLSA
+records.
+
+A TLSA lookup will be done if either of the above options match and the
+host-lookup succeeded using dnssec. If a TLSA lookup is done and succeeds, a
+DANE-verified TLS connection will be required for the host. If it does not, the
+host will not be used; there is no fallback to non-DANE or non-TLS.
+
+If DANE is requested and usable, then the TLS cipher list configuration prefers
+to use the option dane_require_tls_ciphers and falls back to
+tls_require_ciphers only if that is unset. This lets you configure "decent
+crypto" for DANE and "better than nothing crypto" as the default. Note though
+that while GnuTLS lets the string control which versions of TLS/SSL will be
+negotiated, OpenSSL does not and you're limited to ciphersuite constraints.
+
+If DANE is requested and useable (see above) the following transport options
+are ignored:
+
+ hosts_require_tls
+ tls_verify_hosts
+ tls_try_verify_hosts
+ tls_verify_certificates
+ tls_crl
+ tls_verify_cert_hostnames
+ tls_sni
+
+If DANE is not usable, whether requested or not, and CA-anchored verification
+evaluation is wanted, the above variables should be set appropriately.
+
+The router and transport option dnssec_request_domains must not be set to
+"never", and dnssec_require_domains is ignored.
+
+If verification was successful using DANE then the "CV" item in the delivery
+log line will show as "CV=dane".
+
+There is a new variable $tls_out_dane which will have "yes" if verification
+succeeded using DANE and "no" otherwise (only useful in combination with
+events; see 61), and a new variable $tls_out_tlsa_usage (detailed above).
+
+An event (see 61) of type "dane:fail" will be raised on failures to achieve
+DANE-verified connection, if one was either requested and offered, or required.
+This is intended to support TLS-reporting as defined in https://tools.ietf.org/
+html/draft-ietf-uta-smtp-tlsrpt-17. The $event_data will be one of the Result
+Types defined in Section 4.3 of that document.
+
+Under GnuTLS, DANE is only supported from version 3.0.0 onwards.
+
+DANE is specified in published RFCs and decouples certificate authority trust
+selection from a "race to the bottom" of "you must trust everything for mail to
+get through". There is an alternative technology called MTA-STS, which instead
+publishes MX trust anchor information on an HTTPS website. At the time this
+text was last updated, MTA-STS was still a draft, not yet an RFC. Exim has no
+support for MTA-STS as a client, but Exim mail server operators can choose to
+publish information describing their TLS configuration using MTA-STS to let
+those clients who do use that protocol derive trust information.
+
+The MTA-STS design requires a certificate from a public Certificate Authority
+which is recognized by clients sending to you. That selection of which CAs are
+trusted by others is outside your control.
+
+The most interoperable course of action is probably to use Let's Encrypt, with
+automated certificate renewal; to publish the anchor information in
+DNSSEC-secured DNS via TLSA records for DANE clients (such as Exim and Postfix)
+and to publish anchor information for MTA-STS as well. This is what is done for
+the exim.org domain itself (with caveats around occasionally broken MTA-STS
+because of incompatible specification changes prior to reaching RFC status).
+
+
+
+===============================================================================
+44. ACCESS CONTROL LISTS
+
+Access Control Lists (ACLs) are defined in a separate section of the runtime
+configuration file, headed by "begin acl". Each ACL definition starts with a
+name, terminated by a colon. Here is a complete ACL section that contains just
+one very small ACL:
+
+begin acl
+small_acl:
+ accept hosts = one.host.only
+
+You can have as many lists as you like in the ACL section, and the order in
+which they appear does not matter. The lists are self-terminating.
+
+The majority of ACLs are used to control Exim's behaviour when it receives
+certain SMTP commands. This applies both to incoming TCP/IP connections, and
+when a local process submits a message using SMTP by specifying the -bs option.
+The most common use is for controlling which recipients are accepted in
+incoming messages. In addition, you can define an ACL that is used to check
+local non-SMTP messages. The default configuration file contains an example of
+a realistic ACL for checking RCPT commands. This is discussed in chapter 7.
+
+
+44.1 Testing ACLs
+-----------------
+
+The -bh command line option provides a way of testing your ACL configuration
+locally by running a fake SMTP session with which you interact.
+
+
+44.2 Specifying when ACLs are used
+----------------------------------
+
+In order to cause an ACL to be used, you have to name it in one of the relevant
+options in the main part of the configuration. These options are:
+
+ acl_not_smtp ACL for non-SMTP messages
+ acl_not_smtp_mime ACL for non-SMTP MIME parts
+ acl_not_smtp_start ACL at start of non-SMTP message
+ acl_smtp_auth ACL for AUTH
+ acl_smtp_connect ACL for start of SMTP connection
+ acl_smtp_data ACL after DATA is complete
+ acl_smtp_data_prdr ACL for each recipient, after DATA is complete
+ acl_smtp_dkim ACL for each DKIM signer
+ acl_smtp_etrn ACL for ETRN
+ acl_smtp_expn ACL for EXPN
+ acl_smtp_helo ACL for HELO or EHLO
+ acl_smtp_mail ACL for MAIL
+ acl_smtp_mailauth ACL for the AUTH parameter of MAIL
+ acl_smtp_mime ACL for content-scanning MIME parts
+ acl_smtp_notquit ACL for non-QUIT terminations
+ acl_smtp_predata ACL at start of DATA command
+ acl_smtp_quit ACL for QUIT
+ acl_smtp_rcpt ACL for RCPT
+ acl_smtp_starttls ACL for STARTTLS
+ acl_smtp_vrfy ACL for VRFY
+
+For example, if you set
+
+acl_smtp_rcpt = small_acl
+
+the little ACL defined above is used whenever Exim receives a RCPT command in
+an SMTP dialogue. The majority of policy tests on incoming messages can be done
+when RCPT commands arrive. A rejection of RCPT should cause the sending MTA to
+give up on the recipient address contained in the RCPT command, whereas
+rejection at other times may cause the client MTA to keep on trying to deliver
+the message. It is therefore recommended that you do as much testing as
+possible at RCPT time.
+
+
+44.3 The non-SMTP ACLs
+----------------------
+
+The non-SMTP ACLs apply to all non-interactive incoming messages, that is, they
+apply to batched SMTP as well as to non-SMTP messages. (Batched SMTP is not
+really SMTP.) Many of the ACL conditions (for example, host tests, and tests on
+the state of the SMTP connection such as encryption and authentication) are not
+relevant and are forbidden in these ACLs. However, the sender and recipients
+are known, so the senders and sender_domains conditions and the $sender_address
+and $recipients variables can be used. Variables such as $authenticated_sender
+are also available. You can specify added header lines in any of these ACLs.
+
+The acl_not_smtp_start ACL is run right at the start of receiving a non-SMTP
+message, before any of the message has been read. (This is the analogue of the
+acl_smtp_predata ACL for SMTP input.) In the case of batched SMTP input, it
+runs after the DATA command has been reached. The result of this ACL is
+ignored; it cannot be used to reject a message. If you really need to, you
+could set a value in an ACL variable here and reject based on that in the
+acl_not_smtp ACL. However, this ACL can be used to set controls, and in
+particular, it can be used to set
+
+control = suppress_local_fixups
+
+This cannot be used in the other non-SMTP ACLs because by the time they are
+run, it is too late.
+
+The acl_not_smtp_mime ACL is available only when Exim is compiled with the
+content-scanning extension. For details, see chapter 45.
+
+The acl_not_smtp ACL is run just before the local_scan() function. Any kind of
+rejection is treated as permanent, because there is no way of sending a
+temporary error for these kinds of message.
+
+
+44.4 The SMTP connect ACL
+-------------------------
+
+The ACL test specified by acl_smtp_connect happens at the start of an SMTP
+session, after the test specified by host_reject_connection (which is now an
+anomaly) and any TCP Wrappers testing (if configured). If the connection is
+accepted by an accept verb that has a message modifier, the contents of the
+message override the banner message that is otherwise specified by the
+smtp_banner option.
+
+
+44.5 The EHLO/HELO ACL
+----------------------
+
+The ACL test specified by acl_smtp_helo happens when the client issues an EHLO
+or HELO command, after the tests specified by helo_accept_junk_hosts,
+helo_allow_chars, helo_verify_hosts, and helo_try_verify_hosts. Note that a
+client may issue more than one EHLO or HELO command in an SMTP session, and
+indeed is required to issue a new EHLO or HELO after successfully setting up
+encryption following a STARTTLS command.
+
+Note also that a deny neither forces the client to go away nor means that mail
+will be refused on the connection. Consider checking for $sender_helo_name
+being defined in a MAIL or RCPT ACL to do that.
+
+If the command is accepted by an accept verb that has a message modifier, the
+message may not contain more than one line (it will be truncated at the first
+newline and a panic logged if it does). Such a message cannot affect the EHLO
+options that are listed on the second and subsequent lines of an EHLO response.
+
+
+44.6 The DATA ACLs
+------------------
+
+Two ACLs are associated with the DATA command, because it is two-stage command,
+with two responses being sent to the client. When the DATA command is received,
+the ACL defined by acl_smtp_predata is obeyed. This gives you control after all
+the RCPT commands, but before the message itself is received. It offers the
+opportunity to give a negative response to the DATA command before the data is
+transmitted. Header lines added by MAIL or RCPT ACLs are not visible at this
+time, but any that are defined here are visible when the acl_smtp_data ACL is
+run.
+
+You cannot test the contents of the message, for example, to verify addresses
+in the headers, at RCPT time or when the DATA command is received. Such tests
+have to appear in the ACL that is run after the message itself has been
+received, before the final response to the DATA command is sent. This is the
+ACL specified by acl_smtp_data, which is the second ACL that is associated with
+the DATA command.
+
+If CHUNKING was advertised and a BDAT command sequence is received, the
+acl_smtp_predata ACL is not run. The acl_smtp_data is run after the last BDAT
+command and all of the data specified is received.
+
+For both of these ACLs, it is not possible to reject individual recipients. An
+error response rejects the entire message. Unfortunately, it is known that some
+MTAs do not treat hard (5xx) responses to the DATA command (either before or
+after the data) correctly - they keep the message on their queues and try again
+later, but that is their problem, though it does waste some of your resources.
+
+The acl_smtp_data ACL is run after the acl_smtp_data_prdr, the acl_smtp_dkim
+and the acl_smtp_mime ACLs.
+
+
+44.7 The SMTP DKIM ACL
+----------------------
+
+The acl_smtp_dkim ACL is available only when Exim is compiled with DKIM support
+enabled (which is the default).
+
+The ACL test specified by acl_smtp_dkim happens after a message has been
+received, and is executed for each DKIM signature found in a message. If not
+otherwise specified, the default action is to accept.
+
+This ACL is evaluated before acl_smtp_mime and acl_smtp_data.
+
+For details on the operation of DKIM, see section 58.1.
+
+
+44.8 The SMTP MIME ACL
+----------------------
+
+The acl_smtp_mime option is available only when Exim is compiled with the
+content-scanning extension. For details, see chapter 45.
+
+This ACL is evaluated after acl_smtp_dkim but before acl_smtp_data.
+
+
+44.9 The SMTP PRDR ACL
+----------------------
+
+The acl_smtp_data_prdr ACL is available only when Exim is compiled with PRDR
+support enabled (which is the default). It becomes active only when the PRDR
+feature is negotiated between client and server for a message, and more than
+one recipient has been accepted.
+
+The ACL test specified by acl_smtp_data_prdr happens after a message has been
+received, and is executed once for each recipient of the message with
+$local_part and $domain valid. The test may accept, defer or deny for
+individual recipients. The acl_smtp_data will still be called after this ACL
+and can reject the message overall, even if this ACL has accepted it for some
+or all recipients.
+
+PRDR may be used to support per-user content filtering. Without it one must
+defer any recipient after the first that has a different content-filter
+configuration. With PRDR, the RCPT-time check for this can be disabled when the
+variable $prdr_requested is "yes". Any required difference in behaviour of the
+main DATA-time ACL should however depend on the PRDR-time ACL having run, as
+Exim will avoid doing so in some situations (e.g. single-recipient mails).
+
+See also the prdr_enable global option and the hosts_try_prdr smtp transport
+option.
+
+This ACL is evaluated after acl_smtp_dkim but before acl_smtp_data. If the ACL
+is not defined, processing completes as if the feature was not requested by the
+client.
+
+
+44.10 The QUIT ACL
+------------------
+
+The ACL for the SMTP QUIT command is anomalous, in that the outcome of the ACL
+does not affect the response code to QUIT, which is always 221. Thus, the ACL
+does not in fact control any access. For this reason, it may only accept or
+warn as its final result.
+
+This ACL can be used for tasks such as custom logging at the end of an SMTP
+session. For example, you can use ACL variables in other ACLs to count
+messages, recipients, etc., and log the totals at QUIT time using one or more
+logwrite modifiers on a warn verb.
+
+Warning: Only the $acl_cx variables can be used for this, because the $acl_mx
+variables are reset at the end of each incoming message.
+
+You do not need to have a final accept, but if you do, you can use a message
+modifier to specify custom text that is sent as part of the 221 response to
+QUIT.
+
+This ACL is run only for a "normal" QUIT. For certain kinds of disastrous
+failure (for example, failure to open a log file, or when Exim is bombing out
+because it has detected an unrecoverable error), all SMTP commands from the
+client are given temporary error responses until QUIT is received or the
+connection is closed. In these special cases, the QUIT ACL does not run.
+
+
+44.11 The not-QUIT ACL
+----------------------
+
+The not-QUIT ACL, specified by acl_smtp_notquit, is run in most cases when an
+SMTP session ends without sending QUIT. However, when Exim itself is in bad
+trouble, such as being unable to write to its log files, this ACL is not run,
+because it might try to do things (such as write to log files) that make the
+situation even worse.
+
+Like the QUIT ACL, this ACL is provided to make it possible to do customized
+logging or to gather statistics, and its outcome is ignored. The delay modifier
+is forbidden in this ACL, and the only permitted verbs are accept and warn.
+
+When the not-QUIT ACL is running, the variable $smtp_notquit_reason is set to a
+string that indicates the reason for the termination of the SMTP connection.
+The possible values are:
+
+ "acl-drop" Another ACL issued a drop command
+ "bad-commands" Too many unknown or non-mail commands
+ "command-timeout" Timeout while reading SMTP commands
+ "connection-lost" The SMTP connection has been lost
+ "data-timeout" Timeout while reading message data
+ "local-scan-error" The local_scan() function crashed
+ "local-scan-timeout" The local_scan() function timed out
+ "signal-exit" SIGTERM or SIGINT
+ "synchronization-error" SMTP synchronization error
+ "tls-failed" TLS failed to start
+
+In most cases when an SMTP connection is closed without having received QUIT,
+Exim sends an SMTP response message before actually closing the connection.
+With the exception of the "acl-drop" case, the default message can be
+overridden by the message modifier in the not-QUIT ACL. In the case of a drop
+verb in another ACL, it is the message from the other ACL that is used.
+
+
+44.12 Finding an ACL to use
+---------------------------
+
+The value of an acl_smtp_xxx option is expanded before use, so you can use
+different ACLs in different circumstances. For example,
+
+acl_smtp_rcpt = ${if ={25}{$interface_port} \
+ {acl_check_rcpt} {acl_check_rcpt_submit} }
+
+In the default configuration file there are some example settings for providing
+an RFC 4409 message "submission" service on port 587 and an RFC 8314
+"submissions" service on port 465. You can use a string expansion like this to
+choose an ACL for MUAs on these ports which is more appropriate for this
+purpose than the default ACL on port 25.
+
+The expanded string does not have to be the name of an ACL in the configuration
+file; there are other possibilities. Having expanded the string, Exim searches
+for an ACL as follows:
+
+ * If the string begins with a slash, Exim uses it as a filename, and reads
+ its contents as an ACL. The lines are processed in the same way as lines in
+ the Exim configuration file. In particular, continuation lines are
+ supported, blank lines are ignored, as are lines whose first non-whitespace
+ character is "#". If the file does not exist or cannot be read, an error
+ occurs (typically causing a temporary failure of whatever caused the ACL to
+ be run). For example:
+
+ acl_smtp_data = /etc/acls/\
+ ${lookup{$sender_host_address}lsearch\
+ {/etc/acllist}{$value}{default}}
+
+ This looks up an ACL file to use on the basis of the host's IP address,
+ falling back to a default if the lookup fails. If an ACL is successfully
+ read from a file, it is retained in memory for the duration of the Exim
+ process, so that it can be re-used without having to re-read the file.
+
+ * If the string does not start with a slash, and does not contain any spaces,
+ Exim searches the ACL section of the configuration for an ACL whose name
+ matches the string.
+
+ * If no named ACL is found, or if the string contains spaces, Exim parses the
+ string as an inline ACL. This can save typing in cases where you just want
+ to have something like
+
+ acl_smtp_vrfy = accept
+
+ in order to allow free use of the VRFY command. Such a string may contain
+ newlines; it is processed in the same way as an ACL that is read from a
+ file.
+
+
+44.13 ACL return codes
+----------------------
+
+Except for the QUIT ACL, which does not affect the SMTP return code (see
+section 44.10 above), the result of running an ACL is either "accept" or
+"deny", or, if some test cannot be completed (for example, if a database is
+down), "defer". These results cause 2xx, 5xx, and 4xx return codes,
+respectively, to be used in the SMTP dialogue. A fourth return, "error", occurs
+when there is an error such as invalid syntax in the ACL. This also causes a 4
+xx return code.
+
+For the non-SMTP ACL, "defer" and "error" are treated in the same way as
+"deny", because there is no mechanism for passing temporary errors to the
+submitters of non-SMTP messages.
+
+ACLs that are relevant to message reception may also return "discard". This has
+the effect of "accept", but causes either the entire message or an individual
+recipient address to be discarded. In other words, it is a blackholing
+facility. Use it with care.
+
+If the ACL for MAIL returns "discard", all recipients are discarded, and no ACL
+is run for subsequent RCPT commands. The effect of "discard" in a RCPT ACL is
+to discard just the one recipient address. If there are no recipients left when
+the message's data is received, the DATA ACL is not run. A "discard" return
+from the DATA or the non-SMTP ACL discards all the remaining recipients. The
+"discard" return is not permitted for the acl_smtp_predata ACL.
+
+If the ACL for VRFY returns "accept", a recipient verify (without callout) is
+done on the address and the result determines the SMTP response.
+
+The local_scan() function is always run, even if there are no remaining
+recipients; it may create new recipients.
+
+
+44.14 Unset ACL options
+-----------------------
+
+The default actions when any of the acl_xxx options are unset are not all the
+same. Note: These defaults apply only when the relevant ACL is not defined at
+all. For any defined ACL, the default action when control reaches the end of
+the ACL statements is "deny".
+
+For acl_smtp_quit and acl_not_smtp_start there is no default because these two
+are ACLs that are used only for their side effects. They cannot be used to
+accept or reject anything.
+
+For acl_not_smtp, acl_smtp_auth, acl_smtp_connect, acl_smtp_data, acl_smtp_helo
+, acl_smtp_mail, acl_smtp_mailauth, acl_smtp_mime, acl_smtp_predata, and
+acl_smtp_starttls, the action when the ACL is not defined is "accept".
+
+For the others (acl_smtp_etrn, acl_smtp_expn, acl_smtp_rcpt, and acl_smtp_vrfy
+), the action when the ACL is not defined is "deny". This means that
+acl_smtp_rcpt must be defined in order to receive any messages over an SMTP
+connection. For an example, see the ACL in the default configuration file.
+
+
+44.15 Data for message ACLs
+---------------------------
+
+When a MAIL or RCPT ACL, or either of the DATA ACLs, is running, the variables
+that contain information about the host and the message's sender (for example,
+$sender_host_address and $sender_address) are set, and can be used in ACL
+statements. In the case of RCPT (but not MAIL or DATA), $domain and $local_part
+are set from the argument address. The entire SMTP command is available in
+$smtp_command.
+
+When an ACL for the AUTH parameter of MAIL is running, the variables that
+contain information about the host are set, but $sender_address is not yet set.
+Section 33.2 contains a discussion of this parameter and how it is used.
+
+The $message_size variable is set to the value of the SIZE parameter on the
+MAIL command at MAIL, RCPT and pre-data time, or to -1 if that parameter is not
+given. The value is updated to the true message size by the time the final DATA
+ACL is run (after the message data has been received).
+
+The $rcpt_count variable increases by one for each RCPT command received. The
+$recipients_count variable increases by one each time a RCPT command is
+accepted, so while an ACL for RCPT is being processed, it contains the number
+of previously accepted recipients. At DATA time (for both the DATA ACLs),
+$rcpt_count contains the total number of RCPT commands, and $recipients_count
+contains the total number of accepted recipients.
+
+
+44.16 Data for non-message ACLs
+-------------------------------
+
+When an ACL is being run for AUTH, EHLO, ETRN, EXPN, HELO, STARTTLS, or VRFY,
+the remainder of the SMTP command line is placed in $smtp_command_argument, and
+the entire SMTP command is available in $smtp_command. These variables can be
+tested using a condition condition. For example, here is an ACL for use with
+AUTH, which insists that either the session is encrypted, or the CRAM-MD5
+authentication method is used. In other words, it does not permit
+authentication methods that use cleartext passwords on unencrypted connections.
+
+acl_check_auth:
+ accept encrypted = *
+ accept condition = ${if eq{${uc:$smtp_command_argument}}\
+ {CRAM-MD5}}
+ deny message = TLS encryption or CRAM-MD5 required
+
+(Another way of applying this restriction is to arrange for the authenticators
+that use cleartext passwords not to be advertised when the connection is not
+encrypted. You can use the generic server_advertise_condition authenticator
+option to do this.)
+
+
+44.17 Format of an ACL
+----------------------
+
+An individual ACL consists of a number of statements. Each statement starts
+with a verb, optionally followed by a number of conditions and "modifiers".
+Modifiers can change the way the verb operates, define error and log messages,
+set variables, insert delays, and vary the processing of accepted messages.
+
+If all the conditions are met, the verb is obeyed. The same condition may be
+used (with different arguments) more than once in the same statement. This
+provides a means of specifying an "and" conjunction between conditions. For
+example:
+
+deny dnslists = list1.example
+ dnslists = list2.example
+
+If there are no conditions, the verb is always obeyed. Exim stops evaluating
+the conditions and modifiers when it reaches a condition that fails. What
+happens then depends on the verb (and in one case, on a special modifier). Not
+all the conditions make sense at every testing point. For example, you cannot
+test a sender address in the ACL that is run for a VRFY command.
+
+
+44.18 ACL verbs
+---------------
+
+The ACL verbs are as follows:
+
+ * accept: If all the conditions are met, the ACL returns "accept". If any of
+ the conditions are not met, what happens depends on whether endpass appears
+ among the conditions (for syntax see below). If the failing condition is
+ before endpass, control is passed to the next ACL statement; if it is after
+ endpass, the ACL returns "deny". Consider this statement, used to check a
+ RCPT command:
+
+ accept domains = +local_domains
+ endpass
+ verify = recipient
+
+ If the recipient domain does not match the domains condition, control
+ passes to the next statement. If it does match, the recipient is verified,
+ and the command is accepted if verification succeeds. However, if
+ verification fails, the ACL yields "deny", because the failing condition is
+ after endpass.
+
+ The endpass feature has turned out to be confusing to many people, so its
+ use is not recommended nowadays. It is always possible to rewrite an ACL so
+ that endpass is not needed, and it is no longer used in the default
+ configuration.
+
+ If a message modifier appears on an accept statement, its action depends on
+ whether or not endpass is present. In the absence of endpass (when an
+ accept verb either accepts or passes control to the next statement),
+ message can be used to vary the message that is sent when an SMTP command
+ is accepted. For example, in a RCPT ACL you could have:
+
+ accept <some conditions>
+ message = OK, I will allow you through today
+
+ You can specify an SMTP response code, optionally followed by an "extended
+ response code" at the start of the message, but the first digit must be the
+ same as would be sent by default, which is 2 for an accept verb.
+
+ If endpass is present in an accept statement, message specifies an error
+ message that is used when access is denied. This behaviour is retained for
+ backward compatibility, but current "best practice" is to avoid the use of
+ endpass.
+
+ * defer: If all the conditions are true, the ACL returns "defer" which, in an
+ SMTP session, causes a 4xx response to be given. For a non-SMTP ACL, defer
+ is the same as deny, because there is no way of sending a temporary error.
+ For a RCPT command, defer is much the same as using a redirect router and
+ ":defer:" while verifying, but the defer verb can be used in any ACL, and
+ even for a recipient it might be a simpler approach.
+
+ * deny: If all the conditions are met, the ACL returns "deny". If any of the
+ conditions are not met, control is passed to the next ACL statement. For
+ example,
+
+ deny dnslists = blackholes.mail-abuse.org
+
+ rejects commands from hosts that are on a DNS black list.
+
+ * discard: This verb behaves like accept, except that it returns "discard"
+ from the ACL instead of "accept". It is permitted only on ACLs that are
+ concerned with receiving messages. When all the conditions are true, the
+ sending entity receives a "success" response. However, discard causes
+ recipients to be discarded. If it is used in an ACL for RCPT, just the one
+ recipient is discarded; if used for MAIL, DATA or in the non-SMTP ACL, all
+ the message's recipients are discarded. Recipients that are discarded
+ before DATA do not appear in the log line when the received_recipients log
+ selector is set.
+
+ If the log_message modifier is set when discard operates, its contents are
+ added to the line that is automatically written to the log. The message
+ modifier operates exactly as it does for accept.
+
+ * drop: This verb behaves like deny, except that an SMTP connection is
+ forcibly closed after the 5xx error message has been sent. For example:
+
+ drop condition = ${if > {$rcpt_count}{20}}
+ message = I don't take more than 20 RCPTs
+
+ There is no difference between deny and drop for the connect-time ACL. The
+ connection is always dropped after sending a 550 response.
+
+ * require: If all the conditions are met, control is passed to the next ACL
+ statement. If any of the conditions are not met, the ACL returns "deny".
+ For example, when checking a RCPT command,
+
+ require message = Sender did not verify
+ verify = sender
+
+ passes control to subsequent statements only if the message's sender can be
+ verified. Otherwise, it rejects the command. Note the positioning of the
+ message modifier, before the verify condition. The reason for this is
+ discussed in section 44.20.
+
+ * warn: If all the conditions are true, a line specified by the log_message
+ modifier is written to Exim's main log. Control always passes to the next
+ ACL statement. If any condition is false, the log line is not written. If
+ an identical log line is requested several times in the same message, only
+ one copy is actually written to the log. If you want to force duplicates to
+ be written, use the logwrite modifier instead.
+
+ If log_message is not present, a warn verb just checks its conditions and
+ obeys any "immediate" modifiers (such as control, set, logwrite, add_header
+ , and remove_header) that appear before the first failing condition. There
+ is more about adding header lines in section 44.24.
+
+ If any condition on a warn statement cannot be completed (that is, there is
+ some sort of defer), the log line specified by log_message is not written.
+ This does not include the case of a forced failure from a lookup, which is
+ considered to be a successful completion. After a defer, no further
+ conditions or modifiers in the warn statement are processed. The incident
+ is logged, and the ACL continues to be processed, from the next statement
+ onwards.
+
+ When one of the warn conditions is an address verification that fails, the
+ text of the verification failure message is in $acl_verify_message. If you
+ want this logged, you must set it up explicitly. For example:
+
+ warn !verify = sender
+ log_message = sender verify failed: $acl_verify_message
+
+At the end of each ACL there is an implicit unconditional deny.
+
+As you can see from the examples above, the conditions and modifiers are
+written one to a line, with the first one on the same line as the verb, and
+subsequent ones on following lines. If you have a very long condition, you can
+continue it onto several physical lines by the usual backslash continuation
+mechanism. It is conventional to align the conditions vertically.
+
+
+44.19 ACL variables
+-------------------
+
+There are some special variables that can be set during ACL processing. They
+can be used to pass information between different ACLs, different invocations
+of the same ACL in the same SMTP connection, and between ACLs and the routers,
+transports, and filters that are used to deliver a message. The names of these
+variables must begin with $acl_c or $acl_m, followed either by a digit or an
+underscore, but the remainder of the name can be any sequence of alphanumeric
+characters and underscores that you choose. There is no limit on the number of
+ACL variables. The two sets act as follows:
+
+ * The values of those variables whose names begin with $acl_c persist
+ throughout an SMTP connection. They are never reset. Thus, a value that is
+ set while receiving one message is still available when receiving the next
+ message on the same SMTP connection.
+
+ * The values of those variables whose names begin with $acl_m persist only
+ while a message is being received. They are reset afterwards. They are also
+ reset by MAIL, RSET, EHLO, HELO, and after starting up a TLS session.
+
+When a message is accepted, the current values of all the ACL variables are
+preserved with the message and are subsequently made available at delivery
+time. The ACL variables are set by a modifier called set. For example:
+
+accept hosts = whatever
+ set acl_m4 = some value
+accept authenticated = *
+ set acl_c_auth = yes
+
+Note: A leading dollar sign is not used when naming a variable that is to be
+set. If you want to set a variable without taking any action, you can use a
+warn verb without any other modifiers or conditions.
+
+What happens if a syntactically valid but undefined ACL variable is referenced
+depends on the setting of the strict_acl_vars option. If it is false (the
+default), an empty string is substituted; if it is true, an error is generated.
+
+Versions of Exim before 4.64 have a limited set of numbered variables, but
+their names are compatible, so there is no problem with upgrading.
+
+
+44.20 Condition and modifier processing
+---------------------------------------
+
+An exclamation mark preceding a condition negates its result. For example:
+
+deny domains = *.dom.example
+ !verify = recipient
+
+causes the ACL to return "deny" if the recipient domain ends in dom.example and
+the recipient address cannot be verified. Sometimes negation can be used on the
+right-hand side of a condition. For example, these two statements are
+equivalent:
+
+deny hosts = !192.168.3.4
+deny !hosts = 192.168.3.4
+
+However, for many conditions (verify being a good example), only left-hand side
+negation of the whole condition is possible.
+
+The arguments of conditions and modifiers are expanded. A forced failure of an
+expansion causes a condition to be ignored, that is, it behaves as if the
+condition is true. Consider these two statements:
+
+accept senders = ${lookup{$host_name}lsearch\
+ {/some/file}{$value}fail}
+accept senders = ${lookup{$host_name}lsearch\
+ {/some/file}{$value}{}}
+
+Each attempts to look up a list of acceptable senders. If the lookup succeeds,
+the returned list is searched, but if the lookup fails the behaviour is
+different in the two cases. The fail in the first statement causes the
+condition to be ignored, leaving no further conditions. The accept verb
+therefore succeeds. The second statement, however, generates an empty list when
+the lookup fails. No sender can match an empty list, so the condition fails,
+and therefore the accept also fails.
+
+ACL modifiers appear mixed in with conditions in ACL statements. Some of them
+specify actions that are taken as the conditions for a statement are checked;
+others specify text for messages that are used when access is denied or a
+warning is generated. The control modifier affects the way an incoming message
+is handled.
+
+The positioning of the modifiers in an ACL statement is important, because the
+processing of a verb ceases as soon as its outcome is known. Only those
+modifiers that have already been encountered will take effect. For example,
+consider this use of the message modifier:
+
+require message = Can't verify sender
+ verify = sender
+ message = Can't verify recipient
+ verify = recipient
+ message = This message cannot be used
+
+If sender verification fails, Exim knows that the result of the statement is
+"deny", so it goes no further. The first message modifier has been seen, so its
+text is used as the error message. If sender verification succeeds, but
+recipient verification fails, the second message is used. If recipient
+verification succeeds, the third message becomes "current", but is never used
+because there are no more conditions to cause failure.
+
+For the deny verb, on the other hand, it is always the last message modifier
+that is used, because all the conditions must be true for rejection to happen.
+Specifying more than one message modifier does not make sense, and the message
+can even be specified after all the conditions. For example:
+
+deny hosts = ...
+ !senders = *@my.domain.example
+ message = Invalid sender from client host
+
+The "deny" result does not happen until the end of the statement is reached, by
+which time Exim has set up the message.
+
+
+44.21 ACL modifiers
+-------------------
+
+The ACL modifiers are as follows:
+
+add_header = <text>
+
+ This modifier specifies one or more header lines that are to be added to an
+ incoming message, assuming, of course, that the message is ultimately
+ accepted. For details, see section 44.24.
+
+continue = <text>
+
+ This modifier does nothing of itself, and processing of the ACL always
+ continues with the next condition or modifier. The value of continue is in
+ the side effects of expanding its argument. Typically this could be used to
+ update a database. It is really just a syntactic tidiness, to avoid having
+ to write rather ugly lines like this:
+
+ condition = ${if eq{0}{<some expansion>}{true}{true}}
+
+ Instead, all you need is
+
+ continue = <some expansion>
+
+control = <text>
+
+ This modifier affects the subsequent processing of the SMTP connection or
+ of an incoming message that is accepted. The effect of the first type of
+ control lasts for the duration of the connection, whereas the effect of the
+ second type lasts only until the current message has been received. The
+ message-specific controls always apply to the whole message, not to
+ individual recipients, even if the control modifier appears in a RCPT ACL.
+
+ As there are now quite a few controls that can be applied, they are
+ described separately in section 44.22. The control modifier can be used in
+ several different ways. For example:
+
+ + It can be at the end of an accept statement:
+
+ accept ...some conditions
+ control = queue
+
+ In this case, the control is applied when this statement yields
+ "accept", in other words, when the conditions are all true.
+
+ + It can be in the middle of an accept statement:
+
+ accept ...some conditions...
+ control = queue
+ ...some more conditions...
+
+ If the first set of conditions are true, the control is applied, even
+ if the statement does not accept because one of the second set of
+ conditions is false. In this case, some subsequent statement must yield
+ "accept" for the control to be relevant.
+
+ + It can be used with warn to apply the control, leaving the decision
+ about accepting or denying to a subsequent verb. For example:
+
+ warn ...some conditions...
+ control = freeze
+ accept ...
+
+ This example of warn does not contain message, log_message, or logwrite
+ , so it does not add anything to the message and does not write a log
+ entry.
+
+ + If you want to apply a control unconditionally, you can use it with a
+ require verb. For example:
+
+ require control = no_multiline_responses
+
+delay = <time>
+
+ This modifier may appear in any ACL except notquit. It causes Exim to wait
+ for the time interval before proceeding. However, when testing Exim using
+ the -bh option, the delay is not actually imposed (an appropriate message
+ is output instead). The time is given in the usual Exim notation, and the
+ delay happens as soon as the modifier is processed. In an SMTP session,
+ pending output is flushed before the delay is imposed.
+
+ Like control, delay can be used with accept or deny, for example:
+
+ deny ...some conditions...
+ delay = 30s
+
+ The delay happens if all the conditions are true, before the statement
+ returns "deny". Compare this with:
+
+ deny delay = 30s
+ ...some conditions...
+
+ which waits for 30s before processing the conditions. The delay modifier
+ can also be used with warn and together with control:
+
+ warn ...some conditions...
+ delay = 2m
+ control = freeze
+ accept ...
+
+ If delay is encountered when the SMTP PIPELINING extension is in use,
+ responses to several commands are no longer buffered and sent in one packet
+ (as they would normally be) because all output is flushed before imposing
+ the delay. This optimization is disabled so that a number of small delays
+ do not appear to the client as one large aggregated delay that might
+ provoke an unwanted timeout. You can, however, disable output flushing for
+ delay by using a control modifier to set no_delay_flush.
+
+endpass
+
+ This modifier, which has no argument, is recognized only in accept and
+ discard statements. It marks the boundary between the conditions whose
+ failure causes control to pass to the next statement, and the conditions
+ whose failure causes the ACL to return "deny". This concept has proved to
+ be confusing to some people, so the use of endpass is no longer recommended
+ as "best practice". See the description of accept above for more details.
+
+log_message = <text>
+
+ This modifier sets up a message that is used as part of the log message if
+ the ACL denies access or a warn statement's conditions are true. For
+ example:
+
+ require log_message = wrong cipher suite $tls_in_cipher
+ encrypted = DES-CBC3-SHA
+
+ log_message is also used when recipients are discarded by discard. For
+ example:
+
+ discard <some conditions>
+ log_message = Discarded $local_part@$domain because...
+
+ When access is denied, log_message adds to any underlying error message
+ that may exist because of a condition failure. For example, while verifying
+ a recipient address, a :fail: redirection might have already set up a
+ message.
+
+ The message may be defined before the conditions to which it applies,
+ because the string expansion does not happen until Exim decides that access
+ is to be denied. This means that any variables that are set by the
+ condition are available for inclusion in the message. For example, the
+ $dnslist_<xxx> variables are set after a DNS black list lookup succeeds. If
+ the expansion of log_message fails, or if the result is an empty string,
+ the modifier is ignored.
+
+ If you want to use a warn statement to log the result of an address
+ verification, you can use $acl_verify_message to include the verification
+ error message.
+
+ If log_message is used with a warn statement, "Warning:" is added to the
+ start of the logged message. If the same warning log message is requested
+ more than once while receiving a single email message, only one copy is
+ actually logged. If you want to log multiple copies, use logwrite instead
+ of log_message. In the absence of log_message and logwrite, nothing is
+ logged for a successful warn statement.
+
+ If log_message is not present and there is no underlying error message (for
+ example, from the failure of address verification), but message is present,
+ the message text is used for logging rejections. However, if any text for
+ logging contains newlines, only the first line is logged. In the absence of
+ both log_message and message, a default built-in message is used for
+ logging rejections.
+
+log_reject_target = <log name list>
+
+ This modifier makes it possible to specify which logs are used for messages
+ about ACL rejections. Its argument is a colon-separated list of words that
+ can be "main", "reject", or "panic". The default is "main:reject". The list
+ may be empty, in which case a rejection is not logged at all. For example,
+ this ACL fragment writes no logging information when access is denied:
+
+ deny <some conditions>
+ log_reject_target =
+
+ This modifier can be used in SMTP and non-SMTP ACLs. It applies to both
+ permanent and temporary rejections. Its effect lasts for the rest of the
+ current ACL.
+
+logwrite = <text>
+
+ This modifier writes a message to a log file as soon as it is encountered
+ when processing an ACL. (Compare log_message, which, except in the case of
+ warn and discard, is used only if the ACL statement denies access.) The
+ logwrite modifier can be used to log special incidents in ACLs. For
+ example:
+
+ accept <some special conditions>
+ control = freeze
+ logwrite = froze message because ...
+
+ By default, the message is written to the main log. However, it may begin
+ with a colon, followed by a comma-separated list of log names, and then
+ another colon, to specify exactly which logs are to be written. For
+ example:
+
+ logwrite = :main,reject: text for main and reject logs
+ logwrite = :panic: text for panic log only
+
+message = <text>
+
+ This modifier sets up a text string that is expanded and used as a response
+ message when an ACL statement terminates the ACL with an "accept", "deny",
+ or "defer" response. (In the case of the accept and discard verbs, there is
+ some complication if endpass is involved; see the description of accept for
+ details.)
+
+ The expansion of the message happens at the time Exim decides that the ACL
+ is to end, not at the time it processes message. If the expansion fails, or
+ generates an empty string, the modifier is ignored. Here is an example
+ where message must be specified first, because the ACL ends with a
+ rejection if the hosts condition fails:
+
+ require message = Host not recognized
+ hosts = 10.0.0.0/8
+
+ (Once a condition has failed, no further conditions or modifiers are
+ processed.)
+
+ For ACLs that are triggered by SMTP commands, the message is returned as
+ part of the SMTP response. The use of message with accept (or discard) is
+ meaningful only for SMTP, as no message is returned when a non-SMTP message
+ is accepted. In the case of the connect ACL, accepting with a message
+ modifier overrides the value of smtp_banner. For the EHLO/HELO ACL, a
+ customized accept message may not contain more than one line (otherwise it
+ will be truncated at the first newline and a panic logged), and it cannot
+ affect the EHLO options.
+
+ When SMTP is involved, the message may begin with an overriding response
+ code, consisting of three digits optionally followed by an "extended
+ response code" of the form n.n.n, each code being followed by a space. For
+ example:
+
+ deny message = 599 1.2.3 Host not welcome
+ hosts = 192.168.34.0/24
+
+ The first digit of the supplied response code must be the same as would be
+ sent by default. A panic occurs if it is not. Exim uses a 550 code when it
+ denies access, but for the predata ACL, note that the default success code
+ is 354, not 2xx.
+
+ Notwithstanding the previous paragraph, for the QUIT ACL, unlike the
+ others, the message modifier cannot override the 221 response code.
+
+ The text in a message modifier is literal; any quotes are taken as
+ literals, but because the string is expanded, backslash escapes are
+ processed anyway. If the message contains newlines, this gives rise to a
+ multi-line SMTP response.
+
+ For ACLs that are called by an acl = ACL condition, the message is stored
+ in $acl_verify_message, from which the calling ACL may use it.
+
+ If message is used on a statement that verifies an address, the message
+ specified overrides any message that is generated by the verification
+ process. However, the original message is available in the variable
+ $acl_verify_message, so you can incorporate it into your message if you
+ wish. In particular, if you want the text from :fail: items in redirect
+ routers to be passed back as part of the SMTP response, you should either
+ not use a message modifier, or make use of $acl_verify_message.
+
+ For compatibility with previous releases of Exim, a message modifier that
+ is used with a warn verb behaves in a similar way to the add_header
+ modifier, but this usage is now deprecated. However, message acts only when
+ all the conditions are true, wherever it appears in an ACL command, whereas
+ add_header acts as soon as it is encountered. If message is used with warn
+ in an ACL that is not concerned with receiving a message, it has no effect.
+
+queue = <text>
+
+ This modifier specifies the use of a named queue for spool files for the
+ message. It can only be used before the message is received (i.e. not in
+ the DATA ACL). This could be used, for example, for known high-volume burst
+ sources of traffic, or for quarantine of messages. Separate queue-runner
+ processes will be needed for named queues. If the text after expansion is
+ empty, the default queue is used.
+
+remove_header = <text>
+
+ This modifier specifies one or more header names in a colon-separated list
+ that are to be removed from an incoming message, assuming, of course, that
+ the message is ultimately accepted. For details, see section 44.25.
+
+set <acl_name> = <value>
+
+ This modifier puts a value into one of the ACL variables (see section 44.19
+ ).
+
+udpsend = <parameters>
+
+ This modifier sends a UDP packet, for purposes such as statistics
+ collection or behaviour monitoring. The parameters are expanded, and the
+ result of the expansion must be a colon-separated list consisting of a
+ destination server, port number, and the packet contents. The server can be
+ specified as a host name or IPv4 or IPv6 address. The separator can be
+ changed with the usual angle bracket syntax. For example, you might want to
+ collect information on which hosts connect when:
+
+ udpsend = <; 2001:dB8::dead:beef ; 1234 ;\
+ $tod_zulu $sender_host_address
+
+
+44.22 Use of the control modifier
+---------------------------------
+
+The control modifier supports the following settings:
+
+control = allow_auth_unadvertised
+
+ This modifier allows a client host to use the SMTP AUTH command even when
+ it has not been advertised in response to EHLO. Furthermore, because there
+ are apparently some really broken clients that do this, Exim will accept
+ AUTH after HELO (rather than EHLO) when this control is set. It should be
+ used only if you really need it, and you should limit its use to those
+ broken clients that do not work without it. For example:
+
+ warn hosts = 192.168.34.25
+ control = allow_auth_unadvertised
+
+ Normally, when an Exim server receives an AUTH command, it checks the name
+ of the authentication mechanism that is given in the command to ensure that
+ it matches an advertised mechanism. When this control is set, the check
+ that a mechanism has been advertised is bypassed. Any configured mechanism
+ can be used by the client. This control is permitted only in the connection
+ and HELO ACLs.
+
+control = caseful_local_part, control = caselower_local_part
+
+ These two controls are permitted only in the ACL specified by acl_smtp_rcpt
+ (that is, during RCPT processing). By default, the contents of $local_part
+ are lower cased before ACL processing. If "caseful_local_part" is
+ specified, any uppercase letters in the original local part are restored in
+ $local_part for the rest of the ACL, or until a control that sets
+ "caselower_local_part" is encountered.
+
+ These controls affect only the current recipient. Moreover, they apply only
+ to local part handling that takes place directly in the ACL (for example,
+ as a key in lookups). If a test to verify the recipient is obeyed, the
+ case-related handling of the local part during the verification is
+ controlled by the router configuration (see the caseful_local_part generic
+ router option).
+
+ This facility could be used, for example, to add a spam score to local
+ parts containing upper case letters. For example, using $acl_m4 to
+ accumulate the spam score:
+
+ warn control = caseful_local_part
+ set acl_m4 = ${eval:\
+ $acl_m4 + \
+ ${if match{$local_part}{[A-Z]}{1}{0}}\
+ }
+ control = caselower_local_part
+
+ Notice that we put back the lower cased version afterwards, assuming that
+ is what is wanted for subsequent tests.
+
+control = cutthrough_delivery/<options>
+
+ This option requests delivery be attempted while the item is being
+ received.
+
+ The option is usable in the RCPT ACL. If enabled for a message received via
+ smtp and routed to an smtp transport, and only one transport, interface,
+ destination host and port combination is used for all recipients of the
+ message, then the delivery connection is made while the receiving
+ connection is open and data is copied from one to the other.
+
+ An attempt to set this option for any recipient but the first for a mail
+ will be quietly ignored. If a recipient-verify callout (with use_sender)
+ connection is subsequently requested in the same ACL it is held open and
+ used for any subsequent recipients and the data, otherwise one is made
+ after the initial RCPT ACL completes.
+
+ Note that routers are used in verify mode, and cannot depend on content of
+ received headers. Note also that headers cannot be modified by any of the
+ post-data ACLs (DATA, MIME and DKIM). Headers may be modified by routers
+ (subject to the above) and transports. The Received-By: header is generated
+ as soon as the body reception starts, rather than the traditional time
+ after the full message is received; this will affect the timestamp.
+
+ All the usual ACLs are called; if one results in the message being
+ rejected, all effort spent in delivery (including the costs on the ultimate
+ destination) will be wasted. Note that in the case of data-time ACLs this
+ includes the entire message body.
+
+ Cutthrough delivery is not supported via transport-filters or when DKIM
+ signing of outgoing messages is done, because it sends data to the ultimate
+ destination before the entire message has been received from the source. It
+ is not supported for messages received with the SMTP PRDR or CHUNKING
+ options in use.
+
+ Should the ultimate destination system positively accept or reject the
+ mail, a corresponding indication is given to the source system and nothing
+ is queued. If the item is successfully delivered in cutthrough mode the
+ delivery log lines are tagged with ">>" rather than "=>" and appear before
+ the acceptance "<=" line.
+
+ If there is a temporary error the item is queued for later delivery in the
+ usual fashion. This behaviour can be adjusted by appending the option defer
+ =<value> to the control; the default value is "spool" and the alternate
+ value "pass" copies an SMTP defer response from the target back to the
+ initiator and does not queue the message. Note that this is independent of
+ any recipient verify conditions in the ACL.
+
+ Delivery in this mode avoids the generation of a bounce mail to a (possibly
+ faked) sender when the destination system is doing content-scan based
+ rejection.
+
+control = debug/<options>
+
+ This control turns on debug logging, almost as though Exim had been invoked
+ with "-d", with the output going to a new logfile in the usual logs
+ directory, by default called debuglog. The filename can be adjusted with
+ the tag option, which may access any variables already defined. The logging
+ may be adjusted with the opts option, which takes the same values as the
+ "-d" command-line option. Logging started this way may be stopped, and the
+ file removed, with the kill option. Some examples (which depend on
+ variables that don't exist in all contexts):
+
+ control = debug
+ control = debug/tag=.$sender_host_address
+ control = debug/opts=+expand+acl
+ control = debug/tag=.$message_exim_id/opts=+expand
+ control = debug/kill
+
+control = dkim_disable_verify
+
+ This control turns off DKIM verification processing entirely. For details
+ on the operation and configuration of DKIM, see section 58.1.
+
+control = dmarc_disable_verify
+
+ This control turns off DMARC verification processing entirely. For details
+ on the operation and configuration of DMARC, see section 58.5.
+
+control = dscp/<value>
+
+ This option causes the DSCP value associated with the socket for the
+ inbound connection to be adjusted to a given value, given as one of a
+ number of fixed strings or to numeric value. The -bI:dscp option may be
+ used to ask Exim which names it knows of. Common values include
+ "throughput", "mincost", and on newer systems "ef", "af41", etc. Numeric
+ values may be in the range 0 to 0x3F.
+
+ The outbound packets from Exim will be marked with this value in the header
+ (for IPv4, the TOS field; for IPv6, the TCLASS field); there is no
+ guarantee that these values will have any effect, not be stripped by
+ networking equipment, or do much of anything without cooperation with your
+ Network Engineer and those of all network operators between the source and
+ destination.
+
+control = enforce_sync, control = no_enforce_sync
+
+ These controls make it possible to be selective about when SMTP
+ synchronization is enforced. The global option smtp_enforce_sync specifies
+ the initial state of the switch (it is true by default). See the
+ description of this option in chapter 14 for details of SMTP
+ synchronization checking.
+
+ The effect of these two controls lasts for the remainder of the SMTP
+ connection. They can appear in any ACL except the one for the non-SMTP
+ messages. The most straightforward place to put them is in the ACL defined
+ by acl_smtp_connect, which is run at the start of an incoming SMTP
+ connection, before the first synchronization check. The expected use is to
+ turn off the synchronization checks for badly-behaved hosts that you
+ nevertheless need to work with.
+
+control = fakedefer/<message>
+
+ This control works in exactly the same way as fakereject (described below)
+ except that it causes an SMTP 450 response after the message data instead
+ of a 550 response. You must take care when using fakedefer because it
+ causes the messages to be duplicated when the sender retries. Therefore,
+ you should not use fakedefer if the message is to be delivered normally.
+
+control = fakereject/<message>
+
+ This control is permitted only for the MAIL, RCPT, and DATA ACLs, in other
+ words, only when an SMTP message is being received. If Exim accepts the
+ message, instead the final 250 response, a 550 rejection message is sent.
+ However, Exim proceeds to deliver the message as normal. The control
+ applies only to the current message, not to any subsequent ones that may be
+ received in the same SMTP connection.
+
+ The text for the 550 response is taken from the control modifier. If no
+ message is supplied, the following is used:
+
+ 550-Your message has been rejected but is being
+ 550-kept for evaluation.
+ 550-If it was a legitimate message, it may still be
+ 550 delivered to the target recipient(s).
+
+ This facility should be used with extreme caution.
+
+control = freeze
+
+ This control is permitted only for the MAIL, RCPT, DATA, and non-SMTP ACLs,
+ in other words, only when a message is being received. If the message is
+ accepted, it is placed on Exim's queue and frozen. The control applies only
+ to the current message, not to any subsequent ones that may be received in
+ the same SMTP connection.
+
+ This modifier can optionally be followed by "/no_tell". If the global
+ option freeze_tell is set, it is ignored for the current message (that is,
+ nobody is told about the freezing), provided all the control=freeze
+ modifiers that are obeyed for the current message have the "/no_tell"
+ option.
+
+control = no_delay_flush
+
+ Exim normally flushes SMTP output before implementing a delay in an ACL, to
+ avoid unexpected timeouts in clients when the SMTP PIPELINING extension is
+ in use. This control, as long as it is encountered before the delay
+ modifier, disables such output flushing.
+
+control = no_callout_flush
+
+ Exim normally flushes SMTP output before performing a callout in an ACL, to
+ avoid unexpected timeouts in clients when the SMTP PIPELINING extension is
+ in use. This control, as long as it is encountered before the verify
+ condition that causes the callout, disables such output flushing.
+
+control = no_mbox_unspool
+
+ This control is available when Exim is compiled with the content scanning
+ extension. Content scanning may require a copy of the current message, or
+ parts of it, to be written in "mbox format" to a spool file, for passing to
+ a virus or spam scanner. Normally, such copies are deleted when they are no
+ longer needed. If this control is set, the copies are not deleted. The
+ control applies only to the current message, not to any subsequent ones
+ that may be received in the same SMTP connection. It is provided for
+ debugging purposes and is unlikely to be useful in production.
+
+control = no_multiline_responses
+
+ This control is permitted for any ACL except the one for non-SMTP messages.
+ It seems that there are broken clients in use that cannot handle multiline
+ SMTP responses, despite the fact that RFC 821 defined them over 20 years
+ ago.
+
+ If this control is set, multiline SMTP responses from ACL rejections are
+ suppressed. One way of doing this would have been to put out these
+ responses as one long line. However, RFC 2821 specifies a maximum of 512
+ bytes per response ("use multiline responses for more" it says - ha!), and
+ some of the responses might get close to that. So this facility, which is
+ after all only a sop to broken clients, is implemented by doing two very
+ easy things:
+
+ + Extra information that is normally output as part of a rejection caused
+ by sender verification failure is omitted. Only the final line
+ (typically "sender verification failed") is sent.
+
+ + If a message modifier supplies a multiline response, only the first
+ line is output.
+
+ The setting of the switch can, of course, be made conditional on the
+ calling host. Its effect lasts until the end of the SMTP connection.
+
+control = no_pipelining
+
+ This control turns off the advertising of the PIPELINING extension to SMTP
+ in the current session. To be useful, it must be obeyed before Exim sends
+ its response to an EHLO command. Therefore, it should normally appear in an
+ ACL controlled by acl_smtp_connect or acl_smtp_helo. See also
+ pipelining_advertise_hosts.
+
+control = queue/<options>*, control = queue_only
+
+ This control is permitted only for the MAIL, RCPT, DATA, and non-SMTP ACLs,
+ in other words, only when a message is being received. If the message is
+ accepted, it is placed on Exim's queue and left there for delivery by a
+ subsequent queue runner. If used with no options set, no immediate delivery
+ process is started. In other words, it has the effect as the queue_only
+ global option or -odq command-line option.
+
+ If the first_pass_route option is given then the behaviour is like the
+ command-line -oqds option; a delivery process is started which stops short
+ of making any SMTP delivery. The benefit is that the hints database will be
+ updated for the message being waiting for a specific host, and a later
+ queue run will be able to send all such messages on a single connection.
+
+ The control only applies to the current message, not to any subsequent ones
+ that may be received in the same SMTP connection.
+
+control = submission/<options>
+
+ This control is permitted only for the MAIL, RCPT, and start of data ACLs
+ (the latter is the one defined by acl_smtp_predata). Setting it tells Exim
+ that the current message is a submission from a local MUA. In this case,
+ Exim operates in "submission mode", and applies certain fixups to the
+ message if necessary. For example, it adds a Date: header line if one is
+ not present. This control is not permitted in the acl_smtp_data ACL,
+ because that is too late (the message has already been created).
+
+ Chapter 48 describes the processing that Exim applies to messages. Section
+ 48.1 covers the processing that happens in submission mode; the available
+ options for this control are described there. The control applies only to
+ the current message, not to any subsequent ones that may be received in the
+ same SMTP connection.
+
+control = suppress_local_fixups
+
+ This control applies to locally submitted (non TCP/IP) messages, and is the
+ complement of "control = submission". It disables the fixups that are
+ normally applied to locally-submitted messages. Specifically:
+
+ + Any Sender: header line is left alone (in this respect, it is a dynamic
+ version of local_sender_retain).
+
+ + No Message-ID:, From:, or Date: header lines are added.
+
+ + There is no check that From: corresponds to the actual sender.
+
+ This control may be useful when a remotely-originated message is accepted,
+ passed to some scanning program, and then re-submitted for delivery. It can
+ be used only in the acl_smtp_mail, acl_smtp_rcpt, acl_smtp_predata, and
+ acl_not_smtp_start ACLs, because it has to be set before the message's data
+ is read.
+
+ Note: This control applies only to the current message, not to any others
+ that are being submitted at the same time using -bs or -bS.
+
+control = utf8_downconvert
+
+ This control enables conversion of UTF-8 in message envelope addresses to
+ a-label form. For details see section 60.1.
+
+
+44.23 Summary of message fixup control
+--------------------------------------
+
+All four possibilities for message fixups can be specified:
+
+ * Locally submitted, fixups applied: the default.
+
+ * Locally submitted, no fixups applied: use "control =
+ suppress_local_fixups".
+
+ * Remotely submitted, no fixups applied: the default.
+
+ * Remotely submitted, fixups applied: use "control = submission".
+
+
+44.24 Adding header lines in ACLs
+---------------------------------
+
+The add_header modifier can be used to add one or more extra header lines to an
+incoming message, as in this example:
+
+warn dnslists = sbl.spamhaus.org : \
+ dialup.mail-abuse.org
+ add_header = X-blacklisted-at: $dnslist_domain
+
+The add_header modifier is permitted in the MAIL, RCPT, PREDATA, DATA, MIME,
+DKIM, and non-SMTP ACLs (in other words, those that are concerned with
+receiving a message). The message must ultimately be accepted for add_header to
+have any significant effect. You can use add_header with any ACL verb,
+including deny (though this is potentially useful only in a RCPT ACL).
+
+Headers will not be added to the message if the modifier is used in DATA, MIME
+or DKIM ACLs for a message delivered by cutthrough routing.
+
+Leading and trailing newlines are removed from the data for the add_header
+modifier; if it then contains one or more newlines that are not followed by a
+space or a tab, it is assumed to contain multiple header lines. Each one is
+checked for valid syntax; "X-ACL-Warn:" is added to the front of any line that
+is not a valid header line.
+
+Added header lines are accumulated during the MAIL, RCPT, and predata ACLs.
+They are added to the message before processing the DATA and MIME ACLs.
+However, if an identical header line is requested more than once, only one copy
+is actually added to the message. Further header lines may be accumulated
+during the DATA and MIME ACLs, after which they are added to the message, again
+with duplicates suppressed. Thus, it is possible to add two identical header
+lines to an SMTP message, but only if one is added before DATA and one after.
+In the case of non-SMTP messages, new headers are accumulated during the
+non-SMTP ACLs, and are added to the message after all the ACLs have run. If a
+message is rejected after DATA or by the non-SMTP ACL, all added header lines
+are included in the entry that is written to the reject log.
+
+Header lines are not visible in string expansions of message headers until they
+are added to the message. It follows that header lines defined in the MAIL,
+RCPT, and predata ACLs are not visible until the DATA ACL and MIME ACLs are
+run. Similarly, header lines that are added by the DATA or MIME ACLs are not
+visible in those ACLs. Because of this restriction, you cannot use header lines
+as a way of passing data between (for example) the MAIL and RCPT ACLs. If you
+want to do this, you can use ACL variables, as described in section 44.19.
+
+The list of headers yet to be added is given by the $headers_added variable.
+
+The add_header modifier acts immediately as it is encountered during the
+processing of an ACL. Notice the difference between these two cases:
+
+accept add_header = ADDED: some text
+ <some condition>
+
+accept <some condition>
+ add_header = ADDED: some text
+
+In the first case, the header line is always added, whether or not the
+condition is true. In the second case, the header line is added only if the
+condition is true. Multiple occurrences of add_header may occur in the same ACL
+statement. All those that are encountered before a condition fails are
+honoured.
+
+For compatibility with previous versions of Exim, a message modifier for a warn
+verb acts in the same way as add_header, except that it takes effect only if
+all the conditions are true, even if it appears before some of them.
+Furthermore, only the last occurrence of message is honoured. This usage of
+message is now deprecated. If both add_header and message are present on a warn
+verb, both are processed according to their specifications.
+
+By default, new header lines are added to a message at the end of the existing
+header lines. However, you can specify that any particular header line should
+be added right at the start (before all the Received: lines), immediately after
+the first block of Received: lines, or immediately before any line that is not
+a Received: or Resent-something: header.
+
+This is done by specifying ":at_start:", ":after_received:", or
+":at_start_rfc:" (or, for completeness, ":at_end:") before the text of the
+header line, respectively. (Header text cannot start with a colon, as there has
+to be a header name first.) For example:
+
+warn add_header = \
+ :after_received:X-My-Header: something or other...
+
+If more than one header line is supplied in a single add_header modifier, each
+one is treated independently and can therefore be placed differently. If you
+add more than one line at the start, or after the Received: block, they end up
+in reverse order.
+
+Warning: This facility currently applies only to header lines that are added in
+an ACL. It does NOT work for header lines that are added in a system filter or
+in a router or transport.
+
+
+44.25 Removing header lines in ACLs
+-----------------------------------
+
+The remove_header modifier can be used to remove one or more header lines from
+an incoming message, as in this example:
+
+warn message = Remove internal headers
+ remove_header = x-route-mail1 : x-route-mail2
+
+The remove_header modifier is permitted in the MAIL, RCPT, PREDATA, DATA, MIME,
+DKIM, and non-SMTP ACLs (in other words, those that are concerned with
+receiving a message). The message must ultimately be accepted for remove_header
+to have any significant effect. You can use remove_header with any ACL verb,
+including deny, though this is really not useful for any verb that doesn't
+result in a delivered message.
+
+Headers will not be removed from the message if the modifier is used in DATA,
+MIME or DKIM ACLs for a message delivered by cutthrough routing.
+
+More than one header can be removed at the same time by using a colon separated
+list of header names. The header matching is case insensitive. Wildcards are
+not permitted, nor is list expansion performed, so you cannot use hostlists to
+create a list of headers, however both connection and message variable
+expansion are performed ($acl_c_* and $acl_m_*), illustrated in this example:
+
+warn hosts = +internal_hosts
+ set acl_c_ihdrs = x-route-mail1 : x-route-mail2
+warn message = Remove internal headers
+ remove_header = $acl_c_ihdrs
+
+Header names for removal are accumulated during the MAIL, RCPT, and predata
+ACLs. Matching header lines are removed from the message before processing the
+DATA and MIME ACLs. If multiple header lines match, all are removed. There is
+no harm in attempting to remove the same header twice nor in removing a
+non-existent header. Further header lines to be removed may be accumulated
+during the DATA and MIME ACLs, after which they are removed from the message,
+if present. In the case of non-SMTP messages, headers to be removed are
+accumulated during the non-SMTP ACLs, and are removed from the message after
+all the ACLs have run. If a message is rejected after DATA or by the non-SMTP
+ACL, there really is no effect because there is no logging of what headers
+would have been removed.
+
+Header lines are not visible in string expansions until the DATA phase when it
+is received. Any header lines removed in the MAIL, RCPT, and predata ACLs are
+not visible in the DATA ACL and MIME ACLs. Similarly, header lines that are
+removed by the DATA or MIME ACLs are still visible in those ACLs. Because of
+this restriction, you cannot use header lines as a way of controlling data
+passed between (for example) the MAIL and RCPT ACLs. If you want to do this,
+you should instead use ACL variables, as described in section 44.19.
+
+The remove_header modifier acts immediately as it is encountered during the
+processing of an ACL. Notice the difference between these two cases:
+
+accept remove_header = X-Internal
+ <some condition>
+
+accept <some condition>
+ remove_header = X-Internal
+
+In the first case, the header line is always removed, whether or not the
+condition is true. In the second case, the header line is removed only if the
+condition is true. Multiple occurrences of remove_header may occur in the same
+ACL statement. All those that are encountered before a condition fails are
+honoured.
+
+Warning: This facility currently applies only to header lines that are present
+during ACL processing. It does NOT remove header lines that are added in a
+system filter or in a router or transport.
+
+
+44.26 ACL conditions
+--------------------
+
+Some of the conditions listed in this section are available only when Exim is
+compiled with the content-scanning extension. They are included here briefly
+for completeness. More detailed descriptions can be found in the discussion on
+content scanning in chapter 45.
+
+Not all conditions are relevant in all circumstances. For example, testing
+senders and recipients does not make sense in an ACL that is being run as the
+result of the arrival of an ETRN command, and checks on message headers can be
+done only in the ACLs specified by acl_smtp_data and acl_not_smtp. You can use
+the same condition (with different parameters) more than once in the same ACL
+statement. This provides a way of specifying an "and" conjunction. The
+conditions are as follows:
+
+acl = <name of acl or ACL string or file name >
+
+ The possible values of the argument are the same as for the acl_smtp_xxx
+ options. The named or inline ACL is run. If it returns "accept" the
+ condition is true; if it returns "deny" the condition is false. If it
+ returns "defer", the current ACL returns "defer" unless the condition is on
+ a warn verb. In that case, a "defer" return makes the condition false. This
+ means that further processing of the warn verb ceases, but processing of
+ the ACL continues.
+
+ If the argument is a named ACL, up to nine space-separated optional values
+ can be appended; they appear within the called ACL in $acl_arg1 to
+ $acl_arg9, and $acl_narg is set to the count of values. Previous values of
+ these variables are restored after the call returns. The name and values
+ are expanded separately. Note that spaces in complex expansions which are
+ used as arguments will act as argument separators.
+
+ If the nested acl returns "drop" and the outer condition denies access, the
+ connection is dropped. If it returns "discard", the verb must be accept or
+ discard, and the action is taken immediately - no further conditions are
+ tested.
+
+ ACLs may be nested up to 20 deep; the limit exists purely to catch runaway
+ loops. This condition allows you to use different ACLs in different
+ circumstances. For example, different ACLs can be used to handle RCPT
+ commands for different local users or different local domains.
+
+authenticated = <string list>
+
+ If the SMTP connection is not authenticated, the condition is false.
+ Otherwise, the name of the authenticator is tested against the list. To
+ test for authentication by any authenticator, you can set
+
+ authenticated = *
+
+condition = <string>
+
+ This feature allows you to make up custom conditions. If the result of
+ expanding the string is an empty string, the number zero, or one of the
+ strings "no" or "false", the condition is false. If the result is any
+ non-zero number, or one of the strings "yes" or "true", the condition is
+ true. For any other value, some error is assumed to have occurred, and the
+ ACL returns "defer". However, if the expansion is forced to fail, the
+ condition is ignored. The effect is to treat it as true, whether it is
+ positive or negative.
+
+decode = <location>
+
+ This condition is available only when Exim is compiled with the
+ content-scanning extension, and it is allowed only in the ACL defined by
+ acl_smtp_mime. It causes the current MIME part to be decoded into a file.
+ If all goes well, the condition is true. It is false only if there are
+ problems such as a syntax error or a memory shortage. For more details, see
+ chapter 45.
+
+dnslists = <list of domain names and other data>
+
+ This condition checks for entries in DNS black lists. These are also known
+ as "RBL lists", after the original Realtime Blackhole List, but note that
+ the use of the lists at mail-abuse.org now carries a charge. There are too
+ many different variants of this condition to describe briefly here. See
+ sections 44.27-44.37 for details.
+
+domains = <domain list>
+
+ This condition is relevant only after a RCPT command. It checks that the
+ domain of the recipient address is in the domain list. If percent-hack
+ processing is enabled, it is done before this test is done. If the check
+ succeeds with a lookup, the result of the lookup is placed in $domain_data
+ until the next domains test.
+
+ Note carefully (because many people seem to fall foul of this): you cannot
+ use domains in a DATA ACL.
+
+encrypted = <string list>
+
+ If the SMTP connection is not encrypted, the condition is false. Otherwise,
+ the name of the cipher suite in use is tested against the list. To test for
+ encryption without testing for any specific cipher suite(s), set
+
+ encrypted = *
+
+hosts = <host list>
+
+ This condition tests that the calling host matches the host list. If you
+ have name lookups or wildcarded host names and IP addresses in the same
+ host list, you should normally put the IP addresses first. For example, you
+ could have:
+
+ accept hosts = 10.9.8.7 : dbm;/etc/friendly/hosts
+
+ The lookup in this example uses the host name for its key. This is implied
+ by the lookup type "dbm". (For a host address lookup you would use
+ "net-dbm" and it wouldn't matter which way round you had these two items.)
+
+ The reason for the problem with host names lies in the left-to-right way
+ that Exim processes lists. It can test IP addresses without doing any DNS
+ lookups, but when it reaches an item that requires a host name, it fails if
+ it cannot find a host name to compare with the pattern. If the above list
+ is given in the opposite order, the accept statement fails for a host whose
+ name cannot be found, even if its IP address is 10.9.8.7.
+
+ If you really do want to do the name check first, and still recognize the
+ IP address even if the name lookup fails, you can rewrite the ACL like
+ this:
+
+ accept hosts = dbm;/etc/friendly/hosts
+ accept hosts = 10.9.8.7
+
+ The default action on failing to find the host name is to assume that the
+ host is not in the list, so the first accept statement fails. The second
+ statement can then check the IP address.
+
+ If a hosts condition is satisfied by means of a lookup, the result of the
+ lookup is made available in the $host_data variable. This allows you, for
+ example, to set up a statement like this:
+
+ deny hosts = net-lsearch;/some/file
+ message = $host_data
+
+ which gives a custom error message for each denied host.
+
+local_parts = <local part list>
+
+ This condition is relevant only after a RCPT command. It checks that the
+ local part of the recipient address is in the list. If percent-hack
+ processing is enabled, it is done before this test. If the check succeeds
+ with a lookup, the result of the lookup is placed in $local_part_data,
+ which remains set until the next local_parts test.
+
+malware = <option>
+
+ This condition is available only when Exim is compiled with the
+ content-scanning extension and only after a DATA command. It causes the
+ incoming message to be scanned for viruses. For details, see chapter 45.
+
+mime_regex = <list of regular expressions>
+
+ This condition is available only when Exim is compiled with the
+ content-scanning extension, and it is allowed only in the ACL defined by
+ acl_smtp_mime. It causes the current MIME part to be scanned for a match
+ with any of the regular expressions. For details, see chapter 45.
+
+ratelimit = <parameters>
+
+ This condition can be used to limit the rate at which a user or host
+ submits messages. Details are given in section 44.38.
+
+recipients = <address list>
+
+ This condition is relevant only after a RCPT command. It checks the entire
+ recipient address against a list of recipients.
+
+regex = <list of regular expressions>
+
+ This condition is available only when Exim is compiled with the
+ content-scanning extension, and is available only in the DATA, MIME, and
+ non-SMTP ACLs. It causes the incoming message to be scanned for a match
+ with any of the regular expressions. For details, see chapter 45.
+
+sender_domains = <domain list>
+
+ This condition tests the domain of the sender of the message against the
+ given domain list. Note: The domain of the sender address is in
+ $sender_address_domain. It is not put in $domain during the testing of this
+ condition. This is an exception to the general rule for testing domain
+ lists. It is done this way so that, if this condition is used in an ACL for
+ a RCPT command, the recipient's domain (which is in $domain) can be used to
+ influence the sender checking.
+
+ Warning: It is a bad idea to use this condition on its own as a control on
+ relaying, because sender addresses are easily, and commonly, forged.
+
+senders = <address list>
+
+ This condition tests the sender of the message against the given list. To
+ test for a bounce message, which has an empty sender, set
+
+ senders = :
+
+ Warning: It is a bad idea to use this condition on its own as a control on
+ relaying, because sender addresses are easily, and commonly, forged.
+
+spam = <username>
+
+ This condition is available only when Exim is compiled with the
+ content-scanning extension. It causes the incoming message to be scanned by
+ SpamAssassin. For details, see chapter 45.
+
+verify = certificate
+
+ This condition is true in an SMTP session if the session is encrypted, and
+ a certificate was received from the client, and the certificate was
+ verified. The server requests a certificate only if the client matches
+ tls_verify_hosts or tls_try_verify_hosts (see chapter 43).
+
+verify = csa
+
+ This condition checks whether the sending host (the client) is authorized
+ to send email. Details of how this works are given in section 44.50.
+
+verify = header_names_ascii
+
+ This condition is relevant only in an ACL that is run after a message has
+ been received, that is, in an ACL specified by acl_smtp_data or
+ acl_not_smtp. It checks all header names (not the content) to make sure
+ there are no non-ASCII characters, also excluding control characters. The
+ allowable characters are decimal ASCII values 33 through 126.
+
+ Exim itself will handle headers with non-ASCII characters, but it can cause
+ problems for downstream applications, so this option will allow their
+ detection and rejection in the DATA ACL's.
+
+verify = header_sender/<options>
+
+ This condition is relevant only in an ACL that is run after a message has
+ been received, that is, in an ACL specified by acl_smtp_data or
+ acl_not_smtp. It checks that there is a verifiable address in at least one
+ of the Sender:, Reply-To:, or From: header lines. Such an address is
+ loosely thought of as a "sender" address (hence the name of the test).
+ However, an address that appears in one of these headers need not be an
+ address that accepts bounce messages; only sender addresses in envelopes
+ are required to accept bounces. Therefore, if you use the callout option on
+ this check, you might want to arrange for a non-empty address in the MAIL
+ command.
+
+ Details of address verification and the options are given later, starting
+ at section 44.44 (callouts are described in section 44.45). You can combine
+ this condition with the senders condition to restrict it to bounce messages
+ only:
+
+ deny senders = :
+ !verify = header_sender
+ message = A valid sender header is required for bounces
+
+verify = header_syntax
+
+ This condition is relevant only in an ACL that is run after a message has
+ been received, that is, in an ACL specified by acl_smtp_data or
+ acl_not_smtp. It checks the syntax of all header lines that can contain
+ lists of addresses (Sender:, From:, Reply-To:, To:, Cc:, and Bcc:),
+ returning true if there are no problems. Unqualified addresses (local parts
+ without domains) are permitted only in locally generated messages and from
+ hosts that match sender_unqualified_hosts or recipient_unqualified_hosts,
+ as appropriate.
+
+ Note that this condition is a syntax check only. However, a common spamming
+ ploy used to be to send syntactically invalid headers such as
+
+ To: @
+
+ and this condition can be used to reject such messages, though they are not
+ as common as they used to be.
+
+verify = helo
+
+ This condition is true if a HELO or EHLO command has been received from the
+ client host, and its contents have been verified. If there has been no
+ previous attempt to verify the HELO/EHLO contents, it is carried out when
+ this condition is encountered. See the description of the helo_verify_hosts
+ and helo_try_verify_hosts options for details of how to request
+ verification independently of this condition, and for detail of the
+ verification.
+
+ For SMTP input that does not come over TCP/IP (the -bs command line
+ option), this condition is always true.
+
+verify = not_blind/<options>
+
+ This condition checks that there are no blind (bcc) recipients in the
+ message. Every envelope recipient must appear either in a To: header line
+ or in a Cc: header line for this condition to be true. Local parts are
+ checked case-sensitively; domains are checked case-insensitively. If
+ Resent-To: or Resent-Cc: header lines exist, they are also checked. This
+ condition can be used only in a DATA or non-SMTP ACL.
+
+ There is one possible option, "case_insensitive". If this is present then
+ local parts are checked case-insensitively.
+
+ There are, of course, many legitimate messages that make use of blind (bcc)
+ recipients. This check should not be used on its own for blocking messages.
+
+verify = recipient/<options>
+
+ This condition is relevant only after a RCPT command. It verifies the
+ current recipient. Details of address verification are given later,
+ starting at section 44.44. After a recipient has been verified, the value
+ of $address_data is the last value that was set while routing the address.
+ This applies even if the verification fails. When an address that is being
+ verified is redirected to a single address, verification continues with the
+ new address, and in that case, the subsequent value of $address_data is the
+ value for the child address.
+
+verify = reverse_host_lookup/<options>
+
+ This condition ensures that a verified host name has been looked up from
+ the IP address of the client host. (This may have happened already if the
+ host name was needed for checking a host list, or if the host matched
+ host_lookup.) Verification ensures that the host name obtained from a
+ reverse DNS lookup, or one of its aliases, does, when it is itself looked
+ up in the DNS, yield the original IP address.
+
+ There is one possible option, "defer_ok". If this is present and a DNS
+ operation returns a temporary error, the verify condition succeeds.
+
+ If this condition is used for a locally generated message (that is, when
+ there is no client host involved), it always succeeds.
+
+verify = sender/<options>
+
+ This condition is relevant only after a MAIL or RCPT command, or after a
+ message has been received (the acl_smtp_data or acl_not_smtp ACLs). If the
+ message's sender is empty (that is, this is a bounce message), the
+ condition is true. Otherwise, the sender address is verified.
+
+ If there is data in the $address_data variable at the end of routing, its
+ value is placed in $sender_address_data at the end of verification. This
+ value can be used in subsequent conditions and modifiers in the same ACL
+ statement. It does not persist after the end of the current statement. If
+ you want to preserve the value for longer, you can save it in an ACL
+ variable.
+
+ Details of verification are given later, starting at section 44.44. Exim
+ caches the result of sender verification, to avoid doing it more than once
+ per message.
+
+verify = sender=<address>/<options>
+
+ This is a variation of the previous option, in which a modified address is
+ verified as a sender.
+
+ Note that '/' is legal in local-parts; if the address may have such (eg. is
+ generated from the received message) they must be protected from the
+ options parsing by doubling:
+
+ verify = sender=${sg{${address:$h_sender:}}{/}{//}}
+
+
+44.27 Using DNS lists
+---------------------
+
+In its simplest form, the dnslists condition tests whether the calling host is
+on at least one of a number of DNS lists by looking up the inverted IP address
+in one or more DNS domains. (Note that DNS list domains are not mail domains,
+so the "+" syntax for named lists doesn't work - it is used for special options
+instead.) For example, if the calling host's IP address is 192.168.62.43, and
+the ACL statement is
+
+deny dnslists = blackholes.mail-abuse.org : \
+ dialups.mail-abuse.org
+
+the following records are looked up:
+
+43.62.168.192.blackholes.mail-abuse.org
+43.62.168.192.dialups.mail-abuse.org
+
+As soon as Exim finds an existing DNS record, processing of the list stops.
+Thus, multiple entries on the list provide an "or" conjunction. If you want to
+test that a host is on more than one list (an "and" conjunction), you can use
+two separate conditions:
+
+deny dnslists = blackholes.mail-abuse.org
+ dnslists = dialups.mail-abuse.org
+
+If a DNS lookup times out or otherwise fails to give a decisive answer, Exim
+behaves as if the host does not match the list item, that is, as if the DNS
+record does not exist. If there are further items in the DNS list, they are
+processed.
+
+This is usually the required action when dnslists is used with deny (which is
+the most common usage), because it prevents a DNS failure from blocking mail.
+However, you can change this behaviour by putting one of the following special
+items in the list:
+
++include_unknown behave as if the item is on the list
++exclude_unknown behave as if the item is not on the list (default)
++defer_unknown give a temporary error
+
+Each of these applies to any subsequent items on the list. For example:
+
+deny dnslists = +defer_unknown : foo.bar.example
+
+Testing the list of domains stops as soon as a match is found. If you want to
+warn for one list and block for another, you can use two different statements:
+
+deny dnslists = blackholes.mail-abuse.org
+warn dnslists = dialups.mail-abuse.org
+ message = X-Warn: sending host is on dialups list
+
+DNS list lookups are cached by Exim for the duration of the SMTP session (but
+limited by the DNS return TTL value), so a lookup based on the IP address is
+done at most once for any incoming connection (assuming long-enough TTL). Exim
+does not share information between multiple incoming connections (but your
+local name server cache should be active).
+
+There are a number of DNS lists to choose from, some commercial, some free, or
+free for small deployments. An overview can be found at https://
+en.wikipedia.org/wiki/Comparison_of_DNS_blacklists.
+
+
+44.28 Specifying the IP address for a DNS list lookup
+-----------------------------------------------------
+
+By default, the IP address that is used in a DNS list lookup is the IP address
+of the calling host. However, you can specify another IP address by listing it
+after the domain name, introduced by a slash. For example:
+
+deny dnslists = black.list.tld/192.168.1.2
+
+This feature is not very helpful with explicit IP addresses; it is intended for
+use with IP addresses that are looked up, for example, the IP addresses of the
+MX hosts or nameservers of an email sender address. For an example, see section
+44.30 below.
+
+
+44.29 DNS lists keyed on domain names
+-------------------------------------
+
+There are some lists that are keyed on domain names rather than inverted IP
+addresses (see, e.g., the domain based zones link at http://
+www.rfc-ignorant.org/). No reversing of components is used with these lists.
+You can change the name that is looked up in a DNS list by listing it after the
+domain name, introduced by a slash. For example,
+
+deny dnslists = dsn.rfc-ignorant.org/$sender_address_domain
+ message = Sender's domain is listed at $dnslist_domain
+
+This particular example is useful only in ACLs that are obeyed after the RCPT
+or DATA commands, when a sender address is available. If (for example) the
+message's sender is user@tld.example the name that is looked up by this example
+is
+
+tld.example.dsn.rfc-ignorant.org
+
+A single dnslists condition can contain entries for both names and IP
+addresses. For example:
+
+deny dnslists = sbl.spamhaus.org : \
+ dsn.rfc-ignorant.org/$sender_address_domain
+
+The first item checks the sending host's IP address; the second checks a domain
+name. The whole condition is true if either of the DNS lookups succeeds.
+
+
+44.30 Multiple explicit keys for a DNS list
+-------------------------------------------
+
+The syntax described above for looking up explicitly-defined values (either
+names or IP addresses) in a DNS blacklist is a simplification. After the domain
+name for the DNS list, what follows the slash can in fact be a list of items.
+As with all lists in Exim, the default separator is a colon. However, because
+this is a sublist within the list of DNS blacklist domains, it is necessary
+either to double the separators like this:
+
+dnslists = black.list.tld/name.1::name.2
+
+or to change the separator character, like this:
+
+dnslists = black.list.tld/<;name.1;name.2
+
+If an item in the list is an IP address, it is inverted before the DNS
+blacklist domain is appended. If it is not an IP address, no inversion occurs.
+Consider this condition:
+
+dnslists = black.list.tld/<;192.168.1.2;a.domain
+
+The DNS lookups that occur are:
+
+2.1.168.192.black.list.tld
+a.domain.black.list.tld
+
+Once a DNS record has been found (that matches a specific IP return address, if
+specified - see section 44.33), no further lookups are done. If there is a
+temporary DNS error, the rest of the sublist of domains or IP addresses is
+tried. A temporary error for the whole dnslists item occurs only if no other
+DNS lookup in this sublist succeeds. In other words, a successful lookup for
+any of the items in the sublist overrides a temporary error for a previous
+item.
+
+The ability to supply a list of items after the slash is in some sense just a
+syntactic convenience. These two examples have the same effect:
+
+dnslists = black.list.tld/a.domain : black.list.tld/b.domain
+dnslists = black.list.tld/a.domain::b.domain
+
+However, when the data for the list is obtained from a lookup, the second form
+is usually much more convenient. Consider this example:
+
+deny dnslists = sbl.spamhaus.org/<|${lookup dnsdb {>|a=<|\
+ ${lookup dnsdb {>|mxh=\
+ $sender_address_domain} }} }
+ message = The mail servers for the domain \
+ $sender_address_domain \
+ are listed at $dnslist_domain ($dnslist_value); \
+ see $dnslist_text.
+
+Note the use of ">|" in the dnsdb lookup to specify the separator for multiple
+DNS records. The inner dnsdb lookup produces a list of MX hosts and the outer
+dnsdb lookup finds the IP addresses for these hosts. The result of expanding
+the condition might be something like this:
+
+dnslists = sbl.spamhaus.org/<|192.168.2.3|192.168.5.6|...
+
+Thus, this example checks whether or not the IP addresses of the sender
+domain's mail servers are on the Spamhaus black list.
+
+The key that was used for a successful DNS list lookup is put into the variable
+$dnslist_matched (see section 44.32).
+
+
+44.31 Data returned by DNS lists
+--------------------------------
+
+DNS lists are constructed using address records in the DNS. The original RBL
+just used the address 127.0.0.1 on the right hand side of each record, but the
+RBL+ list and some other lists use a number of values with different meanings.
+The values used on the RBL+ list are:
+
+127.1.0.1 RBL
+127.1.0.2 DUL
+127.1.0.3 DUL and RBL
+127.1.0.4 RSS
+127.1.0.5 RSS and RBL
+127.1.0.6 RSS and DUL
+127.1.0.7 RSS and DUL and RBL
+
+Section 44.33 below describes how you can distinguish between different values.
+Some DNS lists may return more than one address record; see section 44.35 for
+details of how they are checked.
+
+
+44.32 Variables set from DNS lists
+----------------------------------
+
+When an entry is found in a DNS list, the variable $dnslist_domain contains the
+name of the overall domain that matched (for example, "spamhaus.example"),
+$dnslist_matched contains the key within that domain (for example,
+"192.168.5.3"), and $dnslist_value contains the data from the DNS record. When
+the key is an IP address, it is not reversed in $dnslist_matched (though it is,
+of course, in the actual lookup). In simple cases, for example:
+
+deny dnslists = spamhaus.example
+
+the key is also available in another variable (in this case,
+$sender_host_address). In more complicated cases, however, this is not true.
+For example, using a data lookup (as described in section 44.30) might generate
+a dnslists lookup like this:
+
+deny dnslists = spamhaus.example/<|192.168.1.2|192.168.6.7|...
+
+If this condition succeeds, the value in $dnslist_matched might be
+"192.168.6.7" (for example).
+
+If more than one address record is returned by the DNS lookup, all the IP
+addresses are included in $dnslist_value, separated by commas and spaces. The
+variable $dnslist_text contains the contents of any associated TXT record. For
+lists such as RBL+ the TXT record for a merged entry is often not very
+meaningful. See section 44.36 for a way of obtaining more information.
+
+You can use the DNS list variables in message or log_message modifiers - even
+if these appear before the condition in the ACL, they are not expanded until
+after it has failed. For example:
+
+deny hosts = !+local_networks
+ message = $sender_host_address is listed \
+ at $dnslist_domain
+ dnslists = rbl-plus.mail-abuse.example
+
+
+44.33 Additional matching conditions for DNS lists
+--------------------------------------------------
+
+You can add an equals sign and an IP address after a dnslists domain name in
+order to restrict its action to DNS records with a matching right hand side.
+For example,
+
+deny dnslists = rblplus.mail-abuse.org=127.0.0.2
+
+rejects only those hosts that yield 127.0.0.2. Without this additional data,
+any address record is considered to be a match. For the moment, we assume that
+the DNS lookup returns just one record. Section 44.35 describes how multiple
+records are handled.
+
+More than one IP address may be given for checking, using a comma as a
+separator. These are alternatives - if any one of them matches, the dnslists
+condition is true. For example:
+
+deny dnslists = a.b.c=127.0.0.2,127.0.0.3
+
+If you want to specify a constraining address list and also specify names or IP
+addresses to be looked up, the constraining address list must be specified
+first. For example:
+
+deny dnslists = dsn.rfc-ignorant.org\
+ =127.0.0.2/$sender_address_domain
+
+If the character "&" is used instead of "=", the comparison for each listed IP
+address is done by a bitwise "and" instead of by an equality test. In other
+words, the listed addresses are used as bit masks. The comparison is true if
+all the bits in the mask are present in the address that is being tested. For
+example:
+
+dnslists = a.b.c&0.0.0.3
+
+matches if the address is x.x.x.3, x.x.x.7, x.x.x.11, etc. If you want to test
+whether one bit or another bit is present (as opposed to both being present),
+you must use multiple values. For example:
+
+dnslists = a.b.c&0.0.0.1,0.0.0.2
+
+matches if the final component of the address is an odd number or two times an
+odd number.
+
+
+44.34 Negated DNS matching conditions
+-------------------------------------
+
+You can supply a negative list of IP addresses as part of a dnslists condition.
+Whereas
+
+deny dnslists = a.b.c=127.0.0.2,127.0.0.3
+
+means "deny if the host is in the black list at the domain a.b.c and the IP
+address yielded by the list is either 127.0.0.2 or 127.0.0.3",
+
+deny dnslists = a.b.c!=127.0.0.2,127.0.0.3
+
+means "deny if the host is in the black list at the domain a.b.c and the IP
+address yielded by the list is not 127.0.0.2 and not 127.0.0.3". In other
+words, the result of the test is inverted if an exclamation mark appears before
+the "=" (or the "&") sign.
+
+Note: This kind of negation is not the same as negation in a domain, host, or
+address list (which is why the syntax is different).
+
+If you are using just one list, the negation syntax does not gain you much. The
+previous example is precisely equivalent to
+
+deny dnslists = a.b.c
+ !dnslists = a.b.c=127.0.0.2,127.0.0.3
+
+However, if you are using multiple lists, the negation syntax is clearer.
+Consider this example:
+
+deny dnslists = sbl.spamhaus.org : \
+ list.dsbl.org : \
+ dnsbl.njabl.org!=127.0.0.3 : \
+ relays.ordb.org
+
+Using only positive lists, this would have to be:
+
+deny dnslists = sbl.spamhaus.org : \
+ list.dsbl.org
+deny dnslists = dnsbl.njabl.org
+ !dnslists = dnsbl.njabl.org=127.0.0.3
+deny dnslists = relays.ordb.org
+
+which is less clear, and harder to maintain.
+
+
+44.35 Handling multiple DNS records from a DNS list
+---------------------------------------------------
+
+A DNS lookup for a dnslists condition may return more than one DNS record,
+thereby providing more than one IP address. When an item in a dnslists list is
+followed by "=" or "&" and a list of IP addresses, in order to restrict the
+match to specific results from the DNS lookup, there are two ways in which the
+checking can be handled. For example, consider the condition:
+
+dnslists = a.b.c=127.0.0.1
+
+What happens if the DNS lookup for the incoming IP address yields both
+127.0.0.1 and 127.0.0.2 by means of two separate DNS records? Is the condition
+true because at least one given value was found, or is it false because at
+least one of the found values was not listed? And how does this affect negated
+conditions? Both possibilities are provided for with the help of additional
+separators "==" and "=&".
+
+ * If "=" or "&" is used, the condition is true if any one of the looked up IP
+ addresses matches one of the listed addresses. For the example above, the
+ condition is true because 127.0.0.1 matches.
+
+ * If "==" or "=&" is used, the condition is true only if every one of the
+ looked up IP addresses matches one of the listed addresses. If the
+ condition is changed to:
+
+ dnslists = a.b.c==127.0.0.1
+
+ and the DNS lookup yields both 127.0.0.1 and 127.0.0.2, the condition is
+ false because 127.0.0.2 is not listed. You would need to have:
+
+ dnslists = a.b.c==127.0.0.1,127.0.0.2
+
+ for the condition to be true.
+
+When "!" is used to negate IP address matching, it inverts the result, giving
+the precise opposite of the behaviour above. Thus:
+
+ * If "!=" or "!&" is used, the condition is true if none of the looked up IP
+ addresses matches one of the listed addresses. Consider:
+
+ dnslists = a.b.c!&0.0.0.1
+
+ If the DNS lookup yields both 127.0.0.1 and 127.0.0.2, the condition is
+ false because 127.0.0.1 matches.
+
+ * If "!==" or "!=&" is used, the condition is true if there is at least one
+ looked up IP address that does not match. Consider:
+
+ dnslists = a.b.c!=&0.0.0.1
+
+ If the DNS lookup yields both 127.0.0.1 and 127.0.0.2, the condition is
+ true, because 127.0.0.2 does not match. You would need to have:
+
+ dnslists = a.b.c!=&0.0.0.1,0.0.0.2
+
+ for the condition to be false.
+
+When the DNS lookup yields only a single IP address, there is no difference
+between "=" and "==" and between "&" and "=&".
+
+
+44.36 Detailed information from merged DNS lists
+------------------------------------------------
+
+When the facility for restricting the matching IP values in a DNS list is used,
+the text from the TXT record that is set in $dnslist_text may not reflect the
+true reason for rejection. This happens when lists are merged and the IP
+address in the A record is used to distinguish them; unfortunately there is
+only one TXT record. One way round this is not to use merged lists, but that
+can be inefficient because it requires multiple DNS lookups where one would do
+in the vast majority of cases when the host of interest is not on any of the
+lists.
+
+A less inefficient way of solving this problem is available. If two domain
+names, comma-separated, are given, the second is used first to do an initial
+check, making use of any IP value restrictions that are set. If there is a
+match, the first domain is used, without any IP value restrictions, to get the
+TXT record. As a byproduct of this, there is also a check that the IP being
+tested is indeed on the first list. The first domain is the one that is put in
+$dnslist_domain. For example:
+
+deny dnslists = \
+ sbl.spamhaus.org,sbl-xbl.spamhaus.org=127.0.0.2 : \
+ dul.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.10
+ message = \
+ rejected because $sender_host_address is blacklisted \
+ at $dnslist_domain\n$dnslist_text
+
+For the first blacklist item, this starts by doing a lookup in
+sbl-xbl.spamhaus.org and testing for a 127.0.0.2 return. If there is a match,
+it then looks in sbl.spamhaus.org, without checking the return value, and as
+long as something is found, it looks for the corresponding TXT record. If there
+is no match in sbl-xbl.spamhaus.org, nothing more is done. The second blacklist
+item is processed similarly.
+
+If you are interested in more than one merged list, the same list must be given
+several times, but because the results of the DNS lookups are cached, the DNS
+calls themselves are not repeated. For example:
+
+deny dnslists = \
+ http.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.2 : \
+ socks.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.3 : \
+ misc.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.4 : \
+ dul.dnsbl.sorbs.net,dnsbl.sorbs.net=127.0.0.10
+
+In this case there is one lookup in dnsbl.sorbs.net, and if none of the IP
+values matches (or if no record is found), this is the only lookup that is
+done. Only if there is a match is one of the more specific lists consulted.
+
+
+44.37 DNS lists and IPv6
+------------------------
+
+If Exim is asked to do a dnslist lookup for an IPv6 address, it inverts it
+nibble by nibble. For example, if the calling host's IP address is
+3ffe:ffff:836f:0a00:000a:0800:200a:c031, Exim might look up
+
+1.3.0.c.a.0.0.2.0.0.8.0.a.0.0.0.0.0.a.0.f.6.3.8.
+ f.f.f.f.e.f.f.3.blackholes.mail-abuse.org
+
+(split over two lines here to fit on the page). Unfortunately, some of the DNS
+lists contain wildcard records, intended for IPv4, that interact badly with
+IPv6. For example, the DNS entry
+
+*.3.some.list.example. A 127.0.0.1
+
+is probably intended to put the entire 3.0.0.0/8 IPv4 network on the list.
+Unfortunately, it also matches the entire 3::/4 IPv6 network.
+
+You can exclude IPv6 addresses from DNS lookups by making use of a suitable
+condition condition, as in this example:
+
+deny condition = ${if isip4{$sender_host_address}}
+ dnslists = some.list.example
+
+If an explicit key is being used for a DNS lookup and it may be an IPv6 address
+you should specify alternate list separators for both the outer (DNS list name)
+list and inner (lookup keys) list:
+
+ dnslists = <; dnsbl.example.com/<|$acl_m_addrslist
+
+
+44.38 Rate limiting incoming messages
+-------------------------------------
+
+The ratelimit ACL condition can be used to measure and control the rate at
+which clients can send email. This is more powerful than the smtp_ratelimit_*
+options, because those options control the rate of commands in a single SMTP
+session only, whereas the ratelimit condition works across all connections
+(concurrent and sequential) from the same client host. The syntax of the
+ratelimit condition is:
+
+ratelimit = <m> / <p> / <options> / <key>
+
+If the average client sending rate is less than m messages per time period p
+then the condition is false; otherwise it is true.
+
+As a side-effect, the ratelimit condition sets the expansion variable
+$sender_rate to the client's computed rate, $sender_rate_limit to the
+configured value of m, and $sender_rate_period to the configured value of p.
+
+The parameter p is the smoothing time constant, in the form of an Exim time
+interval, for example, "8h" for eight hours. A larger time constant means that
+it takes Exim longer to forget a client's past behaviour. The parameter m is
+the maximum number of messages that a client is permitted to send in each time
+interval. It also specifies the number of messages permitted in a fast burst.
+By increasing both m and p but keeping m/p constant, you can allow a client to
+send more messages in a burst without changing its long-term sending rate
+limit. Conversely, if m and p are both small, messages must be sent at an even
+rate.
+
+There is a script in util/ratelimit.pl which extracts sending rates from log
+files, to assist with choosing appropriate settings for m and p when deploying
+the ratelimit ACL condition. The script prints usage instructions when it is
+run with no arguments.
+
+The key is used to look up the data for calculating the client's average
+sending rate. This data is stored in Exim's spool directory, alongside the
+retry and other hints databases. The default key is $sender_host_address, which
+means Exim computes the sending rate of each client host IP address. By
+changing the key you can change how Exim identifies clients for the purpose of
+ratelimiting. For example, to limit the sending rate of each authenticated
+user, independent of the computer they are sending from, set the key to
+$authenticated_id. You must ensure that the lookup key is meaningful; for
+example, $authenticated_id is only meaningful if the client has authenticated
+(which you can check with the authenticated ACL condition).
+
+The lookup key does not have to identify clients: If you want to limit the rate
+at which a recipient receives messages, you can use the key
+"$local_part@$domain" with the per_rcpt option (see below) in a RCPT ACL.
+
+Each ratelimit condition can have up to four options. A per_* option specifies
+what Exim measures the rate of, for example, messages or recipients or bytes.
+You can adjust the measurement using the unique= and/or count= options. You can
+also control when Exim updates the recorded rate using a strict, leaky, or
+readonly option. The options are separated by a slash, like the other
+parameters. They may appear in any order.
+
+Internally, Exim appends the smoothing constant p onto the lookup key with any
+options that alter the meaning of the stored data. The limit m is not stored,
+so you can alter the configured maximum rate and Exim will still remember
+clients' past behaviour. If you change the per_* mode or add or remove the
+unique= option, the lookup key changes so Exim will forget past behaviour. The
+lookup key is not affected by changes to the update mode and the count= option.
+
+
+44.39 Ratelimit options for what is being measured
+--------------------------------------------------
+
+The per_conn option limits the client's connection rate. It is not normally
+used in the acl_not_smtp, acl_not_smtp_mime, or acl_not_smtp_start ACLs.
+
+The per_mail option limits the client's rate of sending messages. This is the
+default if none of the per_* options is specified. It can be used in
+acl_smtp_mail, acl_smtp_rcpt, acl_smtp_predata, acl_smtp_mime, acl_smtp_data,
+or acl_not_smtp.
+
+The per_byte option limits the sender's email bandwidth. It can be used in the
+same ACLs as the per_mail option, though it is best to use this option in the
+acl_smtp_mime, acl_smtp_data or acl_not_smtp ACLs; if it is used in an earlier
+ACL, Exim relies on the SIZE parameter given by the client in its MAIL command,
+which may be inaccurate or completely missing. You can follow the limit m in
+the configuration with K, M, or G to specify limits in kilobytes, megabytes, or
+gigabytes, respectively.
+
+The per_rcpt option causes Exim to limit the rate at which recipients are
+accepted. It can be used in the acl_smtp_rcpt, acl_smtp_predata, acl_smtp_mime,
+acl_smtp_data, or acl_smtp_rcpt ACLs. In acl_smtp_rcpt the rate is updated one
+recipient at a time; in the other ACLs the rate is updated with the total
+(accepted) recipient count in one go. Note that in either case the rate
+limiting engine will see a message with many recipients as a large high-speed
+burst.
+
+The per_addr option is like the per_rcpt option, except it counts the number of
+different recipients that the client has sent messages to in the last time
+period. That is, if the client repeatedly sends messages to the same recipient,
+its measured rate is not increased. This option can only be used in
+acl_smtp_rcpt.
+
+The per_cmd option causes Exim to recompute the rate every time the condition
+is processed. This can be used to limit the rate of any SMTP command. If it is
+used in multiple ACLs it can limit the aggregate rate of multiple different
+commands.
+
+The count= option can be used to alter how much Exim adds to the client's
+measured rate. For example, the per_byte option is equivalent to "per_mail/
+count=$message_size". If there is no count= option, Exim increases the measured
+rate by one (except for the per_rcpt option in ACLs other than acl_smtp_rcpt).
+The count does not have to be an integer.
+
+The unique= option is described in section 44.42 below.
+
+
+44.40 Ratelimit update modes
+----------------------------
+
+You can specify one of three options with the ratelimit condition to control
+when its database is updated. This section describes the readonly mode, and the
+next section describes the strict and leaky modes.
+
+If the ratelimit condition is used in readonly mode, Exim looks up a
+previously-computed rate to check against the limit.
+
+For example, you can test the client's sending rate and deny it access (when it
+is too fast) in the connect ACL. If the client passes this check then it can go
+on to send a message, in which case its recorded rate will be updated in the
+MAIL ACL. Subsequent connections from the same client will check this new rate.
+
+acl_check_connect:
+ deny ratelimit = 100 / 5m / readonly
+ log_message = RATE CHECK: $sender_rate/$sender_rate_period \
+ (max $sender_rate_limit)
+# ...
+acl_check_mail:
+ warn ratelimit = 100 / 5m / strict
+ log_message = RATE UPDATE: $sender_rate/$sender_rate_period \
+ (max $sender_rate_limit)
+
+If Exim encounters multiple ratelimit conditions with the same key when
+processing a message then it may increase the client's measured rate more than
+it should. For example, this will happen if you check the per_rcpt option in
+both acl_smtp_rcpt and acl_smtp_data. However it's OK to check the same
+ratelimit condition multiple times in the same ACL. You can avoid any multiple
+update problems by using the readonly option on later ratelimit checks.
+
+The per_* options described above do not make sense in some ACLs. If you use a
+per_* option in an ACL where it is not normally permitted then the update mode
+defaults to readonly and you cannot specify the strict or leaky modes. In other
+ACLs the default update mode is leaky (see the next section) so you must
+specify the readonly option explicitly.
+
+
+44.41 Ratelimit options for handling fast clients
+-------------------------------------------------
+
+If a client's average rate is greater than the maximum, the rate limiting
+engine can react in two possible ways, depending on the presence of the strict
+or leaky update modes. This is independent of the other counter-measures (such
+as rejecting the message) that may be specified by the rest of the ACL.
+
+The leaky (default) option means that the client's recorded rate is not updated
+if it is above the limit. The effect of this is that Exim measures the client's
+average rate of successfully sent email, up to the given limit. This is
+appropriate if the countermeasure when the condition is true consists of
+refusing the message, and is generally the better choice if you have clients
+that retry automatically. If the action when true is anything more complex then
+this option is likely not what is wanted.
+
+The strict option means that the client's recorded rate is always updated. The
+effect of this is that Exim measures the client's average rate of attempts to
+send email, which can be much higher than the maximum it is actually allowed.
+If the client is over the limit it may be subjected to counter-measures by the
+ACL. It must slow down and allow sufficient time to pass that its computed rate
+falls below the maximum before it can send email again. The time (the number of
+smoothing periods) it must wait and not attempt to send mail can be calculated
+with this formula:
+
+ ln(peakrate/maxrate)
+
+
+44.42 Limiting the rate of different events
+-------------------------------------------
+
+The ratelimit unique= option controls a mechanism for counting the rate of
+different events. For example, the per_addr option uses this mechanism to count
+the number of different recipients that the client has sent messages to in the
+last time period; it is equivalent to "per_rcpt/unique=$local_part@$domain".
+You could use this feature to measure the rate that a client uses different
+sender addresses with the options "per_mail/unique=$sender_address".
+
+For each ratelimit key Exim stores the set of unique= values that it has seen
+for that key. The whole set is thrown away when it is older than the rate
+smoothing period p, so each different event is counted at most once per period.
+In the leaky update mode, an event that causes the client to go over the limit
+is not added to the set, in the same way that the client's recorded rate is not
+updated in the same situation.
+
+When you combine the unique= and readonly options, the specific unique= value
+is ignored, and Exim just retrieves the client's stored rate.
+
+The unique= mechanism needs more space in the ratelimit database than the other
+ratelimit options in order to store the event set. The number of unique values
+is potentially as large as the rate limit, so the extra space required
+increases with larger limits.
+
+The uniqueification is not perfect: there is a small probability that Exim will
+think a new event has happened before. If the sender's rate is less than the
+limit, Exim should be more than 99.9% correct. However in strict mode the
+measured rate can go above the limit, in which case Exim may under-count events
+by a significant margin. Fortunately, if the rate is high enough (2.7 times the
+limit) that the false positive rate goes above 9%, then Exim will throw away
+the over-full event set before the measured rate falls below the limit.
+Therefore the only harm should be that exceptionally high sending rates are
+logged incorrectly; any countermeasures you configure will be as effective as
+intended.
+
+
+44.43 Using rate limiting
+-------------------------
+
+Exim's other ACL facilities are used to define what counter-measures are taken
+when the rate limit is exceeded. This might be anything from logging a warning
+(for example, while measuring existing sending rates in order to define
+policy), through time delays to slow down fast senders, up to rejecting the
+message. For example:
+
+# Log all senders' rates
+warn ratelimit = 0 / 1h / strict
+ log_message = Sender rate $sender_rate / $sender_rate_period
+
+# Slow down fast senders; note the need to truncate $sender_rate
+# at the decimal point.
+warn ratelimit = 100 / 1h / per_rcpt / strict
+ delay = ${eval: ${sg{$sender_rate}{[.].*}{}} - \
+ $sender_rate_limit }s
+
+# Keep authenticated users under control
+deny authenticated = *
+ ratelimit = 100 / 1d / strict / $authenticated_id
+
+# System-wide rate limit
+defer ratelimit = 10 / 1s / $primary_hostname
+ message = Sorry, too busy. Try again later.
+
+# Restrict incoming rate from each host, with a default
+# set using a macro and special cases looked up in a table.
+defer ratelimit = ${lookup {$sender_host_address} \
+ cdb {DB/ratelimits.cdb} \
+ {$value} {RATELIMIT} }
+ message = Sender rate exceeds $sender_rate_limit \
+ messages per $sender_rate_period
+
+Warning: If you have a busy server with a lot of ratelimit tests, especially
+with the per_rcpt option, you may suffer from a performance bottleneck caused
+by locking on the ratelimit hints database. Apart from making your ACLs less
+complicated, you can reduce the problem by using a RAM disk for Exim's hints
+directory (usually /var/spool/exim/db/). However this means that Exim will lose
+its hints data after a reboot (including retry hints, the callout cache, and
+ratelimit data).
+
+
+44.44 Address verification
+--------------------------
+
+Several of the verify conditions described in section 44.26 cause addresses to
+be verified. Section 44.48 discusses the reporting of sender verification
+failures. The verification conditions can be followed by options that modify
+the verification process. The options are separated from the keyword and from
+each other by slashes, and some of them contain parameters. For example:
+
+verify = sender/callout
+verify = recipient/defer_ok/callout=10s,defer_ok
+
+The first stage of address verification, which always happens, is to run the
+address through the routers, in "verify mode". Routers can detect the
+difference between verification and routing for delivery, and their actions can
+be varied by a number of generic options such as verify and verify_only (see
+chapter 15). If routing fails, verification fails. The available options are as
+follows:
+
+ * If the callout option is specified, successful routing to one or more
+ remote hosts is followed by a "callout" to those hosts as an additional
+ check. Callouts and their sub-options are discussed in the next section.
+
+ * If there is a defer error while doing verification routing, the ACL
+ normally returns "defer". However, if you include defer_ok in the options,
+ the condition is forced to be true instead. Note that this is a main
+ verification option as well as a suboption for callouts.
+
+ * The no_details option is covered in section 44.48, which discusses the
+ reporting of sender address verification failures.
+
+ * The success_on_redirect option causes verification always to succeed
+ immediately after a successful redirection. By default, if a redirection
+ generates just one address, that address is also verified. See further
+ discussion in section 44.49.
+
+After an address verification failure, $acl_verify_message contains the error
+message that is associated with the failure. It can be preserved by coding like
+this:
+
+warn !verify = sender
+ set acl_m0 = $acl_verify_message
+
+If you are writing your own custom rejection message or log message when
+denying access, you can use this variable to include information about the
+verification failure.
+
+In addition, $sender_verify_failure or $recipient_verify_failure (as
+appropriate) contains one of the following words:
+
+ * qualify: The address was unqualified (no domain), and the message was
+ neither local nor came from an exempted host.
+
+ * route: Routing failed.
+
+ * mail: Routing succeeded, and a callout was attempted; rejection occurred at
+ or before the MAIL command (that is, on initial connection, HELO, or MAIL).
+
+ * recipient: The RCPT command in a callout was rejected.
+
+ * postmaster: The postmaster check in a callout was rejected.
+
+The main use of these variables is expected to be to distinguish between
+rejections of MAIL and rejections of RCPT in callouts.
+
+The above variables may also be set after a successful address verification to:
+
+ * random: A random local-part callout succeeded
+
+
+44.45 Callout verification
+--------------------------
+
+For non-local addresses, routing verifies the domain, but is unable to do any
+checking of the local part. There are situations where some means of verifying
+the local part is desirable. One way this can be done is to make an SMTP
+callback to a delivery host for the sender address or a callforward to a
+subsequent host for a recipient address, to see if the host accepts the
+address. We use the term callout to cover both cases. Note that for a sender
+address, the callback is not to the client host that is trying to deliver the
+message, but to one of the hosts that accepts incoming mail for the sender's
+domain.
+
+Exim does not do callouts by default. If you want them to happen, you must
+request them by setting appropriate options on the verify condition, as
+described below. This facility should be used with care, because it can add a
+lot of resource usage to the cost of verifying an address. However, Exim does
+cache the results of callouts, which helps to reduce the cost. Details of
+caching are in section 44.47.
+
+Recipient callouts are usually used only between hosts that are controlled by
+the same administration. For example, a corporate gateway host could use
+callouts to check for valid recipients on an internal mailserver. A successful
+callout does not guarantee that a real delivery to the address would succeed;
+on the other hand, a failing callout does guarantee that a delivery would fail.
+
+If the callout option is present on a condition that verifies an address, a
+second stage of verification occurs if the address is successfully routed to
+one or more remote hosts. The usual case is routing by a dnslookup or a
+manualroute router, where the router specifies the hosts. However, if a router
+that does not set up hosts routes to an smtp transport with a hosts setting,
+the transport's hosts are used. If an smtp transport has hosts_override set,
+its hosts are always used, whether or not the router supplies a host list.
+Callouts are only supported on smtp transports.
+
+The port that is used is taken from the transport, if it is specified and is a
+remote transport. (For routers that do verification only, no transport need be
+specified.) Otherwise, the default SMTP port is used. If a remote transport
+specifies an outgoing interface, this is used; otherwise the interface is not
+specified. Likewise, the text that is used for the HELO command is taken from
+the transport's helo_data option; if there is no transport, the value of
+$smtp_active_hostname is used.
+
+For a sender callout check, Exim makes SMTP connections to the remote hosts, to
+test whether a bounce message could be delivered to the sender address. The
+following SMTP commands are sent:
+
+HELO <local host name>
+MAIL FROM:<>
+RCPT TO:<the address to be tested>
+QUIT
+
+LHLO is used instead of HELO if the transport's protocol option is set to
+"lmtp".
+
+The callout may use EHLO, AUTH and/or STARTTLS given appropriate option
+settings.
+
+A recipient callout check is similar. By default, it also uses an empty address
+for the sender. This default is chosen because most hosts do not make use of
+the sender address when verifying a recipient. Using the same address means
+that a single cache entry can be used for each recipient. Some sites, however,
+do make use of the sender address when verifying. These are catered for by the
+use_sender and use_postmaster options, described in the next section.
+
+If the response to the RCPT command is a 2xx code, the verification succeeds.
+If it is 5xx, the verification fails. For any other condition, Exim tries the
+next host, if any. If there is a problem with all the remote hosts, the ACL
+yields "defer", unless the defer_ok parameter of the callout option is given,
+in which case the condition is forced to succeed.
+
+A callout may take a little time. For this reason, Exim normally flushes SMTP
+output before performing a callout in an ACL, to avoid unexpected timeouts in
+clients when the SMTP PIPELINING extension is in use. The flushing can be
+disabled by using a control modifier to set no_callout_flush.
+
+
+44.46 Additional parameters for callouts
+----------------------------------------
+
+The callout option can be followed by an equals sign and a number of optional
+parameters, separated by commas. For example:
+
+verify = recipient/callout=10s,defer_ok
+
+The old syntax, which had callout_defer_ok and check_postmaster as separate
+verify options, is retained for backwards compatibility, but is now deprecated.
+The additional parameters for callout are as follows:
+
+<a time interval>
+
+ This specifies the timeout that applies for the callout attempt to each
+ host. For example:
+
+ verify = sender/callout=5s
+
+ The default is 30 seconds. The timeout is used for each response from the
+ remote host. It is also used for the initial connection, unless overridden
+ by the connect parameter.
+
+connect = <time interval>
+
+ This parameter makes it possible to set a different (usually smaller)
+ timeout for making the SMTP connection. For example:
+
+ verify = sender/callout=5s,connect=1s
+
+ If not specified, this timeout defaults to the general timeout value.
+
+defer_ok
+
+ When this parameter is present, failure to contact any host, or any other
+ kind of temporary error, is treated as success by the ACL. However, the
+ cache is not updated in this circumstance.
+
+fullpostmaster
+
+ This operates like the postmaster option (see below), but if the check for
+ postmaster@domain fails, it tries just postmaster, without a domain, in
+ accordance with the specification in RFC 2821. The RFC states that the
+ unqualified address postmaster should be accepted.
+
+mailfrom = <email address>
+
+ When verifying addresses in header lines using the header_sender
+ verification option, Exim behaves by default as if the addresses are
+ envelope sender addresses from a message. Callout verification therefore
+ tests to see whether a bounce message could be delivered, by using an empty
+ address in the MAIL command. However, it is arguable that these addresses
+ might never be used as envelope senders, and could therefore justifiably
+ reject bounce messages (empty senders). The mailfrom callout parameter
+ allows you to specify what address to use in the MAIL command. For example:
+
+ require verify = header_sender/callout=mailfrom=abcd@x.y.z
+
+ This parameter is available only for the header_sender verification option.
+
+maxwait = <time interval>
+
+ This parameter sets an overall timeout for performing a callout
+ verification. For example:
+
+ verify = sender/callout=5s,maxwait=30s
+
+ This timeout defaults to four times the callout timeout for individual SMTP
+ commands. The overall timeout applies when there is more than one host that
+ can be tried. The timeout is checked before trying the next host. This
+ prevents very long delays if there are a large number of hosts and all are
+ timing out (for example, when network connections are timing out).
+
+no_cache
+
+ When this parameter is given, the callout cache is neither read nor
+ updated.
+
+postmaster
+
+ When this parameter is set, a successful callout check is followed by a
+ similar check for the local part postmaster at the same domain. If this
+ address is rejected, the callout fails (but see fullpostmaster above). The
+ result of the postmaster check is recorded in a cache record; if it is a
+ failure, this is used to fail subsequent callouts for the domain without a
+ connection being made, until the cache record expires.
+
+postmaster_mailfrom = <email address>
+
+ The postmaster check uses an empty sender in the MAIL command by default.
+ You can use this parameter to do a postmaster check using a different
+ address. For example:
+
+ require verify = sender/callout=postmaster_mailfrom=abc@x.y.z
+
+ If both postmaster and postmaster_mailfrom are present, the rightmost one
+ overrides. The postmaster parameter is equivalent to this example:
+
+ require verify = sender/callout=postmaster_mailfrom=
+
+ Warning: The caching arrangements for postmaster checking do not take
+ account of the sender address. It is assumed that either the empty address
+ or a fixed non-empty address will be used. All that Exim remembers is that
+ the postmaster check for the domain succeeded or failed.
+
+random
+
+ When this parameter is set, before doing the normal callout check, Exim
+ does a check for a "random" local part at the same domain. The local part
+ is not really random - it is defined by the expansion of the option
+ callout_random_local_part, which defaults to
+
+ $primary_hostname-$tod_epoch-testing
+
+ The idea here is to try to determine whether the remote host accepts all
+ local parts without checking. If it does, there is no point in doing
+ callouts for specific local parts. If the "random" check succeeds, the
+ result is saved in a cache record, and used to force the current and
+ subsequent callout checks to succeed without a connection being made, until
+ the cache record expires.
+
+use_postmaster
+
+ This parameter applies to recipient callouts only. For example:
+
+ deny !verify = recipient/callout=use_postmaster
+
+ It causes a non-empty postmaster address to be used in the MAIL command
+ when performing the callout for the recipient, and also for a "random"
+ check if that is configured. The local part of the address is "postmaster"
+ and the domain is the contents of $qualify_domain.
+
+use_sender
+
+ This option applies to recipient callouts only. For example:
+
+ require verify = recipient/callout=use_sender
+
+ It causes the message's actual sender address to be used in the MAIL
+ command when performing the callout, instead of an empty address. There is
+ no need to use this option unless you know that the called hosts make use
+ of the sender when checking recipients. If used indiscriminately, it
+ reduces the usefulness of callout caching.
+
+hold
+
+ This option applies to recipient callouts only. For example:
+
+ require verify = recipient/callout=use_sender,hold
+
+ It causes the connection to be held open and used for any further
+ recipients and for eventual delivery (should that be done quickly). Doing
+ this saves on TCP and SMTP startup costs, and TLS costs also when that is
+ used for the connections. The advantage is only gained if there are no
+ callout cache hits (which could be enforced by the no_cache option), if the
+ use_sender option is used, if neither the random nor the use_postmaster
+ option is used, and if no other callouts intervene.
+
+If you use any of the parameters that set a non-empty sender for the MAIL
+command (mailfrom, postmaster_mailfrom, use_postmaster, or use_sender), you
+should think about possible loops. Recipient checking is usually done between
+two hosts that are under the same management, and the host that receives the
+callouts is not normally configured to do callouts itself. Therefore, it is
+normally safe to use use_postmaster or use_sender in these circumstances.
+
+However, if you use a non-empty sender address for a callout to an arbitrary
+host, there is the likelihood that the remote host will itself initiate a
+callout check back to your host. As it is checking what appears to be a message
+sender, it is likely to use an empty address in MAIL, thus avoiding a callout
+loop. However, to be on the safe side it would be best to set up your own ACLs
+so that they do not do sender verification checks when the recipient is the
+address you use for header sender or postmaster callout checking.
+
+Another issue to think about when using non-empty senders for callouts is
+caching. When you set mailfrom or use_sender, the cache record is keyed by the
+sender/recipient combination; thus, for any given recipient, many more actual
+callouts are performed than when an empty sender or postmaster is used.
+
+
+44.47 Callout caching
+---------------------
+
+Exim caches the results of callouts in order to reduce the amount of resources
+used, unless you specify the no_cache parameter with the callout option. A
+hints database called "callout" is used for the cache. Two different record
+types are used: one records the result of a callout check for a specific
+address, and the other records information that applies to the entire domain
+(for example, that it accepts the local part postmaster).
+
+When an original callout fails, a detailed SMTP error message is given about
+the failure. However, for subsequent failures use the cache data, this message
+is not available.
+
+The expiry times for negative and positive address cache records are
+independent, and can be set by the global options callout_negative_expire
+(default 2h) and callout_positive_expire (default 24h), respectively.
+
+If a host gives a negative response to an SMTP connection, or rejects any
+commands up to and including
+
+MAIL FROM:<>
+
+(but not including the MAIL command with a non-empty address), any callout
+attempt is bound to fail. Exim remembers such failures in a domain cache
+record, which it uses to fail callouts for the domain without making new
+connections, until the domain record times out. There are two separate expiry
+times for domain cache records: callout_domain_negative_expire (default 3h) and
+callout_domain_positive_expire (default 7d).
+
+Domain records expire when the negative expiry time is reached if callouts
+cannot be made for the domain, or if the postmaster check failed. Otherwise,
+they expire when the positive expiry time is reached. This ensures that, for
+example, a host that stops accepting "random" local parts will eventually be
+noticed.
+
+The callout caching mechanism is based on the domain of the address that is
+being tested. If the domain routes to several hosts, it is assumed that their
+behaviour will be the same.
+
+
+44.48 Sender address verification reporting
+-------------------------------------------
+
+See section 44.44 for a general discussion of verification. When sender
+verification fails in an ACL, the details of the failure are given as
+additional output lines before the 550 response to the relevant SMTP command
+(RCPT or DATA). For example, if sender callout is in use, you might see:
+
+MAIL FROM:<xyz@abc.example>
+250 OK
+RCPT TO:<pqr@def.example>
+550-Verification failed for <xyz@abc.example>
+550-Called: 192.168.34.43
+550-Sent: RCPT TO:<xyz@abc.example>
+550-Response: 550 Unknown local part xyz in <xyz@abc.example>
+550 Sender verification failed
+
+If more than one RCPT command fails in the same way, the details are given only
+for the first of them. However, some administrators do not want to send out
+this much information. You can suppress the details by adding "/no_details" to
+the ACL statement that requests sender verification. For example:
+
+verify = sender/no_details
+
+
+44.49 Redirection while verifying
+---------------------------------
+
+A dilemma arises when a local address is redirected by aliasing or forwarding
+during verification: should the generated addresses themselves be verified, or
+should the successful expansion of the original address be enough to verify it?
+By default, Exim takes the following pragmatic approach:
+
+ * When an incoming address is redirected to just one child address,
+ verification continues with the child address, and if that fails to verify,
+ the original verification also fails.
+
+ * When an incoming address is redirected to more than one child address,
+ verification does not continue. A success result is returned.
+
+This seems the most reasonable behaviour for the common use of aliasing as a
+way of redirecting different local parts to the same mailbox. It means, for
+example, that a pair of alias entries of the form
+
+A.Wol: aw123
+aw123: :fail: Gone away, no forwarding address
+
+work as expected, with both local parts causing verification failure. When a
+redirection generates more than one address, the behaviour is more like a
+mailing list, where the existence of the alias itself is sufficient for
+verification to succeed.
+
+It is possible, however, to change the default behaviour so that all successful
+redirections count as successful verifications, however many new addresses are
+generated. This is specified by the success_on_redirect verification option.
+For example:
+
+require verify = recipient/success_on_redirect/callout=10s
+
+In this example, verification succeeds if a router generates a new address, and
+the callout does not occur, because no address was routed to a remote host.
+
+When verification is being tested via the -bv option, the treatment of
+redirections is as just described, unless the -v or any debugging option is
+also specified. In that case, full verification is done for every generated
+address and a report is output for each of them.
+
+
+44.50 Client SMTP authorization (CSA)
+-------------------------------------
+
+Client SMTP Authorization is a system that allows a site to advertise which
+machines are and are not permitted to send email. This is done by placing
+special SRV records in the DNS; these are looked up using the client's HELO
+domain. At the time of writing, CSA is still an Internet Draft. Client SMTP
+Authorization checks in Exim are performed by the ACL condition:
+
+verify = csa
+
+This fails if the client is not authorized. If there is a DNS problem, or if no
+valid CSA SRV record is found, or if the client is authorized, the condition
+succeeds. These three cases can be distinguished using the expansion variable
+$csa_status, which can take one of the values "fail", "defer", "unknown", or
+"ok". The condition does not itself defer because that would be likely to cause
+problems for legitimate email.
+
+The error messages produced by the CSA code include slightly more detail. If
+$csa_status is "defer", this may be because of problems looking up the CSA SRV
+record, or problems looking up the CSA target address record. There are four
+reasons for $csa_status being "fail":
+
+ * The client's host name is explicitly not authorized.
+
+ * The client's IP address does not match any of the CSA target IP addresses.
+
+ * The client's host name is authorized but it has no valid target IP
+ addresses (for example, the target's addresses are IPv6 and the client is
+ using IPv4).
+
+ * The client's host name has no CSA SRV record but a parent domain has
+ asserted that all subdomains must be explicitly authorized.
+
+The csa verification condition can take an argument which is the domain to use
+for the DNS query. The default is:
+
+verify = csa/$sender_helo_name
+
+This implementation includes an extension to CSA. If the query domain is an
+address literal such as [192.0.2.95], or if it is a bare IP address, Exim
+searches for CSA SRV records in the reverse DNS as if the HELO domain was (for
+example) 95.2.0.192.in-addr.arpa. Therefore it is meaningful to say:
+
+verify = csa/$sender_host_address
+
+In fact, this is the check that Exim performs if the client does not say HELO.
+This extension can be turned off by setting the main configuration option
+dns_csa_use_reverse to be false.
+
+If a CSA SRV record is not found for the domain itself, a search is performed
+through its parent domains for a record which might be making assertions about
+subdomains. The maximum depth of this search is limited using the main
+configuration option dns_csa_search_limit, which is 5 by default. Exim does not
+look for CSA SRV records in a top level domain, so the default settings handle
+HELO domains as long as seven (hostname.five.four.three.two.one.com). This
+encompasses the vast majority of legitimate HELO domains.
+
+The dnsdb lookup also has support for CSA. Although dnsdb also supports direct
+SRV lookups, this is not sufficient because of the extra parent domain search
+behaviour of CSA, and (as with PTR lookups) dnsdb also turns IP addresses into
+lookups in the reverse DNS space. The result of a successful lookup such as:
+
+${lookup dnsdb {csa=$sender_helo_name}}
+
+has two space-separated fields: an authorization code and a target host name.
+The authorization code can be "Y" for yes, "N" for no, "X" for explicit
+authorization required but absent, or "?" for unknown.
+
+
+44.51 Bounce address tag validation
+-----------------------------------
+
+Bounce address tag validation (BATV) is a scheme whereby the envelope senders
+of outgoing messages have a cryptographic, timestamped "tag" added to them.
+Genuine incoming bounce messages should therefore always be addressed to
+recipients that have a valid tag. This scheme is a way of detecting unwanted
+bounce messages caused by sender address forgeries (often called "collateral
+spam"), because the recipients of such messages do not include valid tags.
+
+There are two expansion items to help with the implementation of the BATV
+"prvs" (private signature) scheme in an Exim configuration. This scheme signs
+the original envelope sender address by using a simple key to add a hash of the
+address and some time-based randomizing information. The prvs expansion item
+creates a signed address, and the prvscheck expansion item checks one. The
+syntax of these expansion items is described in section 11.5. The validity
+period on signed addresses is seven days.
+
+As an example, suppose the secret per-address keys are stored in an MySQL
+database. A query to look up the key for an address could be defined as a macro
+like this:
+
+PRVSCHECK_SQL = ${lookup mysql{SELECT secret FROM batv_prvs \
+ WHERE sender='${quote_mysql:$prvscheck_address}'\
+ }{$value}}
+
+Suppose also that the senders who make use of BATV are defined by an address
+list called batv_senders. Then, in the ACL for RCPT commands, you could use
+this:
+
+# Bounces: drop unsigned addresses for BATV senders
+deny senders = :
+ recipients = +batv_senders
+ message = This address does not send an unsigned reverse path
+
+# Bounces: In case of prvs-signed address, check signature.
+deny senders = :
+ condition = ${prvscheck {$local_part@$domain}\
+ {PRVSCHECK_SQL}{1}}
+ !condition = $prvscheck_result
+ message = Invalid reverse path signature.
+
+The first statement rejects recipients for bounce messages that are addressed
+to plain BATV sender addresses, because it is known that BATV senders do not
+send out messages with plain sender addresses. The second statement rejects
+recipients that are prvs-signed, but with invalid signatures (either because
+the key is wrong, or the signature has timed out).
+
+A non-prvs-signed address is not rejected by the second statement, because the
+prvscheck expansion yields an empty string if its first argument is not a
+prvs-signed address, thus causing the condition condition to be false. If the
+first argument is a syntactically valid prvs-signed address, the yield is the
+third string (in this case "1"), whether or not the cryptographic and timeout
+checks succeed. The $prvscheck_result variable contains the result of the
+checks (empty for failure, "1" for success).
+
+There is one more issue you must consider when implementing prvs-signing: you
+have to ensure that the routers accept prvs-signed addresses and deliver them
+correctly. The easiest way to handle this is to use a redirect router to remove
+the signature with a configuration along these lines:
+
+batv_redirect:
+ driver = redirect
+ data = ${prvscheck {$local_part@$domain}{PRVSCHECK_SQL}}
+
+This works because, if the third argument of prvscheck is empty, the result of
+the expansion of a prvs-signed address is the decoded value of the original
+address. This router should probably be the first of your routers that handles
+local addresses.
+
+To create BATV-signed addresses in the first place, a transport of this form
+can be used:
+
+external_smtp_batv:
+ driver = smtp
+ return_path = ${prvs {$return_path} \
+ {${lookup mysql{SELECT \
+ secret FROM batv_prvs WHERE \
+ sender='${quote_mysql:$sender_address}'} \
+ {$value}fail}}}
+
+If no key can be found for the existing return path, no signing takes place.
+
+
+44.52 Using an ACL to control relaying
+--------------------------------------
+
+An MTA is said to relay a message if it receives it from some host and delivers
+it directly to another host as a result of a remote address contained within
+it. Redirecting a local address via an alias or forward file and then passing
+the message on to another host is not relaying, but a redirection as a result
+of the "percent hack" is.
+
+Two kinds of relaying exist, which are termed "incoming" and "outgoing". A host
+which is acting as a gateway or an MX backup is concerned with incoming
+relaying from arbitrary hosts to a specific set of domains. On the other hand,
+a host which is acting as a smart host for a number of clients is concerned
+with outgoing relaying from those clients to the Internet at large. Often the
+same host is fulfilling both functions, but in principle these two kinds of
+relaying are entirely independent. What is not wanted is the transmission of
+mail from arbitrary remote hosts through your system to arbitrary domains.
+
+You can implement relay control by means of suitable statements in the ACL that
+runs for each RCPT command. For convenience, it is often easiest to use Exim's
+named list facility to define the domains and hosts involved. For example,
+suppose you want to do the following:
+
+ * Deliver a number of domains to mailboxes on the local host (or process them
+ locally in some other way). Let's say these are my.dom1.example and
+ my.dom2.example.
+
+ * Relay mail for a number of other domains for which you are the secondary
+ MX. These might be friend1.example and friend2.example.
+
+ * Relay mail from the hosts on your local LAN, to whatever domains are
+ involved. Suppose your LAN is 192.168.45.0/24.
+
+In the main part of the configuration, you put the following definitions:
+
+domainlist local_domains = my.dom1.example : my.dom2.example
+domainlist relay_to_domains = friend1.example : friend2.example
+hostlist relay_from_hosts = 192.168.45.0/24
+
+Now you can use these definitions in the ACL that is run for every RCPT
+command:
+
+acl_check_rcpt:
+ accept domains = +local_domains : +relay_to_domains
+ accept hosts = +relay_from_hosts
+
+The first statement accepts any RCPT command that contains an address in the
+local or relay domains. For any other domain, control passes to the second
+statement, which accepts the command only if it comes from one of the relay
+hosts. In practice, you will probably want to make your ACL more sophisticated
+than this, for example, by including sender and recipient verification. The
+default configuration includes a more comprehensive example, which is described
+in chapter 7.
+
+
+44.53 Checking a relay configuration
+------------------------------------
+
+You can check the relay characteristics of your configuration in the same way
+that you can test any ACL behaviour for an incoming SMTP connection, by using
+the -bh option to run a fake SMTP session with which you interact.
+
+
+
+===============================================================================
+45. CONTENT SCANNING AT ACL TIME
+
+The extension of Exim to include content scanning at ACL time, formerly known
+as "exiscan", was originally implemented as a patch by Tom Kistner. The code
+was integrated into the main source for Exim release 4.50, and Tom continues to
+maintain it. Most of the wording of this chapter is taken from Tom's
+specification.
+
+It is also possible to scan the content of messages at other times. The
+local_scan() function (see chapter 46) allows for content scanning after all
+the ACLs have run. A transport filter can be used to scan messages at delivery
+time (see the transport_filter option, described in chapter 24).
+
+If you want to include the ACL-time content-scanning features when you compile
+Exim, you need to arrange for WITH_CONTENT_SCAN to be defined in your Local/
+Makefile. When you do that, the Exim binary is built with:
+
+ * Two additional ACLs (acl_smtp_mime and acl_not_smtp_mime) that are run for
+ all MIME parts for SMTP and non-SMTP messages, respectively.
+
+ * Additional ACL conditions and modifiers: decode, malware, mime_regex, regex
+ , and spam. These can be used in the ACL that is run at the end of message
+ reception (the acl_smtp_data ACL).
+
+ * An additional control feature ("no_mbox_unspool") that saves spooled copies
+ of messages, or parts of messages, for debugging purposes.
+
+ * Additional expansion variables that are set in the new ACL and by the new
+ conditions.
+
+ * Two new main configuration options: av_scanner and spamd_address.
+
+Content-scanning is continually evolving, and new features are still being
+added. While such features are still unstable and liable to incompatible
+changes, they are made available in Exim by setting options whose names begin
+EXPERIMENTAL_ in Local/Makefile. Such features are not documented in this
+manual. You can find out about them by reading the file called doc/
+experimental.txt.
+
+All the content-scanning facilities work on a MBOX copy of the message that is
+temporarily created in a file called:
+
+<spool_directory>/scan/<message_id>/<message_id>.eml
+
+The .eml extension is a friendly hint to virus scanners that they can expect an
+MBOX-like structure inside that file. The file is created when the first
+content scanning facility is called. Subsequent calls to content scanning
+conditions open the same file again. The directory is recursively removed when
+the acl_smtp_data ACL has finished running, unless
+
+control = no_mbox_unspool
+
+has been encountered. When the MIME ACL decodes files, they are put into the
+same directory by default.
+
+
+45.1 Scanning for viruses
+-------------------------
+
+The malware ACL condition lets you connect virus scanner software to Exim. It
+supports a "generic" interface to scanners called via the shell, and
+specialized interfaces for "daemon" type virus scanners, which are resident in
+memory and thus are much faster.
+
+Since message data needs to have arrived, the condition may be only called in
+ACL defined by acl_smtp_data, acl_smtp_data_prdr, acl_smtp_mime or
+acl_smtp_dkim
+
+A timeout of 2 minutes is applied to a scanner call (by default); if it expires
+then a defer action is taken.
+
+You can set the av_scanner option in the main part of the configuration to
+specify which scanner to use, together with any additional options that are
+needed. The basic syntax is as follows:
+
+av_scanner = <scanner-type>:<option1>:<option2>:[...]
+
+If you do not set av_scanner, it defaults to
+
+av_scanner = sophie:/var/run/sophie
+
+If the value of av_scanner starts with a dollar character, it is expanded
+before use. The usual list-parsing of the content (see 6.20) applies. The
+following scanner types are supported in this release, though individual ones
+can be included or not at build time:
+
+avast
+
+ This is the scanner daemon of Avast. It has been tested with Avast Core
+ Security (currently at version 2.2.0). You can get a trial version at
+ https://www.avast.com or for Linux at https://www.avast.com/
+ linux-server-antivirus. This scanner type takes one option, which can be
+ either a full path to a UNIX socket, or host and port specifiers separated
+ by white space. The host may be a name or an IP address; the port is either
+ a single number or a pair of numbers with a dash between. A list of options
+ may follow. These options are interpreted on the Exim's side of the malware
+ scanner, or are given on separate lines to the daemon as options before the
+ main scan command.
+
+ If "pass_unscanned" is set, any files the Avast scanner can't scan (e.g.
+ decompression bombs, or invalid archives) are considered clean. Use with
+ care.
+
+ For example:
+
+ av_scanner = avast:/var/run/avast/scan.sock:FLAGS -fullfiles:SENSITIVITY -pup
+ av_scanner = avast:/var/run/avast/scan.sock:pass_unscanned:FLAGS -fullfiles:SENSITIVITY -pup
+ av_scanner = avast:192.168.2.22 5036
+
+ If you omit the argument, the default path /var/run/avast/scan.sock is
+ used. If you use a remote host, you need to make Exim's spool directory
+ available to it, as the scanner is passed a file path, not file contents.
+ For information about available commands and their options you may use
+
+ $ socat UNIX:/var/run/avast/scan.sock STDIO:
+ FLAGS
+ SENSITIVITY
+ PACK
+
+ If the scanner returns a temporary failure (e.g. license issues, or
+ permission problems), the message is deferred and a paniclog entry is
+ written. The usual "defer_ok" option is available.
+
+aveserver
+
+ This is the scanner daemon of Kaspersky Version 5. You can get a trial
+ version at https://www.kaspersky.com/. This scanner type takes one option,
+ which is the path to the daemon's UNIX socket. The default is shown in this
+ example:
+
+ av_scanner = aveserver:/var/run/aveserver
+
+clamd
+
+ This daemon-type scanner is GPL and free. You can get it at https://
+ www.clamav.net/. Some older versions of clamd do not seem to unpack MIME
+ containers, so it used to be recommended to unpack MIME attachments in the
+ MIME ACL. This is no longer believed to be necessary.
+
+ The options are a list of server specifiers, which may be a UNIX socket
+ specification, a TCP socket specification, or a (global) option.
+
+ A socket specification consists of a space-separated list. For a Unix
+ socket the first element is a full path for the socket, for a TCP socket
+ the first element is the IP address and the second a port number, Any
+ further elements are per-server (non-global) options. These per-server
+ options are supported:
+
+ retry=<timespec> Retry on connect fail
+
+ The "retry" option specifies a time after which a single retry for a failed
+ connect is made. The default is to not retry.
+
+ If a Unix socket file is specified, only one server is supported.
+
+ Examples:
+
+ av_scanner = clamd:/opt/clamd/socket
+ av_scanner = clamd:192.0.2.3 1234
+ av_scanner = clamd:192.0.2.3 1234:local
+ av_scanner = clamd:192.0.2.3 1234 retry=10s
+ av_scanner = clamd:192.0.2.3 1234 : 192.0.2.4 1234
+
+ If the value of av_scanner points to a UNIX socket file or contains the
+ "local" option, then the ClamAV interface will pass a filename containing
+ the data to be scanned, which should normally result in less I/O happening
+ and be more efficient. Normally in the TCP case, the data is streamed to
+ ClamAV as Exim does not assume that there is a common filesystem with the
+ remote host.
+
+ The final example shows that multiple TCP targets can be specified. Exim
+ will randomly use one for each incoming email (i.e. it load balances them).
+ Note that only TCP targets may be used if specifying a list of scanners; a
+ UNIX socket cannot be mixed in with TCP targets. If one of the servers
+ becomes unavailable, Exim will try the remaining one(s) until it finds one
+ that works. When a clamd server becomes unreachable, Exim will log a
+ message. Exim does not keep track of scanner state between multiple
+ messages, and the scanner selection is random, so the message will get
+ logged in the mainlog for each email that the down scanner gets chosen
+ first (message wrapped to be readable):
+
+ 2013-10-09 14:30:39 1VTumd-0000Y8-BQ malware acl condition:
+ clamd: connection to localhost, port 3310 failed
+ (Connection refused)
+
+ If the option is unset, the default is /tmp/clamd. Thanks to David Saez for
+ contributing the code for this scanner.
+
+cmdline
+
+ This is the keyword for the generic command line scanner interface. It can
+ be used to attach virus scanners that are invoked from the shell. This
+ scanner type takes 3 mandatory options:
+
+ 1. The full path and name of the scanner binary, with all command line
+ options, and a placeholder ("%s") for the directory to scan.
+
+ 2. A regular expression to match against the STDOUT and STDERR output of
+ the virus scanner. If the expression matches, a virus was found. You
+ must make absolutely sure that this expression matches on "virus
+ found". This is called the "trigger" expression.
+
+ 3. Another regular expression, containing exactly one pair of parentheses,
+ to match the name of the virus found in the scanners output. This is
+ called the "name" expression.
+
+ For example, Sophos Sweep reports a virus on a line like this:
+
+ Virus 'W32/Magistr-B' found in file ./those.bat
+
+ For the trigger expression, we can match the phrase "found in file". For
+ the name expression, we want to extract the W32/Magistr-B string, so we can
+ match for the single quotes left and right of it. Altogether, this makes
+ the configuration setting:
+
+ av_scanner = cmdline:\
+ /path/to/sweep -ss -all -rec -archive %s:\
+ found in file:'(.+)'
+
+drweb
+
+ The DrWeb daemon scanner (https://www.sald.ru/) interface takes one option,
+ either a full path to a UNIX socket, or host and port specifiers separated
+ by white space. The host may be a name or an IP address; the port is either
+ a single number or a pair of numbers with a dash between. For example:
+
+ av_scanner = drweb:/var/run/drwebd.sock
+ av_scanner = drweb:192.168.2.20 31337
+
+ If you omit the argument, the default path /usr/local/drweb/run/drwebd.sock
+ is used. Thanks to Alex Miller for contributing the code for this scanner.
+
+f-protd
+
+ The f-protd scanner is accessed via HTTP over TCP. One argument is taken,
+ being a space-separated hostname and port number (or port-range). For
+ example:
+
+ av_scanner = f-protd:localhost 10200-10204
+
+ If you omit the argument, the default values shown above are used.
+
+f-prot6d
+
+ The f-prot6d scanner is accessed using the FPSCAND protocol over TCP. One
+ argument is taken, being a space-separated hostname and port number. For
+ example:
+
+ av_scanner = f-prot6d:localhost 10200
+
+ If you omit the argument, the default values show above are used.
+
+fsecure
+
+ The F-Secure daemon scanner (https://www.f-secure.com/) takes one argument
+ which is the path to a UNIX socket. For example:
+
+ av_scanner = fsecure:/path/to/.fsav
+
+ If no argument is given, the default is /var/run/.fsav. Thanks to Johan
+ Thelmen for contributing the code for this scanner.
+
+kavdaemon
+
+ This is the scanner daemon of Kaspersky Version 4. This version of the
+ Kaspersky scanner is outdated. Please upgrade (see aveserver above). This
+ scanner type takes one option, which is the path to the daemon's UNIX
+ socket. For example:
+
+ av_scanner = kavdaemon:/opt/AVP/AvpCtl
+
+ The default path is /var/run/AvpCtl.
+
+mksd
+
+ This was a daemon type scanner that is aimed mainly at Polish users, though
+ some documentation was available in English. The history can be shown at
+ https://en.wikipedia.org/wiki/Mks_vir and this appears to be a candidate
+ for removal from Exim, unless we are informed of other virus scanners which
+ use the same protocol to integrate. The only option for this scanner type
+ is the maximum number of processes used simultaneously to scan the
+ attachments, provided that mksd has been run with at least the same number
+ of child processes. For example:
+
+ av_scanner = mksd:2
+
+ You can safely omit this option (the default value is 1).
+
+sock
+
+ This is a general-purpose way of talking to simple scanner daemons running
+ on the local machine. There are four options: an address (which may be an
+ IP address and port, or the path of a Unix socket), a commandline to send
+ (may include a single %s which will be replaced with the path to the mail
+ file to be scanned), an RE to trigger on from the returned data, and an RE
+ to extract malware_name from the returned data. For example:
+
+ av_scanner = sock:127.0.0.1 6001:%s:(SPAM|VIRUS):(.*)$
+
+ Note that surrounding whitespace is stripped from each option, meaning
+ there is no way to specify a trailing newline. The socket specifier and
+ both regular-expressions are required. Default for the commandline is %s\n
+ (note this does have a trailing newline); specify an empty element to get
+ this.
+
+sophie
+
+ Sophie is a daemon that uses Sophos' libsavi library to scan for viruses.
+ You can get Sophie at http://sophie.sourceforge.net/. The only option for
+ this scanner type is the path to the UNIX socket that Sophie uses for
+ client communication. For example:
+
+ av_scanner = sophie:/tmp/sophie
+
+ The default path is /var/run/sophie, so if you are using this, you can omit
+ the option.
+
+When av_scanner is correctly set, you can use the malware condition in the DATA
+ACL. Note: You cannot use the malware condition in the MIME ACL.
+
+The av_scanner option is expanded each time malware is called. This makes it
+possible to use different scanners. See further below for an example. The
+malware condition caches its results, so when you use it multiple times for the
+same message, the actual scanning process is only carried out once. However,
+using expandable items in av_scanner disables this caching, in which case each
+use of the malware condition causes a new scan of the message.
+
+The malware condition takes a right-hand argument that is expanded before use
+and taken as a list, slash-separated by default. The first element can then be
+one of
+
+ * "true", "*", or "1", in which case the message is scanned for viruses. The
+ condition succeeds if a virus was found, and fail otherwise. This is the
+ recommended usage.
+
+ * "false" or "0" or an empty string, in which case no scanning is done and
+ the condition fails immediately.
+
+ * A regular expression, in which case the message is scanned for viruses. The
+ condition succeeds if a virus is found and its name matches the regular
+ expression. This allows you to take special actions on certain types of
+ virus. Note that "/" characters in the RE must be doubled due to the
+ list-processing, unless the separator is changed (in the usual way 6.21).
+
+You can append a "defer_ok" element to the malware argument list to accept
+messages even if there is a problem with the virus scanner. Otherwise, such a
+problem causes the ACL to defer.
+
+You can append a "tmo=<val>" element to the malware argument list to specify a
+non-default timeout. The default is two minutes. For example:
+
+malware = * / defer_ok / tmo=10s
+
+A timeout causes the ACL to defer.
+
+When a connection is made to the scanner the expansion variable
+$callout_address is set to record the actual address used.
+
+When a virus is found, the condition sets up an expansion variable called
+$malware_name that contains the name of the virus. You can use it in a message
+modifier that specifies the error returned to the sender, and/or in logging
+data.
+
+Beware the interaction of Exim's message_size_limit with any size limits
+imposed by your anti-virus scanner.
+
+Here is a very simple scanning example:
+
+deny malware = *
+ message = This message contains malware ($malware_name)
+
+The next example accepts messages when there is a problem with the scanner:
+
+deny malware = */defer_ok
+ message = This message contains malware ($malware_name)
+
+The next example shows how to use an ACL variable to scan with both sophie and
+aveserver. It assumes you have set:
+
+av_scanner = $acl_m0
+
+in the main Exim configuration.
+
+deny set acl_m0 = sophie
+ malware = *
+ message = This message contains malware ($malware_name)
+
+deny set acl_m0 = aveserver
+ malware = *
+ message = This message contains malware ($malware_name)
+
+
+45.2 Scanning with SpamAssassin and Rspamd
+------------------------------------------
+
+The spam ACL condition calls SpamAssassin's spamd daemon to get a spam score
+and a report for the message. Support is also provided for Rspamd.
+
+For more information about installation and configuration of SpamAssassin or
+Rspamd refer to their respective websites at https://spamassassin.apache.org/
+and https://www.rspamd.com/
+
+SpamAssassin can be installed with CPAN by running:
+
+perl -MCPAN -e 'install Mail::SpamAssassin'
+
+SpamAssassin has its own set of configuration files. Please review its
+documentation to see how you can tweak it. The default installation should work
+nicely, however.
+
+By default, SpamAssassin listens on 127.0.0.1, TCP port 783 and if you intend
+to use an instance running on the local host you do not need to set
+spamd_address. If you intend to use another host or port for SpamAssassin, you
+must set the spamd_address option in the global part of the Exim configuration
+as follows (example):
+
+spamd_address = 192.168.99.45 783
+
+The SpamAssassin protocol relies on a TCP half-close from the client. If your
+SpamAssassin client side is running a Linux system with an iptables firewall,
+consider setting net.netfilter.nf_conntrack_tcp_timeout_close_wait to at least
+the timeout, Exim uses when waiting for a response from the SpamAssassin server
+(currently defaulting to 120s). With a lower value the Linux connection
+tracking may consider your half-closed connection as dead too soon.
+
+To use Rspamd (which by default listens on all local addresses on TCP port
+11333) you should add variant=rspamd after the address/port pair, for example:
+
+spamd_address = 127.0.0.1 11333 variant=rspamd
+
+As of version 2.60, SpamAssassin also supports communication over UNIX sockets.
+If you want to us these, supply spamd_address with an absolute filename instead
+of an address/port pair:
+
+spamd_address = /var/run/spamd_socket
+
+You can have multiple spamd servers to improve scalability. These can reside on
+other hardware reachable over the network. To specify multiple spamd servers,
+put multiple address/port pairs in the spamd_address option, separated with
+colons (the separator can be changed in the usual way 6.21):
+
+spamd_address = 192.168.2.10 783 : \
+ 192.168.2.11 783 : \
+ 192.168.2.12 783
+
+Up to 32 spamd servers are supported. When a server fails to respond to the
+connection attempt, all other servers are tried until one succeeds. If no
+server responds, the spam condition defers.
+
+Unix and TCP socket specifications may be mixed in any order. Each element of
+the list is a list itself, space-separated by default and changeable in the
+usual way (6.21); take care to not double the separator.
+
+For TCP socket specifications a host name or IP (v4 or v6, but subject to
+list-separator quoting rules) address can be used, and the port can be one or a
+dash-separated pair. In the latter case, the range is tried in strict order.
+
+Elements after the first for Unix sockets, or second for TCP socket, are
+options. The supported options are:
+
+pri=<priority> Selection priority
+weight=<value> Selection bias
+time=<start>-<end> Use only between these times of day
+retry=<timespec> Retry on connect fail
+tmo=<timespec> Connection time limit
+variant=rspamd Use Rspamd rather than SpamAssassin protocol
+
+The "pri" option specifies a priority for the server within the list, higher
+values being tried first. The default priority is 1.
+
+The "weight" option specifies a selection bias. Within a priority set servers
+are queried in a random fashion, weighted by this value. The default value for
+selection bias is 1.
+
+Time specifications for the "time" option are <hour>.<minute>.<second> in the
+local time zone; each element being one or more digits. Either the seconds or
+both minutes and seconds, plus the leading "." characters, may be omitted and
+will be taken as zero.
+
+Timeout specifications for the "retry" and "tmo" options are the usual Exim
+time interval standard, e.g. "20s" or "1m".
+
+The "tmo" option specifies an overall timeout for communication. The default
+value is two minutes.
+
+The "retry" option specifies a time after which a single retry for a failed
+connect is made. The default is to not retry.
+
+The spamd_address variable is expanded before use if it starts with a dollar
+sign. In this case, the expansion may return a string that is used as the list
+so that multiple spamd servers can be the result of an expansion.
+
+When a connection is made to the server the expansion variable $callout_address
+is set to record the actual address used.
+
+
+45.3 Calling SpamAssassin from an Exim ACL
+------------------------------------------
+
+Here is a simple example of the use of the spam condition in a DATA ACL:
+
+deny spam = joe
+ message = This message was classified as SPAM
+
+The right-hand side of the spam condition specifies a name. This is relevant if
+you have set up multiple SpamAssassin profiles. If you do not want to scan
+using a specific profile, but rather use the SpamAssassin system-wide default
+profile, you can scan for an unknown name, or simply use "nobody". Rspamd does
+not use this setting. However, you must put something on the right-hand side.
+
+The name allows you to use per-domain or per-user antispam profiles in
+principle, but this is not straightforward in practice, because a message may
+have multiple recipients, not necessarily all in the same domain. Because the
+spam condition has to be called from a DATA-time ACL in order to be able to
+read the contents of the message, the variables $local_part and $domain are not
+set. Careful enforcement of single-recipient messages (e.g. by responding with
+defer in the recipient ACL for all recipients after the first), or the use of
+PRDR, are needed to use this feature.
+
+The right-hand side of the spam condition is expanded before being used, so you
+can put lookups or conditions there. When the right-hand side evaluates to "0"
+or "false", no scanning is done and the condition fails immediately.
+
+Scanning with SpamAssassin uses a lot of resources. If you scan every message,
+large ones may cause significant performance degradation. As most spam messages
+are quite small, it is recommended that you do not scan the big ones. For
+example:
+
+deny condition = ${if < {$message_size}{10K}}
+ spam = nobody
+ message = This message was classified as SPAM
+
+The spam condition returns true if the threshold specified in the user's
+SpamAssassin profile has been matched or exceeded. If you want to use the spam
+condition for its side effects (see the variables below), you can make it
+always return "true" by appending ":true" to the username.
+
+When the spam condition is run, it sets up a number of expansion variables.
+Except for $spam_report, these variables are saved with the received message so
+are available for use at delivery time.
+
+$spam_score
+
+ The spam score of the message, for example, "3.4" or "30.5". This is useful
+ for inclusion in log or reject messages.
+
+$spam_score_int
+
+ The spam score of the message, multiplied by ten, as an integer value. For
+ example "34" or "305". It may appear to disagree with $spam_score because
+ $spam_score is rounded and $spam_score_int is truncated. The integer value
+ is useful for numeric comparisons in conditions.
+
+$spam_bar
+
+ A string consisting of a number of "+" or "-" characters, representing the
+ integer part of the spam score value. A spam score of 4.4 would have a
+ $spam_bar value of "++++". This is useful for inclusion in warning headers,
+ since MUAs can match on such strings. The maximum length of the spam bar is
+ 50 characters.
+
+$spam_report
+
+ A multiline text table, containing the full SpamAssassin report for the
+ message. Useful for inclusion in headers or reject messages. This variable
+ is only usable in a DATA-time ACL. Beware that SpamAssassin may return
+ non-ASCII characters, especially when running in country-specific locales,
+ which are not legal unencoded in headers.
+
+$spam_action
+
+ For SpamAssassin either 'reject' or 'no action' depending on the spam score
+ versus threshold. For Rspamd, the recommended action.
+
+The spam condition caches its results unless expansion in spamd_address was
+used. If you call it again with the same user name, it does not scan again, but
+rather returns the same values as before.
+
+The spam condition returns DEFER if there is any error while running the
+message through SpamAssassin or if the expansion of spamd_address failed. If
+you want to treat DEFER as FAIL (to pass on to the next ACL statement block),
+append "/defer_ok" to the right-hand side of the spam condition, like this:
+
+deny spam = joe/defer_ok
+ message = This message was classified as SPAM
+
+This causes messages to be accepted even if there is a problem with spamd.
+
+Here is a longer, commented example of the use of the spam condition:
+
+# put headers in all messages (no matter if spam or not)
+warn spam = nobody:true
+ add_header = X-Spam-Score: $spam_score ($spam_bar)
+ add_header = X-Spam-Report: $spam_report
+
+# add second subject line with *SPAM* marker when message
+# is over threshold
+warn spam = nobody
+ add_header = Subject: *SPAM* $h_Subject:
+
+# reject spam at high scores (> 12)
+deny spam = nobody:true
+ condition = ${if >{$spam_score_int}{120}{1}{0}}
+ message = This message scored $spam_score spam points.
+
+
+45.4 Scanning MIME parts
+------------------------
+
+The acl_smtp_mime global option specifies an ACL that is called once for each
+MIME part of an SMTP message, including multipart types, in the sequence of
+their position in the message. Similarly, the acl_not_smtp_mime option
+specifies an ACL that is used for the MIME parts of non-SMTP messages. These
+options may both refer to the same ACL if you want the same processing in both
+cases.
+
+These ACLs are called (possibly many times) just before the acl_smtp_data ACL
+in the case of an SMTP message, or just before the acl_not_smtp ACL in the case
+of a non-SMTP message. However, a MIME ACL is called only if the message
+contains a Content-Type: header line. When a call to a MIME ACL does not yield
+"accept", ACL processing is aborted and the appropriate result code is sent to
+the client. In the case of an SMTP message, the acl_smtp_data ACL is not called
+when this happens.
+
+You cannot use the malware or spam conditions in a MIME ACL; these can only be
+used in the DATA or non-SMTP ACLs. However, you can use the regex condition to
+match against the raw MIME part. You can also use the mime_regex condition to
+match against the decoded MIME part (see section 45.5).
+
+At the start of a MIME ACL, a number of variables are set from the header
+information for the relevant MIME part. These are described below. The contents
+of the MIME part are not by default decoded into a disk file except for MIME
+parts whose content-type is "message/rfc822". If you want to decode a MIME part
+into a disk file, you can use the decode condition. The general syntax is:
+
+decode = [/<path>/]<filename>
+
+The right hand side is expanded before use. After expansion, the value can be:
+
+ 1. "0" or "false", in which case no decoding is done.
+
+ 2. The string "default". In that case, the file is put in the temporary
+ "default" directory <spool_directory>/scan/<message_id>/ with a sequential
+ filename consisting of the message id and a sequence number. The full path
+ and name is available in $mime_decoded_filename after decoding.
+
+ 3. A full path name starting with a slash. If the full name is an existing
+ directory, it is used as a replacement for the default directory. The
+ filename is then sequentially assigned. If the path does not exist, it is
+ used as the full path and filename.
+
+ 4. If the string does not start with a slash, it is used as the filename, and
+ the default path is then used.
+
+The decode condition normally succeeds. It is only false for syntax errors or
+unusual circumstances such as memory shortages. You can easily decode a file
+with its original, proposed filename using
+
+decode = $mime_filename
+
+However, you should keep in mind that $mime_filename might contain anything. If
+you place files outside of the default path, they are not automatically
+unlinked.
+
+For RFC822 attachments (these are messages attached to messages, with a
+content-type of "message/rfc822"), the ACL is called again in the same manner
+as for the primary message, only that the $mime_is_rfc822 expansion variable is
+set (see below). Attached messages are always decoded to disk before being
+checked, and the files are unlinked once the check is done.
+
+The MIME ACL supports the regex and mime_regex conditions. These can be used to
+match regular expressions against raw and decoded MIME parts, respectively.
+They are described in section 45.5.
+
+The following list describes all expansion variables that are available in the
+MIME ACL:
+
+$mime_anomaly_level, $mime_anomaly_text
+
+ If there are problems decoding, these variables contain information on the
+ detected issue.
+
+$mime_boundary
+
+ If the current part is a multipart (see $mime_is_multipart below), it
+ should have a boundary string, which is stored in this variable. If the
+ current part has no boundary parameter in the Content-Type: header, this
+ variable contains the empty string.
+
+$mime_charset
+
+ This variable contains the character set identifier, if one was found in
+ the Content-Type: header. Examples for charset identifiers are:
+
+ us-ascii
+ gb2312 (Chinese)
+ iso-8859-1
+
+ Please note that this value is not normalized, so you should do matches
+ case-insensitively.
+
+$mime_content_description
+
+ This variable contains the normalized content of the Content-Description:
+ header. It can contain a human-readable description of the parts content.
+ Some implementations repeat the filename for attachments here, but they are
+ usually only used for display purposes.
+
+$mime_content_disposition
+
+ This variable contains the normalized content of the Content-Disposition:
+ header. You can expect strings like "attachment" or "inline" here.
+
+$mime_content_id
+
+ This variable contains the normalized content of the Content-ID: header.
+ This is a unique ID that can be used to reference a part from another part.
+
+$mime_content_size
+
+ This variable is set only after the decode modifier (see above) has been
+ successfully run. It contains the size of the decoded part in kilobytes.
+ The size is always rounded up to full kilobytes, so only a completely empty
+ part has a $mime_content_size of zero.
+
+$mime_content_transfer_encoding
+
+ This variable contains the normalized content of the
+ Content-transfer-encoding: header. This is a symbolic name for an encoding
+ type. Typical values are "base64" and "quoted-printable".
+
+$mime_content_type
+
+ If the MIME part has a Content-Type: header, this variable contains its
+ value, lowercased, and without any options (like "name" or "charset"). Here
+ are some examples of popular MIME types, as they may appear in this
+ variable:
+
+ text/plain
+ text/html
+ application/octet-stream
+ image/jpeg
+ audio/midi
+
+ If the MIME part has no Content-Type: header, this variable contains the
+ empty string.
+
+$mime_decoded_filename
+
+ This variable is set only after the decode modifier (see above) has been
+ successfully run. It contains the full path and filename of the file
+ containing the decoded data.
+
+$mime_filename
+
+ This is perhaps the most important of the MIME variables. It contains a
+ proposed filename for an attachment, if one was found in either the
+ Content-Type: or Content-Disposition: headers. The filename will be RFC2047
+ or RFC2231 decoded, but no additional sanity checks are done. If no
+ filename was found, this variable contains the empty string.
+
+$mime_is_coverletter
+
+ This variable attempts to differentiate the "cover letter" of an e-mail
+ from attached data. It can be used to clamp down on flashy or unnecessarily
+ encoded content in the cover letter, while not restricting attachments at
+ all.
+
+ The variable contains 1 (true) for a MIME part believed to be part of the
+ cover letter, and 0 (false) for an attachment. At present, the algorithm is
+ as follows:
+
+ 1. The outermost MIME part of a message is always a cover letter.
+
+ 2. If a multipart/alternative or multipart/related MIME part is a cover
+ letter, so are all MIME subparts within that multipart.
+
+ 3. If any other multipart is a cover letter, the first subpart is a cover
+ letter, and the rest are attachments.
+
+ 4. All parts contained within an attachment multipart are attachments.
+
+ As an example, the following will ban "HTML mail" (including that sent with
+ alternative plain text), while allowing HTML files to be attached. HTML
+ coverletter mail attached to non-HTML coverletter mail will also be
+ allowed:
+
+ deny !condition = $mime_is_rfc822
+ condition = $mime_is_coverletter
+ condition = ${if eq{$mime_content_type}{text/html}{1}{0}}
+ message = HTML mail is not accepted here
+
+$mime_is_multipart
+
+ This variable has the value 1 (true) when the current part has the main
+ type "multipart", for example, "multipart/alternative" or "multipart/
+ mixed". Since multipart entities only serve as containers for other parts,
+ you may not want to carry out specific actions on them.
+
+$mime_is_rfc822
+
+ This variable has the value 1 (true) if the current part is not a part of
+ the checked message itself, but part of an attached message. Attached
+ message decoding is fully recursive.
+
+$mime_part_count
+
+ This variable is a counter that is raised for each processed MIME part. It
+ starts at zero for the very first part (which is usually a multipart). The
+ counter is per-message, so it is reset when processing RFC822 attachments
+ (see $mime_is_rfc822). The counter stays set after acl_smtp_mime is
+ complete, so you can use it in the DATA ACL to determine the number of MIME
+ parts of a message. For non-MIME messages, this variable contains the value
+ -1.
+
+
+45.5 Scanning with regular expressions
+--------------------------------------
+
+You can specify your own custom regular expression matches on the full body of
+the message, or on individual MIME parts.
+
+The regex condition takes one or more regular expressions as arguments and
+matches them against the full message (when called in the DATA ACL) or a raw
+MIME part (when called in the MIME ACL). The regex condition matches linewise,
+with a maximum line length of 32K characters. That means you cannot have
+multiline matches with the regex condition.
+
+The mime_regex condition can be called only in the MIME ACL. It matches up to
+32K of decoded content (the whole content at once, not linewise). If the part
+has not been decoded with the decode modifier earlier in the ACL, it is decoded
+automatically when mime_regex is executed (using default path and filename
+values). If the decoded data is larger than 32K, only the first 32K characters
+are checked.
+
+The regular expressions are passed as a colon-separated list. To include a
+literal colon, you must double it. Since the whole right-hand side string is
+expanded before being used, you must also escape dollar signs and backslashes
+with more backslashes, or use the "\N" facility to disable expansion. Here is a
+simple example that contains two regular expressions:
+
+deny regex = [Mm]ortgage : URGENT BUSINESS PROPOSAL
+ message = contains blacklisted regex ($regex_match_string)
+
+The conditions returns true if any one of the regular expressions matches. The
+$regex_match_string expansion variable is then set up and contains the matching
+regular expression. The expansion variables $regex1 $regex2 etc are set to any
+substrings captured by the regular expression.
+
+Warning: With large messages, these conditions can be fairly CPU-intensive.
+
+
+
+===============================================================================
+46. ADDING A LOCAL SCAN FUNCTION TO EXIM
+
+In these days of email worms, viruses, and ever-increasing spam, some sites
+want to apply a lot of checking to messages before accepting them.
+
+The content scanning extension (chapter 45) has facilities for passing messages
+to external virus and spam scanning software. You can also do a certain amount
+in Exim itself through string expansions and the condition condition in the ACL
+that runs after the SMTP DATA command or the ACL for non-SMTP messages (see
+chapter 44), but this has its limitations.
+
+To allow for further customization to a site's own requirements, there is the
+possibility of linking Exim with a private message scanning function, written
+in C. If you want to run code that is written in something other than C, you
+can of course use a little C stub to call it.
+
+The local scan function is run once for every incoming message, at the point
+when Exim is just about to accept the message. It can therefore be used to
+control non-SMTP messages from local processes as well as messages arriving via
+SMTP.
+
+Exim applies a timeout to calls of the local scan function, and there is an
+option called local_scan_timeout for setting it. The default is 5 minutes. Zero
+means "no timeout". Exim also sets up signal handlers for SIGSEGV, SIGILL,
+SIGFPE, and SIGBUS before calling the local scan function, so that the most
+common types of crash are caught. If the timeout is exceeded or one of those
+signals is caught, the incoming message is rejected with a temporary error if
+it is an SMTP message. For a non-SMTP message, the message is dropped and Exim
+ends with a non-zero code. The incident is logged on the main and reject logs.
+
+
+46.1 Building Exim to use a local scan function
+-----------------------------------------------
+
+To make use of the local scan function feature, you must tell Exim where your
+function is before building Exim, by setting both HAVE_LOCAL_SCAN and
+LOCAL_SCAN_SOURCE in your Local/Makefile. A recommended place to put it is in
+the Local directory, so you might set
+
+HAVE_LOCAL_SCAN=yes
+LOCAL_SCAN_SOURCE=Local/local_scan.c
+
+for example. The function must be called local_scan();
+
+the source file(s) for it should first #define LOCAL_SCAN and then #include
+"local_scan.h".
+
+It is called by Exim after it has received a message, when the success return
+code is about to be sent. This is after all the ACLs have been run. The return
+code from your function controls whether the message is actually accepted or
+not. There is a commented template function (that just accepts the message) in
+the file _src/local_scan.c_.
+
+If you want to make use of Exim's runtime configuration file to set options for
+your local_scan() function, you must also set
+
+LOCAL_SCAN_HAS_OPTIONS=yes
+
+in Local/Makefile (see section 46.3 below).
+
+
+46.2 API for local_scan()
+-------------------------
+
+You must include this line near the start of your code:
+
+#define LOCAL_SCAN
+#include "local_scan.h"
+
+This header file defines a number of variables and other values, and the
+prototype for the function itself. Exim is coded to use unsigned char values
+almost exclusively, and one of the things this header defines is a shorthand
+for "unsigned char" called "uschar". It also makes available the following
+macro definitions, to simplify casting character strings and pointers to
+character strings:
+
+#define CS (char *)
+#define CCS (const char *)
+#define CSS (char **)
+#define US (unsigned char *)
+#define CUS (const unsigned char *)
+#define USS (unsigned char **)
+
+The function prototype for local_scan() is:
+
+extern int local_scan(int fd, uschar **return_text);
+
+The arguments are as follows:
+
+ * fd is a file descriptor for the file that contains the body of the message
+ (the -D file). The file is open for reading and writing, but updating it is
+ not recommended. Warning: You must not close this file descriptor.
+
+ The descriptor is positioned at character 19 of the file, which is the
+ first character of the body itself, because the first 19 characters are the
+ message id followed by "-D" and a newline. If you rewind the file, you
+ should use the macro SPOOL_DATA_START_OFFSET to reset to the start of the
+ data, just in case this changes in some future version.
+
+ * return_text is an address which you can use to return a pointer to a text
+ string at the end of the function. The value it points to on entry is NULL.
+
+The function must return an int value which is one of the following macros:
+
+"LOCAL_SCAN_ACCEPT"
+
+ The message is accepted. If you pass back a string of text, it is saved
+ with the message, and made available in the variable $local_scan_data. No
+ newlines are permitted (if there are any, they are turned into spaces) and
+ the maximum length of text is 1000 characters.
+
+"LOCAL_SCAN_ACCEPT_FREEZE"
+
+ This behaves as LOCAL_SCAN_ACCEPT, except that the accepted message is
+ queued without immediate delivery, and is frozen.
+
+"LOCAL_SCAN_ACCEPT_QUEUE"
+
+ This behaves as LOCAL_SCAN_ACCEPT, except that the accepted message is
+ queued without immediate delivery.
+
+"LOCAL_SCAN_REJECT"
+
+ The message is rejected; the returned text is used as an error message
+ which is passed back to the sender and which is also logged. Newlines are
+ permitted - they cause a multiline response for SMTP rejections, but are
+ converted to "\n" in log lines. If no message is given, "Administrative
+ prohibition" is used.
+
+"LOCAL_SCAN_TEMPREJECT"
+
+ The message is temporarily rejected; the returned text is used as an error
+ message as for LOCAL_SCAN_REJECT. If no message is given, "Temporary local
+ problem" is used.
+
+"LOCAL_SCAN_REJECT_NOLOGHDR"
+
+ This behaves as LOCAL_SCAN_REJECT, except that the header of the rejected
+ message is not written to the reject log. It has the effect of unsetting
+ the rejected_header log selector for just this rejection. If
+ rejected_header is already unset (see the discussion of the log_selection
+ option in section 53.15), this code is the same as LOCAL_SCAN_REJECT.
+
+"LOCAL_SCAN_TEMPREJECT_NOLOGHDR"
+
+ This code is a variation of LOCAL_SCAN_TEMPREJECT in the same way that
+ LOCAL_SCAN_REJECT_NOLOGHDR is a variation of LOCAL_SCAN_REJECT.
+
+If the message is not being received by interactive SMTP, rejections are
+reported by writing to stderr or by sending an email, as configured by the -oe
+command line options.
+
+
+46.3 Configuration options for local_scan()
+-------------------------------------------
+
+It is possible to have option settings in the main configuration file that set
+values in static variables in the local_scan() module. If you want to do this,
+you must have the line
+
+LOCAL_SCAN_HAS_OPTIONS=yes
+
+in your Local/Makefile when you build Exim. (This line is in OS/
+Makefile-Default, commented out). Then, in the local_scan() source file, you
+must define static variables to hold the option values, and a table to define
+them.
+
+The table must be a vector called local_scan_options, of type "optionlist".
+Each entry is a triplet, consisting of a name, an option type, and a pointer to
+the variable that holds the value. The entries must appear in alphabetical
+order. Following local_scan_options you must also define a variable called
+local_scan_options_count that contains the number of entries in the table. Here
+is a short example, showing two kinds of option:
+
+static int my_integer_option = 42;
+static uschar *my_string_option = US"a default string";
+
+optionlist local_scan_options[] = {
+ { "my_integer", opt_int, &my_integer_option },
+ { "my_string", opt_stringptr, &my_string_option }
+};
+
+int local_scan_options_count =
+ sizeof(local_scan_options)/sizeof(optionlist);
+
+The values of the variables can now be changed from Exim's runtime
+configuration file by including a local scan section as in this example:
+
+begin local_scan
+my_integer = 99
+my_string = some string of text...
+
+The available types of option data are as follows:
+
+opt_bool
+
+ This specifies a boolean (true/false) option. The address should point to a
+ variable of type "BOOL", which will be set to TRUE or FALSE, which are
+ macros that are defined as "1" and "0", respectively. If you want to detect
+ whether such a variable has been set at all, you can initialize it to
+ TRUE_UNSET. (BOOL variables are integers underneath, so can hold more than
+ two values.)
+
+opt_fixed
+
+ This specifies a fixed point number, such as is used for load averages. The
+ address should point to a variable of type "int". The value is stored
+ multiplied by 1000, so, for example, 1.4142 is truncated and stored as
+ 1414.
+
+opt_int
+
+ This specifies an integer; the address should point to a variable of type
+ "int". The value may be specified in any of the integer formats accepted by
+ Exim.
+
+opt_mkint
+
+ This is the same as opt_int, except that when such a value is output in a
+ -bP listing, if it is an exact number of kilobytes or megabytes, it is
+ printed with the suffix K or M.
+
+opt_octint
+
+ This also specifies an integer, but the value is always interpreted as an
+ octal integer, whether or not it starts with the digit zero, and it is
+ always output in octal.
+
+opt_stringptr
+
+ This specifies a string value; the address must be a pointer to a variable
+ that points to a string (for example, of type "uschar *").
+
+opt_time
+
+ This specifies a time interval value. The address must point to a variable
+ of type "int". The value that is placed there is a number of seconds.
+
+If the -bP command line option is followed by "local_scan", Exim prints out the
+values of all the local_scan() options.
+
+
+46.4 Available Exim variables
+-----------------------------
+
+The header local_scan.h gives you access to a number of C variables. These are
+the only ones that are guaranteed to be maintained from release to release.
+Note, however, that you can obtain the value of any Exim expansion variable,
+including $recipients, by calling expand_string(). The exported C variables are
+as follows:
+
+int body_linecount
+
+ This variable contains the number of lines in the message's body. It is not
+ valid if the spool_files_wireformat option is used.
+
+int body_zerocount
+
+ This variable contains the number of binary zero bytes in the message's
+ body. It is not valid if the spool_files_wireformat option is used.
+
+unsigned int debug_selector
+
+ This variable is set to zero when no debugging is taking place. Otherwise,
+ it is a bitmap of debugging selectors. Two bits are identified for use in
+ local_scan(); they are defined as macros:
+
+ + The "D_v" bit is set when -v was present on the command line. This is a
+ testing option that is not privileged - any caller may set it. All the
+ other selector bits can be set only by admin users.
+
+ + The "D_local_scan" bit is provided for use by local_scan(); it is set
+ by the "+local_scan" debug selector. It is not included in the default
+ set of debugging bits.
+
+ Thus, to write to the debugging output only when "+local_scan" has been
+ selected, you should use code like this:
+
+ if ((debug_selector & D_local_scan) != 0)
+ debug_printf("xxx", ...);
+
+uschar *expand_string_message
+
+ After a failing call to expand_string() (returned value NULL), the variable
+ expand_string_message contains the error message, zero-terminated.
+
+header_line *header_list
+
+ A pointer to a chain of header lines. The header_line structure is
+ discussed below.
+
+header_line *header_last
+
+ A pointer to the last of the header lines.
+
+uschar *headers_charset
+
+ The value of the headers_charset configuration option.
+
+BOOL host_checking
+
+ This variable is TRUE during a host checking session that is initiated by
+ the -bh command line option.
+
+uschar *interface_address
+
+ The IP address of the interface that received the message, as a string.
+ This is NULL for locally submitted messages.
+
+int interface_port
+
+ The port on which this message was received. When testing with the -bh
+ command line option, the value of this variable is -1 unless a port has
+ been specified via the -oMi option.
+
+uschar *message_id
+
+ This variable contains Exim's message id for the incoming message (the
+ value of $message_exim_id) as a zero-terminated string.
+
+uschar *received_protocol
+
+ The name of the protocol by which the message was received.
+
+int recipients_count
+
+ The number of accepted recipients.
+
+recipient_item *recipients_list
+
+ The list of accepted recipients, held in a vector of length
+ recipients_count. The recipient_item structure is discussed below. You can
+ add additional recipients by calling receive_add_recipient() (see below).
+ You can delete recipients by removing them from the vector and adjusting
+ the value in recipients_count. In particular, by setting recipients_count
+ to zero you remove all recipients. If you then return the value
+ "LOCAL_SCAN_ACCEPT", the message is accepted, but immediately blackholed.
+ To replace the recipients, you can set recipients_count to zero and then
+ call receive_add_recipient() as often as needed.
+
+uschar *sender_address
+
+ The envelope sender address. For bounce messages this is the empty string.
+
+uschar *sender_host_address
+
+ The IP address of the sending host, as a string. This is NULL for
+ locally-submitted messages.
+
+uschar *sender_host_authenticated
+
+ The name of the authentication mechanism that was used, or NULL if the
+ message was not received over an authenticated SMTP connection.
+
+uschar *sender_host_name
+
+ The name of the sending host, if known.
+
+int sender_host_port
+
+ The port on the sending host.
+
+BOOL smtp_input
+
+ This variable is TRUE for all SMTP input, including BSMTP.
+
+BOOL smtp_batched_input
+
+ This variable is TRUE for BSMTP input.
+
+int store_pool
+
+ The contents of this variable control which pool of memory is used for new
+ requests. See section 46.8 for details.
+
+
+46.5 Structure of header lines
+------------------------------
+
+The header_line structure contains the members listed below. You can add
+additional header lines by calling the header_add() function (see below). You
+can cause header lines to be ignored (deleted) by setting their type to *.
+
+struct header_line *next
+
+ A pointer to the next header line, or NULL for the last line.
+
+int type
+
+ A code identifying certain headers that Exim recognizes. The codes are
+ printing characters, and are documented in chapter 57 of this manual.
+ Notice in particular that any header line whose type is * is not
+ transmitted with the message. This flagging is used for header lines that
+ have been rewritten, or are to be removed (for example, Envelope-sender:
+ header lines.) Effectively, * means "deleted".
+
+int slen
+
+ The number of characters in the header line, including the terminating and
+ any internal newlines.
+
+uschar *text
+
+ A pointer to the text of the header. It always ends with a newline,
+ followed by a zero byte. Internal newlines are preserved.
+
+
+46.6 Structure of recipient items
+---------------------------------
+
+The recipient_item structure contains these members:
+
+uschar *address
+
+ This is a pointer to the recipient address as it was received.
+
+int pno
+
+ This is used in later Exim processing when top level addresses are created
+ by the one_time option. It is not relevant at the time local_scan() is run
+ and must always contain -1 at this stage.
+
+uschar *errors_to
+
+ If this value is not NULL, bounce messages caused by failing to deliver to
+ the recipient are sent to the address it contains. In other words, it
+ overrides the envelope sender for this one recipient. (Compare the
+ errors_to generic router option.) If a local_scan() function sets an
+ errors_to field to an unqualified address, Exim qualifies it using the
+ domain from qualify_recipient. When local_scan() is called, the errors_to
+ field is NULL for all recipients.
+
+
+46.7 Available Exim functions
+-----------------------------
+
+The header local_scan.h gives you access to a number of Exim functions. These
+are the only ones that are guaranteed to be maintained from release to release:
+
+pid_t child_open
+ (uschar **argv, uschar **envp, int newumask, int *infdptr, int *outfdptr,
+ BOOL make_leader)
+
+ This function creates a child process that runs the command specified by
+ argv. The environment for the process is specified by envp, which can be
+ NULL if no environment variables are to be passed. A new umask is supplied
+ for the process in newumask.
+
+ Pipes to the standard input and output of the new process are set up and
+ returned to the caller via the infdptr and outfdptr arguments. The standard
+ error is cloned to the standard output. If there are any file descriptors
+ "in the way" in the new process, they are closed. If the final argument is
+ TRUE, the new process is made into a process group leader.
+
+ The function returns the pid of the new process, or -1 if things go wrong.
+
+int child_close(pid_t pid, int timeout)
+
+ This function waits for a child process to terminate, or for a timeout (in
+ seconds) to expire. A timeout value of zero means wait as long as it takes.
+ The return value is as follows:
+
+ + >= 0
+
+ The process terminated by a normal exit and the value is the process
+ ending status.
+
+ + < 0 and > -256
+
+ The process was terminated by a signal and the value is the negation of
+ the signal number.
+
+ + -256
+
+ The process timed out.
+
+ + -257
+
+ The was some other error in wait(); errno is still set.
+
+pid_t child_open_exim(int *fd)
+
+ This function provide you with a means of submitting a new message to Exim.
+ (Of course, you can also call /usr/sbin/sendmail yourself if you want, but
+ this packages it all up for you.) The function creates a pipe, forks a
+ subprocess that is running
+
+ exim -t -oem -oi -f <>
+
+ and returns to you (via the "int *" argument) a file descriptor for the
+ pipe that is connected to the standard input. The yield of the function is
+ the PID of the subprocess. You can then write a message to the file
+ descriptor, with recipients in To:, Cc:, and/or Bcc: header lines.
+
+ When you have finished, call child_close() to wait for the process to
+ finish and to collect its ending status. A timeout value of zero is usually
+ fine in this circumstance. Unless you have made a mistake with the
+ recipient addresses, you should get a return code of zero.
+
+pid_t child_open_exim2(int *fd, uschar *sender, uschar *sender_authentication)
+
+ This function is a more sophisticated version of child_open(). The command
+ that it runs is:
+
+ exim -t -oem -oi -f sender -oMas sender_authentication
+
+ The third argument may be NULL, in which case the -oMas option is omitted.
+
+void debug_printf(char *, ...)
+
+ This is Exim's debugging function, with arguments as for (printf(). The
+ output is written to the standard error stream. If no debugging is
+ selected, calls to debug_printf() have no effect. Normally, you should make
+ calls conditional on the "local_scan" debug selector by coding like this:
+
+ if ((debug_selector & D_local_scan) != 0)
+ debug_printf("xxx", ...);
+
+uschar *expand_string(uschar *string)
+
+ This is an interface to Exim's string expansion code. The return value is
+ the expanded string, or NULL if there was an expansion failure. The C
+ variable expand_string_message contains an error message after an expansion
+ failure. If expansion does not change the string, the return value is the
+ pointer to the input string. Otherwise, the return value points to a new
+ block of memory that was obtained by a call to store_get(). See section
+ 46.8 below for a discussion of memory handling.
+
+void header_add(int type, char *format, ...)
+
+ This function allows you to an add additional header line at the end of the
+ existing ones. The first argument is the type, and should normally be a
+ space character. The second argument is a format string and any number of
+ substitution arguments as for sprintf(). You may include internal newlines
+ if you want, and you must ensure that the string ends with a newline.
+
+void header_add_at_position
+ (BOOL after, uschar *name, BOOL topnot, int type, char *format, ...)
+
+ This function adds a new header line at a specified point in the header
+ chain. The header itself is specified as for header_add().
+
+ If name is NULL, the new header is added at the end of the chain if after
+ is true, or at the start if after is false. If name is not NULL, the header
+ lines are searched for the first non-deleted header that matches the name.
+ If one is found, the new header is added before it if after is false. If
+ after is true, the new header is added after the found header and any
+ adjacent subsequent ones with the same name (even if marked "deleted"). If
+ no matching non-deleted header is found, the topnot option controls where
+ the header is added. If it is true, addition is at the top; otherwise at
+ the bottom. Thus, to add a header after all the Received: headers, or at
+ the top if there are no Received: headers, you could use
+
+ header_add_at_position(TRUE, US"Received", TRUE,
+ ' ', "X-xxx: ...");
+
+ Normally, there is always at least one non-deleted Received: header, but
+ there may not be if received_header_text expands to an empty string.
+
+void header_remove(int occurrence, uschar *name)
+
+ This function removes header lines. If occurrence is zero or negative, all
+ occurrences of the header are removed. If occurrence is greater than zero,
+ that particular instance of the header is removed. If no header(s) can be
+ found that match the specification, the function does nothing.
+
+BOOL header_testname(header_line *hdr, uschar *name, int length, BOOL notdel)
+
+ This function tests whether the given header has the given name. It is not
+ just a string comparison, because white space is permitted between the name
+ and the colon. If the notdel argument is true, a false return is forced for
+ all "deleted" headers; otherwise they are not treated specially. For
+ example:
+
+ if (header_testname(h, US"X-Spam", 6, TRUE)) ...
+
+uschar *lss_b64encode(uschar *cleartext, int length)
+
+ This function base64-encodes a string, which is passed by address and
+ length. The text may contain bytes of any value, including zero. The result
+ is passed back in dynamic memory that is obtained by calling store_get().
+ It is zero-terminated.
+
+int lss_b64decode(uschar *codetext, uschar **cleartext)
+
+ This function decodes a base64-encoded string. Its arguments are a
+ zero-terminated base64-encoded string and the address of a variable that is
+ set to point to the result, which is in dynamic memory. The length of the
+ decoded string is the yield of the function. If the input is invalid base64
+ data, the yield is -1. A zero byte is added to the end of the output string
+ to make it easy to interpret as a C string (assuming it contains no zeros
+ of its own). The added zero byte is not included in the returned count.
+
+int lss_match_domain(uschar *domain, uschar *list)
+
+ This function checks for a match in a domain list. Domains are always
+ matched caselessly. The return value is one of the following:
+
+ OK match succeeded
+ FAIL match failed
+ DEFER match deferred
+
+ DEFER is usually caused by some kind of lookup defer, such as the inability
+ to contact a database.
+
+int lss_match_local_part(uschar *localpart, uschar *list, BOOL caseless)
+
+ This function checks for a match in a local part list. The third argument
+ controls case-sensitivity. The return values are as for lss_match_domain().
+
+int lss_match_address(uschar *address, uschar *list, BOOL caseless)
+
+ This function checks for a match in an address list. The third argument
+ controls the case-sensitivity of the local part match. The domain is always
+ matched caselessly. The return values are as for lss_match_domain().
+
+int lss_match_host(uschar *host_name, uschar *host_address, uschar *list)
+
+ This function checks for a match in a host list. The most common usage is
+ expected to be
+
+ lss_match_host(sender_host_name, sender_host_address, ...)
+
+ An empty address field matches an empty item in the host list. If the host
+ name is NULL, the name corresponding to $sender_host_address is
+ automatically looked up if a host name is required to match an item in the
+ list. The return values are as for lss_match_domain(), but in addition,
+ lss_match_host() returns ERROR in the case when it had to look up a host
+ name, but the lookup failed.
+
+void log_write(unsigned int selector, int which, char *format, ...)
+
+ This function writes to Exim's log files. The first argument should be zero
+ (it is concerned with log_selector). The second argument can be "LOG_MAIN"
+ or "LOG_REJECT" or "LOG_PANIC" or the inclusive "or" of any combination of
+ them. It specifies to which log or logs the message is written. The
+ remaining arguments are a format and relevant insertion arguments. The
+ string should not contain any newlines, not even at the end.
+
+void receive_add_recipient(uschar *address, int pno)
+
+ This function adds an additional recipient to the message. The first
+ argument is the recipient address. If it is unqualified (has no domain), it
+ is qualified with the qualify_recipient domain. The second argument must
+ always be -1.
+
+ This function does not allow you to specify a private errors_to address (as
+ described with the structure of recipient_item above), because it pre-dates
+ the addition of that field to the structure. However, it is easy to add
+ such a value afterwards. For example:
+
+ receive_add_recipient(US"monitor@mydom.example", -1);
+ recipients_list[recipients_count-1].errors_to =
+ US"postmaster@mydom.example";
+
+BOOL receive_remove_recipient(uschar *recipient)
+
+ This is a convenience function to remove a named recipient from the list of
+ recipients. It returns true if a recipient was removed, and false if no
+ matching recipient could be found. The argument must be a complete email
+ address.
+
+uschar rfc2047_decode
+ (uschar *string, BOOL lencheck, uschar *target, int zeroval, int *lenptr,
+ uschar **error)
+
+ This function decodes strings that are encoded according to RFC 2047.
+ Typically these are the contents of header lines. First, each "encoded
+ word" is decoded from the Q or B encoding into a byte-string. Then, if
+ provided with the name of a charset encoding, and if the iconv() function
+ is available, an attempt is made to translate the result to the named
+ character set. If this fails, the binary string is returned with an error
+ message.
+
+ The first argument is the string to be decoded. If lencheck is TRUE, the
+ maximum MIME word length is enforced. The third argument is the target
+ encoding, or NULL if no translation is wanted.
+
+ If a binary zero is encountered in the decoded string, it is replaced by
+ the contents of the zeroval argument. For use with Exim headers, the value
+ must not be 0 because header lines are handled as zero-terminated strings.
+
+ The function returns the result of processing the string, zero-terminated;
+ if lenptr is not NULL, the length of the result is set in the variable to
+ which it points. When zeroval is 0, lenptr should not be NULL.
+
+ If an error is encountered, the function returns NULL and uses the error
+ argument to return an error message. The variable pointed to by error is
+ set to NULL if there is no error; it may be set non-NULL even when the
+ function returns a non-NULL value if decoding was successful, but there was
+ a problem with translation.
+
+int smtp_fflush(void)
+
+ This function is used in conjunction with smtp_printf(), as described
+ below.
+
+void smtp_printf(char *,BOOL, ...)
+
+ The arguments of this function are almost like printf(); it writes to the
+ SMTP output stream. You should use this function only when there is an SMTP
+ output stream, that is, when the incoming message is being received via
+ interactive SMTP. This is the case when smtp_input is TRUE and
+ smtp_batched_input is FALSE. If you want to test for an incoming message
+ from another host (as opposed to a local process that used the -bs command
+ line option), you can test the value of sender_host_address, which is
+ non-NULL when a remote host is involved.
+
+ If an SMTP TLS connection is established, smtp_printf() uses the TLS output
+ function, so it can be used for all forms of SMTP connection.
+
+ The second argument is used to request that the data be buffered (when
+ TRUE) or flushed (along with any previously buffered, when FALSE). This is
+ advisory only, but likely to save on system-calls and packets sent when a
+ sequence of calls to the function are made.
+
+ The argument was added in Exim version 4.90 - changing the API/ABI. Nobody
+ noticed until 4.93 was imminent, at which point the ABI version number was
+ incremented.
+
+ Strings that are written by smtp_printf() from within local_scan() must
+ start with an appropriate response code: 550 if you are going to return
+ LOCAL_SCAN_REJECT, 451 if you are going to return LOCAL_SCAN_TEMPREJECT,
+ and 250 otherwise. Because you are writing the initial lines of a
+ multi-line response, the code must be followed by a hyphen to indicate that
+ the line is not the final response line. You must also ensure that the
+ lines you write terminate with CRLF. For example:
+
+ smtp_printf("550-this is some extra info\r\n");
+ return LOCAL_SCAN_REJECT;
+
+ Note that you can also create multi-line responses by including newlines in
+ the data returned via the return_text argument. The added value of using
+ smtp_printf() is that, for instance, you could introduce delays between
+ multiple output lines.
+
+ The smtp_printf() function does not return any error indication, because it
+ does not guarantee a flush of pending output, and therefore does not test
+ the state of the stream. (In the main code of Exim, flushing and error
+ detection is done when Exim is ready for the next SMTP input command.) If
+ you want to flush the output and check for an error (for example, the
+ dropping of a TCP/IP connection), you can call smtp_fflush(), which has no
+ arguments. It flushes the output stream, and returns a non-zero value if
+ there is an error.
+
+void *store_get(int,BOOL)
+
+ This function accesses Exim's internal store (memory) manager. It gets a
+ new chunk of memory whose size is given by the first argument. The second
+ argument should be given as TRUE if the memory will be used for data
+ possibly coming from an attacker (eg. the message content), FALSE if it is
+ locally-sourced. Exim bombs out if it ever runs out of memory. See the next
+ section for a discussion of memory handling.
+
+void *store_get_perm(int,BOOL)
+
+ This function is like store_get(), but it always gets memory from the
+ permanent pool. See the next section for a discussion of memory handling.
+
+uschar *string_copy(uschar *string)
+
+ See below.
+
+uschar *string_copyn(uschar *string, int length)
+
+ See below.
+
+uschar *string_sprintf(char *format, ...)
+
+ These three functions create strings using Exim's dynamic memory
+ facilities. The first makes a copy of an entire string. The second copies
+ up to a maximum number of characters, indicated by the second argument. The
+ third uses a format and insertion arguments to create a new string. In each
+ case, the result is a pointer to a new string in the current memory pool.
+ See the next section for more discussion.
+
+
+46.8 More about Exim's memory handling
+--------------------------------------
+
+No function is provided for freeing memory, because that is never needed. The
+dynamic memory that Exim uses when receiving a message is automatically
+recycled if another message is received by the same process (this applies only
+to incoming SMTP connections - other input methods can supply only one message
+at a time). After receiving the last message, a reception process terminates.
+
+Because it is recycled, the normal dynamic memory cannot be used for holding
+data that must be preserved over a number of incoming messages on the same SMTP
+connection. However, Exim in fact uses two pools of dynamic memory; the second
+one is not recycled, and can be used for this purpose.
+
+If you want to allocate memory that remains available for subsequent messages
+in the same SMTP connection, you should set
+
+store_pool = POOL_PERM
+
+before calling the function that does the allocation. There is no need to
+restore the value if you do not need to; however, if you do want to revert to
+the normal pool, you can either restore the previous value of store_pool or set
+it explicitly to POOL_MAIN.
+
+The pool setting applies to all functions that get dynamic memory, including
+expand_string(), store_get(), and the string_xxx() functions. There is also a
+convenience function called store_get_perm() that gets a block of memory from
+the permanent pool while preserving the value of store_pool.
+
+
+
+===============================================================================
+47. SYSTEM-WIDE MESSAGE FILTERING
+
+The previous chapters (on ACLs and the local scan function) describe checks
+that can be applied to messages before they are accepted by a host. There is
+also a mechanism for checking messages once they have been received, but before
+they are delivered. This is called the system filter.
+
+The system filter operates in a similar manner to users' filter files, but it
+is run just once per message (however many recipients the message has). It
+should not normally be used as a substitute for routing, because deliver
+commands in a system router provide new envelope recipient addresses. The
+system filter must be an Exim filter. It cannot be a Sieve filter.
+
+The system filter is run at the start of a delivery attempt, before any routing
+is done. If a message fails to be completely delivered at the first attempt,
+the system filter is run again at the start of every retry. If you want your
+filter to do something only once per message, you can make use of the
+first_delivery condition in an if command in the filter to prevent it happening
+on retries.
+
+Warning: Because the system filter runs just once, variables that are specific
+to individual recipient addresses, such as $local_part and $domain, are not
+set, and the "personal" condition is not meaningful. If you want to run a
+centrally-specified filter for each recipient address independently, you can do
+so by setting up a suitable redirect router, as described in section 47.8
+below.
+
+
+47.1 Specifying a system filter
+-------------------------------
+
+The name of the file that contains the system filter must be specified by
+setting system_filter. If you want the filter to run under a uid and gid other
+than root, you must also set system_filter_user and system_filter_group as
+appropriate. For example:
+
+system_filter = /etc/mail/exim.filter
+system_filter_user = exim
+
+If a system filter generates any deliveries directly to files or pipes (via the
+save or pipe commands), transports to handle these deliveries must be specified
+by setting system_filter_file_transport and system_filter_pipe_transport,
+respectively. Similarly, system_filter_reply_transport must be set to handle
+any messages generated by the reply command.
+
+
+47.2 Testing a system filter
+----------------------------
+
+You can run simple tests of a system filter in the same way as for a user
+filter, but you should use -bF rather than -bf, so that features that are
+permitted only in system filters are recognized.
+
+If you want to test the combined effect of a system filter and a user filter,
+you can use both -bF and -bf on the same command line.
+
+
+47.3 Contents of a system filter
+--------------------------------
+
+The language used to specify system filters is the same as for users' filter
+files. It is described in the separate end-user document Exim's interface to
+mail filtering. However, there are some additional features that are available
+only in system filters; these are described in subsequent sections. If they are
+encountered in a user's filter file or when testing with -bf, they cause
+errors.
+
+There are two special conditions which, though available in users' filter
+files, are designed for use in system filters. The condition first_delivery is
+true only for the first attempt at delivering a message, and manually_thawed is
+true only if the message has been frozen, and subsequently thawed by an admin
+user. An explicit forced delivery counts as a manual thaw, but thawing as a
+result of the auto_thaw setting does not.
+
+Warning: If a system filter uses the first_delivery condition to specify an
+"unseen" (non-significant) delivery, and that delivery does not succeed, it
+will not be tried again. If you want Exim to retry an unseen delivery until it
+succeeds, you should arrange to set it up every time the filter runs.
+
+When a system filter finishes running, the values of the variables $n0 - $n9
+are copied into $sn0 - $sn9 and are thereby made available to users' filter
+files. Thus a system filter can, for example, set up "scores" to which users'
+filter files can refer.
+
+
+47.4 Additional variable for system filters
+-------------------------------------------
+
+The expansion variable $recipients, containing a list of all the recipients of
+the message (separated by commas and white space), is available in system
+filters. It is not available in users' filters for privacy reasons.
+
+
+47.5 Defer, freeze, and fail commands for system filters
+--------------------------------------------------------
+
+There are three extra commands (defer, freeze and fail) which are always
+available in system filters, but are not normally enabled in users' filters.
+(See the allow_defer, allow_freeze and allow_fail options for the redirect
+router.) These commands can optionally be followed by the word text and a
+string containing an error message, for example:
+
+fail text "this message looks like spam to me"
+
+The keyword text is optional if the next character is a double quote.
+
+The defer command defers delivery of the original recipients of the message.
+The fail command causes all the original recipients to be failed, and a bounce
+message to be created. The freeze command suspends all delivery attempts for
+the original recipients. In all cases, any new deliveries that are specified by
+the filter are attempted as normal after the filter has run.
+
+The freeze command is ignored if the message has been manually unfrozen and not
+manually frozen since. This means that automatic freezing by a system filter
+can be used as a way of checking out suspicious messages. If a message is found
+to be all right, manually unfreezing it allows it to be delivered.
+
+The text given with a fail command is used as part of the bounce message as
+well as being written to the log. If the message is quite long, this can fill
+up a lot of log space when such failures are common. To reduce the size of the
+log message, Exim interprets the text in a special way if it starts with the
+two characters "<<" and contains ">>" later. The text between these two strings
+is written to the log, and the rest of the text is used in the bounce message.
+For example:
+
+fail "<<filter test 1>>Your message is rejected \
+ because it contains attachments that we are \
+ not prepared to receive."
+
+Take great care with the fail command when basing the decision to fail on the
+contents of the message, because the bounce message will of course include the
+contents of the original message and will therefore trigger the fail command
+again (causing a mail loop) unless steps are taken to prevent this. Testing the
+error_message condition is one way to prevent this. You could use, for example
+
+if $message_body contains "this is spam" and not error_message
+then fail text "spam is not wanted here" endif
+
+though of course that might let through unwanted bounce messages. The
+alternative is clever checking of the body and/or headers to detect bounces
+generated by the filter.
+
+The interpretation of a system filter file ceases after a defer, freeze, or
+fail command is obeyed. However, any deliveries that were set up earlier in the
+filter file are honoured, so you can use a sequence such as
+
+mail ...
+freeze
+
+to send a specified message when the system filter is freezing (or deferring or
+failing) a message. The normal deliveries for the message do not, of course,
+take place.
+
+
+47.6 Adding and removing headers in a system filter
+---------------------------------------------------
+
+Two filter commands that are available only in system filters are:
+
+headers add <string>
+headers remove <string>
+
+The argument for the headers add is a string that is expanded and then added to
+the end of the message's headers. It is the responsibility of the filter
+maintainer to make sure it conforms to RFC 2822 syntax. Leading white space is
+ignored, and if the string is otherwise empty, or if the expansion is forced to
+fail, the command has no effect.
+
+You can use "\n" within the string, followed by white space, to specify
+continued header lines. More than one header may be added in one command by
+including "\n" within the string without any following white space. For
+example:
+
+headers add "X-header-1: ....\n \
+ continuation of X-header-1 ...\n\
+ X-header-2: ...."
+
+Note that the header line continuation white space after the first newline must
+be placed before the backslash that continues the input string, because white
+space after input continuations is ignored.
+
+The argument for headers remove is a colon-separated list of header names. This
+command applies only to those headers that are stored with the message; those
+that are added at delivery time (such as Envelope-To: and Return-Path:) cannot
+be removed by this means. If there is more than one header with the same name,
+they are all removed.
+
+The headers command in a system filter makes an immediate change to the set of
+header lines that was received with the message (with possible additions from
+ACL processing). Subsequent commands in the system filter operate on the
+modified set, which also forms the basis for subsequent message delivery.
+Unless further modified during routing or transporting, this set of headers is
+used for all recipients of the message.
+
+During routing and transporting, the variables that refer to the contents of
+header lines refer only to those lines that are in this set. Thus, header lines
+that are added by a system filter are visible to users' filter files and to all
+routers and transports. This contrasts with the manipulation of header lines by
+routers and transports, which is not immediate, but which instead is saved up
+until the message is actually being written (see section 48.17).
+
+If the message is not delivered at the first attempt, header lines that were
+added by the system filter are stored with the message, and so are still
+present at the next delivery attempt. Header lines that were removed are still
+present, but marked "deleted" so that they are not transported with the
+message. For this reason, it is usual to make the headers command conditional
+on first_delivery so that the set of header lines is not modified more than
+once.
+
+Because header modification in a system filter acts immediately, you have to
+use an indirect approach if you want to modify the contents of a header line.
+For example:
+
+headers add "Old-Subject: $h_subject:"
+headers remove "Subject"
+headers add "Subject: new subject (was: $h_old-subject:)"
+headers remove "Old-Subject"
+
+
+47.7 Setting an errors address in a system filter
+-------------------------------------------------
+
+In a system filter, if a deliver command is followed by
+
+errors_to <some address>
+
+in order to change the envelope sender (and hence the error reporting) for that
+delivery, any address may be specified. (In a user filter, only the current
+user's address can be set.) For example, if some mail is being monitored, you
+might use
+
+unseen deliver monitor@spying.example errors_to root@local.example
+
+to take a copy which would not be sent back to the normal error reporting
+address if its delivery failed.
+
+
+47.8 Per-address filtering
+--------------------------
+
+In contrast to the system filter, which is run just once per message for each
+delivery attempt, it is also possible to set up a system-wide filtering
+operation that runs once for each recipient address. In this case, variables
+such as $local_part and $domain can be used, and indeed, the choice of filter
+file could be made dependent on them. This is an example of a router which
+implements such a filter:
+
+central_filter:
+ check_local_user
+ driver = redirect
+ domains = +local_domains
+ file = /central/filters/$local_part_data
+ no_verify
+ allow_filter
+ allow_freeze
+
+The filter is run in a separate process under its own uid. Therefore, either
+check_local_user must be set (as above), in which case the filter is run as the
+local user, or the user option must be used to specify which user to use. If
+both are set, user overrides.
+
+Care should be taken to ensure that none of the commands in the filter file
+specify a significant delivery if the message is to go on to be delivered to
+its intended recipient. The router will not then claim to have dealt with the
+address, so it will be passed on to subsequent routers to be delivered in the
+normal way.
+
+
+
+===============================================================================
+48. MESSAGE PROCESSING
+
+Exim performs various transformations on the sender and recipient addresses of
+all messages that it handles, and also on the messages' header lines. Some of
+these are optional and configurable, while others always take place. All of
+this processing, except rewriting as a result of routing, and the addition or
+removal of header lines while delivering, happens when a message is received,
+before it is placed on Exim's queue.
+
+Some of the automatic processing takes place by default only for
+"locally-originated" messages. This adjective is used to describe messages that
+are not received over TCP/IP, but instead are passed to an Exim process on its
+standard input. This includes the interactive "local SMTP" case that is set up
+by the -bs command line option.
+
+Note: Messages received over TCP/IP on the loopback interface (127.0.0.1 or
+::1) are not considered to be locally-originated. Exim does not treat the
+loopback interface specially in any way.
+
+If you want the loopback interface to be treated specially, you must ensure
+that there are appropriate entries in your ACLs.
+
+
+48.1 Submission mode for non-local messages
+-------------------------------------------
+
+Processing that happens automatically for locally-originated messages (unless
+suppress_local_fixups is set) can also be requested for messages that are
+received over TCP/IP. The term "submission mode" is used to describe this
+state. Submission mode is set by the modifier
+
+control = submission
+
+in a MAIL, RCPT, or pre-data ACL for an incoming message (see sections 44.21
+and 44.22). This makes Exim treat the message as a local submission, and is
+normally used when the source of the message is known to be an MUA running on a
+client host (as opposed to an MTA). For example, to set submission mode for
+messages originating on the IPv4 loopback interface, you could include the
+following in the MAIL ACL:
+
+warn hosts = 127.0.0.1
+ control = submission
+
+There are some options that can be used when setting submission mode. A slash
+is used to separate options. For example:
+
+control = submission/sender_retain
+
+Specifying sender_retain has the effect of setting local_sender_retain true and
+local_from_check false for the current incoming message. The first of these
+allows an existing Sender: header in the message to remain, and the second
+suppresses the check to ensure that From: matches the authenticated sender.
+With this setting, Exim still fixes up messages by adding Date: and Message-ID:
+header lines if they are missing, but makes no attempt to check sender
+authenticity in header lines.
+
+When sender_retain is not set, a submission mode setting may specify a domain
+to be used when generating a From: or Sender: header line. For example:
+
+control = submission/domain=some.domain
+
+The domain may be empty. How this value is used is described in sections 48.11
+and 48.16. There is also a name option that allows you to specify the user's
+full name for inclusion in a created Sender: or From: header line. For example:
+
+accept authenticated = *
+ control = submission/domain=wonderland.example/\
+ name=${lookup {$authenticated_id} \
+ lsearch {/etc/exim/namelist}}
+
+Because the name may contain any characters, including slashes, the name option
+must be given last. The remainder of the string is used as the name. For the
+example above, if /etc/exim/namelist contains:
+
+bigegg: Humpty Dumpty
+
+then when the sender has authenticated as bigegg, the generated Sender: line
+would be:
+
+Sender: Humpty Dumpty <bigegg@wonderland.example>
+
+By default, submission mode forces the return path to the same address as is
+used to create the Sender: header. However, if sender_retain is specified, the
+return path is also left unchanged.
+
+Note: The changes caused by submission mode take effect after the predata ACL.
+This means that any sender checks performed before the fix-ups use the
+untrusted sender address specified by the user, not the trusted sender address
+specified by submission mode. Although this might be slightly unexpected, it
+does mean that you can configure ACL checks to spot that a user is trying to
+spoof another's address.
+
+
+48.2 Line endings
+-----------------
+
+RFC 2821 specifies that CRLF (two characters: carriage-return, followed by
+linefeed) is the line ending for messages transmitted over the Internet using
+SMTP over TCP/IP. However, within individual operating systems, different
+conventions are used. For example, Unix-like systems use just LF, but others
+use CRLF or just CR.
+
+Exim was designed for Unix-like systems, and internally, it stores messages
+using the system's convention of a single LF as a line terminator. When
+receiving a message, all line endings are translated to this standard format.
+Originally, it was thought that programs that passed messages directly to an
+MTA within an operating system would use that system's convention. Experience
+has shown that this is not the case; for example, there are Unix applications
+that use CRLF in this circumstance. For this reason, and for compatibility with
+other MTAs, the way Exim handles line endings for all messages is now as
+follows:
+
+ * LF not preceded by CR is treated as a line ending.
+
+ * CR is treated as a line ending; if it is immediately followed by LF, the LF
+ is ignored.
+
+ * The sequence "CR, dot, CR" does not terminate an incoming SMTP message, nor
+ a local message in the state where a line containing only a dot is a
+ terminator.
+
+ * If a bare CR is encountered within a header line, an extra space is added
+ after the line terminator so as not to end the header line. The reasoning
+ behind this is that bare CRs in header lines are most likely either to be
+ mistakes, or people trying to play silly games.
+
+ * If the first header line received in a message ends with CRLF, a subsequent
+ bare LF in a header line is treated in the same way as a bare CR in a
+ header line.
+
+
+48.3 Unqualified addresses
+--------------------------
+
+By default, Exim expects every envelope address it receives from an external
+host to be fully qualified. Unqualified addresses cause negative responses to
+SMTP commands. However, because SMTP is used as a means of transporting
+messages from MUAs running on personal workstations, there is sometimes a
+requirement to accept unqualified addresses from specific hosts or IP networks.
+
+Exim has two options that separately control which hosts may send unqualified
+sender or recipient addresses in SMTP commands, namely sender_unqualified_hosts
+and recipient_unqualified_hosts. In both cases, if an unqualified address is
+accepted, it is qualified by adding the value of qualify_domain or
+qualify_recipient, as appropriate.
+
+Unqualified addresses in header lines are automatically qualified for messages
+that are locally originated, unless the -bnq option is given on the command
+line. For messages received over SMTP, unqualified addresses in header lines
+are qualified only if unqualified addresses are permitted in SMTP commands. In
+other words, such qualification is also controlled by sender_unqualified_hosts
+and recipient_unqualified_hosts,
+
+
+48.4 The UUCP From line
+-----------------------
+
+Messages that have come from UUCP (and some other applications) often begin
+with a line containing the envelope sender and a timestamp, following the word
+"From". Examples of two common formats are:
+
+From a.oakley@berlin.mus Fri Jan 5 12:35 GMT 1996
+From f.butler@berlin.mus Fri, 7 Jan 97 14:00:00 GMT
+
+This line precedes the RFC 2822 header lines. For compatibility with Sendmail,
+Exim recognizes such lines at the start of messages that are submitted to it
+via the command line (that is, on the standard input). It does not recognize
+such lines in incoming SMTP messages, unless the sending host matches
+ignore_fromline_hosts or the -bs option was used for a local message and
+ignore_fromline_local is set. The recognition is controlled by a regular
+expression that is defined by the uucp_from_pattern option, whose default value
+matches the two common cases shown above and puts the address that follows
+"From" into $1.
+
+When the caller of Exim for a non-SMTP message that contains a "From" line is a
+trusted user, the message's sender address is constructed by expanding the
+contents of uucp_sender_address, whose default value is "$1". This is then
+parsed as an RFC 2822 address. If there is no domain, the local part is
+qualified with qualify_domain unless it is the empty string. However, if the
+command line -f option is used, it overrides the "From" line.
+
+If the caller of Exim is not trusted, the "From" line is recognized, but the
+sender address is not changed. This is also the case for incoming SMTP messages
+that are permitted to contain "From" lines.
+
+Only one "From" line is recognized. If there is more than one, the second is
+treated as a data line that starts the body of the message, as it is not valid
+as a header line. This also happens if a "From" line is present in an incoming
+SMTP message from a source that is not permitted to send them.
+
+
+48.5 Resent- header lines
+-------------------------
+
+RFC 2822 makes provision for sets of header lines starting with the string
+"Resent-" to be added to a message when it is resent by the original recipient
+to somebody else. These headers are Resent-Date:, Resent-From:, Resent-Sender:,
+Resent-To:, Resent-Cc:, Resent-Bcc: and Resent-Message-ID:. The RFC says:
+
+ Resent fields are strictly informational. They MUST NOT be used in the
+ normal processing of replies or other such automatic actions on messages.
+
+This leaves things a bit vague as far as other processing actions such as
+address rewriting are concerned. Exim treats Resent- header lines as follows:
+
+ * A Resent-From: line that just contains the login id of the submitting user
+ is automatically rewritten in the same way as From: (see below).
+
+ * If there's a rewriting rule for a particular header line, it is also
+ applied to Resent- header lines of the same type. For example, a rule that
+ rewrites From: also rewrites Resent-From:.
+
+ * For local messages, if Sender: is removed on input, Resent-Sender: is also
+ removed.
+
+ * For a locally-submitted message, if there are any Resent- header lines but
+ no Resent-Date:, Resent-From:, or Resent-Message-Id:, they are added as
+ necessary. It is the contents of Resent-Message-Id: (rather than
+ Message-Id:) which are included in log lines in this case.
+
+ * The logic for adding Sender: is duplicated for Resent-Sender: when any
+ Resent- header lines are present.
+
+
+48.6 The Auto-Submitted: header line
+------------------------------------
+
+Whenever Exim generates an autoreply, a bounce, or a delay warning message, it
+includes the header line:
+
+Auto-Submitted: auto-replied
+
+
+48.7 The Bcc: header line
+-------------------------
+
+If Exim is called with the -t option, to take recipient addresses from a
+message's header, it removes any Bcc: header line that may exist (after
+extracting its addresses). If -t is not present on the command line, any
+existing Bcc: is not removed.
+
+
+48.8 The Date: header line
+--------------------------
+
+If a locally-generated or submission-mode message has no Date: header line,
+Exim adds one, using the current date and time, unless the
+suppress_local_fixups control has been specified.
+
+
+48.9 The Delivery-date: header line
+-----------------------------------
+
+Delivery-date: header lines are not part of the standard RFC 2822 header set.
+Exim can be configured to add them to the final delivery of messages. (See the
+generic delivery_date_add transport option.) They should not be present in
+messages in transit. If the delivery_date_remove configuration option is set
+(the default), Exim removes Delivery-date: header lines from incoming messages.
+
+
+48.10 The Envelope-to: header line
+----------------------------------
+
+Envelope-to: header lines are not part of the standard RFC 2822 header set.
+Exim can be configured to add them to the final delivery of messages. (See the
+generic envelope_to_add transport option.) They should not be present in
+messages in transit. If the envelope_to_remove configuration option is set (the
+default), Exim removes Envelope-to: header lines from incoming messages.
+
+
+48.11 The From: header line
+---------------------------
+
+If a submission-mode message does not contain a From: header line, Exim adds
+one if either of the following conditions is true:
+
+ * The envelope sender address is not empty (that is, this is not a bounce
+ message). The added header line copies the envelope sender address.
+
+ * The SMTP session is authenticated and $authenticated_id is not empty.
+
+ 1. If no domain is specified by the submission control, the local part is
+ $authenticated_id and the domain is $qualify_domain.
+
+ 2. If a non-empty domain is specified by the submission control, the local
+ part is $authenticated_id, and the domain is the specified domain.
+
+ 3. If an empty domain is specified by the submission control,
+ $authenticated_id is assumed to be the complete address.
+
+A non-empty envelope sender takes precedence.
+
+If a locally-generated incoming message does not contain a From: header line,
+and the suppress_local_fixups control is not set, Exim adds one containing the
+sender's address. The calling user's login name and full name are used to
+construct the address, as described in section 48.18. They are obtained from
+the password data by calling getpwuid() (but see the unknown_login
+configuration option). The address is qualified with qualify_domain.
+
+For compatibility with Sendmail, if an incoming, non-SMTP message has a From:
+header line containing just the unqualified login name of the calling user,
+this is replaced by an address containing the user's login name and full name
+as described in section 48.18.
+
+
+48.12 The Message-ID: header line
+---------------------------------
+
+If a locally-generated or submission-mode incoming message does not contain a
+Message-ID: or Resent-Message-ID: header line, and the suppress_local_fixups
+control is not set, Exim adds a suitable header line to the message. If there
+are any Resent-: headers in the message, it creates Resent-Message-ID:. The id
+is constructed from Exim's internal message id, preceded by the letter E to
+ensure it starts with a letter, and followed by @ and the primary host name.
+Additional information can be included in this header line by setting the
+message_id_header_text and/or message_id_header_domain options.
+
+
+48.13 The Received: header line
+-------------------------------
+
+A Received: header line is added at the start of every message. The contents
+are defined by the received_header_text configuration option, and Exim
+automatically adds a semicolon and a timestamp to the configured string.
+
+The Received: header is generated as soon as the message's header lines have
+been received. At this stage, the timestamp in the Received: header line is the
+time that the message started to be received. This is the value that is seen by
+the DATA ACL and by the local_scan() function.
+
+Once a message is accepted, the timestamp in the Received: header line is
+changed to the time of acceptance, which is (apart from a small delay while the
+-H spool file is written) the earliest time at which delivery could start.
+
+
+48.14 The References: header line
+---------------------------------
+
+Messages created by the autoreply transport include a References: header line.
+This is constructed according to the rules that are described in section 3.64
+of RFC 2822 (which states that replies should contain such a header line), and
+section 3.14 of RFC 3834 (which states that automatic responses are not
+different in this respect). However, because some mail processing software does
+not cope well with very long header lines, no more than 12 message IDs are
+copied from the References: header line in the incoming message. If there are
+more than 12, the first one and then the final 11 are copied, before adding the
+message ID of the incoming message.
+
+
+48.15 The Return-path: header line
+----------------------------------
+
+Return-path: header lines are defined as something an MTA may insert when it
+does the final delivery of messages. (See the generic return_path_add transport
+option.) Therefore, they should not be present in messages in transit. If the
+return_path_remove configuration option is set (the default), Exim removes
+Return-path: header lines from incoming messages.
+
+
+48.16 The Sender: header line
+-----------------------------
+
+For a locally-originated message from an untrusted user, Exim may remove an
+existing Sender: header line, and it may add a new one. You can modify these
+actions by setting the local_sender_retain option true, the local_from_check
+option false, or by using the suppress_local_fixups control setting.
+
+When a local message is received from an untrusted user and local_from_check is
+true (the default), and the suppress_local_fixups control has not been set, a
+check is made to see if the address given in the From: header line is the
+correct (local) sender of the message. The address that is expected has the
+login name as the local part and the value of qualify_domain as the domain.
+Prefixes and suffixes for the local part can be permitted by setting
+local_from_prefix and local_from_suffix appropriately. If From: does not
+contain the correct sender, a Sender: line is added to the message.
+
+If you set local_from_check false, this checking does not occur. However, the
+removal of an existing Sender: line still happens, unless you also set
+local_sender_retain to be true. It is not possible to set both of these options
+true at the same time.
+
+By default, no processing of Sender: header lines is done for messages received
+over TCP/IP or for messages submitted by trusted users. However, when a message
+is received over TCP/IP in submission mode, and sender_retain is not specified
+on the submission control, the following processing takes place:
+
+First, any existing Sender: lines are removed. Then, if the SMTP session is
+authenticated, and $authenticated_id is not empty, a sender address is created
+as follows:
+
+ * If no domain is specified by the submission control, the local part is
+ $authenticated_id and the domain is $qualify_domain.
+
+ * If a non-empty domain is specified by the submission control, the local
+ part is $authenticated_id, and the domain is the specified domain.
+
+ * If an empty domain is specified by the submission control,
+ $authenticated_id is assumed to be the complete address.
+
+This address is compared with the address in the From: header line. If they are
+different, a Sender: header line containing the created address is added.
+Prefixes and suffixes for the local part in From: can be permitted by setting
+local_from_prefix and local_from_suffix appropriately.
+
+Note: Whenever a Sender: header line is created, the return path for the
+message (the envelope sender address) is changed to be the same address, except
+in the case of submission mode when sender_retain is specified.
+
+
+48.17 Adding and removing header lines in routers and transports
+----------------------------------------------------------------
+
+When a message is delivered, the addition and removal of header lines can be
+specified in a system filter, or on any of the routers and transports that
+process the message. Section 47.6 contains details about modifying headers in a
+system filter. Header lines can also be added in an ACL as a message is
+received (see section 44.24).
+
+In contrast to what happens in a system filter, header modifications that are
+specified on routers and transports apply only to the particular recipient
+addresses that are being processed by those routers and transports. These
+changes do not actually take place until a copy of the message is being
+transported. Therefore, they do not affect the basic set of header lines, and
+they do not affect the values of the variables that refer to header lines.
+
+Note: In particular, this means that any expansions in the configuration of the
+transport cannot refer to the modified header lines, because such expansions
+all occur before the message is actually transported.
+
+For both routers and transports, the argument of a headers_add option must be
+in the form of one or more RFC 2822 header lines, separated by newlines (coded
+as "\n"). For example:
+
+headers_add = X-added-header: added by $primary_hostname\n\
+ X-added-second: another added header line
+
+Exim does not check the syntax of these added header lines.
+
+Multiple headers_add options for a single router or transport can be specified;
+the values will append to a single list of header lines. Each header-line is
+separately expanded.
+
+The argument of a headers_remove option must consist of a colon-separated list
+of header names. This is confusing, because header names themselves are often
+terminated by colons. In this case, the colons are the list separators, not
+part of the names. For example:
+
+headers_remove = return-receipt-to:acknowledge-to
+
+Multiple headers_remove options for a single router or transport can be
+specified; the arguments will append to a single header-names list. Each item
+is separately expanded. Note that colons in complex expansions which are used
+to form all or part of a headers_remove list will act as list separators.
+
+When headers_add or headers_remove is specified on a router, items are expanded
+at routing time, and then associated with all addresses that are accepted by
+that router, and also with any new addresses that it generates. If an address
+passes through several routers as a result of aliasing or forwarding, the
+changes are cumulative.
+
+However, this does not apply to multiple routers that result from the use of
+the unseen option. Any header modifications that were specified by the "unseen"
+router or its predecessors apply only to the "unseen" delivery.
+
+Addresses that end up with different headers_add or headers_remove settings
+cannot be delivered together in a batch, so a transport is always dealing with
+a set of addresses that have the same header-processing requirements.
+
+The transport starts by writing the original set of header lines that arrived
+with the message, possibly modified by the system filter. As it writes out
+these lines, it consults the list of header names that were attached to the
+recipient address(es) by headers_remove options in routers, and it also
+consults the transport's own headers_remove option. Header lines whose names
+are on either of these lists are not written out. If there are multiple
+instances of any listed header, they are all skipped.
+
+After the remaining original header lines have been written, new header lines
+that were specified by routers' headers_add options are written, in the order
+in which they were attached to the address. These are followed by any header
+lines specified by the transport's headers_add option.
+
+This way of handling header line modifications in routers and transports has
+the following consequences:
+
+ * The original set of header lines, possibly modified by the system filter,
+ remains "visible", in the sense that the $header_xxx variables refer to it,
+ at all times.
+
+ * Header lines that are added by a router's headers_add option are not
+ accessible by means of the $header_xxx expansion syntax in subsequent
+ routers or the transport.
+
+ * Conversely, header lines that are specified for removal by headers_remove
+ in a router remain visible to subsequent routers and the transport.
+
+ * Headers added to an address by headers_add in a router cannot be removed by
+ a later router or by a transport.
+
+ * An added header can refer to the contents of an original header that is to
+ be removed, even it has the same name as the added header. For example:
+
+ headers_remove = subject
+ headers_add = Subject: new subject (was: $h_subject:)
+
+Warning: The headers_add and headers_remove options cannot be used for a
+redirect router that has the one_time option set.
+
+
+48.18 Constructed addresses
+---------------------------
+
+When Exim constructs a sender address for a locally-generated message, it uses
+the form
+
+<user name> <login@qualify_domain>
+
+For example:
+
+Zaphod Beeblebrox <zaphod@end.univ.example>
+
+The user name is obtained from the -F command line option if set, or otherwise
+by looking up the calling user by getpwuid() and extracting the "gecos" field
+from the password entry. If the "gecos" field contains an ampersand character,
+this is replaced by the login name with the first letter upper cased, as is
+conventional in a number of operating systems. See the gecos_name option for a
+way to tailor the handling of the "gecos" field. The unknown_username option
+can be used to specify user names in cases when there is no password file
+entry.
+
+In all cases, the user name is made to conform to RFC 2822 by quoting all or
+parts of it if necessary. In addition, if it contains any non-printing
+characters, it is encoded as described in RFC 2047, which defines a way of
+including non-ASCII characters in header lines. The value of the
+headers_charset option specifies the name of the encoding that is used (the
+characters are assumed to be in this encoding). The setting of
+print_topbitchars controls whether characters with the top bit set (that is,
+with codes greater than 127) count as printing characters or not.
+
+
+48.19 Case of local parts
+-------------------------
+
+RFC 2822 states that the case of letters in the local parts of addresses cannot
+be assumed to be non-significant. Exim preserves the case of local parts of
+addresses, but by default it uses a lower-cased form when it is routing,
+because on most Unix systems, usernames are in lower case and case-insensitive
+routing is required. However, any particular router can be made to use the
+original case for local parts by setting the caseful_local_part generic router
+option.
+
+If you must have mixed-case user names on your system, the best way to proceed,
+assuming you want case-independent handling of incoming email, is to set up
+your first router to convert incoming local parts in your domains to the
+correct case by means of a file lookup. For example:
+
+correct_case:
+ driver = redirect
+ domains = +local_domains
+ data = ${lookup{$local_part}cdb\
+ {/etc/usercased.cdb}{$value}fail}\
+ @$domain
+
+For this router, the local part is forced to lower case by the default action (
+caseful_local_part is not set). The lower-cased local part is used to look up a
+new local part in the correct case. If you then set caseful_local_part on any
+subsequent routers which process your domains, they will operate on local parts
+with the correct case in a case-sensitive manner.
+
+
+48.20 Dots in local parts
+-------------------------
+
+RFC 2822 forbids empty components in local parts. That is, an unquoted local
+part may not begin or end with a dot, nor have two consecutive dots in the
+middle. However, it seems that many MTAs do not enforce this, so Exim permits
+empty components for compatibility.
+
+
+48.21 Rewriting addresses
+-------------------------
+
+Rewriting of sender and recipient addresses, and addresses in headers, can
+happen automatically, or as the result of configuration options, as described
+in chapter 31. The headers that may be affected by this are Bcc:, Cc:, From:,
+Reply-To:, Sender:, and To:.
+
+Automatic rewriting includes qualification, as mentioned above. The other case
+in which it can happen is when an incomplete non-local domain is given. The
+routing process may cause this to be expanded into the full domain name. For
+example, a header such as
+
+To: hare@teaparty
+
+might get rewritten as
+
+To: hare@teaparty.wonderland.fict.example
+
+Rewriting as a result of routing is the one kind of message processing that
+does not happen at input time, as it cannot be done until the address has been
+routed.
+
+Strictly, one should not do any deliveries of a message until all its addresses
+have been routed, in case any of the headers get changed as a result of
+routing. However, doing this in practice would hold up many deliveries for
+unreasonable amounts of time, just because one address could not immediately be
+routed. Exim therefore does not delay other deliveries when routing of one or
+more addresses is deferred.
+
+
+
+===============================================================================
+49. SMTP PROCESSING
+
+Exim supports a number of different ways of using the SMTP protocol, and its
+LMTP variant, which is an interactive protocol for transferring messages into a
+closed mail store application. This chapter contains details of how SMTP is
+processed. For incoming mail, the following are available:
+
+ * SMTP over TCP/IP (Exim daemon or inetd);
+
+ * SMTP over the standard input and output (the -bs option);
+
+ * Batched SMTP on the standard input (the -bS option).
+
+For mail delivery, the following are available:
+
+ * SMTP over TCP/IP (the smtp transport);
+
+ * LMTP over TCP/IP (the smtp transport with the protocol option set to
+ "lmtp");
+
+ * LMTP over a pipe to a process running in the local host (the lmtp
+ transport);
+
+ * Batched SMTP to a file or pipe (the appendfile and pipe transports with the
+ use_bsmtp option set).
+
+Batched SMTP is the name for a process in which batches of messages are stored
+in or read from files (or pipes), in a format in which SMTP commands are used
+to contain the envelope information.
+
+
+49.1 Outgoing SMTP and LMTP over TCP/IP
+---------------------------------------
+
+Outgoing SMTP and LMTP over TCP/IP is implemented by the smtp transport. The
+protocol option selects which protocol is to be used, but the actual processing
+is the same in both cases.
+
+If, in response to its EHLO command, Exim is told that the SIZE extension is
+supported, it adds SIZE=<n> to each subsequent MAIL command. The value of <n>
+is the message size plus the value of the size_addition option (default 1024)
+to allow for additions to the message such as per-transport header lines, or
+changes made in a transport filter. If size_addition is set negative, the use
+of SIZE is suppressed.
+
+If the remote server advertises support for PIPELINING, Exim uses the
+pipelining extension to SMTP (RFC 2197) to reduce the number of TCP/IP packets
+required for the transaction.
+
+If the remote server advertises support for the STARTTLS command, and Exim was
+built to support TLS encryption, it tries to start a TLS session unless the
+server matches hosts_avoid_tls. See chapter 43 for more details. Either a match
+in that or hosts_verify_avoid_tls apply when the transport is called for
+verification.
+
+If the remote server advertises support for the AUTH command, Exim scans the
+authenticators configuration for any suitable client settings, as described in
+chapter 33.
+
+Responses from the remote host are supposed to be terminated by CR followed by
+LF. However, there are known to be hosts that do not send CR characters, so in
+order to be able to interwork with such hosts, Exim treats LF on its own as a
+line terminator.
+
+If a message contains a number of different addresses, all those with the same
+characteristics (for example, the same envelope sender) that resolve to the
+same set of hosts, in the same order, are sent in a single SMTP transaction,
+even if they are for different domains, unless there are more than the setting
+of the max_rcpts option in the smtp transport allows, in which case they are
+split into groups containing no more than max_rcpts addresses each. If
+remote_max_parallel is greater than one, such groups may be sent in parallel
+sessions. The order of hosts with identical MX values is not significant when
+checking whether addresses can be batched in this way.
+
+When the smtp transport suffers a temporary failure that is not
+message-related, Exim updates its transport-specific database, which contains
+records indexed by host name that remember which messages are waiting for each
+particular host. It also updates the retry database with new retry times.
+
+Exim's retry hints are based on host name plus IP address, so if one address of
+a multi-homed host is broken, it will soon be skipped most of the time. See the
+next section for more detail about error handling.
+
+When a message is successfully delivered over a TCP/IP SMTP connection, Exim
+looks in the hints database for the transport to see if there are any queued
+messages waiting for the host to which it is connected. If it finds one, it
+creates a new Exim process using the -MC option (which can only be used by a
+process running as root or the Exim user) and passes the TCP/IP socket to it so
+that it can deliver another message using the same socket. The new process does
+only those deliveries that are routed to the connected host, and may in turn
+pass the socket on to a third process, and so on.
+
+The connection_max_messages option of the smtp transport can be used to limit
+the number of messages sent down a single TCP/IP connection.
+
+The second and subsequent messages delivered down an existing connection are
+identified in the main log by the addition of an asterisk after the closing
+square bracket of the IP address.
+
+
+49.2 Errors in outgoing SMTP
+----------------------------
+
+Three different kinds of error are recognized for outgoing SMTP: host errors,
+message errors, and recipient errors.
+
+Host errors
+
+ A host error is not associated with a particular message or with a
+ particular recipient of a message. The host errors are:
+
+ + Connection refused or timed out,
+
+ + Any error response code on connection,
+
+ + Any error response code to EHLO or HELO,
+
+ + Loss of connection at any time, except after ".",
+
+ + I/O errors at any time,
+
+ + Timeouts during the session, other than in response to MAIL, RCPT or
+ the "." at the end of the data.
+
+ For a host error, a permanent error response on connection, or in response
+ to EHLO, causes all addresses routed to the host to be failed. Any other
+ host error causes all addresses to be deferred, and retry data to be
+ created for the host. It is not tried again, for any message, until its
+ retry time arrives. If the current set of addresses are not all delivered
+ in this run (to some alternative host), the message is added to the list of
+ those waiting for this host, so if it is still undelivered when a
+ subsequent successful delivery is made to the host, it will be sent down
+ the same SMTP connection.
+
+Message errors
+
+ A message error is associated with a particular message when sent to a
+ particular host, but not with a particular recipient of the message. The
+ message errors are:
+
+ + Any error response code to MAIL, DATA, or the "." that terminates the
+ data,
+
+ + Timeout after MAIL,
+
+ + Timeout or loss of connection after the "." that terminates the data. A
+ timeout after the DATA command itself is treated as a host error, as is
+ loss of connection at any other time.
+
+ For a message error, a permanent error response (5xx) causes all addresses
+ to be failed, and a delivery error report to be returned to the sender. A
+ temporary error response (4xx), or one of the timeouts, causes all
+ addresses to be deferred. Retry data is not created for the host, but
+ instead, a retry record for the combination of host plus message id is
+ created. The message is not added to the list of those waiting for this
+ host. This ensures that the failing message will not be sent to this host
+ again until the retry time arrives. However, other messages that are routed
+ to the host are not affected, so if it is some property of the message that
+ is causing the error, it will not stop the delivery of other mail.
+
+ If the remote host specified support for the SIZE parameter in its response
+ to EHLO, Exim adds SIZE=nnn to the MAIL command, so an over-large message
+ will cause a message error because the error arrives as a response to MAIL.
+
+Recipient errors
+
+ A recipient error is associated with a particular recipient of a message.
+ The recipient errors are:
+
+ + Any error response to RCPT,
+
+ + Timeout after RCPT.
+
+ For a recipient error, a permanent error response (5xx) causes the
+ recipient address to be failed, and a bounce message to be returned to the
+ sender. A temporary error response (4xx) or a timeout causes the failing
+ address to be deferred, and routing retry data to be created for it. This
+ is used to delay processing of the address in subsequent queue runs, until
+ its routing retry time arrives. This applies to all messages, but because
+ it operates only in queue runs, one attempt will be made to deliver a new
+ message to the failing address before the delay starts to operate. This
+ ensures that, if the failure is really related to the message rather than
+ the recipient ("message too big for this recipient" is a possible example),
+ other messages have a chance of getting delivered. If a delivery to the
+ address does succeed, the retry information gets cleared, so all stuck
+ messages get tried again, and the retry clock is reset.
+
+ The message is not added to the list of those waiting for this host. Use of
+ the host for other messages is unaffected, and except in the case of a
+ timeout, other recipients are processed independently, and may be
+ successfully delivered in the current SMTP session. After a timeout it is
+ of course impossible to proceed with the session, so all addresses get
+ deferred. However, those other than the one that failed do not suffer any
+ subsequent retry delays. Therefore, if one recipient is causing trouble,
+ the others have a chance of getting through when a subsequent delivery
+ attempt occurs before the failing recipient's retry time.
+
+In all cases, if there are other hosts (or IP addresses) available for the
+current set of addresses (for example, from multiple MX records), they are
+tried in this run for any undelivered addresses, subject of course to their own
+retry data. In other words, recipient error retry data does not take effect
+until the next delivery attempt.
+
+Some hosts have been observed to give temporary error responses to every MAIL
+command at certain times ("insufficient space" has been seen). It would be nice
+if such circumstances could be recognized, and defer data for the host itself
+created, but this is not possible within the current Exim design. What actually
+happens is that retry data for every (host, message) combination is created.
+
+The reason that timeouts after MAIL and RCPT are treated specially is that
+these can sometimes arise as a result of the remote host's verification
+procedures. Exim makes this assumption, and treats them as if a temporary error
+response had been received. A timeout after "." is treated specially because it
+is known that some broken implementations fail to recognize the end of the
+message if the last character of the last line is a binary zero. Thus, it is
+helpful to treat this case as a message error.
+
+Timeouts at other times are treated as host errors, assuming a problem with the
+host, or the connection to it. If a timeout after MAIL, RCPT, or "." is really
+a connection problem, the assumption is that at the next try the timeout is
+likely to occur at some other point in the dialogue, causing it then to be
+treated as a host error.
+
+There is experimental evidence that some MTAs drop the connection after the
+terminating "." if they do not like the contents of the message for some
+reason, in contravention of the RFC, which indicates that a 5xx response should
+be given. That is why Exim treats this case as a message rather than a host
+error, in order not to delay other messages to the same host.
+
+
+49.3 Incoming SMTP messages over TCP/IP
+---------------------------------------
+
+Incoming SMTP messages can be accepted in one of two ways: by running a
+listening daemon, or by using inetd. In the latter case, the entry in /etc/
+inetd.conf should be like this:
+
+smtp stream tcp nowait exim /opt/exim/bin/exim in.exim -bs
+
+Exim distinguishes between this case and the case of a locally running user
+agent using the -bs option by checking whether or not the standard input is a
+socket. When it is, either the port must be privileged (less than 1024), or the
+caller must be root or the Exim user. If any other user passes a socket with an
+unprivileged port number, Exim prints a message on the standard error stream
+and exits with an error code.
+
+By default, Exim does not make a log entry when a remote host connects or
+disconnects (either via the daemon or inetd), unless the disconnection is
+unexpected. It can be made to write such log entries by setting the
+smtp_connection log selector.
+
+Commands from the remote host are supposed to be terminated by CR followed by
+LF. However, there are known to be hosts that do not send CR characters. In
+order to be able to interwork with such hosts, Exim treats LF on its own as a
+line terminator. Furthermore, because common code is used for receiving
+messages from all sources, a CR on its own is also interpreted as a line
+terminator. However, the sequence "CR, dot, CR" does not terminate incoming
+SMTP data.
+
+One area that sometimes gives rise to problems concerns the EHLO or HELO
+commands. Some clients send syntactically invalid versions of these commands,
+which Exim rejects by default. (This is nothing to do with verifying the data
+that is sent, so helo_verify_hosts is not relevant.) You can tell Exim not to
+apply a syntax check by setting helo_accept_junk_hosts to match the broken
+hosts that send invalid commands.
+
+The amount of disk space available is checked whenever SIZE is received on a
+MAIL command, independently of whether message_size_limit or check_spool_space
+is configured, unless smtp_check_spool_space is set false. A temporary error is
+given if there is not enough space. If check_spool_space is set, the check is
+for that amount of space plus the value given with SIZE, that is, it checks
+that the addition of the incoming message will not reduce the space below the
+threshold.
+
+When a message is successfully received, Exim includes the local message id in
+its response to the final "." that terminates the data. If the remote host logs
+this text it can help with tracing what has happened to a message.
+
+The Exim daemon can limit the number of simultaneous incoming connections it is
+prepared to handle (see the smtp_accept_max option). It can also limit the
+number of simultaneous incoming connections from a single remote host (see the
+smtp_accept_max_per_host option). Additional connection attempts are rejected
+using the SMTP temporary error code 421.
+
+The Exim daemon does not rely on the SIGCHLD signal to detect when a subprocess
+has finished, as this can get lost at busy times. Instead, it looks for
+completed subprocesses every time it wakes up. Provided there are other things
+happening (new incoming calls, starts of queue runs), completed processes will
+be noticed and tidied away. On very quiet systems you may sometimes see a
+"defunct" Exim process hanging about. This is not a problem; it will be noticed
+when the daemon next wakes up.
+
+When running as a daemon, Exim can reserve some SMTP slots for specific hosts,
+and can also be set up to reject SMTP calls from non-reserved hosts at times of
+high system load - for details see the smtp_accept_reserve, smtp_load_reserve,
+and smtp_reserve_hosts options. The load check applies in both the daemon and
+inetd cases.
+
+Exim normally starts a delivery process for each message received, though this
+can be varied by means of the -odq command line option and the queue_only,
+queue_only_file, and queue_only_load options. The number of simultaneously
+running delivery processes started in this way from SMTP input can be limited
+by the smtp_accept_queue and smtp_accept_queue_per_connection options. When
+either limit is reached, subsequently received messages are just put on the
+input queue without starting a delivery process.
+
+The controls that involve counts of incoming SMTP calls (smtp_accept_max,
+smtp_accept_queue, smtp_accept_reserve) are not available when Exim is started
+up from the inetd daemon, because in that case each connection is handled by an
+entirely independent Exim process. Control by load average is, however,
+available with inetd.
+
+Exim can be configured to verify addresses in incoming SMTP commands as they
+are received. See chapter 44 for details. It can also be configured to rewrite
+addresses at this time - before any syntax checking is done. See section 31.9.
+
+Exim can also be configured to limit the rate at which a client host submits
+MAIL and RCPT commands in a single SMTP session. See the smtp_ratelimit_hosts
+option.
+
+
+49.4 Unrecognized SMTP commands
+-------------------------------
+
+If Exim receives more than smtp_max_unknown_commands unrecognized SMTP commands
+during a single SMTP connection, it drops the connection after sending the
+error response to the last command. The default value for
+smtp_max_unknown_commands is 3. This is a defence against some kinds of abuse
+that subvert web servers into making connections to SMTP ports; in these
+circumstances, a number of non-SMTP lines are sent first.
+
+
+49.5 Syntax and protocol errors in SMTP commands
+------------------------------------------------
+
+A syntax error is detected if an SMTP command is recognized, but there is
+something syntactically wrong with its data, for example, a malformed email
+address in a RCPT command. Protocol errors include invalid command sequencing
+such as RCPT before MAIL. If Exim receives more than smtp_max_synprot_errors
+such commands during a single SMTP connection, it drops the connection after
+sending the error response to the last command. The default value for
+smtp_max_synprot_errors is 3. This is a defence against broken clients that
+loop sending bad commands (yes, it has been seen).
+
+
+49.6 Use of non-mail SMTP commands
+----------------------------------
+
+The "non-mail" SMTP commands are those other than MAIL, RCPT, and DATA. Exim
+counts such commands, and drops the connection if there are too many of them in
+a single SMTP session. This action catches some denial-of-service attempts and
+things like repeated failing AUTHs, or a mad client looping sending EHLO. The
+global option smtp_accept_max_nonmail defines what "too many" means. Its
+default value is 10.
+
+When a new message is expected, one occurrence of RSET is not counted. This
+allows a client to send one RSET between messages (this is not necessary, but
+some clients do it). Exim also allows one uncounted occurrence of HELO or EHLO,
+and one occurrence of STARTTLS between messages. After starting up a TLS
+session, another EHLO is expected, and so it too is not counted.
+
+The first occurrence of AUTH in a connection, or immediately following STARTTLS
+is also not counted. Otherwise, all commands other than MAIL, RCPT, DATA, and
+QUIT are counted.
+
+You can control which hosts are subject to the limit set by
+smtp_accept_max_nonmail by setting smtp_accept_max_nonmail_hosts. The default
+value is "*", which makes the limit apply to all hosts. This option means that
+you can exclude any specific badly-behaved hosts that you have to live with.
+
+
+49.7 The VRFY and EXPN commands
+-------------------------------
+
+When Exim receives a VRFY or EXPN command on a TCP/IP connection, it runs the
+ACL specified by acl_smtp_vrfy or acl_smtp_expn (as appropriate) in order to
+decide whether the command should be accepted or not.
+
+When no ACL is defined for VRFY, or if it rejects without setting an explicit
+response code, the command is accepted (with a 252 SMTP response code) in order
+to support awkward clients that do a VRFY before every RCPT. When VRFY is
+accepted, it runs exactly the same code as when Exim is called with the -bv
+option, and returns 250/451/550 SMTP response codes.
+
+If no ACL for EXPN is defined, the command is rejected. When EXPN is accepted,
+a single-level expansion of the address is done. EXPN is treated as an "address
+test" (similar to the -bt option) rather than a verification (the -bv option).
+If an unqualified local part is given as the argument to EXPN, it is qualified
+with qualify_domain. Rejections of VRFY and EXPN commands are logged on the
+main and reject logs, and VRFY verification failures are logged on the main log
+for consistency with RCPT failures.
+
+
+49.8 The ETRN command
+---------------------
+
+RFC 1985 describes an ESMTP command called ETRN that is designed to overcome
+the security problems of the TURN command (which has fallen into disuse). When
+Exim receives an ETRN command on a TCP/IP connection, it runs the ACL specified
+by acl_smtp_etrn in order to decide whether the command should be accepted or
+not. If no ACL is defined, the command is rejected.
+
+The ETRN command is concerned with "releasing" messages that are awaiting
+delivery to certain hosts. As Exim does not organize its message queue by host,
+the only form of ETRN that is supported by default is the one where the text
+starts with the "#" prefix, in which case the remainder of the text is specific
+to the SMTP server. A valid ETRN command causes a run of Exim with the -R
+option to happen, with the remainder of the ETRN text as its argument. For
+example,
+
+ETRN #brigadoon
+
+runs the command
+
+exim -R brigadoon
+
+which causes a delivery attempt on all messages with undelivered addresses
+containing the text "brigadoon". When smtp_etrn_serialize is set (the default),
+Exim prevents the simultaneous execution of more than one queue run for the
+same argument string as a result of an ETRN command. This stops a misbehaving
+client from starting more than one queue runner at once.
+
+Exim implements the serialization by means of a hints database in which a
+record is written whenever a process is started by ETRN, and deleted when the
+process completes. However, Exim does not keep the SMTP session waiting for the
+ETRN process to complete. Once ETRN is accepted, the client is sent a "success"
+return code. Obviously there is scope for hints records to get left lying
+around if there is a system or program crash. To guard against this, Exim
+ignores any records that are more than six hours old.
+
+For more control over what ETRN does, the smtp_etrn_command option can used.
+This specifies a command that is run whenever ETRN is received, whatever the
+form of its argument. For example:
+
+smtp_etrn_command = /etc/etrn_command $domain \
+ $sender_host_address
+
+The string is split up into arguments which are independently expanded. The
+expansion variable $domain is set to the argument of the ETRN command, and no
+syntax checking is done on the contents of this argument. Exim does not wait
+for the command to complete, so its status code is not checked. Exim runs under
+its own uid and gid when receiving incoming SMTP, so it is not possible for it
+to change them before running the command.
+
+
+49.9 Incoming local SMTP
+------------------------
+
+Some user agents use SMTP to pass messages to their local MTA using the
+standard input and output, as opposed to passing the envelope on the command
+line and writing the message to the standard input. This is supported by the
+-bs option. This form of SMTP is handled in the same way as incoming messages
+over TCP/IP (including the use of ACLs), except that the envelope sender given
+in a MAIL command is ignored unless the caller is trusted. In an ACL you can
+detect this form of SMTP input by testing for an empty host identification. It
+is common to have this as the first line in the ACL that runs for RCPT
+commands:
+
+accept hosts = :
+
+This accepts SMTP messages from local processes without doing any other tests.
+
+
+49.10 Outgoing batched SMTP
+---------------------------
+
+Both the appendfile and pipe transports can be used for handling batched SMTP.
+Each has an option called use_bsmtp which causes messages to be output in BSMTP
+format. No SMTP responses are possible for this form of delivery. All it is
+doing is using SMTP commands as a way of transmitting the envelope along with
+the message.
+
+The message is written to the file or pipe preceded by the SMTP commands MAIL
+and RCPT, and followed by a line containing a single dot. Lines in the message
+that start with a dot have an extra dot added. The SMTP command HELO is not
+normally used. If it is required, the message_prefix option can be used to
+specify it.
+
+Because appendfile and pipe are both local transports, they accept only one
+recipient address at a time by default. However, you can arrange for them to
+handle several addresses at once by setting the batch_max option. When this is
+done for BSMTP, messages may contain multiple RCPT commands. See chapter 25 for
+more details.
+
+When one or more addresses are routed to a BSMTP transport by a router that
+sets up a host list, the name of the first host on the list is available to the
+transport in the variable $host. Here is an example of such a transport and
+router:
+
+begin routers
+route_append:
+ driver = manualroute
+ transport = smtp_appendfile
+ route_list = domain.example batch.host.example
+
+begin transports
+smtp_appendfile:
+ driver = appendfile
+ directory = /var/bsmtp/$host
+ batch_max = 1000
+ use_bsmtp
+ user = exim
+
+This causes messages addressed to domain.example to be written in BSMTP format
+to /var/bsmtp/batch.host.example, with only a single copy of each message
+(unless there are more than 1000 recipients).
+
+
+49.11 Incoming batched SMTP
+---------------------------
+
+The -bS command line option causes Exim to accept one or more messages by
+reading SMTP on the standard input, but to generate no responses. If the caller
+is trusted, the senders in the MAIL commands are believed; otherwise the sender
+is always the caller of Exim. Unqualified senders and receivers are not
+rejected (there seems little point) but instead just get qualified. HELO and
+EHLO act as RSET; VRFY, EXPN, ETRN and HELP, act as NOOP; QUIT quits.
+
+Minimal policy checking is done for BSMTP input. Only the non-SMTP ACL is run
+in the same way as for non-SMTP local input.
+
+If an error is detected while reading a message, including a missing "." at the
+end, Exim gives up immediately. It writes details of the error to the standard
+output in a stylized way that the calling program should be able to make some
+use of automatically, for example:
+
+554 Unexpected end of file
+Transaction started in line 10
+Error detected in line 14
+
+It writes a more verbose version, for human consumption, to the standard error
+file, for example:
+
+An error was detected while processing a file of BSMTP input.
+The error message was:
+
+501 '>' missing at end of address
+
+The SMTP transaction started in line 10.
+The error was detected in line 12.
+The SMTP command at fault was:
+
+rcpt to:<malformed@in.com.plete
+
+1 previous message was successfully processed.
+The rest of the batch was abandoned.
+
+The return code from Exim is zero only if there were no errors. It is 1 if some
+messages were accepted before an error was detected, and 2 if no messages were
+accepted.
+
+
+
+===============================================================================
+50. CUSTOMIZING BOUNCE AND WARNING MESSAGES
+
+When a message fails to be delivered, or remains in the queue for more than a
+configured amount of time, Exim sends a message to the original sender, or to
+an alternative configured address. The text of these messages is built into the
+code of Exim, but it is possible to change it, either by adding a single
+string, or by replacing each of the paragraphs by text supplied in a file.
+
+The From: and To: header lines are automatically generated; you can cause a
+Reply-To: line to be added by setting the errors_reply_to option. Exim also
+adds the line
+
+Auto-Submitted: auto-generated
+
+to all warning and bounce messages,
+
+
+50.1 Customizing bounce messages
+--------------------------------
+
+If bounce_message_text is set, its contents are included in the default message
+immediately after "This message was created automatically by mail delivery
+software." The string is not expanded. It is not used if bounce_message_file is
+set.
+
+When bounce_message_file is set, it must point to a template file for
+constructing error messages. The file consists of a series of text items,
+separated by lines consisting of exactly four asterisks. If the file cannot be
+opened, default text is used and a message is written to the main and panic
+logs. If any text item in the file is empty, default text is used for that
+item.
+
+Each item of text that is read from the file is expanded, and there are two
+expansion variables which can be of use here: $bounce_recipient is set to the
+recipient of an error message while it is being created, and
+$bounce_return_size_limit contains the value of the return_size_limit option,
+rounded to a whole number.
+
+The items must appear in the file in the following order:
+
+ * The first item is included in the headers, and should include at least a
+ Subject: header. Exim does not check the syntax of these headers.
+
+ * The second item forms the start of the error message. After it, Exim lists
+ the failing addresses with their error messages.
+
+ * The third item is used to introduce any text from pipe transports that is
+ to be returned to the sender. It is omitted if there is no such text.
+
+ * The fourth, fifth and sixth items will be ignored and may be empty. The
+ fields exist for back-compatibility
+
+The default state (bounce_message_file unset) is equivalent to the following
+file, in which the sixth item is empty. The Subject: and some other lines have
+been split in order to fit them on the page:
+
+Subject: Mail delivery failed
+ ${if eq{$sender_address}{$bounce_recipient}
+ {: returning message to sender}}
+****
+This message was created automatically by mail delivery software.
+
+A message ${if eq{$sender_address}{$bounce_recipient}
+ {that you sent }{sent by
+
+<$sender_address>
+
+}}could not be delivered to all of its recipients.
+This is a permanent error. The following address(es) failed:
+****
+The following text was generated during the delivery attempt(s):
+****
+------ This is a copy of the message, including all the headers.
+ ------
+****
+------ The body of the message is $message_size characters long;
+ only the first
+------ $bounce_return_size_limit or so are included here.
+****
+
+
+50.2 Customizing warning messages
+---------------------------------
+
+The option warn_message_file can be pointed at a template file for use when
+warnings about message delays are created. In this case there are only three
+text sections:
+
+ * The first item is included in the headers, and should include at least a
+ Subject: header. Exim does not check the syntax of these headers.
+
+ * The second item forms the start of the warning message. After it, Exim
+ lists the delayed addresses.
+
+ * The third item then ends the message.
+
+The default state is equivalent to the following file, except that some lines
+have been split here, in order to fit them on the page:
+
+Subject: Warning: message $message_exim_id delayed
+ $warn_message_delay
+****
+This message was created automatically by mail delivery software.
+
+A message ${if eq{$sender_address}{$warn_message_recipients}
+{that you sent }{sent by
+
+<$sender_address>
+
+}}has not been delivered to all of its recipients after
+more than $warn_message_delay in the queue on $primary_hostname.
+
+The message identifier is: $message_exim_id
+The subject of the message is: $h_subject
+The date of the message is: $h_date
+
+The following address(es) have not yet been delivered:
+****
+No action is required on your part. Delivery attempts will
+continue for some time, and this warning may be repeated at
+intervals if the message remains undelivered. Eventually the
+mail delivery software will give up, and when that happens,
+the message will be returned to you.
+
+However, in the default state the subject and date lines are omitted if no
+appropriate headers exist. During the expansion of this file,
+$warn_message_delay is set to the delay time in one of the forms "<n> minutes"
+or "<n> hours", and $warn_message_recipients contains a list of recipients for
+the warning message. There may be more than one if there are multiple addresses
+with different errors_to settings on the routers that handled them.
+
+
+
+===============================================================================
+51. SOME COMMON CONFIGURATION SETTINGS
+
+This chapter discusses some configuration settings that seem to be fairly
+common. More examples and discussion can be found in the Exim book.
+
+
+51.1 Sending mail to a smart host
+---------------------------------
+
+If you want to send all mail for non-local domains to a "smart host", you
+should replace the default dnslookup router with a router which does the
+routing explicitly:
+
+send_to_smart_host:
+ driver = manualroute
+ route_list = !+local_domains smart.host.name
+ transport = remote_smtp
+
+You can use the smart host's IP address instead of the name if you wish. If you
+are using Exim only to submit messages to a smart host, and not for receiving
+incoming messages, you can arrange for it to do the submission synchronously by
+setting the mua_wrapper option (see chapter 52).
+
+
+51.2 Using Exim to handle mailing lists
+---------------------------------------
+
+Exim can be used to run simple mailing lists, but for large and/or complicated
+requirements, the use of additional specialized mailing list software such as
+Majordomo or Mailman is recommended.
+
+The redirect router can be used to handle mailing lists where each list is
+maintained in a separate file, which can therefore be managed by an independent
+manager. The domains router option can be used to run these lists in a separate
+domain from normal mail. For example:
+
+lists:
+ driver = redirect
+ domains = lists.example
+ file = ${lookup {$local_part} dsearch,ret=full {/usr/lists}}
+ forbid_pipe
+ forbid_file
+ errors_to = ${quote_local_part:$local_part-request}@lists.example
+ no_more
+
+This router is skipped for domains other than lists.example. For addresses in
+that domain, it looks for a file that matches the local part. If there is no
+such file, the router declines, but because no_more is set, no subsequent
+routers are tried, and so the whole delivery fails.
+
+The forbid_pipe and forbid_file options prevent a local part from being
+expanded into a filename or a pipe delivery, which is usually inappropriate in
+a mailing list.
+
+The errors_to option specifies that any delivery errors caused by addresses
+taken from a mailing list are to be sent to the given address rather than the
+original sender of the message. However, before acting on this, Exim verifies
+the error address, and ignores it if verification fails.
+
+For example, using the configuration above, mail sent to dicts@lists.example is
+passed on to those addresses contained in /usr/lists/dicts, with error reports
+directed to dicts-request@lists.example, provided that this address can be
+verified. There could be a file called /usr/lists/dicts-request containing the
+address(es) of this particular list's manager(s), but other approaches, such as
+setting up an earlier router (possibly using the local_part_prefix or
+local_part_suffix options) to handle addresses of the form owner-xxx or xxx-
+request, are also possible.
+
+
+51.3 Syntax errors in mailing lists
+-----------------------------------
+
+If an entry in redirection data contains a syntax error, Exim normally defers
+delivery of the original address. That means that a syntax error in a mailing
+list holds up all deliveries to the list. This may not be appropriate when a
+list is being maintained automatically from data supplied by users, and the
+addresses are not rigorously checked.
+
+If the skip_syntax_errors option is set, the redirect router just skips entries
+that fail to parse, noting the incident in the log. If in addition
+syntax_errors_to is set to a verifiable address, a message is sent to it
+whenever a broken address is skipped. It is usually appropriate to set
+syntax_errors_to to the same address as errors_to.
+
+
+51.4 Re-expansion of mailing lists
+----------------------------------
+
+Exim remembers every individual address to which a message has been delivered,
+in order to avoid duplication, but it normally stores only the original
+recipient addresses with a message. If all the deliveries to a mailing list
+cannot be done at the first attempt, the mailing list is re-expanded when the
+delivery is next tried. This means that alterations to the list are taken into
+account at each delivery attempt, so addresses that have been added to the list
+since the message arrived will therefore receive a copy of the message, even
+though it pre-dates their subscription.
+
+If this behaviour is felt to be undesirable, the one_time option can be set on
+the redirect router. If this is done, any addresses generated by the router
+that fail to deliver at the first attempt are added to the message as "top
+level" addresses, and the parent address that generated them is marked
+"delivered". Thus, expansion of the mailing list does not happen again at the
+subsequent delivery attempts. The disadvantage of this is that if any of the
+failing addresses are incorrect, correcting them in the file has no effect on
+pre-existing messages.
+
+The original top-level address is remembered with each of the generated
+addresses, and is output in any log messages. However, any intermediate parent
+addresses are not recorded. This makes a difference to the log only if the
+all_parents selector is set, but for mailing lists there is normally only one
+level of expansion anyway.
+
+
+51.5 Closed mailing lists
+-------------------------
+
+The examples so far have assumed open mailing lists, to which anybody may send
+mail. It is also possible to set up closed lists, where mail is accepted from
+specified senders only. This is done by making use of the generic senders
+option to restrict the router that handles the list.
+
+The following example uses the same file as a list of recipients and as a list
+of permitted senders. It requires three routers:
+
+lists_request:
+ driver = redirect
+ domains = lists.example
+ local_part_suffix = -request
+ local_parts = ${lookup {$local_part} dsearch,filter=file {/usr/lists}}
+ file = /usr/lists/${local_part_data}-request
+ no_more
+
+lists_post:
+ driver = redirect
+ domains = lists.example
+ senders = ${if exists {/usr/lists/$local_part}\
+ {lsearch;/usr/lists/$local_part}{*}}
+ file = ${lookup {$local_part} dsearch,ret=full {/usr/lists}}
+ forbid_pipe
+ forbid_file
+ errors_to = ${quote_local_part:$local_part-request}@lists.example
+ no_more
+
+lists_closed:
+ driver = redirect
+ domains = lists.example
+ allow_fail
+ data = :fail: $local_part@lists.example is a closed mailing list
+
+All three routers have the same domains setting, so for any other domains, they
+are all skipped. The first router runs only if the local part ends in -request.
+It handles messages to the list manager(s) by means of an open mailing list.
+
+The second router runs only if the senders precondition is satisfied. It checks
+for the existence of a list that corresponds to the local part, and then checks
+that the sender is on the list by means of a linear search. It is necessary to
+check for the existence of the file before trying to search it, because
+otherwise Exim thinks there is a configuration error. If the file does not
+exist, the expansion of senders is *, which matches all senders. This means
+that the router runs, but because there is no list, declines, and no_more
+ensures that no further routers are run. The address fails with an "unrouteable
+address" error.
+
+The third router runs only if the second router is skipped, which happens when
+a mailing list exists, but the sender is not on it. This router forcibly fails
+the address, giving a suitable error message.
+
+
+51.6 Variable Envelope Return Paths (VERP)
+------------------------------------------
+
+Variable Envelope Return Paths - see https://cr.yp.to/proto/verp.txt - are a
+way of helping mailing list administrators discover which subscription address
+is the cause of a particular delivery failure. The idea is to encode the
+original recipient address in the outgoing envelope sender address, so that if
+the message is forwarded by another host and then subsequently bounces, the
+original recipient can be extracted from the recipient address of the bounce.
+
+Envelope sender addresses can be modified by Exim using two different
+facilities: the errors_to option on a router (as shown in previous mailing list
+examples), or the return_path option on a transport. The second of these is
+effective only if the message is successfully delivered to another host; it is
+not used for errors detected on the local host (see the description of
+return_path in chapter 24). Here is an example of the use of return_path to
+implement VERP on an smtp transport:
+
+verp_smtp:
+ driver = smtp
+ max_rcpt = 1
+ return_path = \
+ ${if match {$return_path}{^(.+?)-request@your.dom.example\$}\
+ {${quote_local_part:$1-request+$local_part=$domain}@your.dom.example}fail}
+
+This has the effect of rewriting the return path (envelope sender) on outgoing
+SMTP messages, if the local part of the original return path ends in
+"-request", and the domain is your.dom.example. The rewriting inserts the local
+part and domain of the recipient into the return path. Suppose, for example,
+that a message whose return path has been set to
+somelist-request@your.dom.example is sent to subscriber@other.dom.example. In
+the transport, the return path is rewritten as
+
+somelist-request+subscriber=other.dom.example@your.dom.example
+
+For this to work, you must tell Exim to send multiple copies of messages that
+have more than one recipient, so that each copy has just one recipient. This is
+achieved by setting max_rcpt to 1. Without this, a single copy of a message
+might be sent to several different recipients in the same domain, in which case
+$local_part is not available in the transport, because it is not unique.
+
+Unless your host is doing nothing but mailing list deliveries, you should
+probably use a separate transport for the VERP deliveries, so as not to use
+extra resources in making one-per-recipient copies for other deliveries. This
+can easily be done by expanding the transport option in the router:
+
+dnslookup:
+ driver = dnslookup
+ domains = ! +local_domains
+ transport = \
+ ${if match {$return_path}{^(.+?)-request@your.dom.example\$}\
+ {verp_smtp}{remote_smtp}}
+ no_more
+
+If you want to change the return path using errors_to in a router instead of
+using return_path in the transport, you need to set errors_to on all routers
+that handle mailing list addresses. This will ensure that all delivery errors,
+including those detected on the local host, are sent to the VERP address.
+
+On a host that does no local deliveries and has no manual routing, only the
+dnslookup router needs to be changed. A special transport is not needed for
+SMTP deliveries. Every mailing list recipient has its own return path value,
+and so Exim must hand them to the transport one at a time. Here is an example
+of a dnslookup router that implements VERP:
+
+verp_dnslookup:
+ driver = dnslookup
+ domains = ! +local_domains
+ transport = remote_smtp
+ errors_to = \
+ ${if match {$return_path}{^(.+?)-request@your.dom.example\$}}
+ {${quote_local_part:$1-request+$local_part=$domain}@your.dom.example}fail}
+ no_more
+
+Before you start sending out messages with VERPed return paths, you must also
+configure Exim to accept the bounce messages that come back to those paths.
+Typically this is done by setting a local_part_suffix option for a router, and
+using this to route the messages to wherever you want to handle them.
+
+The overhead incurred in using VERP depends very much on the size of the
+message, the number of recipient addresses that resolve to the same remote
+host, and the speed of the connection over which the message is being sent. If
+a lot of addresses resolve to the same host and the connection is slow, sending
+a separate copy of the message for each address may take substantially longer
+than sending a single copy with many recipients (for which VERP cannot be
+used).
+
+
+51.7 Virtual domains
+--------------------
+
+The phrase virtual domain is unfortunately used with two rather different
+meanings:
+
+ * A domain for which there are no real mailboxes; all valid local parts are
+ aliases for other email addresses. Common examples are organizational
+ top-level domains and "vanity" domains.
+
+ * One of a number of independent domains that are all handled by the same
+ host, with mailboxes on that host, but where the mailbox owners do not
+ necessarily have login accounts on that host.
+
+The first usage is probably more common, and does seem more "virtual" than the
+second. This kind of domain can be handled in Exim with a straightforward
+aliasing router. One approach is to create a separate alias file for each
+virtual domain. Exim can test for the existence of the alias file to determine
+whether the domain exists. The dsearch lookup type is useful here, leading to a
+router of this form:
+
+virtual:
+ driver = redirect
+ domains = dsearch;/etc/mail/virtual
+ data = ${lookup{$local_part}lsearch{/etc/mail/virtual/$domain_data}}
+ no_more
+
+The domains option specifies that the router is to be skipped, unless there is
+a file in the /etc/mail/virtual directory whose name is the same as the domain
+that is being processed. The dsearch lookup used results in an untainted
+version of $domain being placed into the $domain_data variable.
+
+When the router runs, it looks up the local part in the file to find a new
+address (or list of addresses). The no_more setting ensures that if the lookup
+fails (leading to data being an empty string), Exim gives up on the address
+without trying any subsequent routers.
+
+This one router can handle all the virtual domains because the alias filenames
+follow a fixed pattern. Permissions can be arranged so that appropriate people
+can edit the different alias files. A successful aliasing operation results in
+a new envelope recipient address, which is then routed from scratch.
+
+The other kind of "virtual" domain can also be handled in a straightforward
+way. One approach is to create a file for each domain containing a list of
+valid local parts, and use it in a router like this:
+
+my_domains:
+ driver = accept
+ domains = dsearch;/etc/mail/domains
+ local_parts = lsearch;/etc/mail/domains/$domain
+ transport = my_mailboxes
+
+The address is accepted if there is a file for the domain, and the local part
+can be found in the file. The domains option is used to check for the file's
+existence because domains is tested before the local_parts option (see section
+3.12). You cannot use require_files, because that option is tested after
+local_parts. The transport is as follows:
+
+my_mailboxes:
+ driver = appendfile
+ file = /var/mail/$domain/$local_part_data
+ user = mail
+
+This uses a directory of mailboxes for each domain. The user setting is
+required, to specify which uid is to be used for writing to the mailboxes.
+
+The configuration shown here is just one example of how you might support this
+requirement. There are many other ways this kind of configuration can be set
+up, for example, by using a database instead of separate files to hold all the
+information about the domains.
+
+
+51.8 Multiple user mailboxes
+----------------------------
+
+Heavy email users often want to operate with multiple mailboxes, into which
+incoming mail is automatically sorted. A popular way of handling this is to
+allow users to use multiple sender addresses, so that replies can easily be
+identified. Users are permitted to add prefixes or suffixes to their local
+parts for this purpose. The wildcard facility of the generic router options
+local_part_prefix and local_part_suffix can be used for this. For example,
+consider this router:
+
+userforward:
+ driver = redirect
+ check_local_user
+ file = $home/.forward
+ local_part_suffix = -*
+ local_part_suffix_optional
+ allow_filter
+
+It runs a user's .forward file for all local parts of the form username-*.
+Within the filter file the user can distinguish different cases by testing the
+variable $local_part_suffix. For example:
+
+if $local_part_suffix contains -special then
+save /home/$local_part/Mail/special
+endif
+
+If the filter file does not exist, or does not deal with such addresses, they
+fall through to subsequent routers, and, assuming no subsequent use of the
+local_part_suffix option is made, they presumably fail. Thus, users have
+control over which suffixes are valid.
+
+Alternatively, a suffix can be used to trigger the use of a different .forward
+file - which is the way a similar facility is implemented in another MTA:
+
+userforward:
+ driver = redirect
+ check_local_user
+ local_part_suffix = -*
+ local_part_suffix_optional
+ file = ${lookup {.forward$local_part_suffix} dsearch,ret=full {$home} {$value}fail}
+ allow_filter
+
+If there is no suffix, .forward is used; if the suffix is -special, for
+example, .forward-special is used. Once again, if the appropriate file does not
+exist, or does not deal with the address, it is passed on to subsequent
+routers, which could, if required, look for an unqualified .forward file to use
+as a default.
+
+
+51.9 Simplified vacation processing
+-----------------------------------
+
+The traditional way of running the vacation program is for a user to set up a
+pipe command in a .forward file (see section 22.6 for syntax details). This is
+prone to error by inexperienced users. There are two features of Exim that can
+be used to make this process simpler for users:
+
+ * A local part prefix such as "vacation-" can be specified on a router which
+ can cause the message to be delivered directly to the vacation program, or
+ alternatively can use Exim's autoreply transport. The contents of a user's
+ .forward file are then much simpler. For example:
+
+ spqr, vacation-spqr
+
+ * The require_files generic router option can be used to trigger a vacation
+ delivery by checking for the existence of a certain file in the user's home
+ directory. The unseen generic option should also be used, to ensure that
+ the original delivery also proceeds. In this case, all the user has to do
+ is to create a file called, say, .vacation, containing a vacation message.
+
+Another advantage of both these methods is that they both work even when the
+use of arbitrary pipes by users is locked out.
+
+
+51.10 Taking copies of mail
+---------------------------
+
+Some installations have policies that require archive copies of all messages to
+be made. A single copy of each message can easily be taken by an appropriate
+command in a system filter, which could, for example, use a different file for
+each day's messages.
+
+There is also a shadow transport mechanism that can be used to take copies of
+messages that are successfully delivered by local transports, one copy per
+delivery. This could be used, inter alia, to implement automatic notification
+of delivery by sites that insist on doing such things.
+
+
+51.11 Intermittently connected hosts
+------------------------------------
+
+It has become quite common (because it is cheaper) for hosts to connect to the
+Internet periodically rather than remain connected all the time. The normal
+arrangement is that mail for such hosts accumulates on a system that is
+permanently connected.
+
+Exim was designed for use on permanently connected hosts, and so it is not
+particularly well-suited to use in an intermittently connected environment.
+Nevertheless there are some features that can be used.
+
+
+51.12 Exim on the upstream server host
+--------------------------------------
+
+It is tempting to arrange for incoming mail for the intermittently connected
+host to remain in Exim's queue until the client connects. However, this
+approach does not scale very well. Two different kinds of waiting message are
+being mixed up in the same queue - those that cannot be delivered because of
+some temporary problem, and those that are waiting for their destination host
+to connect. This makes it hard to manage the queue, as well as wasting
+resources, because each queue runner scans the entire queue.
+
+A better approach is to separate off those messages that are waiting for an
+intermittently connected host. This can be done by delivering these messages
+into local files in batch SMTP, "mailstore", or other envelope-preserving
+format, from where they are transmitted by other software when their
+destination connects. This makes it easy to collect all the mail for one host
+in a single directory, and to apply local timeout rules on a per-message basis
+if required.
+
+On a very small scale, leaving the mail on Exim's queue can be made to work. If
+you are doing this, you should configure Exim with a long retry period for the
+intermittent host. For example:
+
+cheshire.wonderland.fict.example * F,5d,24h
+
+This stops a lot of failed delivery attempts from occurring, but Exim remembers
+which messages it has queued up for that host. Once the intermittent host comes
+online, forcing delivery of one message (either by using the -M or -R options,
+or by using the ETRN SMTP command (see section 49.8) causes all the queued up
+messages to be delivered, often down a single SMTP connection. While the host
+remains connected, any new messages get delivered immediately.
+
+If the connecting hosts do not have fixed IP addresses, that is, if a host is
+issued with a different IP address each time it connects, Exim's retry
+mechanisms on the holding host get confused, because the IP address is normally
+used as part of the key string for holding retry information. This can be
+avoided by unsetting retry_include_ip_address on the smtp transport. Since this
+has disadvantages for permanently connected hosts, it is best to arrange a
+separate transport for the intermittently connected ones.
+
+
+51.13 Exim on the intermittently connected client host
+------------------------------------------------------
+
+The value of smtp_accept_queue_per_connection should probably be increased, or
+even set to zero (that is, disabled) on the intermittently connected host, so
+that all incoming messages down a single connection get delivered immediately.
+
+Mail waiting to be sent from an intermittently connected host will probably not
+have been routed, because without a connection DNS lookups are not possible.
+This means that if a normal queue run is done at connection time, each message
+is likely to be sent in a separate SMTP session. This can be avoided by
+starting the queue run with a command line option beginning with -qq instead of
+-q. In this case, the queue is scanned twice. In the first pass, routing is
+done but no deliveries take place. The second pass is a normal queue run; since
+all the messages have been previously routed, those destined for the same host
+are likely to get sent as multiple deliveries in a single SMTP connection.
+
+
+
+===============================================================================
+52. USING EXIM AS A NON-QUEUEING CLIENT
+
+On a personal computer, it is a common requirement for all email to be sent to
+a "smart host". There are plenty of MUAs that can be configured to operate that
+way, for all the popular operating systems. However, there are some MUAs for
+Unix-like systems that cannot be so configured: they submit messages using the
+command line interface of /usr/sbin/sendmail. Furthermore, utility programs
+such as cron submit messages this way.
+
+If the personal computer runs continuously, there is no problem, because it can
+run a conventional MTA that handles delivery to the smart host, and deal with
+any delays via its queueing mechanism. However, if the computer does not run
+continuously or runs different operating systems at different times, queueing
+email is not desirable.
+
+There is therefore a requirement for something that can provide the /usr/sbin/
+sendmail interface but deliver messages to a smart host without any queueing or
+retrying facilities. Furthermore, the delivery to the smart host should be
+synchronous, so that if it fails, the sending MUA is immediately informed. In
+other words, we want something that extends an MUA that submits to a local MTA
+via the command line so that it behaves like one that submits to a remote smart
+host using TCP/SMTP.
+
+There are a number of applications (for example, there is one called ssmtp)
+that do this job. However, people have found them to be lacking in various
+ways. For instance, you might want to allow aliasing and forwarding to be done
+before sending a message to the smart host.
+
+Exim already had the necessary infrastructure for doing this job. Just a few
+tweaks were needed to make it behave as required, though it is somewhat of an
+overkill to use a fully-featured MTA for this purpose.
+
+There is a Boolean global option called mua_wrapper, defaulting false. Setting
+mua_wrapper true causes Exim to run in a special mode where it assumes that it
+is being used to "wrap" a command-line MUA in the manner just described. As
+well as setting mua_wrapper, you also need to provide a compatible router and
+transport configuration. Typically there will be just one router and one
+transport, sending everything to a smart host.
+
+When run in MUA wrapping mode, the behaviour of Exim changes in the following
+ways:
+
+ * A daemon cannot be run, nor will Exim accept incoming messages from inetd.
+ In other words, the only way to submit messages is via the command line.
+
+ * Each message is synchronously delivered as soon as it is received (-odi is
+ assumed). All queueing options (queue_only, queue_smtp_domains, control in
+ an ACL, etc.) are quietly ignored. The Exim reception process does not
+ finish until the delivery attempt is complete. If the delivery is
+ successful, a zero return code is given.
+
+ * Address redirection is permitted, but the final routing for all addresses
+ must be to the same remote transport, and to the same list of hosts.
+ Furthermore, the return address (envelope sender) must be the same for all
+ recipients, as must any added or deleted header lines. In other words, it
+ must be possible to deliver the message in a single SMTP transaction,
+ however many recipients there are.
+
+ * If these conditions are not met, or if routing any address results in a
+ failure or defer status, or if Exim is unable to deliver all the recipients
+ successfully to one of the smart hosts, delivery of the entire message
+ fails.
+
+ * Because no queueing is allowed, all failures are treated as permanent;
+ there is no distinction between 4xx and 5xx SMTP response codes from the
+ smart host. Furthermore, because only a single yes/no response can be given
+ to the caller, it is not possible to deliver to some recipients and not
+ others. If there is an error (temporary or permanent) for any recipient,
+ all are failed.
+
+ * If more than one smart host is listed, Exim will try another host after a
+ connection failure or a timeout, in the normal way. However, if this kind
+ of failure happens for all the hosts, the delivery fails.
+
+ * When delivery fails, an error message is written to the standard error
+ stream (as well as to Exim's log), and Exim exits to the caller with a
+ return code value 1. The message is expunged from Exim's spool files. No
+ bounce messages are ever generated.
+
+ * No retry data is maintained, and any retry rules are ignored.
+
+ * A number of Exim options are overridden: deliver_drop_privilege is forced
+ true, max_rcpt in the smtp transport is forced to "unlimited",
+ remote_max_parallel is forced to one, and fallback hosts are ignored.
+
+The overall effect is that Exim makes a single synchronous attempt to deliver
+the message, failing if there is any kind of problem. Because no local
+deliveries are done and no daemon can be run, Exim does not need root
+privilege. It should be possible to run it setuid to exim instead of setuid to
+root. See section 56.3 for a general discussion about the advantages and
+disadvantages of running without root privilege.
+
+
+
+===============================================================================
+53. LOG FILES
+
+Exim writes three different logs, referred to as the main log, the reject log,
+and the panic log:
+
+ * The main log records the arrival of each message and each delivery in a
+ single line in each case. The format is as compact as possible, in an
+ attempt to keep down the size of log files. Two-character flag sequences
+ make it easy to pick out these lines. A number of other events are recorded
+ in the main log. Some of them are optional, in which case the log_selector
+ option controls whether they are included or not. A Perl script called
+ eximstats, which does simple analysis of main log files, is provided in the
+ Exim distribution (see section 54.7).
+
+ * The reject log records information from messages that are rejected as a
+ result of a configuration option (that is, for policy reasons). The first
+ line of each rejection is a copy of the line that is also written to the
+ main log. Then, if the message's header has been read at the time the log
+ is written, its contents are written to this log. Only the original header
+ lines are available; header lines added by ACLs are not logged. You can use
+ the reject log to check that your policy controls are working correctly; on
+ a busy host this may be easier than scanning the main log for rejection
+ messages. You can suppress the writing of the reject log by setting
+ write_rejectlog false.
+
+ * When certain serious errors occur, Exim writes entries to its panic log. If
+ the error is sufficiently disastrous, Exim bombs out afterwards. Panic log
+ entries are usually written to the main log as well, but can get lost amid
+ the mass of other entries. The panic log should be empty under normal
+ circumstances. It is therefore a good idea to check it (or to have a cron
+ script check it) regularly, in order to become aware of any problems. When
+ Exim cannot open its panic log, it tries as a last resort to write to the
+ system log (syslog). This is opened with LOG_PID+LOG_CONS and the facility
+ code of LOG_MAIL. The message itself is written at priority LOG_CRIT.
+
+Every log line starts with a timestamp, in the format shown in the following
+example. Note that many of the examples shown in this chapter are line-wrapped.
+In the log file, this would be all on one line:
+
+2001-09-16 16:09:47 SMTP connection from [127.0.0.1] closed
+ by QUIT
+
+By default, the timestamps are in the local timezone. There are two ways of
+changing this:
+
+ * You can set the timezone option to a different time zone; in particular, if
+ you set
+
+ timezone = UTC
+
+ the timestamps will be in UTC (aka GMT).
+
+ * If you set log_timezone true, the time zone is added to the timestamp, for
+ example:
+
+ 2003-04-25 11:17:07 +0100 Start queue run: pid=12762
+
+Exim does not include its process id in log lines by default, but you can
+request that it does so by specifying the "pid" log selector (see section 53.15
+). When this is set, the process id is output, in square brackets, immediately
+after the time and date.
+
+
+53.1 Where the logs are written
+-------------------------------
+
+The logs may be written to local files, or to syslog, or both. However, it
+should be noted that many syslog implementations use UDP as a transport, and
+are therefore unreliable in the sense that messages are not guaranteed to
+arrive at the loghost, nor is the ordering of messages necessarily maintained.
+It has also been reported that on large log files (tens of megabytes) you may
+need to tweak syslog to prevent it syncing the file with each write - on Linux
+this has been seen to make syslog take 90% plus of CPU time.
+
+The destination for Exim's logs is configured by setting LOG_FILE_PATH in Local
+/Makefile or by setting log_file_path in the runtime configuration. This latter
+string is expanded, so it can contain, for example, references to the host
+name:
+
+log_file_path = /var/log/$primary_hostname/exim_%slog
+
+It is generally advisable, however, to set the string in Local/Makefile rather
+than at runtime, because then the setting is available right from the start of
+Exim's execution. Otherwise, if there's something it wants to log before it has
+read the configuration file (for example, an error in the configuration file)
+it will not use the path you want, and may not be able to log at all.
+
+The value of LOG_FILE_PATH or log_file_path is a colon-separated list,
+currently limited to at most two items. This is one option where the facility
+for changing a list separator may not be used. The list must always be
+colon-separated. If an item in the list is "syslog" then syslog is used;
+otherwise the item must either be an absolute path, containing "%s" at the
+point where "main", "reject", or "panic" is to be inserted, or be empty,
+implying the use of a default path.
+
+When Exim encounters an empty item in the list, it searches the list defined by
+LOG_FILE_PATH, and uses the first item it finds that is neither empty nor
+"syslog". This means that an empty item in log_file_path can be used to mean
+"use the path specified at build time". It no such item exists, log files are
+written in the log subdirectory of the spool directory. This is equivalent to
+the setting:
+
+log_file_path = $spool_directory/log/%slog
+
+If you do not specify anything at build time or runtime, or if you unset the
+option at runtime (i.e. "log_file_path = "), that is where the logs are
+written.
+
+A log file path may also contain "%D" or "%M" if datestamped log filenames are
+in use - see section 53.3 below.
+
+Here are some examples of possible settings:
+
+LOG_FILE_PATH=syslog syslog only
+LOG_FILE_PATH=:syslog syslog and default path
+LOG_FILE_PATH=syslog : /usr/log/exim_%s syslog and specified path
+LOG_FILE_PATH=/usr/log/exim_%s specified path only
+
+If there are more than two paths in the list, the first is used and a panic
+error is logged.
+
+
+53.2 Logging to local files that are periodically "cycled"
+----------------------------------------------------------
+
+Some operating systems provide centralized and standardized methods for cycling
+log files. For those that do not, a utility script called exicyclog is provided
+(see section 54.6). This renames and compresses the main and reject logs each
+time it is called. The maximum number of old logs to keep can be set. It is
+suggested this script is run as a daily cron job.
+
+An Exim delivery process opens the main log when it first needs to write to it,
+and it keeps the file open in case subsequent entries are required - for
+example, if a number of different deliveries are being done for the same
+message. However, remote SMTP deliveries can take a long time, and this means
+that the file may be kept open long after it is renamed if exicyclog or
+something similar is being used to rename log files on a regular basis. To
+ensure that a switch of log files is noticed as soon as possible, Exim calls
+stat() on the main log's name before reusing an open file, and if the file does
+not exist, or its inode has changed, the old file is closed and Exim tries to
+open the main log from scratch. Thus, an old log file may remain open for quite
+some time, but no Exim processes should write to it once it has been renamed.
+
+
+53.3 Datestamped log files
+--------------------------
+
+Instead of cycling the main and reject log files by renaming them periodically,
+some sites like to use files whose names contain a datestamp, for example,
+mainlog-20031225. The datestamp is in the form yyyymmdd or yyyymm. Exim has
+support for this way of working. It is enabled by setting the log_file_path
+option to a path that includes "%D" or "%M" at the point where the datestamp is
+required. For example:
+
+log_file_path = /var/spool/exim/log/%slog-%D
+log_file_path = /var/log/exim-%s-%D.log
+log_file_path = /var/spool/exim/log/%D-%slog
+log_file_path = /var/log/exim/%s.%M
+
+As before, "%s" is replaced by "main" or "reject"; the following are examples
+of names generated by the above examples:
+
+/var/spool/exim/log/mainlog-20021225
+/var/log/exim-reject-20021225.log
+/var/spool/exim/log/20021225-mainlog
+/var/log/exim/main.200212
+
+When this form of log file is specified, Exim automatically switches to new
+files at midnight. It does not make any attempt to compress old logs; you will
+need to write your own script if you require this. You should not run exicyclog
+with this form of logging.
+
+The location of the panic log is also determined by log_file_path, but it is
+not datestamped, because rotation of the panic log does not make sense. When
+generating the name of the panic log, "%D" or "%M" are removed from the string.
+In addition, if it immediately follows a slash, a following non-alphanumeric
+character is removed; otherwise a preceding non-alphanumeric character is
+removed. Thus, the four examples above would give these panic log names:
+
+/var/spool/exim/log/paniclog
+/var/log/exim-panic.log
+/var/spool/exim/log/paniclog
+/var/log/exim/panic
+
+
+53.4 Logging to syslog
+----------------------
+
+The use of syslog does not change what Exim logs or the format of its messages,
+except in one respect. If syslog_timestamp is set false, the timestamps on
+Exim's log lines are omitted when these lines are sent to syslog. Apart from
+that, the same strings are written to syslog as to log files. The syslog
+"facility" is set to LOG_MAIL, and the program name to "exim" by default, but
+you can change these by setting the syslog_facility and syslog_processname
+options, respectively. If Exim was compiled with SYSLOG_LOG_PID set in Local/
+Makefile (this is the default in src/EDITME), then, on systems that permit it
+(all except ULTRIX), the LOG_PID flag is set so that the syslog() call adds the
+pid as well as the time and host name to each line. The three log streams are
+mapped onto syslog priorities as follows:
+
+ * mainlog is mapped to LOG_INFO
+
+ * rejectlog is mapped to LOG_NOTICE
+
+ * paniclog is mapped to LOG_ALERT
+
+Many log lines are written to both mainlog and rejectlog, and some are written
+to both mainlog and paniclog, so there will be duplicates if these are routed
+by syslog to the same place. You can suppress this duplication by setting
+syslog_duplication false.
+
+Exim's log lines can sometimes be very long, and some of its rejectlog entries
+contain multiple lines when headers are included. To cope with both these
+cases, entries written to syslog are split into separate syslog() calls at each
+internal newline, and also after a maximum of 870 data characters. (This allows
+for a total syslog line length of 1024, when additions such as timestamps are
+added.) If you are running a syslog replacement that can handle lines longer
+than the 1024 characters allowed by RFC 3164, you should set
+
+SYSLOG_LONG_LINES=yes
+
+in Local/Makefile before building Exim. That stops Exim from splitting long
+lines, but it still splits at internal newlines in reject log entries.
+
+To make it easy to re-assemble split lines later, each component of a split
+entry starts with a string of the form [<n>/<m>] or [<n>\<m>] where <n> is the
+component number and <m> is the total number of components in the entry. The /
+delimiter is used when the line was split because it was too long; if it was
+split because of an internal newline, the \ delimiter is used. For example,
+supposing the length limit to be 50 instead of 870, the following would be the
+result of a typical rejection message to mainlog (LOG_INFO), each line in
+addition being preceded by the time, host name, and pid as added by syslog:
+
+[1/5] 2002-09-16 16:09:43 16RdAL-0006pc-00 rejected from
+[2/5] [127.0.0.1] (ph10): syntax error in 'From' header
+[3/5] when scanning for sender: missing or malformed lo
+[4/5] cal part in "<>" (envelope sender is <ph10@cam.exa
+[5/5] mple>)
+
+The same error might cause the following lines to be written to "rejectlog"
+(LOG_NOTICE):
+
+[1/18] 2002-09-16 16:09:43 16RdAL-0006pc-00 rejected fro
+[2/18] m [127.0.0.1] (ph10): syntax error in 'From' head
+[3/18] er when scanning for sender: missing or malformed
+[4/18] local part in "<>" (envelope sender is <ph10@cam
+[5\18] .example>)
+[6\18] Recipients: ph10@some.domain.cam.example
+[7\18] P Received: from [127.0.0.1] (ident=ph10)
+[8\18] by xxxxx.cam.example with smtp (Exim 4.00)
+[9\18] id 16RdAL-0006pc-00
+[10/18] for ph10@cam.example; Mon, 16 Sep 2002 16:
+[11\18] 09:43 +0100
+[12\18] F From: <>
+[13\18] Subject: this is a test header
+[18\18] X-something: this is another header
+[15/18] I Message-Id: <E16RdAL-0006pc-00@xxxxx.cam.examp
+[16\18] le>
+[17\18] B Bcc:
+[18/18] Date: Mon, 16 Sep 2002 16:09:43 +0100
+
+Log lines that are neither too long nor contain newlines are written to syslog
+without modification.
+
+If only syslog is being used, the Exim monitor is unable to provide a log tail
+display, unless syslog is routing mainlog to a file on the local host and the
+environment variable EXIMON_LOG_FILE_PATH is set to tell the monitor where it
+is.
+
+
+53.5 Log line flags
+-------------------
+
+One line is written to the main log for each message received, and for each
+successful, unsuccessful, and delayed delivery. These lines can readily be
+picked out by the distinctive two-character flags that immediately follow the
+timestamp. The flags are:
+
+<= message arrival
+(= message fakereject
+=> normal message delivery
+-> additional address in same delivery
+>> cutthrough message delivery
+*> delivery suppressed by -N
+** delivery failed; address bounced
+== delivery deferred; temporary problem
+
+
+53.6 Logging message reception
+------------------------------
+
+The format of the single-line entry in the main log that is written for every
+message received is shown in the basic example below, which is split over
+several lines in order to fit it on the page:
+
+2002-10-31 08:57:53 16ZCW1-0005MB-00 <= kryten@dwarf.fict.example
+ H=mailer.fict.example [192.168.123.123] U=exim
+ P=smtp S=5678 id=<incoming message id>
+
+The address immediately following "<=" is the envelope sender address. A bounce
+message is shown with the sender address "<>", and if it is locally generated,
+this is followed by an item of the form
+
+R=<message id>
+
+which is a reference to the message that caused the bounce to be sent.
+
+For messages from other hosts, the H and U fields identify the remote host and
+record the RFC 1413 identity of the user that sent the message, if one was
+received. The number given in square brackets is the IP address of the sending
+host. If there is a single, unparenthesized host name in the H field, as above,
+it has been verified to correspond to the IP address (see the host_lookup
+option). If the name is in parentheses, it was the name quoted by the remote
+host in the SMTP HELO or EHLO command, and has not been verified. If
+verification yields a different name to that given for HELO or EHLO, the
+verified name appears first, followed by the HELO or EHLO name in parentheses.
+
+Misconfigured hosts (and mail forgers) sometimes put an IP address, with or
+without brackets, in the HELO or EHLO command, leading to entries in the log
+containing text like these examples:
+
+H=(10.21.32.43) [192.168.8.34]
+H=([10.21.32.43]) [192.168.8.34]
+
+This can be confusing. Only the final address in square brackets can be relied
+on.
+
+For locally generated messages (that is, messages not received over TCP/IP),
+the H field is omitted, and the U field contains the login name of the caller
+of Exim.
+
+For all messages, the P field specifies the protocol used to receive the
+message. This is the value that is stored in $received_protocol. In the case of
+incoming SMTP messages, the value indicates whether or not any SMTP extensions
+(ESMTP), encryption, or authentication were used. If the SMTP session was
+encrypted, there is an additional X field that records the cipher suite that
+was used.
+
+The protocol is set to "esmtpsa" or "esmtpa" for messages received from hosts
+that have authenticated themselves using the SMTP AUTH command. The first value
+is used when the SMTP connection was encrypted ("secure"). In this case there
+is an additional item A= followed by the name of the authenticator that was
+used. If an authenticated identification was set up by the authenticator's
+server_set_id option, this is logged too, separated by a colon from the
+authenticator name.
+
+The id field records the existing message id, if present. The size of the
+received message is given by the S field. When the message is delivered,
+headers may be removed or added, so that the size of delivered copies of the
+message may not correspond with this value (and indeed may be different to each
+other).
+
+The log_selector option can be used to request the logging of additional data
+when a message is received. See section 53.15 below.
+
+
+53.7 Logging deliveries
+-----------------------
+
+The format of the single-line entry in the main log that is written for every
+delivery is shown in one of the examples below, for local and remote
+deliveries, respectively. Each example has been split into multiple lines in
+order to fit it on the page:
+
+2002-10-31 08:59:13 16ZCW1-0005MB-00 => marv
+ <marv@hitch.fict.example> R=localuser T=local_delivery
+2002-10-31 09:00:10 16ZCW1-0005MB-00 =>
+ monk@holistic.fict.example R=dnslookup T=remote_smtp
+ H=holistic.fict.example [192.168.234.234]
+
+For ordinary local deliveries, the original address is given in angle brackets
+after the final delivery address, which might be a pipe or a file. If
+intermediate address(es) exist between the original and the final address, the
+last of these is given in parentheses after the final address. The R and T
+fields record the router and transport that were used to process the address.
+
+If SMTP AUTH was used for the delivery there is an additional item A= followed
+by the name of the authenticator that was used. If an authenticated
+identification was set up by the authenticator's client_set_id option, this is
+logged too, separated by a colon from the authenticator name.
+
+If a shadow transport was run after a successful local delivery, the log line
+for the successful delivery has an item added on the end, of the form
+
+ST=<shadow transport name>
+
+If the shadow transport did not succeed, the error message is put in
+parentheses afterwards.
+
+When more than one address is included in a single delivery (for example, two
+SMTP RCPT commands in one transaction) the second and subsequent addresses are
+flagged with "->" instead of "=>". When two or more messages are delivered down
+a single SMTP connection, an asterisk follows the IP address in the log lines
+for the second and subsequent messages. When two or more messages are delivered
+down a single TLS connection, the DNS and some TLS-related information logged
+for the first message delivered will not be present in the log lines for the
+second and subsequent messages. TLS cipher information is still available.
+
+When delivery is done in cutthrough mode it is flagged with ">>" and the log
+line precedes the reception line, since cutthrough waits for a possible
+rejection from the destination in case it can reject the sourced item.
+
+The generation of a reply message by a filter file gets logged as a "delivery"
+to the addressee, preceded by ">".
+
+The log_selector option can be used to request the logging of additional data
+when a message is delivered. See section 53.15 below.
+
+
+53.8 Discarded deliveries
+-------------------------
+
+When a message is discarded as a result of the command "seen finish" being
+obeyed in a filter file which generates no deliveries, a log entry of the form
+
+2002-12-10 00:50:49 16auJc-0001UB-00 => discarded
+ <low.club@bridge.example> R=userforward
+
+is written, to record why no deliveries are logged. When a message is discarded
+because it is aliased to ":blackhole:" the log line is like this:
+
+1999-03-02 09:44:33 10HmaX-0005vi-00 => :blackhole:
+ <hole@nowhere.example> R=blackhole_router
+
+
+53.9 Deferred deliveries
+------------------------
+
+When a delivery is deferred, a line of the following form is logged:
+
+2002-12-19 16:20:23 16aiQz-0002Q5-00 == marvin@endrest.example
+ R=dnslookup T=smtp defer (146): Connection refused
+
+In the case of remote deliveries, the error is the one that was given for the
+last IP address that was tried. Details of individual SMTP failures are also
+written to the log, so the above line would be preceded by something like
+
+2002-12-19 16:20:23 16aiQz-0002Q5-00 Failed to connect to
+ mail1.endrest.example [192.168.239.239]: Connection refused
+
+When a deferred address is skipped because its retry time has not been reached,
+a message is written to the log, but this can be suppressed by setting an
+appropriate value in log_selector.
+
+
+53.10 Delivery failures
+-----------------------
+
+If a delivery fails because an address cannot be routed, a line of the
+following form is logged:
+
+1995-12-19 16:20:23 0tRiQz-0002Q5-00 ** jim@trek99.example
+ <jim@trek99.example>: unknown mail domain
+
+If a delivery fails at transport time, the router and transport are shown, and
+the response from the remote host is included, as in this example:
+
+2002-07-11 07:14:17 17SXDU-000189-00 ** ace400@pb.example
+ R=dnslookup T=remote_smtp: SMTP error from remote mailer
+ after pipelined RCPT TO:<ace400@pb.example>: host
+ pbmail3.py.example [192.168.63.111]: 553 5.3.0
+ <ace400@pb.example>...Addressee unknown
+
+The word "pipelined" indicates that the SMTP PIPELINING extension was being
+used. See hosts_avoid_esmtp in the smtp transport for a way of disabling
+PIPELINING. The log lines for all forms of delivery failure are flagged with
+"**".
+
+
+53.11 Fake deliveries
+---------------------
+
+If a delivery does not actually take place because the -N option has been used
+to suppress it, a normal delivery line is written to the log, except that "=>"
+is replaced by "*>".
+
+
+53.12 Completion
+----------------
+
+A line of the form
+
+2002-10-31 09:00:11 16ZCW1-0005MB-00 Completed
+
+is written to the main log when a message is about to be removed from the spool
+at the end of its processing.
+
+
+53.13 Summary of Fields in Log Lines
+------------------------------------
+
+A summary of the field identifiers that are used in log lines is shown in the
+following table:
+
+A authenticator name (and optional id and sender)
+C SMTP confirmation on delivery
+ command list for "no mail in SMTP session"
+CV certificate verification status
+D duration of "no mail in SMTP session"
+DKIM domain verified in incoming message
+DN distinguished name from peer certificate
+DS DNSSEC secured lookups
+DT on =>, == and ** lines: time taken for, or to attempt, a delivery
+F sender address (on delivery lines)
+H host name and IP address
+I local interface used
+id message id (from header) for incoming message
+K CHUNKING extension used
+L on <= and => lines: PIPELINING extension used
+M8S 8BITMIME status for incoming message
+P on <= lines: protocol used
+ on => and ** lines: return path
+PRDR PRDR extension used
+PRX on <= and => lines: proxy address
+Q alternate queue name
+QT on => lines: time spent on queue so far
+ on "Completed" lines: time spent on queue
+R on <= lines: reference for local bounce
+ on => >> ** and == lines: router name
+RT on <= lines: time taken for reception
+S size of message in bytes
+SNI server name indication from TLS client hello
+ST shadow transport name
+T on <= lines: message subject (topic)
+TFO connection took advantage of TCP Fast Open
+ on => ** and == lines: transport name
+U local user or RFC 1413 identity
+X TLS cipher suite
+
+
+53.14 Other log entries
+-----------------------
+
+Various other types of log entry are written from time to time. Most should be
+self-explanatory. Among the more common are:
+
+ * retry time not reached An address previously suffered a temporary error
+ during routing or local delivery, and the time to retry has not yet
+ arrived. This message is not written to an individual message log file
+ unless it happens during the first delivery attempt.
+
+ * retry time not reached for any host An address previously suffered
+ temporary errors during remote delivery, and the retry time has not yet
+ arrived for any of the hosts to which it is routed.
+
+ * spool file locked An attempt to deliver a message cannot proceed because
+ some other Exim process is already working on the message. This can be
+ quite common if queue running processes are started at frequent intervals.
+ The exiwhat utility script can be used to find out what Exim processes are
+ doing.
+
+ * error ignored There are several circumstances that give rise to this
+ message:
+
+ 1. Exim failed to deliver a bounce message whose age was greater than
+ ignore_bounce_errors_after. The bounce was discarded.
+
+ 2. A filter file set up a delivery using the "noerror" option, and the
+ delivery failed. The delivery was discarded.
+
+ 3. A delivery set up by a router configured with
+
+ errors_to = <>
+
+ failed. The delivery was discarded.
+
+ * DKIM: d= Verbose results of a DKIM verification attempt, if enabled for
+ logging and the message has a DKIM signature header.
+
+
+53.15 Reducing or increasing what is logged
+-------------------------------------------
+
+By setting the log_selector global option, you can disable some of Exim's
+default logging, or you can request additional logging. The value of
+log_selector is made up of names preceded by plus or minus characters. For
+example:
+
+log_selector = +arguments -retry_defer
+
+The list of optional log items is in the following table, with the default
+selection marked by asterisks:
+
+ 8bitmime received 8BITMIME status
+*acl_warn_skipped skipped warn statement in ACL
+ address_rewrite address rewriting
+ all_parents all parents in => lines
+ arguments command line arguments
+*connection_reject connection rejections
+*delay_delivery immediate delivery delayed
+ deliver_time time taken to attempt delivery
+ delivery_size add S=nnn to => lines
+*dkim DKIM verified domain on <= lines
+ dkim_verbose separate full DKIM verification result line, per signature
+*dnslist_defer defers of DNS list (aka RBL) lookups
+ dnssec DNSSEC secured lookups
+*etrn ETRN commands
+*host_lookup_failed as it says
+ ident_timeout timeout for ident connection
+ incoming_interface local interface on <= and => lines
+ incoming_port remote port on <= lines
+*lost_incoming_connection as it says (includes timeouts)
+ millisec millisecond timestamps and RT,QT,DT,D times
+*msg_id on <= lines, Message-ID: header value
+ msg_id_created on <=
+ lines, Message-ID: header value when one had to be added
+ outgoing_interface local interface on => lines
+ outgoing_port add remote port to => lines
+*queue_run start and end queue runs
+ queue_time time on queue for one recipient
+ queue_time_overall time on queue for whole message
+ pid Exim process id
+ pipelining PIPELINING use, on <= and => lines
+ proxy proxy address on <= and => lines
+ receive_time time taken to receive message
+ received_recipients recipients on <= lines
+ received_sender sender on <= lines
+*rejected_header header contents on reject log
+*retry_defer "retry time not reached"
+ return_path_on_delivery put return path on => and ** lines
+ sender_on_delivery add sender to => lines
+*sender_verify_fail sender verification failures
+*size_reject rejection because too big
+*skip_delivery delivery skipped in a queue run
+*smtp_confirmation SMTP confirmation on => lines
+ smtp_connection incoming SMTP connections
+ smtp_incomplete_transaction incomplete SMTP transactions
+ smtp_mailauth AUTH argument to MAIL commands
+ smtp_no_mail session with no MAIL commands
+ smtp_protocol_error SMTP protocol errors
+ smtp_syntax_error SMTP syntax errors
+ subject contents of Subject: on <= lines
+*tls_certificate_verified certificate verification status
+*tls_cipher TLS cipher suite on <= and => lines
+ tls_peerdn TLS peer DN on <= and => lines
+ tls_sni TLS SNI on <= lines
+ unknown_in_list DNS lookup failed in list match
+
+ all all of the above
+
+See also the slow_lookup_log main configuration option, section 14.4
+
+More details on each of these items follows:
+
+ * 8bitmime: This causes Exim to log any 8BITMIME status of received messages,
+ which may help in tracking down interoperability issues with ancient MTAs
+ that are not 8bit clean. This is added to the "<=" line, tagged with "M8S="
+ and a value of "0", "7" or "8", corresponding to "not given", "7BIT" and
+ "8BITMIME" respectively.
+
+ * acl_warn_skipped: When an ACL warn statement is skipped because one of its
+ conditions cannot be evaluated, a log line to this effect is written if
+ this log selector is set.
+
+ * address_rewrite: This applies both to global rewrites and per-transport
+ rewrites, but not to rewrites in filters run as an unprivileged user
+ (because such users cannot access the log).
+
+ * all_parents: Normally only the original and final addresses are logged on
+ delivery lines; with this selector, intermediate parents are given in
+ parentheses between them.
+
+ * arguments: This causes Exim to write the arguments with which it was called
+ to the main log, preceded by the current working directory. This is a
+ debugging feature, added to make it easier to find out how certain MUAs
+ call /usr/sbin/sendmail. The logging does not happen if Exim has given up
+ root privilege because it was called with the -C or -D options. Arguments
+ that are empty or that contain white space are quoted. Non-printing
+ characters are shown as escape sequences. This facility cannot log
+ unrecognized arguments, because the arguments are checked before the
+ configuration file is read. The only way to log such cases is to interpose
+ a script such as util/logargs.sh between the caller and Exim.
+
+ * connection_reject: A log entry is written whenever an incoming SMTP
+ connection is rejected, for whatever reason.
+
+ * delay_delivery: A log entry is written whenever a delivery process is not
+ started for an incoming message because the load is too high or too many
+ messages were received on one connection. Logging does not occur if no
+ delivery process is started because queue_only is set or -odq was used.
+
+ * deliver_time: For each delivery, the amount of real time it has taken to
+ perform the actual delivery is logged as DT=<time>, for example, "DT=1s".
+ If millisecond logging is enabled, short times will be shown with greater
+ precision, eg. "DT=0.304s".
+
+ * delivery_size: For each delivery, the size of message delivered is added to
+ the "=>" line, tagged with S=.
+
+ * dkim: For message acceptance log lines, when an DKIM signature in the
+ header verifies successfully a tag of DKIM is added, with one of the
+ verified domains.
+
+ * dkim_verbose: A log entry is written for each attempted DKIM verification.
+
+ * dnslist_defer: A log entry is written if an attempt to look up a host in a
+ DNS black list suffers a temporary error.
+
+ * dnssec: For message acceptance and (attempted) delivery log lines, when dns
+ lookups gave secure results a tag of DS is added. For acceptance this
+ covers the reverse and forward lookups for host name verification. It does
+ not cover helo-name verification. For delivery this covers the SRV, MX, A
+ and/or AAAA lookups.
+
+ * etrn: Every valid ETRN command that is received is logged, before the ACL
+ is run to determine whether or not it is actually accepted. An invalid ETRN
+ command, or one received within a message transaction is not logged by this
+ selector (see smtp_syntax_error and smtp_protocol_error).
+
+ * host_lookup_failed: When a lookup of a host's IP addresses fails to find
+ any addresses, or when a lookup of an IP address fails to find a host name,
+ a log line is written. This logging does not apply to direct DNS lookups
+ when routing email addresses, but it does apply to "byname" lookups.
+
+ * ident_timeout: A log line is written whenever an attempt to connect to a
+ client's ident port times out.
+
+ * incoming_interface: The interface on which a message was received is added
+ to the "<=" line as an IP address in square brackets, tagged by I= and
+ followed by a colon and the port number. The local interface and port are
+ also added to other SMTP log lines, for example, "SMTP connection from", to
+ rejection lines, and (despite the name) to outgoing "=>" and "->" lines.
+ The latter can be disabled by turning off the outgoing_interface option.
+
+ * proxy: The internal (closest to the system running Exim) IP address of the
+ proxy, tagged by PRX=, on the "<=" line for a message accepted on a proxied
+ connection or the "=>" line for a message delivered on a proxied
+ connection. See 59.1 for more information.
+
+ * incoming_port: The remote port number from which a message was received is
+ added to log entries and Received: header lines, following the IP address
+ in square brackets, and separated from it by a colon. This is implemented
+ by changing the value that is put in the $sender_fullhost and
+ $sender_rcvhost variables. Recording the remote port number has become more
+ important with the widening use of NAT (see RFC 2505).
+
+ * lost_incoming_connection: A log line is written when an incoming SMTP
+ connection is unexpectedly dropped.
+
+ * millisec: Timestamps have a period and three decimal places of finer
+ granularity appended to the seconds value.
+
+ * msg_id: The value of the Message-ID: header.
+
+ * msg_id_created: The value of the Message-ID: header, when one had to be
+ created. This will be either because the message is a bounce, or was
+ submitted locally (submission mode) without one. The field identifier will
+ have an asterix appended: "id*=".
+
+ * outgoing_interface: If incoming_interface is turned on, then the interface
+ on which a message was sent is added to delivery lines as an I= tag
+ followed by IP address in square brackets. You can disable this by turning
+ off the outgoing_interface option.
+
+ * outgoing_port: The remote port number is added to delivery log lines (those
+ containing => tags) following the IP address. The local port is also added
+ if incoming_interface and outgoing_interface are both enabled. This option
+ is not included in the default setting, because for most ordinary
+ configurations, the remote port number is always 25 (the SMTP port), and
+ the local port is a random ephemeral port.
+
+ * pid: The current process id is added to every log line, in square brackets,
+ immediately after the time and date.
+
+ * pipelining: A field is added to delivery and accept log lines when the
+ ESMTP PIPELINING extension was used. The field is a single "L".
+
+ On accept lines, where PIPELINING was offered but not used by the client,
+ the field has a minus appended.
+
+ If Exim is built with the SUPPORT_PIPE_CONNECT build option accept "L"
+ fields have a period appended if the feature was offered but not used, or
+ an asterisk appended if used. Delivery "L" fields have an asterisk appended
+ if used.
+
+ * queue_run: The start and end of every queue run are logged.
+
+ * queue_time: The amount of time the message has been in the queue on the
+ local host is logged as QT=<time> on delivery ("=>") lines, for example,
+ "QT=3m45s". The clock starts when Exim starts to receive the message, so it
+ includes reception time as well as the delivery time for the current
+ address. This means that it may be longer than the difference between the
+ arrival and delivery log line times, because the arrival log line is not
+ written until the message has been successfully received. If millisecond
+ logging is enabled, short times will be shown with greater precision, eg.
+ "QT=1.578s".
+
+ * queue_time_overall: The amount of time the message has been in the queue on
+ the local host is logged as QT=<time> on "Completed" lines, for example,
+ "QT=3m45s". The clock starts when Exim starts to receive the message, so it
+ includes reception time as well as the total delivery time.
+
+ * receive_time: For each message, the amount of real time it has taken to
+ perform the reception is logged as RT=<time>, for example, "RT=1s". If
+ millisecond logging is enabled, short times will be shown with greater
+ precision, eg. "RT=0.204s".
+
+ * received_recipients: The recipients of a message are listed in the main log
+ as soon as the message is received. The list appears at the end of the log
+ line that is written when a message is received, preceded by the word
+ "for". The addresses are listed after they have been qualified, but before
+ any rewriting has taken place. Recipients that were discarded by an ACL for
+ MAIL or RCPT do not appear in the list.
+
+ * received_sender: The unrewritten original sender of a message is added to
+ the end of the log line that records the message's arrival, after the word
+ "from" (before the recipients if received_recipients is also set).
+
+ * rejected_header: If a message's header has been received at the time a
+ rejection is written to the reject log, the complete header is added to the
+ log. Header logging can be turned off individually for messages that are
+ rejected by the local_scan() function (see section 46.2).
+
+ * retry_defer: A log line is written if a delivery is deferred because a
+ retry time has not yet been reached. However, this "retry time not reached"
+ message is always omitted from individual message logs after the first
+ delivery attempt.
+
+ * return_path_on_delivery: The return path that is being transmitted with the
+ message is included in delivery and bounce lines, using the tag P=. This is
+ omitted if no delivery actually happens, for example, if routing fails, or
+ if delivery is to /dev/null or to ":blackhole:".
+
+ * sender_on_delivery: The message's sender address is added to every delivery
+ and bounce line, tagged by F= (for "from"). This is the original sender
+ that was received with the message; it is not necessarily the same as the
+ outgoing return path.
+
+ * sender_verify_fail: If this selector is unset, the separate log line that
+ gives details of a sender verification failure is not written. Log lines
+ for the rejection of SMTP commands contain just "sender verify failed", so
+ some detail is lost.
+
+ * size_reject: A log line is written whenever a message is rejected because
+ it is too big.
+
+ * skip_delivery: A log line is written whenever a message is skipped during a
+ queue run because it is frozen or because another process is already
+ delivering it. The message that is written is "spool file is locked".
+
+ * smtp_confirmation: The response to the final "." in the SMTP or LMTP
+ dialogue for outgoing messages is added to delivery log lines in the form
+ "C="<text>. A number of MTAs (including Exim) return an identifying string
+ in this response.
+
+ * smtp_connection: A log line is written whenever an incoming SMTP connection
+ is established or closed, unless the connection is from a host that matches
+ hosts_connection_nolog. (In contrast, lost_incoming_connection applies only
+ when the closure is unexpected.) This applies to connections from local
+ processes that use -bs as well as to TCP/IP connections. If a connection is
+ dropped in the middle of a message, a log line is always written, whether
+ or not this selector is set, but otherwise nothing is written at the start
+ and end of connections unless this selector is enabled.
+
+ For TCP/IP connections to an Exim daemon, the current number of connections
+ is included in the log message for each new connection, but note that the
+ count is reset if the daemon is restarted. Also, because connections are
+ closed (and the closure is logged) in subprocesses, the count may not
+ include connections that have been closed but whose termination the daemon
+ has not yet noticed. Thus, while it is possible to match up the opening and
+ closing of connections in the log, the value of the logged counts may not
+ be entirely accurate.
+
+ * smtp_incomplete_transaction: When a mail transaction is aborted by RSET,
+ QUIT, loss of connection, or otherwise, the incident is logged, and the
+ message sender plus any accepted recipients are included in the log line.
+ This can provide evidence of dictionary attacks.
+
+ * smtp_no_mail: A line is written to the main log whenever an accepted SMTP
+ connection terminates without having issued a MAIL command. This includes
+ both the case when the connection is dropped, and the case when QUIT is
+ used. It does not include cases where the connection is rejected right at
+ the start (by an ACL, or because there are too many connections, or
+ whatever). These cases already have their own log lines.
+
+ The log line that is written contains the identity of the client in the
+ usual way, followed by D= and a time, which records the duration of the
+ connection. If the connection was authenticated, this fact is logged
+ exactly as it is for an incoming message, with an A= item. If the
+ connection was encrypted, CV=, DN=, and X= items may appear as they do for
+ an incoming message, controlled by the same logging options.
+
+ Finally, if any SMTP commands were issued during the connection, a C= item
+ is added to the line, listing the commands that were used. For example,
+
+ C=EHLO,QUIT
+
+ shows that the client issued QUIT straight after EHLO. If there were fewer
+ than 20 commands, they are all listed. If there were more than 20 commands,
+ the last 20 are listed, preceded by "...". However, with the default
+ setting of 10 for smtp_accept_max_nonmail, the connection will in any case
+ have been aborted before 20 non-mail commands are processed.
+
+ * smtp_mailauth: A third subfield with the authenticated sender,
+ colon-separated, is appended to the A= item for a message arrival or
+ delivery log line, if an AUTH argument to the SMTP MAIL command (see 33.2)
+ was accepted or used.
+
+ * smtp_protocol_error: A log line is written for every SMTP protocol error
+ encountered. Exim does not have perfect detection of all protocol errors
+ because of transmission delays and the use of pipelining. If PIPELINING has
+ been advertised to a client, an Exim server assumes that the client will
+ use it, and therefore it does not count "expected" errors (for example,
+ RCPT received after rejecting MAIL) as protocol errors.
+
+ * smtp_syntax_error: A log line is written for every SMTP syntax error
+ encountered. An unrecognized command is treated as a syntax error. For an
+ external connection, the host identity is given; for an internal connection
+ using -bs the sender identification (normally the calling user) is given.
+
+ * subject: The subject of the message is added to the arrival log line,
+ preceded by "T=" (T for "topic", since S is already used for "size"). Any
+ MIME "words" in the subject are decoded. The print_topbitchars option
+ specifies whether characters with values greater than 127 should be logged
+ unchanged, or whether they should be rendered as escape sequences.
+
+ * tls_certificate_verified: An extra item is added to <= and => log lines
+ when TLS is in use. The item is "CV=yes" if the peer's certificate was
+ verified using a CA trust anchor, "CA=dane" if using a DNS trust anchor,
+ and "CV=no" if not.
+
+ * tls_cipher: When a message is sent or received over an encrypted
+ connection, the cipher suite used is added to the log line, preceded by X=.
+
+ * tls_peerdn: When a message is sent or received over an encrypted
+ connection, and a certificate is supplied by the remote host, the peer DN
+ is added to the log line, preceded by DN=.
+
+ * tls_sni: When a message is received over an encrypted connection, and the
+ remote host provided the Server Name Indication extension, the SNI is added
+ to the log line, preceded by SNI=.
+
+ * unknown_in_list: This setting causes a log entry to be written when the
+ result of a list match is failure because a DNS lookup failed.
+
+
+53.16 Message log
+-----------------
+
+In addition to the general log files, Exim writes a log file for each message
+that it handles. The names of these per-message logs are the message ids, and
+they are kept in the msglog sub-directory of the spool directory. Each message
+log contains copies of the log lines that apply to the message. This makes it
+easier to inspect the status of an individual message without having to search
+the main log. A message log is deleted when processing of the message is
+complete, unless preserve_message_logs is set, but this should be used only
+with great care because they can fill up your disk very quickly.
+
+On a heavily loaded system, it may be desirable to disable the use of
+per-message logs, in order to reduce disk I/O. This can be done by setting the
+message_logs option false.
+
+
+
+===============================================================================
+54. EXIM UTILITIES
+
+A number of utility scripts and programs are supplied with Exim and are
+described in this chapter. There is also the Exim Monitor, which is covered in
+the next chapter. The utilities described here are:
+
+ 54.1 exiwhat list what Exim processes are doing
+ 54.2 exiqgrep grep the queue
+ 54.3 exiqsumm summarize the queue
+ 54.4 exigrep search the main log
+ 54.5 exipick select messages on various criteria
+ 54.6 exicyclog cycle (rotate) log files
+ 54.7 eximstats extract statistics from the log
+ 54.8 exim_checkaccess check address acceptance from given IP
+ 54.9 exim_dbmbuild build a DBM file
+ 54.10 exinext extract retry information
+ 54.12 exim_dumpdb dump a hints database
+ 54.13 exim_tidydb clean up a hints database
+ 54.14 exim_fixdb patch a hints database
+ 54.15 exim_lock lock a mailbox file
+
+Another utility that might be of use to sites with many MTAs is Tom Kistner's
+exilog. It provides log visualizations across multiple Exim servers. See https:
+//duncanthrax.net/exilog/ for details.
+
+
+54.1 Finding out what Exim processes are doing (exiwhat)
+--------------------------------------------------------
+
+On operating systems that can restart a system call after receiving a signal
+(most modern OS), an Exim process responds to the SIGUSR1 signal by writing a
+line describing what it is doing to the file exim-process.info in the Exim
+spool directory. The exiwhat script sends the signal to all Exim processes it
+can find, having first emptied the file. It then waits for one second to allow
+the Exim processes to react before displaying the results. In order to run
+exiwhat successfully you have to have sufficient privilege to send the signal
+to the Exim processes, so it is normally run as root.
+
+Warning: This is not an efficient process. It is intended for occasional use by
+system administrators. It is not sensible, for example, to set up a script that
+sends SIGUSR1 signals to Exim processes at short intervals.
+
+Unfortunately, the ps command that exiwhat uses to find Exim processes varies
+in different operating systems. Not only are different options used, but the
+format of the output is different. For this reason, there are some system
+configuration options that configure exactly how exiwhat works. If it doesn't
+seem to be working for you, check the following compile-time options:
+
+EXIWHAT_PS_CMD the command for running ps
+EXIWHAT_PS_ARG the argument for ps
+EXIWHAT_EGREP_ARG the argument for egrep to select from ps output
+EXIWHAT_KILL_ARG the argument for the kill command
+
+An example of typical output from exiwhat is
+
+164 daemon: -q1h, listening on port 25
+10483 running queue: waiting for 0tAycK-0002ij-00 (10492)
+10492 delivering 0tAycK-0002ij-00 to mail.ref.example
+ [10.19.42.42] (editor@ref.example)
+10592 handling incoming call from [192.168.243.242]
+10628 accepting a local non-SMTP message
+
+The first number in the output line is the process number. The third line has
+been split here, in order to fit it on the page.
+
+
+54.2 Selective queue listing (exiqgrep)
+---------------------------------------
+
+This utility is a Perl script contributed by Matt Hubbard. It runs
+
+exim -bpu
+
+or (in case -a switch is specified)
+
+exim -bp
+
+The -C option is used to specify an alternate exim.conf which might contain
+alternate exim configuration the queue management might be using.
+
+to obtain a queue listing, and then greps the output to select messages that
+match given criteria. The following selection options are available:
+
+-f <regex>
+
+ Match the sender address using a case-insensitive search. The field that is
+ tested is enclosed in angle brackets, so you can test for bounce messages
+ with
+
+ exiqgrep -f '^<>$'
+
+-r <regex>
+
+ Match a recipient address using a case-insensitive search. The field that
+ is tested is not enclosed in angle brackets.
+
+-s <regex>
+
+ Match against the size field.
+
+-y <seconds>
+
+ Match messages that are younger than the given time.
+
+-o <seconds>
+
+ Match messages that are older than the given time.
+
+-z
+
+ Match only frozen messages.
+
+-x
+
+ Match only non-frozen messages.
+
+-G <queuename>
+
+ Match only messages in the given queue. Without this, the default queue is
+ searched.
+
+The following options control the format of the output:
+
+-c
+
+ Display only the count of matching messages.
+
+-l
+
+ Long format - display the full message information as output by Exim. This
+ is the default.
+
+-i
+
+ Display message ids only.
+
+-b
+
+ Brief format - one line per message.
+
+-R
+
+ Display messages in reverse order.
+
+-a
+
+ Include delivered recipients in queue listing.
+
+There is one more option, -h, which outputs a list of options.
+
+
+54.3 Summarizing the queue (exiqsumm)
+-------------------------------------
+
+The exiqsumm utility is a Perl script which reads the output of "exim -bp" and
+produces a summary of the messages in the queue. Thus, you use it by running a
+command such as
+
+exim -bp | exiqsumm
+
+The output consists of one line for each domain that has messages waiting for
+it, as in the following example:
+
+3 2322 74m 66m msn.com.example
+
+Each line lists the number of pending deliveries for a domain, their total
+volume, and the length of time that the oldest and the newest messages have
+been waiting. Note that the number of pending deliveries is greater than the
+number of messages when messages have more than one recipient.
+
+A summary line is output at the end. By default the output is sorted on the
+domain name, but exiqsumm has the options -a and -c, which cause the output to
+be sorted by oldest message and by count of messages, respectively. There are
+also three options that split the messages for each domain into two or more
+subcounts: -b separates bounce messages, -f separates frozen messages, and -s
+separates messages according to their sender.
+
+The output of exim -bp contains the original addresses in the message, so this
+also applies to the output from exiqsumm. No domains from addresses generated
+by aliasing or forwarding are included (unless the one_time option of the
+redirect router has been used to convert them into "top level" addresses).
+
+
+54.4 Extracting specific information from the log (exigrep)
+-----------------------------------------------------------
+
+The exigrep utility is a Perl script that searches one or more main log files
+for entries that match a given pattern. When it finds a match, it extracts all
+the log entries for the relevant message, not just those that match the
+pattern. Thus, exigrep can extract complete log entries for a given message, or
+all mail for a given user, or for a given host, for example. The input files
+can be in Exim log format or syslog format. If a matching log line is not
+associated with a specific message, it is included in exigrep's output without
+any additional lines. The usage is:
+
+exigrep [-t<n>] [-I] [-l] [-M] [-v] <pattern> [<log file>] ...
+
+If no log filenames are given on the command line, the standard input is read.
+
+The -t argument specifies a number of seconds. It adds an additional condition
+for message selection. Messages that are complete are shown only if they spent
+more than <n> seconds in the queue.
+
+By default, exigrep does case-insensitive matching. The -I option makes it
+case-sensitive. This may give a performance improvement when searching large
+log files. Without -I, the Perl pattern matches use Perl's "/i" option; with -I
+they do not. In both cases it is possible to change the case sensitivity within
+the pattern by using "(?i)" or "(?-i)".
+
+The -l option means "literal", that is, treat all characters in the pattern as
+standing for themselves. Otherwise the pattern must be a Perl regular
+expression.
+
+The -v option inverts the matching condition. That is, a line is selected if it
+does not match the pattern.
+
+The -M options means "related messages". exigrep will show messages that are
+generated as a result/response to a message that exigrep matched normally.
+
+Example of -M: user_a sends a message to user_b, which generates a bounce back
+to user_b. If exigrep is used to search for "user_a", only the first message
+will be displayed. But if exigrep is used to search for "user_b", the first and
+the second (bounce) message will be displayed. Using -M with exigrep when
+searching for "user_a" will show both messages since the bounce is "related" to
+or a "result" of the first message that was found by the search term.
+
+If the location of a zcat command is known from the definition of ZCAT_COMMAND
+in Local/Makefile, exigrep automatically passes any file whose name ends in
+COMPRESS_SUFFIX through zcat as it searches it. If the ZCAT_COMMAND is not
+executable, exigrep tries to use autodetection of some well known compression
+extensions.
+
+
+54.5 Selecting messages by various criteria (exipick)
+-----------------------------------------------------
+
+John Jetmore's exipick utility is included in the Exim distribution. It lists
+messages from the queue according to a variety of criteria. For details of
+exipick's facilities, run exipick with the --help option.
+
+
+54.6 Cycling log files (exicyclog)
+----------------------------------
+
+The exicyclog script can be used to cycle (rotate) mainlog and rejectlog files.
+This is not necessary if only syslog is being used, or if you are using log
+files with datestamps in their names (see section 53.3). Some operating systems
+have their own standard mechanisms for log cycling, and these can be used
+instead of exicyclog if preferred. There are two command line options for
+exicyclog:
+
+ * -k <count> specifies the number of log files to keep, overriding the
+ default that is set when Exim is built. The default default is 10.
+
+ * -l <path> specifies the log file path, in the same format as Exim's
+ log_file_path option (for example, "/var/log/exim_%slog"), again overriding
+ the script's default, which is to find the setting from Exim's
+ configuration.
+
+Each time exicyclog is run the filenames get "shuffled down" by one. If the
+main log filename is mainlog (the default) then when exicyclog is run mainlog
+becomes mainlog.01, the previous mainlog.01 becomes mainlog.02 and so on, up to
+the limit that is set in the script or by the -k option. Log files whose
+numbers exceed the limit are discarded. Reject logs are handled similarly.
+
+If the limit is greater than 99, the script uses 3-digit numbers such as
+mainlog.001, mainlog.002, etc. If you change from a number less than 99 to one
+that is greater, or vice versa, you will have to fix the names of any existing
+log files.
+
+If no mainlog file exists, the script does nothing. Files that "drop off" the
+end are deleted. All files with numbers greater than 01 are compressed, using a
+compression command which is configured by the COMPRESS_COMMAND setting in
+Local/Makefile. It is usual to run exicyclog daily from a root crontab entry of
+the form
+
+1 0 * * * su exim -c /usr/exim/bin/exicyclog
+
+assuming you have used the name "exim" for the Exim user. You can run exicyclog
+as root if you wish, but there is no need.
+
+
+54.7 Mail statistics (eximstats)
+--------------------------------
+
+A Perl script called eximstats is provided for extracting statistical
+information from log files. The output is either plain text, or HTML.
+
+The eximstats script has been hacked about quite a bit over time. The latest
+version is the result of some extensive revision by Steve Campbell. A lot of
+information is given by default, but there are options for suppressing various
+parts of it. Following any options, the arguments to the script are a list of
+files, which should be main log files. For example:
+
+eximstats -nr /var/spool/exim/log/mainlog.01
+
+By default, eximstats extracts information about the number and volume of
+messages received from or delivered to various hosts. The information is sorted
+both by message count and by volume, and the top fifty hosts in each category
+are listed on the standard output. Similar information, based on email
+addresses or domains instead of hosts can be requested by means of various
+options. For messages delivered and received locally, similar statistics are
+also produced per user.
+
+The output also includes total counts and statistics about delivery errors, and
+histograms showing the number of messages received and deliveries made in each
+hour of the day. A delivery with more than one address in its envelope (for
+example, an SMTP transaction with more than one RCPT command) is counted as a
+single delivery by eximstats.
+
+Though normally more deliveries than receipts are reported (as messages may
+have multiple recipients), it is possible for eximstats to report more messages
+received than delivered, even though the queue is empty at the start and end of
+the period in question. If an incoming message contains no valid recipients, no
+deliveries are recorded for it. A bounce message is handled as an entirely
+separate message.
+
+eximstats always outputs a grand total summary giving the volume and number of
+messages received and deliveries made, and the number of hosts involved in each
+case. It also outputs the number of messages that were delayed (that is, not
+completely delivered at the first attempt), and the number that had at least
+one address that failed.
+
+The remainder of the output is in sections that can be independently disabled
+or modified by various options. It consists of a summary of deliveries by
+transport, histograms of messages received and delivered per time interval
+(default per hour), information about the time messages spent in the queue, a
+list of relayed messages, lists of the top fifty sending hosts, local senders,
+destination hosts, and destination local users by count and by volume, and a
+list of delivery errors that occurred.
+
+The relay information lists messages that were actually relayed, that is, they
+came from a remote host and were directly delivered to some other remote host,
+without being processed (for example, for aliasing or forwarding) locally.
+
+There are quite a few options for eximstats to control exactly what it outputs.
+These are documented in the Perl script itself, and can be extracted by running
+the command perldoc on the script. For example:
+
+perldoc /usr/exim/bin/eximstats
+
+
+54.8 Checking access policy (exim_checkaccess)
+----------------------------------------------
+
+The -bh command line argument allows you to run a fake SMTP session with
+debugging output, in order to check what Exim is doing when it is applying
+policy controls to incoming SMTP mail. However, not everybody is sufficiently
+familiar with the SMTP protocol to be able to make full use of -bh, and
+sometimes you just want to answer the question "Does this address have access?"
+without bothering with any further details.
+
+The exim_checkaccess utility is a "packaged" version of -bh. It takes two
+arguments, an IP address and an email address:
+
+exim_checkaccess 10.9.8.7 A.User@a.domain.example
+
+The utility runs a call to Exim with the -bh option, to test whether the given
+email address would be accepted in a RCPT command in a TCP/IP connection from
+the host with the given IP address. The output of the utility is either the
+word "accepted", or the SMTP error response, for example:
+
+Rejected:
+550 Relay not permitted
+
+When running this test, the utility uses "<>" as the envelope sender address
+for the MAIL command, but you can change this by providing additional options.
+These are passed directly to the Exim command. For example, to specify that the
+test is to be run with the sender address himself@there.example you can use:
+
+exim_checkaccess 10.9.8.7 A.User@a.domain.example \
+ -f himself@there.example
+
+Note that these additional Exim command line items must be given after the two
+mandatory arguments.
+
+Because the exim_checkaccess uses -bh, it does not perform callouts while
+running its checks. You can run checks that include callouts by using -bhc, but
+this is not yet available in a "packaged" form.
+
+
+54.9 Making DBM files (exim_dbmbuild)
+-------------------------------------
+
+The exim_dbmbuild program reads an input file containing keys and data in the
+format used by the lsearch lookup (see section 9.3). It writes a DBM file using
+the lower-cased alias names as keys and the remainder of the information as
+data. The lower-casing can be prevented by calling the program with the -nolc
+option.
+
+A terminating zero is included as part of the key string. This is expected by
+the dbm lookup type. However, if the option -nozero is given, exim_dbmbuild
+creates files without terminating zeroes in either the key strings or the data
+strings. The dbmnz lookup type can be used with such files.
+
+The program requires two arguments: the name of the input file (which can be a
+single hyphen to indicate the standard input), and the name of the output file.
+It creates the output under a temporary name, and then renames it if all went
+well.
+
+If the native DB interface is in use (USE_DB is set in a compile-time
+configuration file - this is common in free versions of Unix) the two filenames
+must be different, because in this mode the Berkeley DB functions create a
+single output file using exactly the name given. For example,
+
+exim_dbmbuild /etc/aliases /etc/aliases.db
+
+reads the system alias file and creates a DBM version of it in /etc/aliases.db.
+
+In systems that use the ndbm routines (mostly proprietary versions of Unix),
+two files are used, with the suffixes .dir and .pag. In this environment, the
+suffixes are added to the second argument of exim_dbmbuild, so it can be the
+same as the first. This is also the case when the Berkeley functions are used
+in compatibility mode (though this is not recommended), because in that case it
+adds a .db suffix to the filename.
+
+If a duplicate key is encountered, the program outputs a warning, and when it
+finishes, its return code is 1 rather than zero, unless the -noduperr option is
+used. By default, only the first of a set of duplicates is used - this makes it
+compatible with lsearch lookups. There is an option -lastdup which causes it to
+use the data for the last duplicate instead. There is also an option -nowarn,
+which stops it listing duplicate keys to stderr. For other errors, where it
+doesn't actually make a new file, the return code is 2.
+
+
+54.10 Finding individual retry times (exinext)
+----------------------------------------------
+
+A utility called exinext (mostly a Perl script) provides the ability to fish
+specific information out of the retry database. Given a mail domain (or a
+complete address), it looks up the hosts for that domain, and outputs any retry
+information for the hosts or for the domain. At present, the retry information
+is obtained by running exim_dumpdb (see below) and post-processing the output.
+For example:
+
+$ exinext piglet@milne.fict.example
+kanga.milne.example:192.168.8.1 error 146: Connection refused
+ first failed: 21-Feb-1996 14:57:34
+ last tried: 21-Feb-1996 14:57:34
+ next try at: 21-Feb-1996 15:02:34
+roo.milne.example:192.168.8.3 error 146: Connection refused
+ first failed: 20-Jan-1996 13:12:08
+ last tried: 21-Feb-1996 11:42:03
+ next try at: 21-Feb-1996 19:42:03
+ past final cutoff time
+
+You can also give exinext a local part, without a domain, and it will give any
+retry information for that local part in your default domain. A message id can
+be used to obtain retry information pertaining to a specific message. This
+exists only when an attempt to deliver a message to a remote host suffers a
+message-specific error (see section 49.2). exinext is not particularly
+efficient, but then it is not expected to be run very often.
+
+The exinext utility calls Exim to find out information such as the location of
+the spool directory. The utility has -C and -D options, which are passed on to
+the exim commands. The first specifies an alternate Exim configuration file,
+and the second sets macros for use within the configuration file. These
+features are mainly to help in testing, but might also be useful in
+environments where more than one configuration file is in use.
+
+
+54.11 Hints database maintenance
+--------------------------------
+
+Three utility programs are provided for maintaining the DBM files that Exim
+uses to contain its delivery hint information. Each program requires two
+arguments. The first specifies the name of Exim's spool directory, and the
+second is the name of the database it is to operate on. These are as follows:
+
+ * retry: the database of retry information
+
+ * wait-<transport name>: databases of information about messages waiting for
+ remote hosts
+
+ * callout: the callout cache
+
+ * ratelimit: the data for implementing the ratelimit ACL condition
+
+ * misc: other hints data
+
+The misc database is used for
+
+ * Serializing ETRN runs (when smtp_etrn_serialize is set)
+
+ * Serializing delivery to a specific host (when serialize_hosts is set in an
+ smtp transport)
+
+ * Limiting the concurrency of specific transports (when max_parallel is set
+ in a transport)
+
+
+54.12 exim_dumpdb
+-----------------
+
+The entire contents of a database are written to the standard output by the
+exim_dumpdb program, which has no options or arguments other than the spool and
+database names. For example, to dump the retry database:
+
+exim_dumpdb /var/spool/exim retry
+
+Two lines of output are produced for each entry:
+
+T:mail.ref.example:192.168.242.242 146 77 Connection refused
+31-Oct-1995 12:00:12 02-Nov-1995 12:21:39 02-Nov-1995 20:21:39 *
+
+The first item on the first line is the key of the record. It starts with one
+of the letters R, or T, depending on whether it refers to a routing or
+transport retry. For a local delivery, the next part is the local address; for
+a remote delivery it is the name of the remote host, followed by its failing IP
+address (unless retry_include_ip_address is set false on the smtp transport).
+If the remote port is not the standard one (port 25), it is added to the IP
+address. Then there follows an error code, an additional error code, and a
+textual description of the error.
+
+The three times on the second line are the time of first failure, the time of
+the last delivery attempt, and the computed time for the next attempt. The line
+ends with an asterisk if the cutoff time for the last retry rule has been
+exceeded.
+
+Each output line from exim_dumpdb for the wait-xxx databases consists of a host
+name followed by a list of ids for messages that are or were waiting to be
+delivered to that host. If there are a very large number for any one host,
+continuation records, with a sequence number added to the host name, may be
+seen. The data in these records is often out of date, because a message may be
+routed to several alternative hosts, and Exim makes no effort to keep
+cross-references.
+
+
+54.13 exim_tidydb
+-----------------
+
+The exim_tidydb utility program is used to tidy up the contents of a hints
+database. If run with no options, it removes all records that are more than 30
+days old. The age is calculated from the date and time that the record was last
+updated. Note that, in the case of the retry database, it is not the time since
+the first delivery failure. Information about a host that has been down for
+more than 30 days will remain in the database, provided that the record is
+updated sufficiently often.
+
+The cutoff date can be altered by means of the -t option, which must be
+followed by a time. For example, to remove all records older than a week from
+the retry database:
+
+exim_tidydb -t 7d /var/spool/exim retry
+
+Both the wait-xxx and retry databases contain items that involve message ids.
+In the former these appear as data in records keyed by host - they were
+messages that were waiting for that host - and in the latter they are the keys
+for retry information for messages that have suffered certain types of error.
+When exim_tidydb is run, a check is made to ensure that message ids in database
+records are those of messages that are still on the queue. Message ids for
+messages that no longer exist are removed from wait-xxx records, and if this
+leaves any records empty, they are deleted. For the retry database, records
+whose keys are non-existent message ids are removed. The exim_tidydb utility
+outputs comments on the standard output whenever it removes information from
+the database.
+
+Certain records are automatically removed by Exim when they are no longer
+needed, but others are not. For example, if all the MX hosts for a domain are
+down, a retry record is created for each one. If the primary MX host comes back
+first, its record is removed when Exim successfully delivers to it, but the
+records for the others remain because Exim has not tried to use those hosts.
+
+It is important, therefore, to run exim_tidydb periodically on all the hints
+databases. You should do this at a quiet time of day, because it requires a
+database to be locked (and therefore inaccessible to Exim) while it does its
+work. Removing records from a DBM file does not normally make the file smaller,
+but all the common DBM libraries are able to re-use the space that is released.
+After an initial phase of increasing in size, the databases normally reach a
+point at which they no longer get any bigger, as long as they are regularly
+tidied.
+
+Warning: If you never run exim_tidydb, the space used by the hints databases is
+likely to keep on increasing.
+
+
+54.14 exim_fixdb
+----------------
+
+The exim_fixdb program is a utility for interactively modifying databases. Its
+main use is for testing Exim, but it might also be occasionally useful for
+getting round problems in a live system. It has no options, and its interface
+is somewhat crude. On entry, it prompts for input with a right angle-bracket. A
+key of a database record can then be entered, and the data for that record is
+displayed.
+
+If "d" is typed at the next prompt, the entire record is deleted. For all
+except the retry database, that is the only operation that can be carried out.
+For the retry database, each field is output preceded by a number, and data for
+individual fields can be changed by typing the field number followed by new
+data, for example:
+
+> 4 951102:1000
+
+resets the time of the next delivery attempt. Time values are given as a
+sequence of digit pairs for year, month, day, hour, and minute. Colons can be
+used as optional separators.
+
+
+54.15 Mailbox maintenance (exim_lock)
+-------------------------------------
+
+The exim_lock utility locks a mailbox file using the same algorithm as Exim.
+For a discussion of locking issues, see section 26.3. Exim_lock can be used to
+prevent any modification of a mailbox by Exim or a user agent while
+investigating a problem. The utility requires the name of the file as its first
+argument. If the locking is successful, the second argument is run as a command
+(using C's system() function); if there is no second argument, the value of the
+SHELL environment variable is used; if this is unset or empty, /bin/sh is run.
+When the command finishes, the mailbox is unlocked and the utility ends. The
+following options are available:
+
+-fcntl
+
+ Use fcntl() locking on the open mailbox.
+
+-flock
+
+ Use flock() locking on the open mailbox, provided the operating system
+ supports it.
+
+-interval
+
+ This must be followed by a number, which is a number of seconds; it sets
+ the interval to sleep between retries (default 3).
+
+-lockfile
+
+ Create a lock file before opening the mailbox.
+
+-mbx
+
+ Lock the mailbox using MBX rules.
+
+-q
+
+ Suppress verification output.
+
+-retries
+
+ This must be followed by a number; it sets the number of times to try to
+ get the lock (default 10).
+
+-restore_time
+
+ This option causes exim_lock to restore the modified and read times to the
+ locked file before exiting. This allows you to access a locked mailbox (for
+ example, to take a backup copy) without disturbing the times that the user
+ subsequently sees.
+
+-timeout
+
+ This must be followed by a number, which is a number of seconds; it sets a
+ timeout to be used with a blocking fcntl() lock. If it is not set (the
+ default), a non-blocking call is used.
+
+-v
+
+ Generate verbose output.
+
+If none of -fcntl, -flock, -lockfile or -mbx are given, the default is to
+create a lock file and also to use fcntl() locking on the mailbox, which is the
+same as Exim's default. The use of -flock or -fcntl requires that the file be
+writeable; the use of -lockfile requires that the directory containing the file
+be writeable. Locking by lock file does not last forever; Exim assumes that a
+lock file is expired if it is more than 30 minutes old.
+
+The -mbx option can be used with either or both of -fcntl or -flock. It assumes
+-fcntl by default. MBX locking causes a shared lock to be taken out on the open
+mailbox, and an exclusive lock on the file /tmp/.n.m where n and m are the
+device number and inode number of the mailbox file. When the locking is
+released, if an exclusive lock can be obtained for the mailbox, the file in /
+tmp is deleted.
+
+The default output contains verification of the locking that takes place. The
+-v option causes some additional information to be given. The -q option
+suppresses all output except error messages.
+
+A command such as
+
+exim_lock /var/spool/mail/spqr
+
+runs an interactive shell while the file is locked, whereas
+
+exim_lock -q /var/spool/mail/spqr <<End
+<some commands>
+End
+
+runs a specific non-interactive sequence of commands while the file is locked,
+suppressing all verification output. A single command can be run by a command
+such as
+
+exim_lock -q /var/spool/mail/spqr \
+ "cp /var/spool/mail/spqr /some/where"
+
+Note that if a command is supplied, it must be entirely contained within the
+second argument - hence the quotes.
+
+
+
+===============================================================================
+55. THE EXIM MONITOR
+
+The Exim monitor is an application which displays in an X window information
+about the state of Exim's queue and what Exim is doing. An admin user can
+perform certain operations on messages from this GUI interface; however all
+such facilities are also available from the command line, and indeed, the
+monitor itself makes use of the command line to perform any actions requested.
+
+
+55.1 Running the monitor
+------------------------
+
+The monitor is started by running the script called eximon. This is a shell
+script that sets up a number of environment variables, and then runs the binary
+called eximon.bin. The default appearance of the monitor window can be changed
+by editing the Local/eximon.conf file created by editing exim_monitor/EDITME.
+Comments in that file describe what the various parameters are for.
+
+The parameters that get built into the eximon script can be overridden for a
+particular invocation by setting up environment variables of the same names,
+preceded by "EXIMON_". For example, a shell command such as
+
+EXIMON_LOG_DEPTH=400 eximon
+
+(in a Bourne-compatible shell) runs eximon with an overriding setting of the
+LOG_DEPTH parameter. If EXIMON_LOG_FILE_PATH is set in the environment, it
+overrides the Exim log file configuration. This makes it possible to have
+eximon tailing log data that is written to syslog, provided that MAIL.INFO
+syslog messages are routed to a file on the local host.
+
+X resources can be used to change the appearance of the window in the normal
+way. For example, a resource setting of the form
+
+Eximon*background: gray94
+
+changes the colour of the background to light grey rather than white. The
+stripcharts are drawn with both the data lines and the reference lines in
+black. This means that the reference lines are not visible when on top of the
+data. However, their colour can be changed by setting a resource called
+"highlight" (an odd name, but that's what the Athena stripchart widget uses).
+For example, if your X server is running Unix, you could set up lighter
+reference lines in the stripcharts by obeying
+
+xrdb -merge <<End
+Eximon*highlight: gray
+End
+
+In order to see the contents of messages in the queue, and to operate on them,
+eximon must either be run as root or by an admin user.
+
+The command-line parameters of eximon are passed to eximon.bin and may contain
+X11 resource parameters interpreted by the X11 library. In addition, if the
+first parameter starts with the string "gdb" then it is removed and the binary
+is invoked under gdb (the parameter is used as the gdb command-name, so
+versioned variants of gdb can be invoked).
+
+The monitor's window is divided into three parts. The first contains one or
+more stripcharts and two action buttons, the second contains a "tail" of the
+main log file, and the third is a display of the queue of messages awaiting
+delivery, with two more action buttons. The following sections describe these
+different parts of the display.
+
+
+55.2 The stripcharts
+--------------------
+
+The first stripchart is always a count of messages in the queue. Its name can
+be configured by setting QUEUE_STRIPCHART_NAME in the Local/eximon.conf file.
+The remaining stripcharts are defined in the configuration script by regular
+expression matches on log file entries, making it possible to display, for
+example, counts of messages delivered to certain hosts or using certain
+transports. The supplied defaults display counts of received and delivered
+messages, and of local and SMTP deliveries. The default period between
+stripchart updates is one minute; this can be adjusted by a parameter in the
+Local/eximon.conf file.
+
+The stripchart displays rescale themselves automatically as the value they are
+displaying changes. There are always 10 horizontal lines in each chart; the
+title string indicates the value of each division when it is greater than one.
+For example, "x2" means that each division represents a value of 2.
+
+It is also possible to have a stripchart which shows the percentage fullness of
+a particular disk partition, which is useful when local deliveries are confined
+to a single partition.
+
+This relies on the availability of the statvfs() function or equivalent in the
+operating system. Most, but not all versions of Unix that support Exim have
+this. For this particular stripchart, the top of the chart always represents
+100%, and the scale is given as "x10%". This chart is configured by setting
+SIZE_STRIPCHART and (optionally) SIZE_STRIPCHART_NAME in the Local/eximon.conf
+file.
+
+
+55.3 Main action buttons
+------------------------
+
+Below the stripcharts there is an action button for quitting the monitor. Next
+to this is another button marked "Size". They are placed here so that shrinking
+the window to its default minimum size leaves just the queue count stripchart
+and these two buttons visible. Pressing the "Size" button causes the window to
+expand to its maximum size, unless it is already at the maximum, in which case
+it is reduced to its minimum.
+
+When expanding to the maximum, if the window cannot be fully seen where it
+currently is, it is moved back to where it was the last time it was at full
+size. When it is expanding from its minimum size, the old position is
+remembered, and next time it is reduced to the minimum it is moved back there.
+
+The idea is that you can keep a reduced window just showing one or two
+stripcharts at a convenient place on your screen, easily expand it to show the
+full window when required, and just as easily put it back to what it was. The
+idea is copied from what the twm window manager does for its f.fullzoom action.
+The minimum size of the window can be changed by setting the MIN_HEIGHT and
+MIN_WIDTH values in Local/eximon.conf.
+
+Normally, the monitor starts up with the window at its full size, but it can be
+built so that it starts up with the window at its smallest size, by setting
+START_SMALL=yes in Local/eximon.conf.
+
+
+55.4 The log display
+--------------------
+
+The second section of the window is an area in which a display of the tail of
+the main log is maintained. To save space on the screen, the timestamp on each
+log line is shortened by removing the date and, if log_timezone is set, the
+timezone. The log tail is not available when the only destination for logging
+data is syslog, unless the syslog lines are routed to a local file whose name
+is passed to eximon via the EXIMON_LOG_FILE_PATH environment variable.
+
+The log sub-window has a scroll bar at its lefthand side which can be used to
+move back to look at earlier text, and the up and down arrow keys also have a
+scrolling effect. The amount of log that is kept depends on the setting of
+LOG_BUFFER in Local/eximon.conf, which specifies the amount of memory to use.
+When this is full, the earlier 50% of data is discarded - this is much more
+efficient than throwing it away line by line. The sub-window also has a
+horizontal scroll bar for accessing the ends of long log lines. This is the
+only means of horizontal scrolling; the right and left arrow keys are not
+available. Text can be cut from this part of the window using the mouse in the
+normal way. The size of this subwindow is controlled by parameters in the
+configuration file Local/eximon.conf.
+
+Searches of the text in the log window can be carried out by means of the ^R
+and ^S keystrokes, which default to a reverse and a forward search,
+respectively. The search covers only the text that is displayed in the window.
+It cannot go further back up the log.
+
+The point from which the search starts is indicated by a caret marker. This is
+normally at the end of the text in the window, but can be positioned explicitly
+by pointing and clicking with the left mouse button, and is moved automatically
+by a successful search. If new text arrives in the window when it is scrolled
+back, the caret remains where it is, but if the window is not scrolled back,
+the caret is moved to the end of the new text.
+
+Pressing ^R or ^S pops up a window into which the search text can be typed.
+There are buttons for selecting forward or reverse searching, for carrying out
+the search, and for cancelling. If the "Search" button is pressed, the search
+happens and the window remains so that further searches can be done. If the
+"Return" key is pressed, a single search is done and the window is closed. If ^
+C is typed the search is cancelled.
+
+The searching facility is implemented using the facilities of the Athena text
+widget. By default this pops up a window containing both "search" and "replace"
+options. In order to suppress the unwanted "replace" portion for eximon, a
+modified version of the TextPop widget is distributed with Exim. However, the
+linkers in BSDI and HP-UX seem unable to handle an externally provided version
+of TextPop when the remaining parts of the text widget come from the standard
+libraries. The compile-time option EXIMON_TEXTPOP can be unset to cut out the
+modified TextPop, making it possible to build Eximon on these systems, at the
+expense of having unwanted items in the search popup window.
+
+
+55.5 The queue display
+----------------------
+
+The bottom section of the monitor window contains a list of all messages that
+are in the queue, which includes those currently being received or delivered,
+as well as those awaiting delivery. The size of this subwindow is controlled by
+parameters in the configuration file Local/eximon.conf, and the frequency at
+which it is updated is controlled by another parameter in the same file - the
+default is 5 minutes, since queue scans can be quite expensive. However, there
+is an "Update" action button just above the display which can be used to force
+an update of the queue display at any time.
+
+When a host is down for some time, a lot of pending mail can build up for it,
+and this can make it hard to deal with other messages in the queue. To help
+with this situation there is a button next to "Update" called "Hide". If
+pressed, a dialogue box called "Hide addresses ending with" is put up. If you
+type anything in here and press "Return", the text is added to a chain of such
+texts, and if every undelivered address in a message matches at least one of
+the texts, the message is not displayed.
+
+If there is an address that does not match any of the texts, all the addresses
+are displayed as normal. The matching happens on the ends of addresses so, for
+example, cam.ac.uk specifies all addresses in Cambridge, while
+xxx@foo.com.example specifies just one specific address. When any hiding has
+been set up, a button called "Unhide" is displayed. If pressed, it cancels all
+hiding. Also, to ensure that hidden messages do not get forgotten, a hide
+request is automatically cancelled after one hour.
+
+While the dialogue box is displayed, you can't press any buttons or do anything
+else to the monitor window. For this reason, if you want to cut text from the
+queue display to use in the dialogue box, you have to do the cutting before
+pressing the "Hide" button.
+
+The queue display contains, for each unhidden queued message, the length of
+time it has been in the queue, the size of the message, the message id, the
+message sender, and the first undelivered recipient, all on one line. If it is
+a bounce message, the sender is shown as "<>". If there is more than one
+recipient to which the message has not yet been delivered, subsequent ones are
+listed on additional lines, up to a maximum configured number, following which
+an ellipsis is displayed. Recipients that have already received the message are
+not shown.
+
+If a message is frozen, an asterisk is displayed at the left-hand side.
+
+The queue display has a vertical scroll bar, and can also be scrolled by means
+of the arrow keys. Text can be cut from it using the mouse in the normal way.
+The text searching facilities, as described above for the log window, are also
+available, but the caret is always moved to the end of the text when the queue
+display is updated.
+
+
+55.6 The queue menu
+-------------------
+
+If the shift key is held down and the left button is clicked when the mouse
+pointer is over the text for any message, an action menu pops up, and the first
+line of the queue display for the message is highlighted. This does not affect
+any selected text.
+
+If you want to use some other event for popping up the menu, you can set the
+MENU_EVENT parameter in Local/eximon.conf to change the default, or set
+EXIMON_MENU_EVENT in the environment before starting the monitor. The value set
+in this parameter is a standard X event description. For example, to run eximon
+using ctrl rather than shift you could use
+
+EXIMON_MENU_EVENT='Ctrl<Btn1Down>' eximon
+
+The title of the menu is the message id, and it contains entries which act as
+follows:
+
+ * message log: The contents of the message log for the message are displayed
+ in a new text window.
+
+ * headers: Information from the spool file that contains the envelope
+ information and headers is displayed in a new text window. See chapter 57
+ for a description of the format of spool files.
+
+ * body: The contents of the spool file containing the body of the message are
+ displayed in a new text window. There is a default limit of 20,000 bytes to
+ the amount of data displayed. This can be changed by setting the BODY_MAX
+ option at compile time, or the EXIMON_BODY_MAX option at runtime.
+
+ * deliver message: A call to Exim is made using the -M option to request
+ delivery of the message. This causes an automatic thaw if the message is
+ frozen. The -v option is also set, and the output from Exim is displayed in
+ a new text window. The delivery is run in a separate process, to avoid
+ holding up the monitor while the delivery proceeds.
+
+ * freeze message: A call to Exim is made using the -Mf option to request that
+ the message be frozen.
+
+ * thaw message: A call to Exim is made using the -Mt option to request that
+ the message be thawed.
+
+ * give up on msg: A call to Exim is made using the -Mg option to request that
+ Exim gives up trying to deliver the message. A bounce message is generated
+ for any remaining undelivered addresses.
+
+ * remove message: A call to Exim is made using the -Mrm option to request
+ that the message be deleted from the system without generating a bounce
+ message.
+
+ * add recipient: A dialog box is displayed into which a recipient address can
+ be typed. If the address is not qualified and the QUALIFY_DOMAIN parameter
+ is set in Local/eximon.conf, the address is qualified with that domain.
+ Otherwise it must be entered as a fully qualified address. Pressing RETURN
+ causes a call to Exim to be made using the -Mar option to request that an
+ additional recipient be added to the message, unless the entry box is
+ empty, in which case no action is taken.
+
+ * mark delivered: A dialog box is displayed into which a recipient address
+ can be typed. If the address is not qualified and the QUALIFY_DOMAIN
+ parameter is set in Local/eximon.conf, the address is qualified with that
+ domain. Otherwise it must be entered as a fully qualified address. Pressing
+ RETURN causes a call to Exim to be made using the -Mmd option to mark the
+ given recipient address as already delivered, unless the entry box is
+ empty, in which case no action is taken.
+
+ * mark all delivered: A call to Exim is made using the -Mmad option to mark
+ all recipient addresses as already delivered.
+
+ * edit sender: A dialog box is displayed initialized with the current
+ sender's address. Pressing RETURN causes a call to Exim to be made using
+ the -Mes option to replace the sender address, unless the entry box is
+ empty, in which case no action is taken. If you want to set an empty sender
+ (as in bounce messages), you must specify it as "<>". Otherwise, if the
+ address is not qualified and the QUALIFY_DOMAIN parameter is set in Local/
+ eximon.conf, the address is qualified with that domain.
+
+When a delivery is forced, a window showing the -v output is displayed. In
+other cases when a call to Exim is made, if there is any output from Exim (in
+particular, if the command fails) a window containing the command and the
+output is displayed. Otherwise, the results of the action are normally apparent
+from the log and queue displays. However, if you set ACTION_OUTPUT=yes in Local
+/eximon.conf, a window showing the Exim command is always opened, even if no
+output is generated.
+
+The queue display is automatically updated for actions such as freezing and
+thawing, unless ACTION_QUEUE_UPDATE=no has been set in Local/eximon.conf. In
+this case the "Update" button has to be used to force an update of the display
+after one of these actions.
+
+In any text window that is displayed as result of a menu action, the normal
+cut-and-paste facility is available, and searching can be carried out using ^R
+and ^S, as described above for the log tail window.
+
+
+
+===============================================================================
+56. SECURITY CONSIDERATIONS
+
+This chapter discusses a number of issues concerned with security, some of
+which are also covered in other parts of this manual.
+
+For reasons that this author does not understand, some people have promoted
+Exim as a "particularly secure" mailer. Perhaps it is because of the existence
+of this chapter in the documentation. However, the intent of the chapter is
+simply to describe the way Exim works in relation to certain security concerns,
+not to make any specific claims about the effectiveness of its security as
+compared with other MTAs.
+
+What follows is a description of the way Exim is supposed to be. Best efforts
+have been made to try to ensure that the code agrees with the theory, but an
+absence of bugs can never be guaranteed. Any that are reported will get fixed
+as soon as possible.
+
+
+56.1 Building a more "hardened" Exim
+------------------------------------
+
+There are a number of build-time options that can be set in Local/Makefile to
+create Exim binaries that are "harder" to attack, in particular by a rogue Exim
+administrator who does not have the root password, or by someone who has
+penetrated the Exim (but not the root) account. These options are as follows:
+
+ * ALT_CONFIG_PREFIX can be set to a string that is required to match the
+ start of any filenames used with the -C option. When it is set, these
+ filenames are also not allowed to contain the sequence "/../". (However, if
+ the value of the -C option is identical to the value of CONFIGURE_FILE in
+ Local/Makefile, Exim ignores -C and proceeds as usual.) There is no default
+ setting for ALT_CONFIG_PREFIX.
+
+ If the permitted configuration files are confined to a directory to which
+ only root has access, this guards against someone who has broken into the
+ Exim account from running a privileged Exim with an arbitrary configuration
+ file, and using it to break into other accounts.
+
+ * If a non-trusted configuration file (i.e. not the default configuration
+ file or one which is trusted by virtue of being listed in the
+ TRUSTED_CONFIG_LIST file) is specified with -C, or if macros are given with
+ -D (but see the next item), then root privilege is retained only if the
+ caller of Exim is root. This locks out the possibility of testing a
+ configuration using -C right through message reception and delivery, even
+ if the caller is root. The reception works, but by that time, Exim is
+ running as the Exim user, so when it re-execs to regain privilege for the
+ delivery, the use of -C causes privilege to be lost. However, root can test
+ reception and delivery using two separate commands.
+
+ * The WHITELIST_D_MACROS build option declares some macros to be safe to
+ override with -D if the real uid is one of root, the Exim run-time user or
+ the CONFIGURE_OWNER, if defined. The potential impact of this option is
+ limited by requiring the run-time value supplied to -D to match a regex
+ that errs on the restrictive side. Requiring build-time selection of safe
+ macros is onerous but this option is intended solely as a transition
+ mechanism to permit previously-working configurations to continue to work
+ after release 4.73.
+
+ * If DISABLE_D_OPTION is defined, the use of the -D command line option is
+ disabled.
+
+ * FIXED_NEVER_USERS can be set to a colon-separated list of users that are
+ never to be used for any deliveries. This is like the never_users runtime
+ option, but it cannot be overridden; the runtime option adds additional
+ users to the list. The default setting is "root"; this prevents a non-root
+ user who is permitted to modify the runtime file from using Exim as a way
+ to get root.
+
+
+56.2 Root privilege
+-------------------
+
+The Exim binary is normally setuid to root, which means that it gains root
+privilege (runs as root) when it starts execution. In some special cases (for
+example, when the daemon is not in use and there are no local deliveries), it
+may be possible to run Exim setuid to some user other than root. This is
+discussed in the next section. However, in most installations, root privilege
+is required for two things:
+
+ * To set up a socket connected to the standard SMTP port (25) when
+ initialising the listening daemon. If Exim is run from inetd, this
+ privileged action is not required.
+
+ * To be able to change uid and gid in order to read users' .forward files and
+ perform local deliveries as the receiving user or as specified in the
+ configuration.
+
+It is not necessary to be root to do any of the other things Exim does, such as
+receiving messages and delivering them externally over SMTP, and it is
+obviously more secure if Exim does not run as root except when necessary. For
+this reason, a user and group for Exim to use must be defined in Local/Makefile
+. These are known as "the Exim user" and "the Exim group". Their values can be
+changed by the runtime configuration, though this is not recommended. Often a
+user called exim is used, but some sites use mail or another user name
+altogether.
+
+Exim uses setuid() whenever it gives up root privilege. This is a permanent
+abdication; the process cannot regain root afterwards. Prior to release 4.00,
+seteuid() was used in some circumstances, but this is no longer the case.
+
+After a new Exim process has interpreted its command line options, it changes
+uid and gid in the following cases:
+
+ * If the -C option is used to specify an alternate configuration file, or if
+ the -D option is used to define macro values for the configuration, and the
+ calling process is not running as root, the uid and gid are changed to
+ those of the calling process. However, if DISABLE_D_OPTION is defined in
+ Local/Makefile, the -D option may not be used at all. If WHITELIST_D_MACROS
+ is defined in Local/Makefile, then some macro values can be supplied if the
+ calling process is running as root, the Exim run-time user or
+ CONFIGURE_OWNER, if defined.
+
+ * If the expansion test option (-be) or one of the filter testing options (
+ -bf or -bF) are used, the uid and gid are changed to those of the calling
+ process.
+
+ * If the process is not a daemon process or a queue runner process or a
+ delivery process or a process for testing address routing (started with -bt
+ ), the uid and gid are changed to the Exim user and group. This means that
+ Exim always runs under its own uid and gid when receiving messages. This
+ also applies when testing address verification (the -bv option) and testing
+ incoming message policy controls (the -bh option).
+
+ * For a daemon, queue runner, delivery, or address testing process, the uid
+ remains as root at this stage, but the gid is changed to the Exim group.
+
+The processes that initially retain root privilege behave as follows:
+
+ * A daemon process changes the gid to the Exim group and the uid to the Exim
+ user after setting up one or more listening sockets. The initgroups()
+ function is called, so that if the Exim user is in any additional groups,
+ they will be used during message reception.
+
+ * A queue runner process retains root privilege throughout its execution. Its
+ job is to fork a controlled sequence of delivery processes.
+
+ * A delivery process retains root privilege throughout most of its execution,
+ but any actual deliveries (that is, the transports themselves) are run in
+ subprocesses which always change to a non-root uid and gid. For local
+ deliveries this is typically the uid and gid of the owner of the mailbox;
+ for remote deliveries, the Exim uid and gid are used. Once all the delivery
+ subprocesses have been run, a delivery process changes to the Exim uid and
+ gid while doing post-delivery tidying up such as updating the retry
+ database and generating bounce and warning messages.
+
+ While the recipient addresses in a message are being routed, the delivery
+ process runs as root. However, if a user's filter file has to be processed,
+ this is done in a subprocess that runs under the individual user's uid and
+ gid. A system filter is run as root unless system_filter_user is set.
+
+ * A process that is testing addresses (the -bt option) runs as root so that
+ the routing is done in the same environment as a message delivery.
+
+
+56.3 Running Exim without privilege
+-----------------------------------
+
+Some installations like to run Exim in an unprivileged state for more of its
+operation, for added security. Support for this mode of operation is provided
+by the global option deliver_drop_privilege. When this is set, the uid and gid
+are changed to the Exim user and group at the start of a delivery process (and
+also queue runner and address testing processes). This means that address
+routing is no longer run as root, and the deliveries themselves cannot change
+to any other uid.
+
+Leaving the binary setuid to root, but setting deliver_drop_privilege means
+that the daemon can still be started in the usual way, and it can respond
+correctly to SIGHUP because the re-invocation regains root privilege.
+
+An alternative approach is to make Exim setuid to the Exim user and also setgid
+to the Exim group. If you do this, the daemon must be started from a root
+process. (Calling Exim from a root process makes it behave in the way it does
+when it is setuid root.) However, the daemon cannot restart itself after a
+SIGHUP signal because it cannot regain privilege.
+
+It is still useful to set deliver_drop_privilege in this case, because it stops
+Exim from trying to re-invoke itself to do a delivery after a message has been
+received. Such a re-invocation is a waste of resources because it has no
+effect.
+
+If restarting the daemon is not an issue (for example, if mua_wrapper is set,
+or inetd is being used instead of a daemon), having the binary setuid to the
+Exim user seems a clean approach, but there is one complication:
+
+In this style of operation, Exim is running with the real uid and gid set to
+those of the calling process, and the effective uid/gid set to Exim's values.
+Ideally, any association with the calling process' uid/gid should be dropped,
+that is, the real uid/gid should be reset to the effective values so as to
+discard any privileges that the caller may have. While some operating systems
+have a function that permits this action for a non-root effective uid, quite a
+number of them do not. Because of this lack of standardization, Exim does not
+address this problem at this time.
+
+For this reason, the recommended approach for "mostly unprivileged" running is
+to keep the Exim binary setuid to root, and to set deliver_drop_privilege. This
+also has the advantage of allowing a daemon to be used in the most
+straightforward way.
+
+If you configure Exim not to run delivery processes as root, there are a number
+of restrictions on what you can do:
+
+ * You can deliver only as the Exim user/group. You should explicitly use the
+ user and group options to override routers or local transports that
+ normally deliver as the recipient. This makes sure that configurations that
+ work in this mode function the same way in normal mode. Any implicit or
+ explicit specification of another user causes an error.
+
+ * Use of .forward files is severely restricted, such that it is usually not
+ worthwhile to include them in the configuration.
+
+ * Users who wish to use .forward would have to make their home directory and
+ the file itself accessible to the Exim user. Pipe and append-to-file
+ entries, and their equivalents in Exim filters, cannot be used. While they
+ could be enabled in the Exim user's name, that would be insecure and not
+ very useful.
+
+ * Unless the local user mailboxes are all owned by the Exim user (possible in
+ some POP3 or IMAP-only environments):
+
+ 1. They must be owned by the Exim group and be writeable by that group.
+ This implies you must set mode in the appendfile configuration, as well
+ as the mode of the mailbox files themselves.
+
+ 2. You must set no_check_owner, since most or all of the files will not be
+ owned by the Exim user.
+
+ 3. You must set file_must_exist, because Exim cannot set the owner
+ correctly on a newly created mailbox when unprivileged. This also
+ implies that new mailboxes need to be created manually.
+
+These restrictions severely restrict what can be done in local deliveries.
+However, there are no restrictions on remote deliveries. If you are running a
+gateway host that does no local deliveries, setting deliver_drop_privilege
+gives more security at essentially no cost.
+
+If you are using the mua_wrapper facility (see chapter 52),
+deliver_drop_privilege is forced to be true.
+
+
+56.4 Delivering to local files
+------------------------------
+
+Full details of the checks applied by appendfile before it writes to a file are
+given in chapter 26.
+
+
+56.5 Running local commands
+---------------------------
+
+There are a number of ways in which an administrator can configure Exim to run
+commands based upon received, untrustworthy, data. Further, in some
+configurations a user who can control a .forward file can also arrange to run
+commands. Configuration to check includes, but is not limited to:
+
+ * Use of use_shell in the pipe transport: various forms of shell command
+ injection may be possible with this option present. It is dangerous and
+ should be used only with considerable caution. Consider constraints which
+ whitelist allowed characters in a variable which is to be used in a pipe
+ transport that has use_shell enabled.
+
+ * A number of options such as forbid_filter_run, forbid_filter_perl,
+ forbid_filter_dlfunc and so forth which restrict facilities available to
+ .forward files in a redirect router. If Exim is running on a central mail
+ hub to which ordinary users do not have shell access, but home directories
+ are NFS mounted (for instance) then administrators should review the list
+ of these forbid options available, and should bear in mind that the options
+ that may need forbidding can change as new features are added between
+ releases.
+
+ * The ${run...} expansion item does not use a shell by default, but
+ administrators can configure use of /bin/sh as part of the command. Such
+ invocations should be viewed with prejudicial suspicion.
+
+ * Administrators who use embedded Perl are advised to explore how Perl's
+ taint checking might apply to their usage.
+
+ * Use of ${expand...} is somewhat analogous to shell's eval builtin and
+ administrators are well advised to view its use with suspicion, in case
+ (for instance) it allows a local-part to contain embedded Exim directives.
+
+ * Use of ${match_local_part...} and friends becomes more dangerous if Exim
+ was built with EXPAND_LISTMATCH_RHS defined: the second string in each can
+ reference arbitrary lists and files, rather than just being a list of
+ opaque strings. The EXPAND_LISTMATCH_RHS option was added and set false by
+ default because of real-world security vulnerabilities caused by its use
+ with untrustworthy data injected in, for SQL injection attacks. Consider
+ the use of the inlisti expansion condition instead.
+
+
+56.6 Trust in configuration data
+--------------------------------
+
+If configuration data for Exim can come from untrustworthy sources, there are
+some issues to be aware of:
+
+ * Use of ${expand...} may provide a path for shell injection attacks.
+
+ * Letting untrusted data provide a regular expression is unwise.
+
+ * Using ${match...} to apply a fixed regular expression against untrusted
+ data may result in pathological behaviour within PCRE. Be aware of what
+ "backtracking" means and consider options for being more strict with a
+ regular expression. Avenues to explore include limiting what can match
+ (avoiding "." when "[a-z0-9]" or other character class will do), use of
+ atomic grouping and possessive quantifiers or just not using regular
+ expressions against untrusted data.
+
+ * It can be important to correctly use ${quote:...}, ${quote_local_part:...}
+ and ${quote_<lookup-type>:...} expansion items to ensure that data is
+ correctly constructed.
+
+ * Some lookups might return multiple results, even though normal usage is
+ only expected to yield one result.
+
+
+56.7 IPv4 source routing
+------------------------
+
+Many operating systems suppress IP source-routed packets in the kernel, but
+some cannot be made to do this, so Exim does its own check. It logs incoming
+IPv4 source-routed TCP calls, and then drops them. Things are all different in
+IPv6. No special checking is currently done.
+
+
+56.8 The VRFY, EXPN, and ETRN commands in SMTP
+----------------------------------------------
+
+Support for these SMTP commands is disabled by default. If required, they can
+be enabled by defining suitable ACLs.
+
+
+56.9 Privileged users
+---------------------
+
+Exim recognizes two sets of users with special privileges. Trusted users are
+able to submit new messages to Exim locally, but supply their own sender
+addresses and information about a sending host. For other users submitting
+local messages, Exim sets up the sender address from the uid, and doesn't
+permit a remote host to be specified.
+
+However, an untrusted user is permitted to use the -f command line option in
+the special form -f <> to indicate that a delivery failure for the message
+should not cause an error report. This affects the message's envelope, but it
+does not affect the Sender: header. Untrusted users may also be permitted to
+use specific forms of address with the -f option by setting the
+untrusted_set_sender option.
+
+Trusted users are used to run processes that receive mail messages from some
+other mail domain and pass them on to Exim for delivery either locally, or over
+the Internet. Exim trusts a caller that is running as root, as the Exim user,
+as any user listed in the trusted_users configuration option, or under any
+group listed in the trusted_groups option.
+
+Admin users are permitted to do things to the messages on Exim's queue. They
+can freeze or thaw messages, cause them to be returned to their senders, remove
+them entirely, or modify them in various ways. In addition, admin users can run
+the Exim monitor and see all the information it is capable of providing, which
+includes the contents of files on the spool.
+
+By default, the use of the -M and -q options to cause Exim to attempt delivery
+of messages on its queue is restricted to admin users. This restriction can be
+relaxed by setting the no_prod_requires_admin option. Similarly, the use of -bp
+(and its variants) to list the contents of the queue is also restricted to
+admin users. This restriction can be relaxed by setting
+no_queue_list_requires_admin.
+
+Exim recognizes an admin user if the calling process is running as root or as
+the Exim user or if any of the groups associated with the calling process is
+the Exim group. It is not necessary actually to be running under the Exim
+group. However, if admin users who are not root or the Exim user are to access
+the contents of files on the spool via the Exim monitor (which runs
+unprivileged), Exim must be built to allow group read access to its spool
+files.
+
+By default, regular users are trusted to perform basic testing and
+introspection commands, as themselves. This setting can be tightened by setting
+the commandline_checks_require_admin option. This affects most of the checking
+options, such as -be and anything else -b*.
+
+
+56.10 Spool files
+-----------------
+
+Exim's spool directory and everything it contains is owned by the Exim user and
+set to the Exim group. The mode for spool files is defined in the Local/
+Makefile configuration file, and defaults to 0640. This means that any user who
+is a member of the Exim group can access these files.
+
+
+56.11 Use of argv[0]
+--------------------
+
+Exim examines the last component of argv[0], and if it matches one of a set of
+specific strings, Exim assumes certain options. For example, calling Exim with
+the last component of argv[0] set to "rsmtp" is exactly equivalent to calling
+it with the option -bS. There are no security implications in this.
+
+
+56.12 Use of %f formatting
+--------------------------
+
+The only use made of "%f" by Exim is in formatting load average values. These
+are actually stored in integer variables as 1000 times the load average.
+Consequently, their range is limited and so therefore is the length of the
+converted output.
+
+
+56.13 Embedded Exim path
+------------------------
+
+Exim uses its own path name, which is embedded in the code, only when it needs
+to re-exec in order to regain root privilege. Therefore, it is not root when it
+does so. If some bug allowed the path to get overwritten, it would lead to an
+arbitrary program's being run as exim, not as root.
+
+
+56.14 Dynamic module directory
+------------------------------
+
+Any dynamically loadable modules must be installed into the directory defined
+in "LOOKUP_MODULE_DIR" in Local/Makefile for Exim to permit loading it.
+
+
+56.15 Use of sprintf()
+----------------------
+
+A large number of occurrences of "sprintf" in the code are actually calls to
+string_sprintf(), a function that returns the result in malloc'd store. The
+intermediate formatting is done into a large fixed buffer by a function that
+runs through the format string itself, and checks the length of each conversion
+before performing it, thus preventing buffer overruns.
+
+The remaining uses of sprintf() happen in controlled circumstances where the
+output buffer is known to be sufficiently long to contain the converted string.
+
+
+56.16 Use of debug_printf() and log_write()
+-------------------------------------------
+
+Arbitrary strings are passed to both these functions, but they do their
+formatting by calling the function string_vformat(), which runs through the
+format string itself, and checks the length of each conversion.
+
+
+56.17 Use of strcat() and strcpy()
+----------------------------------
+
+These are used only in cases where the output buffer is known to be large
+enough to hold the result.
+
+
+
+===============================================================================
+57. FORMAT OF SPOOL FILES
+
+A message on Exim's queue consists of two files, whose names are the message id
+followed by -D and -H, respectively. The data portion of the message is kept in
+the -D file on its own. The message's envelope, status, and headers are all
+kept in the -H file, whose format is described in this chapter. Each of these
+two files contains the final component of its own name as its first line. This
+is insurance against disk crashes where the directory is lost but the files
+themselves are recoverable.
+
+The file formats may be changed, or new formats added, at any release. Spool
+files are not intended as an interface to other programs and should not be used
+as such.
+
+Some people are tempted into editing -D files in order to modify messages. You
+need to be extremely careful if you do this; it is not recommended and you are
+on your own if you do it. Here are some of the pitfalls:
+
+ * You must ensure that Exim does not try to deliver the message while you are
+ fiddling with it. The safest way is to take out a write lock on the -D
+ file, which is what Exim itself does, using fcntl(). If you update the file
+ in place, the lock will be retained. If you write a new file and rename it,
+ the lock will be lost at the instant of rename.
+
+ * If you change the number of lines in the file, the value of $body_linecount
+ , which is stored in the -H file, will be incorrect and can cause
+ incomplete transmission of messages or undeliverable messages.
+
+ * If the message is in MIME format, you must take care not to break it.
+
+ * If the message is cryptographically signed, any change will invalidate the
+ signature.
+
+All in all, modifying -D files is fraught with danger.
+
+Files whose names end with -J may also be seen in the input directory (or its
+subdirectories when split_spool_directory is set). These are journal files,
+used to record addresses to which the message has been delivered during the
+course of a delivery attempt. If there are still undelivered recipients at the
+end, the -H file is updated, and the -J file is deleted. If, however, there is
+some kind of crash (for example, a power outage) before this happens, the -J
+file remains in existence. When Exim next processes the message, it notices the
+-J file and uses it to update the -H file before starting the next delivery
+attempt.
+
+Files whose names end with -K or .eml may also be seen in the spool. These are
+temporaries used for DKIM or malware processing, when that is used. They should
+be tidied up by normal operations; any old ones are probably relics of crashes
+and can be removed.
+
+
+57.1 Format of the -H file
+--------------------------
+
+The second line of the -H file contains the login name for the uid of the
+process that called Exim to read the message, followed by the numerical uid and
+gid. For a locally generated message, this is normally the user who sent the
+message. For a message received over TCP/IP via the daemon, it is normally the
+Exim user.
+
+The third line of the file contains the address of the message's sender as
+transmitted in the envelope, contained in angle brackets. The sender address is
+empty for bounce messages. For incoming SMTP mail, the sender address is given
+in the MAIL command. For locally generated mail, the sender address is created
+by Exim from the login name of the current user and the configured
+qualify_domain. However, this can be overridden by the -f option or a leading
+"From " line if the caller is trusted, or if the supplied address is "<>" or an
+address that matches untrusted_set_senders.
+
+The fourth line contains two numbers. The first is the time that the message
+was received, in the conventional Unix form - the number of seconds since the
+start of the epoch. The second number is a count of the number of messages
+warning of delayed delivery that have been sent to the sender.
+
+There follow a number of lines starting with a hyphen. These can appear in any
+order, and are omitted when not relevant:
+
+-acl <number> <length>
+
+ This item is obsolete, and is not generated from Exim release 4.61 onwards;
+ -aclc and -aclm are used instead. However, -acl is still recognized, to
+ provide backward compatibility. In the old format, a line of this form is
+ present for every ACL variable that is not empty. The number identifies the
+ variable; the acl_cx variables are numbered 0-9 and the acl_mx variables
+ are numbered 10-19. The length is the length of the data string for the
+ variable. The string itself starts at the beginning of the next line, and
+ is followed by a newline character. It may contain internal newlines.
+
+-aclc <rest-of-name> <length>
+
+ A line of this form is present for every ACL connection variable that is
+ defined. Note that there is a space between -aclc and the rest of the name.
+ The length is the length of the data string for the variable. The string
+ itself starts at the beginning of the next line, and is followed by a
+ newline character. It may contain internal newlines.
+
+-aclm <rest-of-name> <length>
+
+ A line of this form is present for every ACL message variable that is
+ defined. Note that there is a space between -aclm and the rest of the name.
+ The length is the length of the data string for the variable. The string
+ itself starts at the beginning of the next line, and is followed by a
+ newline character. It may contain internal newlines.
+
+-active_hostname <hostname>
+
+ This is present if, when the message was received over SMTP, the value of
+ $smtp_active_hostname was different to the value of $primary_hostname.
+
+-allow_unqualified_recipient
+
+ This is present if unqualified recipient addresses are permitted in header
+ lines (to stop such addresses from being qualified if rewriting occurs at
+ transport time). Local messages that were input using -bnq and remote
+ messages from hosts that match recipient_unqualified_hosts set this flag.
+
+-allow_unqualified_sender
+
+ This is present if unqualified sender addresses are permitted in header
+ lines (to stop such addresses from being qualified if rewriting occurs at
+ transport time). Local messages that were input using -bnq and remote
+ messages from hosts that match sender_unqualified_hosts set this flag.
+
+-auth_id <text>
+
+ The id information for a message received on an authenticated SMTP
+ connection - the value of the $authenticated_id variable.
+
+-auth_sender <address>
+
+ The address of an authenticated sender - the value of the
+ $authenticated_sender variable.
+
+-body_linecount <number>
+
+ This records the number of lines in the body of the message, and is present
+ unless -spool_file_wireformat is.
+
+-body_zerocount <number>
+
+ This records the number of binary zero bytes in the body of the message,
+ and is present if the number is greater than zero.
+
+-deliver_firsttime
+
+ This is written when a new message is first added to the spool. When the
+ spool file is updated after a deferral, it is omitted.
+
+-frozen <time>
+
+ The message is frozen, and the freezing happened at <time>.
+
+-helo_name <text>
+
+ This records the host name as specified by a remote host in a HELO or EHLO
+ command.
+
+-host_address <address>.<port>
+
+ This records the IP address of the host from which the message was received
+ and the remote port number that was used. It is omitted for locally
+ generated messages.
+
+-host_auth <text>
+
+ If the message was received on an authenticated SMTP connection, this
+ records the name of the authenticator - the value of the
+ $sender_host_authenticated variable.
+
+-host_lookup_failed
+
+ This is present if an attempt to look up the sending host's name from its
+ IP address failed. It corresponds to the $host_lookup_failed variable.
+
+-host_name <text>
+
+ This records the name of the remote host from which the message was
+ received, if the host name was looked up from the IP address when the
+ message was being received. It is not present if no reverse lookup was
+ done.
+
+-ident <text>
+
+ For locally submitted messages, this records the login of the originating
+ user, unless it was a trusted user and the -oMt option was used to specify
+ an ident value. For messages received over TCP/IP, this records the ident
+ string supplied by the remote host, if any.
+
+-interface_address <address>.<port>
+
+ This records the IP address of the local interface and the port number
+ through which a message was received from a remote host. It is omitted for
+ locally generated messages.
+
+-local
+
+ The message is from a local sender.
+
+-localerror
+
+ The message is a locally-generated bounce message.
+
+-local_scan <string>
+
+ This records the data string that was returned by the local_scan() function
+ when the message was received - the value of the $local_scan_data variable.
+ It is omitted if no data was returned.
+
+-manual_thaw
+
+ The message was frozen but has been thawed manually, that is, by an
+ explicit Exim command rather than via the auto-thaw process.
+
+-N
+
+ A testing delivery process was started using the -N option to suppress any
+ actual deliveries, but delivery was deferred. At any further delivery
+ attempts, -N is assumed.
+
+-received_protocol
+
+ This records the value of the $received_protocol variable, which contains
+ the name of the protocol by which the message was received.
+
+-sender_set_untrusted
+
+ The envelope sender of this message was set by an untrusted local caller
+ (used to ensure that the caller is displayed in queue listings).
+
+-spam_score_int <number>
+
+ If a message was scanned by SpamAssassin, this is present. It records the
+ value of $spam_score_int.
+
+-spool_file_wireformat
+
+ The -D file for this message is in wire-format (for ESMTP CHUNKING) rather
+ than Unix-format. The line-ending is CRLF rather than newline. There is
+ still, however, no leading-dot-stuffing.
+
+-tls_certificate_verified
+
+ A TLS certificate was received from the client that sent this message, and
+ the certificate was verified by the server.
+
+-tls_cipher <cipher name>
+
+ When the message was received over an encrypted connection, this records
+ the name of the cipher suite that was used.
+
+-tls_peerdn <peer DN>
+
+ When the message was received over an encrypted connection, and a
+ certificate was received from the client, this records the Distinguished
+ Name from that certificate.
+
+Any of the above may have an extra hyphen prepended, to indicate the the
+corresponding data is untrusted.
+
+Following the options there is a list of those addresses to which the message
+is not to be delivered. This set of addresses is initialized from the command
+line when the -t option is used and extract_addresses_remove_arguments is set;
+otherwise it starts out empty. Whenever a successful delivery is made, the
+address is added to this set. The addresses are kept internally as a balanced
+binary tree, and it is a representation of that tree which is written to the
+spool file. If an address is expanded via an alias or forward file, the
+original address is added to the tree when deliveries to all its child
+addresses are complete.
+
+If the tree is empty, there is a single line in the spool file containing just
+the text "XX". Otherwise, each line consists of two letters, which are either Y
+or N, followed by an address. The address is the value for the node of the
+tree, and the letters indicate whether the node has a left branch and/or a
+right branch attached to it, respectively. If branches exist, they immediately
+follow. Here is an example of a three-node tree:
+
+YY darcy@austen.fict.example
+NN alice@wonderland.fict.example
+NN editor@thesaurus.ref.example
+
+After the non-recipients tree, there is a list of the message's recipients.
+This is a simple list, preceded by a count. It includes all the original
+recipients of the message, including those to whom the message has already been
+delivered. In the simplest case, the list contains one address per line. For
+example:
+
+4
+editor@thesaurus.ref.example
+darcy@austen.fict.example
+rdo@foundation
+alice@wonderland.fict.example
+
+However, when a child address has been added to the top-level addresses as a
+result of the use of the one_time option on a redirect router, each line is of
+the following form:
+
+<top-level address> <errors_to address> <length>,<parent number>#<flag bits>
+
+The 01 flag bit indicates the presence of the three other fields that follow
+the top-level address. Other bits may be used in future to support additional
+fields. The <parent number> is the offset in the recipients list of the
+original parent of the "one time" address. The first two fields are the
+envelope sender that is associated with this address and its length. If the
+length is zero, there is no special envelope sender (there are then two space
+characters in the line). A non-empty field can arise from a redirect router
+that has an errors_to setting.
+
+A blank line separates the envelope and status information from the headers
+which follow. A header may occupy several lines of the file, and to save effort
+when reading it in, each header is preceded by a number and an identifying
+character. The number is the number of characters in the header, including any
+embedded newlines and the terminating newline. The character is one of the
+following:
+
+<blank> header in which Exim has no special interest
+"B" Bcc: header
+"C" Cc: header
+"F" From: header
+"I" Message-id: header
+"P" Received: header - P for "postmark"
+"R" Reply-To: header
+"S" Sender: header
+"T" To: header
+"*" replaced or deleted header
+
+Deleted or replaced (rewritten) headers remain in the spool file for debugging
+purposes. They are not transmitted when the message is delivered. Here is a
+typical set of headers:
+
+111P Received: by hobbit.fict.example with local (Exim 4.00)
+id 14y9EI-00026G-00; Fri, 11 May 2001 10:28:59 +0100
+049 Message-Id: <E14y9EI-00026G-00@hobbit.fict.example>
+038* X-rewrote-sender: bb@hobbit.fict.example
+042* From: Bilbo Baggins <bb@hobbit.fict.example>
+049F From: Bilbo Baggins <B.Baggins@hobbit.fict.example>
+099* To: alice@wonderland.fict.example, rdo@foundation,
+darcy@austen.fict.example, editor@thesaurus.ref.example
+104T To: alice@wonderland.fict.example, rdo@foundation.example,
+darcy@austen.fict.example, editor@thesaurus.ref.example
+038 Date: Fri, 11 May 2001 10:28:59 +0100
+
+The asterisked headers indicate that the envelope sender, From: header, and To:
+header have been rewritten, the last one because routing expanded the
+unqualified domain foundation.
+
+
+57.2 Format of the -D file
+--------------------------
+
+The data file is traditionally in Unix-standard format: lines are ended with an
+ASCII newline character. However, when the spool_wireformat main option is used
+some -D files can have an alternate format. This is flagged by a
+-spool_file_wireformat line in the corresponding -H file. The -D file lines
+(not including the first name-component line) are suitable for direct copying
+to the wire when transmitting using the ESMTP CHUNKING option, meaning lower
+processing overhead. Lines are terminated with an ASCII CRLF pair. There is no
+dot-stuffing (and no dot-termination).
+
+
+
+===============================================================================
+58. DKIM, SPF AND DMARC
+
+
+58.1 DKIM (DomainKeys Identified Mail)
+--------------------------------------
+
+DKIM is a mechanism by which messages sent by some entity can be provably
+linked to a domain which that entity controls. It permits reputation to be
+tracked on a per-domain basis, rather than merely upon source IP address. DKIM
+is documented in RFC 6376.
+
+As DKIM relies on the message being unchanged in transit, messages handled by a
+mailing-list (which traditionally adds to the message) will not match any
+original DKIM signature.
+
+DKIM support is compiled into Exim by default if TLS support is present. It can
+be disabled by setting DISABLE_DKIM=yes in Local/Makefile.
+
+Exim's DKIM implementation allows for
+
+ 1. Signing outgoing messages: This function is implemented in the SMTP
+ transport. It can co-exist with all other Exim features (including
+ transport filters) except cutthrough delivery.
+
+ 2. Verifying signatures in incoming messages: This is implemented by an
+ additional ACL (acl_smtp_dkim), which can be called several times per
+ message, with different signature contexts.
+
+In typical Exim style, the verification implementation does not include any
+default "policy". Instead it enables you to build your own policy using Exim's
+standard controls.
+
+Please note that verification of DKIM signatures in incoming mail is turned on
+by default for logging (in the <= line) purposes.
+
+Additional log detail can be enabled using the dkim_verbose log_selector. When
+set, for each signature in incoming email, exim will log a line displaying the
+most important signature details, and the signature status. Here is an example
+(with line-breaks added for clarity):
+
+2009-09-09 10:22:28 1MlIRf-0003LU-U3 DKIM:
+ d=facebookmail.com s=q1-2009b
+ c=relaxed/relaxed a=rsa-sha1
+ i=@facebookmail.com t=1252484542 [verification succeeded]
+
+You might want to turn off DKIM verification processing entirely for internal
+or relay mail sources. To do that, set the dkim_disable_verify ACL control
+modifier. This should typically be done in the RCPT ACL, at points where you
+accept mail from relay sources (internal hosts or authenticated senders).
+
+
+58.2 Signing outgoing messages
+------------------------------
+
+For signing to be usable you must have published a DKIM record in DNS. Note
+that RFC 8301 (which does not cover EC keys) says:
+
+rsa-sha1 MUST NOT be used for signing or verifying.
+
+Signers MUST use RSA keys of at least 1024 bits for all keys.
+Signers SHOULD use RSA keys of at least 2048 bits.
+
+Note also that the key content (the 'p=' field) in the DNS record is different
+between RSA and EC keys; for the former it is the base64 of the ASN.1 for the
+RSA public key (equivalent to the private-key .pem with the header/trailer
+stripped) but for EC keys it is the base64 of the pure key; no ASN.1 wrapping.
+
+Signing is enabled by setting private options on the SMTP transport. These
+options take (expandable) strings as arguments.
+
++-------------------------------------------------+
+|dkim_domain|Use: smtp|Type: string|Default: list*|
++-------------------------------------------------+
+
+The domain(s) you want to sign with. After expansion, this can be a list. Each
+element in turn, lowercased, is put into the $dkim_domain expansion variable
+while expanding the remaining signing options. If it is empty after expansion,
+DKIM signing is not done, and no error will result even if dkim_strict is set.
+
++---------------------------------------------------+
+|dkim_selector|Use: smtp|Type: string|Default: list*|
++---------------------------------------------------+
+
+This sets the key selector string. After expansion, which can use $dkim_domain,
+this can be a list. Each element in turn is put in the expansion variable
+$dkim_selector which may be used in the dkim_private_key option along with
+$dkim_domain. If the option is empty after expansion, DKIM signing is not done
+for this domain, and no error will result even if dkim_strict is set.
+
++-------------------------------------------------------+
+|dkim_private_key|Use: smtp|Type: string*|Default: unset|
++-------------------------------------------------------+
+
+This sets the private key to use. You can use the $dkim_domain and
+$dkim_selector expansion variables to determine the private key to use. The
+result can either
+
+ * be a valid RSA private key in ASCII armor (.pem file), including line
+ breaks
+
+ * with GnuTLS 3.6.0 or OpenSSL 1.1.1 or later, be a valid Ed25519 private key
+ (same format as above)
+
+ * start with a slash, in which case it is treated as a file that contains the
+ private key
+
+ * be "0", "false" or the empty string, in which case the message will not be
+ signed. This case will not result in an error, even if dkim_strict is set.
+
+To generate keys under OpenSSL:
+
+openssl genrsa -out dkim_rsa.private 2048
+openssl rsa -in dkim_rsa.private -out /dev/stdout -pubout -outform PEM
+
+The result file from the first command should be retained, and this option set
+to use it. Take the base-64 lines from the output of the second command,
+concatenated, for the DNS TXT record. See section 3.6 of RFC6376 for the record
+specification.
+
+Under GnuTLS:
+
+certtool --generate-privkey --rsa --bits=2048 --password='' -8 --outfile=dkim_rsa.private
+certtool --load-privkey=dkim_rsa.private --pubkey-info
+
+Note that RFC 8301 says:
+
+Signers MUST use RSA keys of at least 1024 bits for all keys.
+Signers SHOULD use RSA keys of at least 2048 bits.
+
+EC keys for DKIM are defined by RFC 8463. They are considerably smaller than
+RSA keys for equivalent protection. As they are a recent development, users
+should consider dual-signing (by setting a list of selectors, and an expansion
+for this option) for some transition period. The "_CRYPTO_SIGN_ED25519" macro
+will be defined if support is present for EC keys.
+
+OpenSSL 1.1.1 and GnuTLS 3.6.0 can create Ed25519 private keys:
+
+openssl genpkey -algorithm ed25519 -out dkim_ed25519.private
+certtool --generate-privkey --key-type=ed25519 --outfile=dkim_ed25519.private
+
+To produce the required public key value for a DNS record:
+
+openssl pkey -outform DER -pubout -in dkim_ed25519.private | tail -c +13 | base64
+certtool --load_privkey=dkim_ed25519.private --pubkey_info --outder | tail -c +13 | base64
+
+Exim also supports an alternate format of Ed25519 keys in DNS which was a
+candidate during development of the standard, but not adopted. A future release
+will probably drop that support.
+
++-------------------------------------------------+
+|dkim_hash|Use: smtp|Type: string*|Default: sha256|
++-------------------------------------------------+
+
+Can be set to any one of the supported hash methods, which are:
+
+ * "sha1" - should not be used, is old and insecure
+
+ * "sha256" - the default
+
+ * "sha512" - possibly more secure but less well supported
+
+Note that RFC 8301 says:
+
+rsa-sha1 MUST NOT be used for signing or verifying.
+
++----------------------------------------------------+
+|dkim_identity|Use: smtp|Type: string*|Default: unset|
++----------------------------------------------------+
+
+If set after expansion, the value is used to set an "i=" tag in the signing
+header. The DKIM standards restrict the permissible syntax of this optional tag
+to a mail address, with possibly-empty local part, an @, and a domain identical
+to or subdomain of the "d=" tag value. Note that Exim does not check the value.
+
++-------------------------------------------------+
+|dkim_canon|Use: smtp|Type: string*|Default: unset|
++-------------------------------------------------+
+
+This option sets the canonicalization method used when signing a message. The
+DKIM RFC currently supports two methods: "simple" and "relaxed". The option
+defaults to "relaxed" when unset. Note: the current implementation only
+supports signing with the same canonicalization method for both headers and
+body.
+
++--------------------------------------------------+
+|dkim_strict|Use: smtp|Type: string*|Default: unset|
++--------------------------------------------------+
+
+This option defines how Exim behaves when signing a message that should be
+signed fails for some reason. When the expansion evaluates to either "1" or
+"true", Exim will defer. Otherwise Exim will send the message unsigned. You can
+use the $dkim_domain and $dkim_selector expansion variables here.
+
++------------------------------------------------------------+
+|dkim_sign_headers|Use: smtp|Type: string*|Default: see below|
++------------------------------------------------------------+
+
+If set, this option must expand to a colon-separated list of header names.
+Headers with these names, or the absence or such a header, will be included in
+the message signature. When unspecified, the header names listed in RFC4871
+will be used, whether or not each header is present in the message. The default
+list is available for the expansion in the macro "_DKIM_SIGN_HEADERS"
+
+and an oversigning variant is in "_DKIM_OVERSIGN_HEADERS".
+
+If a name is repeated, multiple headers by that name (or the absence thereof)
+will be signed. The textually later headers in the headers part of the message
+are signed first, if there are multiples.
+
+A name can be prefixed with either an "=" or a "+" character. If an "=" prefix
+is used, all headers that are present with this name will be signed. If a "+"
+prefix if used, all headers that are present with this name will be signed, and
+one signature added for a missing header with the name will be appended.
+
++-------------------------------------------------------+
+|dkim_timestamps|Use: smtp|Type: integer*|Default: unset|
++-------------------------------------------------------+
+
+This option controls the inclusion of timestamp information in the signature.
+If not set, no such information will be included. Otherwise, must be an
+unsigned number giving an offset in seconds from the current time for the
+expiry tag (eg. 1209600 for two weeks); both creation (t=) and expiry (x=) tags
+will be included.
+
+RFC 6376 lists these tags as RECOMMENDED.
+
+
+58.3 Verifying DKIM signatures in incoming mail
+-----------------------------------------------
+
+Verification of DKIM signatures in SMTP incoming email is done for all messages
+for which an ACL control dkim_disable_verify has not been set. Individual
+classes of signature algorithm can be ignored by changing the main options
+dkim_verify_hashes or dkim_verify_keytypes. The dkim_verify_minimal option can
+be set to cease verification processing for a message once the first passing
+signature is found.
+
+Performing verification sets up information used by the authresults expansion
+item.
+
+For most purposes the default option settings suffice and the remainder of this
+section can be ignored.
+
+The results of verification are made available to the acl_smtp_dkim ACL, which
+can examine and modify them. A missing ACL definition defaults to accept. By
+default, the ACL is called once for each syntactically(!) correct signature in
+the incoming message. If any ACL call does not accept, the message is not
+accepted. If a cutthrough delivery was in progress for the message, that is
+summarily dropped (having wasted the transmission effort).
+
+To evaluate the verification result in the ACL a large number of expansion
+variables containing the signature status and its details are set up during the
+runtime of the ACL.
+
+Calling the ACL only for existing signatures is not sufficient to build more
+advanced policies. For that reason, the main option dkim_verify_signers, and an
+expansion variable $dkim_signers exist.
+
+The main option dkim_verify_signers can be set to a colon-separated list of
+DKIM domains or identities for which the ACL acl_smtp_dkim is called. It is
+expanded when the message has been received. At this point, the expansion
+variable $dkim_signers already contains a colon-separated list of signer
+domains and identities for the message. When dkim_verify_signers is not
+specified in the main configuration, it defaults as:
+
+dkim_verify_signers = $dkim_signers
+
+This leads to the default behaviour of calling acl_smtp_dkim for each DKIM
+signature in the message. Current DKIM verifiers may want to explicitly call
+the ACL for known domains or identities. This would be achieved as follows:
+
+dkim_verify_signers = paypal.com:ebay.com:$dkim_signers
+
+This would result in acl_smtp_dkim always being called for "paypal.com" and
+"ebay.com", plus all domains and identities that have signatures in the
+message. You can also be more creative in constructing your policy. For
+example:
+
+dkim_verify_signers = $sender_address_domain:$dkim_signers
+
+If a domain or identity is listed several times in the (expanded) value of
+dkim_verify_signers, the ACL is only called once for that domain or identity.
+
+Note that if the option is set using untrustworthy data (such as the From:
+header) care should be taken to force lowercase for domains and for the domain
+part if identities. The default setting can be regarded as trustworthy in this
+respect.
+
+If multiple signatures match a domain (or identity), the ACL is called once for
+each matching signature.
+
+Inside the DKIM ACL, the following expansion variables are available (from most
+to least important):
+
+$dkim_cur_signer
+
+ The signer that is being evaluated in this ACL run. This can be a domain or
+ an identity. This is one of the list items from the expanded main option
+ dkim_verify_signers (see above).
+
+$dkim_verify_status
+
+ Within the DKIM ACL, a string describing the general status of the
+ signature. One of
+
+ + none: There is no signature in the message for the current domain or
+ identity (as reflected by $dkim_cur_signer).
+
+ + invalid: The signature could not be verified due to a processing error.
+ More detail is available in $dkim_verify_reason.
+
+ + fail: Verification of the signature failed. More detail is available in
+ $dkim_verify_reason.
+
+ + pass: The signature passed verification. It is valid.
+
+ This variable can be overwritten using an ACL 'set' modifier. This might,
+ for instance, be done to enforce a policy restriction on hash-method or
+ key-size:
+
+ warn condition = ${if eq {$dkim_verify_status}{pass}}
+ condition = ${if eq {${length_3:$dkim_algo}}{rsa}}
+ condition = ${if or {{eq {$dkim_algo}{rsa-sha1}} \
+ {< {$dkim_key_length}{1024}}}}
+ logwrite = NOTE: forcing DKIM verify fail (was pass)
+ set dkim_verify_status = fail
+ set dkim_verify_reason = hash too weak or key too short
+
+ So long as a DKIM ACL is defined (it need do no more than accept), after
+ all the DKIM ACL runs have completed, the value becomes a colon-separated
+ list of the values after each run. This is maintained for the mime, prdr
+ and data ACLs.
+
+$dkim_verify_reason
+
+ A string giving a little bit more detail when $dkim_verify_status is either
+ "fail" or "invalid". One of
+
+ + pubkey_unavailable (when $dkim_verify_status="invalid"): The public key
+ for the domain could not be retrieved. This may be a temporary problem.
+
+ + pubkey_syntax (when $dkim_verify_status="invalid"): The public key
+ record for the domain is syntactically invalid.
+
+ + bodyhash_mismatch (when $dkim_verify_status="fail"): The calculated
+ body hash does not match the one specified in the signature header.
+ This means that the message body was modified in transit.
+
+ + signature_incorrect (when $dkim_verify_status="fail"): The signature
+ could not be verified. This may mean that headers were modified,
+ re-written or otherwise changed in a way which is incompatible with
+ DKIM verification. It may of course also mean that the signature is
+ forged.
+
+ This variable can be overwritten, with any value, using an ACL 'set'
+ modifier.
+
+$dkim_domain
+
+ The signing domain. IMPORTANT: This variable is only populated if there is
+ an actual signature in the message for the current domain or identity (as
+ reflected by $dkim_cur_signer).
+
+$dkim_identity
+
+ The signing identity, if present. IMPORTANT: This variable is only
+ populated if there is an actual signature in the message for the current
+ domain or identity (as reflected by $dkim_cur_signer).
+
+$dkim_selector
+
+ The key record selector string.
+
+$dkim_algo
+
+ The algorithm used. One of 'rsa-sha1' or 'rsa-sha256'. If running under
+ GnuTLS 3.6.0 or OpenSSL 1.1.1 or later, may also be 'ed25519-sha256'. The
+ "_CRYPTO_SIGN_ED25519" macro will be defined if support is present for EC
+ keys.
+
+ Note that RFC 8301 says:
+
+ rsa-sha1 MUST NOT be used for signing or verifying.
+
+ DKIM signatures identified as having been signed with historic
+ algorithms (currently, rsa-sha1) have permanently failed evaluation
+
+ To enforce this you must either have a DKIM ACL which checks this variable
+ and overwrites the $dkim_verify_status variable as discussed above, or have
+ set the main option dkim_verify_hashes to exclude processing of such
+ signatures.
+
+$dkim_canon_body
+
+ The body canonicalization method. One of 'relaxed' or 'simple'.
+
+$dkim_canon_headers
+
+ The header canonicalization method. One of 'relaxed' or 'simple'.
+
+$dkim_copiedheaders
+
+ A transcript of headers and their values which are included in the
+ signature (copied from the 'z=' tag of the signature). Note that RFC6376
+ requires that verification fail if the From: header is not included in the
+ signature. Exim does not enforce this; sites wishing strict enforcement
+ should code the check explicitly.
+
+$dkim_bodylength
+
+ The number of signed body bytes. If zero ("0"), the body is unsigned. If no
+ limit was set by the signer, "9999999999999" is returned. This makes sure
+ that this variable always expands to an integer value. Note: The presence
+ of the signature tag specifying a signing body length is one possible route
+ to spoofing of valid DKIM signatures. A paranoid implementation might wish
+ to regard signature where this variable shows less than the "no limit"
+ return as being invalid.
+
+$dkim_created
+
+ UNIX timestamp reflecting the date and time when the signature was created.
+ When this was not specified by the signer, "0" is returned.
+
+$dkim_expires
+
+ UNIX timestamp reflecting the date and time when the signer wants the
+ signature to be treated as "expired". When this was not specified by the
+ signer, "9999999999999" is returned. This makes it possible to do useful
+ integer size comparisons against this value. Note that Exim does not check
+ this value.
+
+$dkim_headernames
+
+ A colon-separated list of names of headers included in the signature.
+
+$dkim_key_testing
+
+ "1" if the key record has the "testing" flag set, "0" if not.
+
+$dkim_key_nosubdomains
+
+ "1" if the key record forbids subdomaining, "0" otherwise.
+
+$dkim_key_srvtype
+
+ Service type (tag s=) from the key record. Defaults to "*" if not specified
+ in the key record.
+
+$dkim_key_granularity
+
+ Key granularity (tag g=) from the key record. Defaults to "*" if not
+ specified in the key record.
+
+$dkim_key_notes
+
+ Notes from the key record (tag n=).
+
+$dkim_key_length
+
+ Number of bits in the key.
+
+ Valid only once the key is loaded, which is at the time the header
+ signature is verified, which is after the body hash is.
+
+ Note that RFC 8301 says:
+
+ Verifiers MUST NOT consider signatures using RSA keys of
+ less than 1024 bits as valid signatures.
+
+ This is enforced by the default setting for the dkim_verify_min_keysizes
+ option.
+
+In addition, two ACL conditions are provided:
+
+dkim_signers
+
+ ACL condition that checks a colon-separated list of domains or identities
+ for a match against the domain or identity that the ACL is currently
+ verifying (reflected by $dkim_cur_signer). This is typically used to
+ restrict an ACL verb to a group of domains or identities. For example:
+
+ # Warn when Mail purportedly from GMail has no gmail signature
+ warn sender_domains = gmail.com
+ dkim_signers = gmail.com
+ dkim_status = none
+ log_message = GMail sender without gmail.com DKIM signature
+
+ Note that the above does not check for a total lack of DKIM signing; for
+ that check for empty $h_DKIM-Signature: in the data ACL.
+
+dkim_status
+
+ ACL condition that checks a colon-separated list of possible DKIM
+ verification results against the actual result of verification. This is
+ typically used to restrict an ACL verb to a list of verification outcomes,
+ for example:
+
+ deny sender_domains = paypal.com:paypal.de
+ dkim_signers = paypal.com:paypal.de
+ dkim_status = none:invalid:fail
+ message = Mail from Paypal with invalid/missing signature
+
+ The possible status keywords are: 'none','invalid','fail' and 'pass'.
+ Please see the documentation of the $dkim_verify_status expansion variable
+ above for more information of what they mean.
+
+
+58.4 SPF (Sender Policy Framework)
+----------------------------------
+
+SPF is a mechanism whereby a domain may assert which IP addresses may transmit
+messages with its domain in the envelope from, documented by RFC 7208. For more
+information on SPF see http://www.open-spf.org, a static copy of the http://
+openspf.org.
+
+Messages sent by a system not authorised will fail checking of such assertions.
+This includes retransmissions done by traditional forwarders.
+
+SPF verification support is built into Exim if SUPPORT_SPF=yes is set in Local/
+Makefile. The support uses the libspf2 library https://www.libspf2.org/. There
+is no Exim involvement in the transmission of messages; publishing certain DNS
+records is all that is required.
+
+For verification, an ACL condition and an expansion lookup are provided.
+Performing verification sets up information used by the authresults expansion
+item.
+
+The ACL condition "spf" can be used at or after the MAIL ACL. It takes as an
+argument a list of strings giving the outcome of the SPF check, and will
+succeed for any matching outcome. Valid strings are:
+
+pass
+
+ The SPF check passed, the sending host is positively verified by SPF.
+
+fail
+
+ The SPF check failed, the sending host is NOT allowed to send mail for the
+ domain in the envelope-from address.
+
+softfail
+
+ The SPF check failed, but the queried domain can't absolutely confirm that
+ this is a forgery.
+
+none
+
+ The queried domain does not publish SPF records.
+
+neutral
+
+ The SPF check returned a "neutral" state. This means the queried domain has
+ published a SPF record, but wants to allow outside servers to send mail
+ under its domain as well. This should be treated like "none".
+
+permerror
+
+ This indicates a syntax error in the SPF record of the queried domain. You
+ may deny messages when this occurs.
+
+temperror
+
+ This indicates a temporary error during all processing, including Exim's
+ SPF processing. You may defer messages when this occurs.
+
+You can prefix each string with an exclamation mark to invert its meaning, for
+example "!fail" will match all results but "fail". The string list is evaluated
+left-to-right, in a short-circuit fashion.
+
+Example:
+
+deny spf = fail
+ message = $sender_host_address is not allowed to send mail from \
+ ${if def:sender_address_domain \
+ {$sender_address_domain}{$sender_helo_name}}. \
+ Please see http://www.open-spf.org/Why;\
+ identity=${if def:sender_address_domain \
+ {$sender_address}{$sender_helo_name}};\
+ ip=$sender_host_address
+
+Note: The above mentioned URL may not be as helpful as expected. You are
+encouraged to replace the link with a link to a site with more explanations.
+
+When the spf condition has run, it sets up several expansion variables:
+
+$spf_header_comment
+
+ This contains a human-readable string describing the outcome of the SPF
+ check. You can add it to a custom header or use it for logging purposes.
+
+$spf_received
+
+ This contains a complete Received-SPF: header that can be added to the
+ message. Please note that according to the SPF draft, this header must be
+ added at the top of the header list. Please see section 10 on how you can
+ do this.
+
+ Note: in case of "Best-guess" (see below), the convention is to put this
+ string in a header called X-SPF-Guess: instead.
+
+$spf_result
+
+ This contains the outcome of the SPF check in string form, one of pass,
+ fail, softfail, none, neutral, permerror or temperror.
+
+$spf_result_guessed
+
+ This boolean is true only if a best-guess operation was used and required
+ in order to obtain a result.
+
+$spf_smtp_comment
+
+ This contains a string that can be used in a SMTP response to the calling
+ party. Useful for "fail".
+
+ The string is generated by the SPF library from the template configured in
+ the main config option spf_smtp_comment_template.
+
+In addition to SPF, you can also perform checks for so-called "Best-guess".
+Strictly speaking, "Best-guess" is not standard SPF, but it is supported by the
+same framework that enables SPF capability. Refer to http://www.open-spf.org/
+FAQ/Best_guess_record for a description of what it means.
+
+To access this feature, simply use the spf_guess condition in place of the spf
+one. For example:
+
+deny spf_guess = fail
+ message = $sender_host_address doesn't look trustworthy to me
+
+In case you decide to reject messages based on this check, you should note that
+although it uses the same framework, "Best-guess" is not SPF, and therefore you
+should not mention SPF at all in your reject message.
+
+When the spf_guess condition has run, it sets up the same expansion variables
+as when spf condition is run, described above.
+
+Additionally, since Best-guess is not standardized, you may redefine what
+"Best-guess" means to you by redefining the main configuration spf_guess
+option. For example, the following:
+
+spf_guess = v=spf1 a/16 mx/16 ptr ?all
+
+would relax host matching rules to a broader network range.
+
+A lookup expansion is also available. It takes an email address as the key and
+an IP address (v4 or v6) as the database:
+
+ ${lookup {username@domain} spf {ip.ip.ip.ip}}
+
+The lookup will return the same result strings as can appear in $spf_result
+(pass,fail,softfail,neutral,none,err_perm,err_temp).
+
+
+58.5 DMARC
+----------
+
+DMARC combines feedback from SPF, DKIM, and header From: in order to attempt to
+provide better indicators of the authenticity of an email. This document does
+not explain the fundamentals; you should read and understand how it works by
+visiting the website at http://www.dmarc.org/.
+
+If Exim is built with DMARC support, the libopendmarc library is used.
+
+For building Exim yourself, obtain the library from http://sourceforge.net/
+projects/opendmarc/ to obtain a copy, or find it in your favorite package
+repository. You will need to attend to the local/Makefile feature SUPPORT_DMARC
+and the associated LDFLAGS addition. This description assumes that headers will
+be in /usr/local/include, and that the libraries are in /usr/local/lib.
+
+There are three main-configuration options:
+
+The dmarc_tld_file option defines the location of a text file of valid top
+level domains the opendmarc library uses during domain parsing. Maintained by
+Mozilla, the most current version can be downloaded from a link at https://
+publicsuffix.org/list/public_suffix_list.dat. See also the util/
+renew-opendmarc-tlds.sh script.
+
+The default for the option is unset. If not set, DMARC processing is disabled.
+
+The dmarc_history_file option, if set defines the location of a file to log
+results of dmarc verification on inbound emails. The contents are importable by
+the opendmarc tools which will manage the data, send out DMARC reports, and
+expire the data. Make sure the directory of this file is writable by the user
+exim runs as. The default is unset.
+
+The dmarc_forensic_sender option defines an alternate email address to use when
+sending a forensic report detailing alignment failures if a sender domain's
+dmarc record specifies it and you have configured Exim to send them. If set,
+this is expanded and used for the From: header line; the address is extracted
+from it and used for the envelope from. If not set (the default), the From:
+header is expanded from the dsn_from option, and <> is used for the envelope
+from.
+
+By default, the DMARC processing will run for any remote, non-authenticated
+user. It makes sense to only verify DMARC status of messages coming from
+remote, untrusted sources. You can use standard conditions such as hosts,
+senders, etc, to decide that DMARC verification should *not* be performed for
+them and disable DMARC with an ACL control modifier:
+
+ control = dmarc_disable_verify
+
+A DMARC record can also specify a "forensic address", which gives exim an email
+address to submit reports about failed alignment. Exim does not do this by
+default because in certain conditions it results in unintended information
+leakage (what lists a user might be subscribed to, etc). You must configure
+exim to submit forensic reports to the owner of the domain. If the DMARC record
+contains a forensic address and you specify the control statement below, then
+exim will send these forensic emails. It is also advised that you configure a
+dmarc_forensic_sender because the default sender address construction might be
+inadequate.
+
+ control = dmarc_enable_forensic
+
+(AGAIN: You can choose not to send these forensic reports by simply not putting
+the dmarc_enable_forensic control line at any point in your exim config. If you
+don't tell exim to send them, it will not send them.)
+
+There are no options to either control. Both must appear before the DATA acl.
+
+DMARC checks cam be run on incoming SMTP messages by using the "dmarc_status"
+ACL condition in the DATA ACL. You are required to call the "spf" condition
+first in the ACLs, then the "dmarc_status" condition. Putting this condition in
+the ACLs is required in order for a DMARC check to actually occur. All of the
+variables are set up before the DATA ACL, but there is no actual DMARC check
+that occurs until a "dmarc_status" condition is encountered in the ACLs.
+
+The "dmarc_status" condition takes a list of strings on its right-hand side.
+These strings describe recommended action based on the DMARC check. To
+understand what the policy recommendations mean, refer to the DMARC website
+above. Valid strings are:
+
+accept
+ The DMARC check passed and the library recommends accepting the email.
+reject
+ The DMARC check failed and the library recommends rejecting the email.
+quarantine
+ The DMARC check failed and the library recommends keeping it for further inspection.
+none
+ The DMARC check passed and the library recommends no specific action, neutral.
+norecord No policy section in the DMARC record for this sender domain.
+nofrom Unable to determine the domain of the sender.
+temperror Library error or dns error.
+off The DMARC check was disabled for this email.
+
+You can prefix each string with an exclamation mark to invert its meaning, for
+example "!accept" will match all results but "accept". The string list is
+evaluated left-to-right in a short-circuit fashion. When a string matches the
+outcome of the DMARC check, the condition succeeds. If none of the listed
+strings matches the outcome of the DMARC check, the condition fails.
+
+Of course, you can also use any other lookup method that Exim supports,
+including LDAP, Postgres, MySQL, etc, as long as the result is a list of
+colon-separated strings.
+
+Performing the check sets up information used by the authresults expansion
+item.
+
+Several expansion variables are set before the DATA ACL is processed, and you
+can use them in this ACL. The following expansion variables are available:
+
+$dmarc_status
+
+ A one word status indicating what the DMARC library thinks of the email. It
+ is a combination of the results of DMARC record lookup and the SPF/DKIM/
+ DMARC processing results (if a DMARC record was found). The actual policy
+ declared in the DMARC record is in a separate expansion variable.
+
+$dmarc_status_text
+
+ Slightly longer, human readable status.
+
+$dmarc_used_domain
+
+ The domain which DMARC used to look up the DMARC policy record.
+
+$dmarc_domain_policy
+
+ The policy declared in the DMARC record. Valid values are "none", "reject"
+ and "quarantine". It is blank when there is any error, including no DMARC
+ record.
+
+By default, Exim's DMARC configuration is intended to be non-intrusive and
+conservative. To facilitate this, Exim will not create any type of logging
+files without explicit configuration by you, the admin. Nor will Exim send out
+any emails/reports about DMARC issues without explicit configuration by you,
+the admin (other than typical bounce messages that may come about due to ACL
+processing or failure delivery issues).
+
+In order to log statistics suitable to be imported by the opendmarc tools, you
+need to:
+
+ * Configure the global option dmarc_history_file
+
+ * Configure cron jobs to call the appropriate opendmarc history import
+ scripts and truncating the dmarc_history_file
+
+In order to send forensic reports, you need to:
+
+ * Configure the global option dmarc_forensic_sender
+
+ * Configure, somewhere before the DATA ACL, the control option to enable
+ sending DMARC forensic reports
+
+Example usage:
+
+(RCPT ACL)
+ warn domains = +local_domains
+ hosts = +local_hosts
+ control = dmarc_disable_verify
+
+ warn !domains = +screwed_up_dmarc_records
+ control = dmarc_enable_forensic
+
+ warn condition = (lookup if destined to mailing list)
+ set acl_m_mailing_list = 1
+
+(DATA ACL)
+ warn dmarc_status = accept : none : off
+ !authenticated = *
+ log_message = DMARC DEBUG: $dmarc_status $dmarc_used_domain
+
+ warn dmarc_status = !accept
+ !authenticated = *
+ log_message = DMARC DEBUG: '$dmarc_status' for $dmarc_used_domain
+
+ warn dmarc_status = quarantine
+ !authenticated = *
+ set $acl_m_quarantine = 1
+ # Do something in a transport with this flag variable
+
+ deny condition = ${if eq{$dmarc_domain_policy}{reject}}
+ condition = ${if eq{$acl_m_mailing_list}{1}}
+ message = Messages from $dmarc_used_domain break mailing lists
+
+ deny dmarc_status = reject
+ !authenticated = *
+ message = Message from $dmarc_used_domain failed sender's DMARC policy, REJECT
+
+ warn add_header = :at_start:${authresults {$primary_hostname}}
+
+
+
+===============================================================================
+59. PROXIES
+
+A proxy is an intermediate system through which communication is passed.
+Proxies may provide a security, availability or load-distribution function.
+
+
+59.1 Inbound proxies
+--------------------
+
+Exim has support for receiving inbound SMTP connections via a proxy that uses
+"Proxy Protocol" to speak to it. To include this support, include
+"SUPPORT_PROXY=yes" in Local/Makefile.
+
+It was built on the HAProxy specification, found at https://www.haproxy.org/
+download/1.8/doc/proxy-protocol.txt.
+
+The purpose of this facility is so that an application load balancer, such as
+HAProxy, can sit in front of several Exim servers to distribute load. Exim uses
+the local protocol communication with the proxy to obtain the remote SMTP
+system IP address and port information. There is no logging if a host passes or
+fails Proxy Protocol negotiation, but it can easily be determined and recorded
+in an ACL (example is below).
+
+Use of a proxy is enabled by setting the hosts_proxy main configuration option
+to a hostlist; connections from these hosts will use Proxy Protocol. Exim
+supports both version 1 and version 2 of the Proxy Protocol and automatically
+determines which version is in use.
+
+The Proxy Protocol header is the first data received on a TCP connection and is
+inserted before any TLS-on-connect handshake from the client; Exim negotiates
+TLS between Exim-as-server and the remote client, not between Exim and the
+proxy server.
+
+The following expansion variables are usable ("internal" and "external" here
+refer to the interfaces of the proxy):
+
+proxy_external_address
+ IP of host being proxied or IP of remote interface of proxy
+proxy_external_port
+ Port of host being proxied or Port on remote interface of proxy
+proxy_local_address
+ IP of proxy server inbound or IP of local interface of proxy
+proxy_local_port
+ Port of proxy server inbound or Port on local interface of proxy
+proxy_session boolean: SMTP connection via proxy
+
+If $proxy_session is set but $proxy_external_address is empty there was a
+protocol error. The variables $sender_host_address and $sender_host_port will
+have values for the actual client system, not the proxy.
+
+Since the real connections are all coming from the proxy, and the per host
+connection tracking is done before Proxy Protocol is evaluated,
+smtp_accept_max_per_host must be set high enough to handle all of the parallel
+volume you expect per inbound proxy. With the option set so high, you lose the
+ability to protect your server from many connections from one IP. In order to
+prevent your server from overload, you need to add a per connection ratelimit
+to your connect ACL. A possible solution is:
+
+ # Set max number of connections per host
+ LIMIT = 5
+ # Or do some kind of IP lookup in a flat file or database
+ # LIMIT = ${lookup{$sender_host_address}iplsearch{/etc/exim/proxy_limits}}
+
+ defer ratelimit = LIMIT / 5s / per_conn / strict
+ message = Too many connections from this IP right now
+
+
+59.2 Outbound proxies
+---------------------
+
+Exim has support for sending outbound SMTP via a proxy using a protocol called
+SOCKS5 (defined by RFC1928). The support can be optionally included by defining
+SUPPORT_SOCKS=yes in Local/Makefile.
+
+Use of a proxy is enabled by setting the socks_proxy option on an smtp
+transport. The option value is expanded and should then be a list
+(colon-separated by default) of proxy specifiers. Each proxy specifier is a
+list (space-separated by default) where the initial element is an IP address
+and any subsequent elements are options.
+
+Options are a string <name>=<value>. The list of options is in the following
+table:
+
+auth authentication method
+name authentication username
+pass authentication password
+port tcp port
+tmo connection timeout
+pri priority
+weight selection bias
+
+More details on each of these options follows:
+
+ * auth: Either "none" (default) or "name". Using "name" selects username/
+ password authentication per RFC 1929 for access to the proxy. Default is
+ "none".
+
+ * name: sets the username for the "name" authentication method. Default is
+ empty.
+
+ * pass: sets the password for the "name" authentication method. Default is
+ empty.
+
+ * port: the TCP port number to use for the connection to the proxy. Default
+ is 1080.
+
+ * tmo: sets a connection timeout in seconds for this proxy. Default is 5.
+
+ * pri: specifies a priority for the proxy within the list, higher values
+ being tried first. The default priority is 1.
+
+ * weight: specifies a selection bias. Within a priority set servers are
+ queried in a random fashion, weighted by this value. The default value for
+ selection bias is 1.
+
+Proxies from the list are tried according to their priority and weight settings
+until one responds. The timeout for the overall connection applies to the set
+of proxied attempts.
+
+
+59.3 Logging
+------------
+
+To log the (local) IP of a proxy in the incoming or delivery logline, add
+"+proxy" to the log_selector option. This will add a component tagged with "PRX
+=" to the line.
+
+
+
+===============================================================================
+60. INTERNATIONALISATION
+
+Exim has support for Internationalised mail names. To include this it must be
+built with SUPPORT_I18N and the libidn library. Standards supported are RFCs
+2060, 5890, 6530 and 6533.
+
+If Exim is built with SUPPORT_I18N_2008 (in addition to SUPPORT_I18N, not
+instead of it) then IDNA2008 is supported; this adds an extra library
+requirement, upon libidn2.
+
+
+60.1 MTA operations
+-------------------
+
+The main configuration option smtputf8_advertise_hosts specifies a host list.
+If this matches the sending host and accept_8bitmime is true (the default) then
+the ESMTP option SMTPUTF8 will be advertised.
+
+If the sender specifies the SMTPUTF8 option on a MAIL command international
+handling for the message is enabled and the expansion variable
+$message_smtputf8 will have value TRUE.
+
+The option allow_utf8_domains is set to true for this message. All DNS lookups
+are converted to a-label form whatever the setting of allow_utf8_domains when
+Exim is built with SUPPORT_I18N.
+
+Both localparts and domain are maintained as the original UTF-8 form
+internally; any comparison or regular-expression use will require appropriate
+care. Filenames created, eg. by the appendfile transport, will have UTF-8
+names.
+
+HELO names sent by the smtp transport will have any UTF-8 components expanded
+to a-label form, and any certificate name checks will be done using the a-label
+form of the name.
+
+Log lines and Received-by: header lines will acquire a "utf8" prefix on the
+protocol element, eg. utf8esmtp.
+
+The following expansion operators can be used:
+
+${utf8_domain_to_alabel:str}
+${utf8_domain_from_alabel:str}
+${utf8_localpart_to_alabel:str}
+${utf8_localpart_from_alabel:str}
+
+The RCPT ACL may use the following modifier:
+
+control = utf8_downconvert
+control = utf8_downconvert/<value>
+
+This sets a flag requiring that envelope addresses are converted to a-label
+form before smtp delivery. This is usually for use in a Message Submission
+Agent context, but could be used for any message.
+
+If a value is appended it may be:
+
+1 mandatory downconversion
+0 no downconversion
+-1 if SMTPUTF8 not supported by destination host
+
+If no value is given, 1 is used.
+
+If mua_wrapper is set, the utf8_downconvert control is initially set to -1.
+
+The smtp transport has an option utf8_downconvert. If set it must expand to one
+of the three values described above, or an empty string. If non-empty it
+overrides value previously set (due to mua_wrapper or by an ACL control).
+
+There is no explicit support for VRFY and EXPN. Configurations supporting these
+should inspect $smtp_command_argument for an SMTPUTF8 argument.
+
+There is no support for LMTP on Unix sockets. Using the "lmtp" protocol option
+on an smtp transport, for LMTP over TCP, should work as expected.
+
+There is no support for DSN unitext handling, and no provision for converting
+logging from or to UTF-8.
+
+
+60.2 MDA operations
+-------------------
+
+To aid in constructing names suitable for IMAP folders the following expansion
+operator can be used:
+
+${imapfolder {<string>} {<sep>} {<specials>}}
+
+The string is converted from the charset specified by the "headers charset"
+command (in a filter file) or headers_charset main configuration option
+(otherwise), to the modified UTF-7 encoding specified by RFC 2060, with the
+following exception: All occurrences of <sep> (which has to be a single
+character) are replaced with periods ("."), and all periods and slashes that
+are not <sep> and are not in the <specials> string are BASE64 encoded.
+
+The third argument can be omitted, defaulting to an empty string. The second
+argument can be omitted, defaulting to "/".
+
+This is the encoding used by Courier for Maildir names on disk, and followed by
+many other IMAP servers.
+
+Examples:
+
+${imapfolder {Foo/Bar}} yields Foo.Bar
+${imapfolder {Foo/Bar}{.}{/}} yields Foo&AC8-Bar
+${imapfolder {R?ksm?rg?s}} yields R&AOQ-ksm&APY-rg&AOU-s
+
+Note that the source charset setting is vital, and also that characters must be
+representable in UTF-16.
+
+
+
+===============================================================================
+61. EVENTS
+
+The events mechanism in Exim can be used to intercept processing at a number of
+points. It was originally invented to give a way to do customised logging
+actions (for example, to a database) but can also be used to modify some
+processing actions.
+
+Most installations will never need to use Events. The support can be left out
+of a build by defining DISABLE_EVENT=yes in Local/Makefile.
+
+There are two major classes of events: main and transport. The main
+configuration option event_action controls reception events; a transport option
+event_action controls delivery events.
+
+Both options are a string which is expanded when the event fires. An example
+might look like:
+
+event_action = ${if eq {msg:delivery}{$event_name} \
+{${lookup pgsql {SELECT * FROM record_Delivery( \
+ '${quote_pgsql:$sender_address_domain}',\
+ '${quote_pgsql:${lc:$sender_address_local_part}}', \
+ '${quote_pgsql:$domain}', \
+ '${quote_pgsql:${lc:$local_part}}', \
+ '${quote_pgsql:$host_address}', \
+ '${quote_pgsql:${lc:$host}}', \
+ '${quote_pgsql:$message_exim_id}')}} \
+} {}}
+
+Events have names which correspond to the point in process at which they fire.
+The name is placed in the variable $event_name and the event action expansion
+must check this, as it will be called for every possible event type.
+
+The current list of events is:
+
+dane:fail after transport per connection
+msg:complete after main per message
+msg:defer after transport per message per delivery try
+msg:delivery after transport per recipient
+msg:rcpt:host:defer after transport per recipient per host
+msg:rcpt:defer after transport per recipient
+msg:host:defer after transport per host per delivery try;
+ host errors
+msg:fail:delivery after transport per recipient
+msg:fail:internal after main per recipient
+tcp:connect before transport per connection
+tcp:close after transport per connection
+tls:cert before both per certificate in verification chain
+smtp:connect after transport per connection
+smtp:ehlo after transport per connection
+
+New event types may be added in future.
+
+The event name is a colon-separated list, defining the type of event in a tree
+of possibilities. It may be used as a list or just matched on as a whole. There
+will be no spaces in the name.
+
+The second column in the table above describes whether the event fires before
+or after the action is associates with. Those which fire before can be used to
+affect that action (more on this below).
+
+The third column in the table above says what section of the configuration
+should define the event action.
+
+An additional variable, $event_data, is filled with information varying with
+the event type:
+
+dane:fail failure reason
+msg:defer error string
+msg:delivery smtp confirmation message
+msg:fail:internal failure reason
+msg:fail:delivery smtp error message
+msg:host:defer error string
+msg:rcpt:host:defer error string
+msg:rcpt:defer error string
+tls:cert verification chain depth
+smtp:connect smtp banner
+smtp:ehlo smtp ehlo response
+
+The :defer events populate one extra variable: $event_defer_errno.
+
+For complex operations an ACL expansion can be used in event_action however due
+to the multiple contexts that Exim operates in during the course of its
+processing:
+
+ * variables set in transport events will not be visible outside that
+ transport call
+
+ * acl_m variables in a server context are lost on a new connection, and after
+ smtp helo/ehlo/mail/starttls/rset commands
+
+Using an ACL expansion with the logwrite modifier can be a useful way of
+writing to the main log.
+
+The expansion of the event_action option should normally return an empty
+string. Should it return anything else the following will be forced:
+
+tcp:connect do not connect
+tls:cert refuse verification
+smtp:connect close connection
+
+All other message types ignore the result string, and no other use is made of
+it.
+
+For a tcp:connect event, if the connection is being made to a proxy then the
+address and port variables will be that of the proxy and not the target system.
+
+For tls:cert events, if GnuTLS is in use this will trigger only per chain
+element received on the connection. For OpenSSL it will trigger for every chain
+element including those loaded locally.
+
+
+
+===============================================================================
+62. ADDING NEW DRIVERS OR LOOKUP TYPES
+
+The following actions have to be taken in order to add a new router, transport,
+authenticator, or lookup type to Exim:
+
+ 1. Choose a name for the driver or lookup type that does not conflict with any
+ existing name; I will use "newdriver" in what follows.
+
+ 2. Add to src/EDITME the line:
+
+ <type>_NEWDRIVER=yes
+
+ where <type> is ROUTER, TRANSPORT, AUTH, or LOOKUP. If the code is not to
+ be included in the binary by default, comment this line out. You should
+ also add any relevant comments about the driver or lookup type.
+
+ 3. Add to src/config.h.defaults the line:
+
+ #define <type>_NEWDRIVER
+
+ 4. Edit src/drtables.c, adding conditional code to pull in the private header
+ and create a table entry as is done for all the other drivers and lookup
+ types.
+
+ 5. Edit scripts/lookups-Makefile if this is a new lookup; there is a for-loop
+ near the bottom, ranging the "name_mod" variable over a list of all
+ lookups. Add your "NEWDRIVER" to that list. As long as the dynamic module
+ would be named newdriver.so, you can use the simple form that most lookups
+ have.
+
+ 6. Edit Makefile in the appropriate sub-directory (src/routers, src/transports
+ , src/auths, or src/lookups); add a line for the new driver or lookup type
+ and add it to the definition of OBJ.
+
+ 7. Edit OS/Makefile-Base adding a .o file for the predefined-macros, to the
+ definition of OBJ_MACRO. Add a set of line to do the compile also.
+
+ 8. Create newdriver.h and newdriver.c in the appropriate sub-directory of src.
+
+ 9. Edit scripts/MakeLinks and add commands to link the .h and .c files as for
+ other drivers and lookups.
+
+Then all you need to do is write the code! A good way to start is to make a
+proforma by copying an existing module of the same type, globally changing all
+occurrences of the name, and cutting out most of the code. Note that any
+options you create must be listed in alphabetical order, because the tables are
+searched using a binary chop procedure.
+
+There is a README file in each of the sub-directories of src describing the
+interface that is expected.
+