path: root/man/man8/smtp.8

.TH SMTP 8 
.ad
.fi
.SH NAME
smtp
\-
Postfix SMTP+LMTP client
.SH "SYNOPSIS"
.na
.nf
\fBsmtp\fR [generic Postfix daemon options] [flags=DORX]
.SH DESCRIPTION
.ad
.fi
The Postfix SMTP+LMTP client implements the SMTP and LMTP mail
delivery protocols. It processes message delivery requests from
the queue manager. Each request specifies a queue file, a sender
address, a domain or host to deliver to, and recipient information.
This program expects to be run from the \fBmaster\fR(8) process
manager.

The SMTP+LMTP client updates the queue file and marks recipients
as finished, or it informs the queue manager that delivery should
be tried again at a later time. Delivery status reports are sent
to the \fBbounce\fR(8), \fBdefer\fR(8) or \fBtrace\fR(8) daemon as
appropriate.

The SMTP+LMTP client looks up a list of mail exchanger addresses for
the destination host, sorts the list by preference, and connects
to each listed address until it finds a server that responds.

When a server is not reachable, or when mail delivery fails due
to a recoverable error condition, the SMTP+LMTP client will try to
deliver the mail to an alternate host.

After a successful mail transaction, a connection may be saved
to the \fBscache\fR(8) connection cache server, so that it
may be used by any SMTP+LMTP client for a subsequent transaction.

By default, connection caching is enabled temporarily for
destinations that have a high volume of mail in the active
queue. Connection caching can be enabled permanently for
specific destinations.
.SH "SMTP DESTINATION SYNTAX"
.na
.nf
.ad
.fi
The Postfix SMTP+LMTP client supports multiple destinations
separated by comma or whitespace (Postfix 3.5 and later).
SMTP destinations have the following form:
.IP \fIdomainname\fR
.IP \fIdomainname\fR:\fIport\fR
Look up the mail exchangers for the specified domain, and
connect to the specified port (default: \fBsmtp\fR).
.IP [\fIhostname\fR]
.IP [\fIhostname\fR]:\fIport\fR
Look up the address(es) of the specified host, and connect to
the specified port (default: \fBsmtp\fR).
.IP [\fIaddress\fR]
.IP [\fIaddress\fR]:\fIport\fR
Connect to the host at the specified address, and connect
to the specified port (default: \fBsmtp\fR). An IPv6 address
must be formatted as [\fBipv6\fR:\fIaddress\fR].
.SH "LMTP DESTINATION SYNTAX"
.na
.nf
.ad
.fi
The Postfix SMTP+LMTP client supports multiple destinations
separated by comma or whitespace (Postfix 3.5 and later).
LMTP destinations have the following form:
.IP \fBunix\fR:\fIpathname\fR
Connect to the local UNIX\-domain server that is bound to the specified
\fIpathname\fR. If the process runs chrooted, an absolute pathname
is interpreted relative to the Postfix queue directory.
.IP \fBinet\fR:\fIhostname\fR
.IP \fBinet\fR:\fIhostname\fR:\fIport\fR
.IP \fBinet\fR:[\fIaddress\fR]
.IP \fBinet\fR:[\fIaddress\fR]:\fIport\fR
Connect to the specified TCP port on the specified local or
remote host. If no port is specified, connect to the port defined as
\fBlmtp\fR in \fBservices\fR(4).
If no such service is found, the \fBlmtp_tcp_port\fR configuration
parameter (default value of 24) will be used.
An IPv6 address must be formatted as [\fBipv6\fR:\fIaddress\fR].
.SH "SINGLE-RECIPIENT DELIVERY"
.na
.nf
.ad
.fi
By default, the Postfix SMTP+LMTP client delivers mail to
multiple recipients per delivery request. This is undesirable
when prepending a \fBDelivered\-to:\fR or \fBX\-Original\-To:\fR
message header. To prevent Postfix from sending multiple
recipients per delivery request, specify
.sp
.nf
    \fItransport\fB_destination_recipient_limit = 1\fR
.fi

in the Postfix \fBmain.cf\fR file, where \fItransport\fR
is the name in the first column of the Postfix \fBmaster.cf\fR
entry for this mail delivery service.
.SH "COMMAND ATTRIBUTE SYNTAX"
.na
.nf
.ad
.fi
.IP "\fBflags=DORX\fR (optional)"
Optional message processing flags.
.RS
.IP \fBD\fR
Prepend a "\fBDelivered\-To: \fIrecipient\fR" message header
with the envelope recipient address. Note: for this to work,
the \fItransport\fB_destination_recipient_limit\fR must be
1 (see SINGLE\-RECIPIENT DELIVERY above for details).
.sp
The \fBD\fR flag also enforces loop detection: if a message
already contains a \fBDelivered\-To:\fR header with the same
recipient address, then the message is returned as
undeliverable. The address comparison is case insensitive.
.sp
This feature is available as of Postfix 3.5.
.IP \fBO\fR
Prepend an "\fBX\-Original\-To: \fIrecipient\fR" message
header with the recipient address as given to Postfix. Note:
for this to work, the
\fItransport\fB_destination_recipient_limit\fR must be 1
(see SINGLE\-RECIPIENT DELIVERY above for details).
.sp
This feature is available as of Postfix 3.5.
.IP \fBR\fR
Prepend a "\fBReturn\-Path: <\fIsender\fB>\fR" message header
with the envelope sender address.
.sp
This feature is available as of Postfix 3.5.
.IP \fBX\fR
Indicates that the delivery is final. This flag affects
the status reported in "success" DSN (delivery status
notification) messages, and changes it from "relayed" into
"delivered".
.sp
This feature is available as of Postfix 3.5.
.RE
.SH "SECURITY"
.na
.nf
The SMTP+LMTP client is moderately security\-sensitive. It
talks to SMTP or LMTP servers and to DNS servers on the
network. The SMTP+LMTP client can be run chrooted at fixed
low privilege.
.SH "STANDARDS"
.na
.nf
RFC 821 (SMTP protocol)
RFC 822 (ARPA Internet Text Messages)
RFC 1651 (SMTP service extensions)
RFC 1652 (8bit\-MIME transport)
RFC 1870 (Message Size Declaration)
RFC 2033 (LMTP protocol)
RFC 2034 (SMTP Enhanced Error Codes)
RFC 2045 (MIME: Format of Internet Message Bodies)
RFC 2046 (MIME: Media Types)
RFC 2554 (AUTH command)
RFC 2821 (SMTP protocol)
RFC 2782 (SRV resource records)
RFC 2920 (SMTP Pipelining)
RFC 3207 (STARTTLS command)
RFC 3461 (SMTP DSN Extension)
RFC 3463 (Enhanced Status Codes)
RFC 4954 (AUTH command)
RFC 5321 (SMTP protocol)
RFC 6531 (Internationalized SMTP)
RFC 6533 (Internationalized Delivery Status Notifications)
RFC 7672 (SMTP security via opportunistic DANE TLS)
.SH DIAGNOSTICS
.ad
.fi
Problems and transactions are logged to \fBsyslogd\fR(8)
or \fBpostlogd\fR(8).
Corrupted message files are marked so that the queue manager can
move them to the \fBcorrupt\fR queue for further inspection.

Depending on the setting of the \fBnotify_classes\fR parameter,
the postmaster is notified of bounces, protocol problems, and of
other trouble.
.SH BUGS
.ad
.fi
SMTP and LMTP connection reuse for TLS (without closing the
SMTP or LMTP connection) is not supported before Postfix 3.4.

SMTP and LMTP connection reuse assumes that SASL credentials
are valid for all destinations that map onto the same IP
address and TCP port.
.SH "CONFIGURATION PARAMETERS"
.na
.nf
.ad
.fi
Before Postfix version 2.3, the LMTP client is a separate
program that implements only a subset of the functionality
available with SMTP: there is no support for TLS, and
connections are cached in\-process, making it ineffective
when the client is used for multiple domains.

Most smtp_\fIxxx\fR configuration parameters have an
lmtp_\fIxxx\fR "mirror" parameter for the equivalent LMTP
feature. This document describes only those LMTP\-related
parameters that aren't simply "mirror" parameters.

Changes to \fBmain.cf\fR are picked up automatically, as \fBsmtp\fR(8)
processes run for only a limited amount of time. Use the command
"\fBpostfix reload\fR" to speed up a change.

The text below provides only a parameter summary. See
\fBpostconf\fR(5) for more details including examples.
.SH "COMPATIBILITY CONTROLS"
.na
.nf
.ad
.fi
.IP "\fBignore_mx_lookup_error (no)\fR"
Ignore DNS MX lookups that produce no response.
.IP "\fBsmtp_always_send_ehlo (yes)\fR"
Always send EHLO at the start of an SMTP session.
.IP "\fBsmtp_never_send_ehlo (no)\fR"
Never send EHLO at the start of an SMTP session.
.IP "\fBsmtp_defer_if_no_mx_address_found (no)\fR"
Defer mail delivery when no MX record resolves to an IP address.
.IP "\fBsmtp_line_length_limit (998)\fR"
The maximal length of message header and body lines that Postfix
will send via SMTP.
.IP "\fBsmtp_pix_workaround_delay_time (10s)\fR"
How long the Postfix SMTP client pauses before sending
".<CR><LF>" in order to work around the PIX firewall
"<CR><LF>.<CR><LF>" bug.
.IP "\fBsmtp_pix_workaround_threshold_time (500s)\fR"
How long a message must be queued before the Postfix SMTP client
turns on the PIX firewall "<CR><LF>.<CR><LF>"
bug workaround for delivery through firewalls with "smtp fixup"
mode turned on.
.IP "\fBsmtp_pix_workarounds (disable_esmtp, delay_dotcrlf)\fR"
A list that specifies zero or more workarounds for CISCO PIX
firewall bugs.
.IP "\fBsmtp_pix_workaround_maps (empty)\fR"
Lookup tables, indexed by the remote SMTP server address, with
per\-destination workarounds for CISCO PIX firewall bugs.
.IP "\fBsmtp_quote_rfc821_envelope (yes)\fR"
Quote addresses in Postfix SMTP client MAIL FROM and RCPT TO commands
as required
by RFC 5321.
.IP "\fBsmtp_reply_filter (empty)\fR"
A mechanism to transform replies from remote SMTP servers one
line at a time.
.IP "\fBsmtp_skip_5xx_greeting (yes)\fR"
Skip remote SMTP servers that greet with a 5XX status code.
.IP "\fBsmtp_skip_quit_response (yes)\fR"
Do not wait for the response to the SMTP QUIT command.
.PP
Available in Postfix version 2.0 and earlier:
.IP "\fBsmtp_skip_4xx_greeting (yes)\fR"
Skip SMTP servers that greet with a 4XX status code (go away, try
again later).
.PP
Available in Postfix version 2.2 and later:
.IP "\fBsmtp_discard_ehlo_keyword_address_maps (empty)\fR"
Lookup tables, indexed by the remote SMTP server address, with
case insensitive lists of EHLO keywords (pipelining, starttls, auth,
etc.) that the Postfix SMTP client will ignore in the EHLO response from a
remote SMTP server.
.IP "\fBsmtp_discard_ehlo_keywords (empty)\fR"
A case insensitive list of EHLO keywords (pipelining, starttls,
auth, etc.) that the Postfix SMTP client will ignore in the EHLO
response from a remote SMTP server.
.IP "\fBsmtp_generic_maps (empty)\fR"
Optional lookup tables that perform address rewriting in the
Postfix SMTP client, typically to transform a locally valid address into
a globally valid address when sending mail across the Internet.
.PP
Available in Postfix version 2.2.9 and later:
.IP "\fBsmtp_cname_overrides_servername (version dependent)\fR"
When the remote SMTP servername is a DNS CNAME, replace the
servername with the result from CNAME expansion for the purpose of
logging, SASL password lookup, TLS
policy decisions, or TLS certificate verification.
.PP
Available in Postfix version 2.3 and later:
.IP "\fBlmtp_discard_lhlo_keyword_address_maps (empty)\fR"
Lookup tables, indexed by the remote LMTP server address, with
case insensitive lists of LHLO keywords (pipelining, starttls,
auth, etc.) that the Postfix LMTP client will ignore in the LHLO
response
from a remote LMTP server.
.IP "\fBlmtp_discard_lhlo_keywords (empty)\fR"
A case insensitive list of LHLO keywords (pipelining, starttls,
auth, etc.) that the Postfix LMTP client will ignore in the LHLO
response
from a remote LMTP server.
.PP
Available in Postfix version 2.4.4 and later:
.IP "\fBsend_cyrus_sasl_authzid (no)\fR"
When authenticating to a remote SMTP or LMTP server with the
default setting "no", send no SASL authoriZation ID (authzid); send
only the SASL authentiCation ID (authcid) plus the authcid's password.
.PP
Available in Postfix version 2.5 and later:
.IP "\fBsmtp_header_checks (empty)\fR"
Restricted \fBheader_checks\fR(5) tables for the Postfix SMTP client.
.IP "\fBsmtp_mime_header_checks (empty)\fR"
Restricted \fBmime_header_checks\fR(5) tables for the Postfix SMTP
client.
.IP "\fBsmtp_nested_header_checks (empty)\fR"
Restricted \fBnested_header_checks\fR(5) tables for the Postfix SMTP
client.
.IP "\fBsmtp_body_checks (empty)\fR"
Restricted \fBbody_checks\fR(5) tables for the Postfix SMTP client.
.PP
Available in Postfix version 2.6 and later:
.IP "\fBtcp_windowsize (0)\fR"
An optional workaround for routers that break TCP window scaling.
.PP
Available in Postfix version 2.8 and later:
.IP "\fBsmtp_dns_resolver_options (empty)\fR"
DNS Resolver options for the Postfix SMTP client.
.PP
Available in Postfix version 2.9 \- 3.6:
.IP "\fBsmtp_per_record_deadline (no)\fR"
Change the behavior of the smtp_*_timeout time limits, from a
time limit per read or write system call, to a time limit to send
or receive a complete record (an SMTP command line, SMTP response
line, SMTP message content line, or TLS protocol message).
.PP
Available in Postfix version 2.9 and later:
.IP "\fBsmtp_send_dummy_mail_auth (no)\fR"
Whether or not to append the "AUTH=<>" option to the MAIL
FROM command in SASL\-authenticated SMTP sessions.
.PP
Available in Postfix version 2.11 and later:
.IP "\fBsmtp_dns_support_level (empty)\fR"
Level of DNS support in the Postfix SMTP client.
.PP
Available in Postfix version 3.0 and later:
.IP "\fBsmtp_delivery_status_filter ($default_delivery_status_filter)\fR"
Optional filter for the \fBsmtp\fR(8) delivery agent to change the
delivery status code or explanatory text of successful or unsuccessful
deliveries.
.IP "\fBsmtp_dns_reply_filter (empty)\fR"
Optional filter for Postfix SMTP client DNS lookup results.
.PP
Available in Postfix version 3.3 and later:
.IP "\fBsmtp_balance_inet_protocols (yes)\fR"
When a remote destination resolves to a combination of IPv4 and
IPv6 addresses, ensure that the Postfix SMTP client can try both
address types before it runs into the smtp_mx_address_limit.
.PP
Available in Postfix 3.5 and later:
.IP "\fBinfo_log_address_format (external)\fR"
The email address form that will be used in non\-debug logging
(info, warning, etc.).
.PP
Available in Postfix 3.6 and later:
.IP "\fBdnssec_probe (ns:.)\fR"
The DNS query type (default: "ns") and DNS query name (default:
".") that Postfix may use to determine whether DNSSEC validation
is available.
.IP "\fBknown_tcp_ports (lmtp=24, smtp=25, smtps=submissions=465, submission=587)\fR"
Optional setting that avoids lookups in the \fBservices\fR(5) database.
.PP
Available in Postfix version 3.7 and later:
.IP "\fBsmtp_per_request_deadline (no)\fR"
Change the behavior of the smtp_*_timeout time limits, from a
time limit per plaintext or TLS read or write call, to a combined
time limit for sending a complete SMTP request and for receiving a
complete SMTP response.
.IP "\fBsmtp_min_data_rate (500)\fR"
The minimum plaintext data transfer rate in bytes/second for
DATA requests, when deadlines are enabled with smtp_per_request_deadline.
.IP "\fBheader_from_format (standard)\fR"
The format of the Postfix\-generated \fBFrom:\fR header.
.PP
Available in Postfix version 3.8 and later:
.IP "\fBuse_srv_lookup (empty)\fR"
Enables discovery for the specified service(s) using DNS SRV
records.
.IP "\fBignore_srv_lookup_error (no)\fR"
When SRV record lookup fails, fall back to MX or IP address
lookup as if SRV record lookup was not enabled.
.IP "\fBallow_srv_lookup_fallback (no)\fR"
When SRV record lookup fails or no SRV record exists, fall back
to MX or IP address lookup as if SRV record lookup was not enabled.
.SH "MIME PROCESSING CONTROLS"
.na
.nf
.ad
.fi
Available in Postfix version 2.0 and later:
.IP "\fBdisable_mime_output_conversion (no)\fR"
Disable the conversion of 8BITMIME format to 7BIT format.
.IP "\fBmime_boundary_length_limit (2048)\fR"
The maximal length of MIME multipart boundary strings.
.IP "\fBmime_nesting_limit (100)\fR"
The maximal recursion level that the MIME processor will handle.
.SH "EXTERNAL CONTENT INSPECTION CONTROLS"
.na
.nf
.ad
.fi
Available in Postfix version 2.1 and later:
.IP "\fBsmtp_send_xforward_command (no)\fR"
Send the non\-standard XFORWARD command when the Postfix SMTP server
EHLO response announces XFORWARD support.
.SH "SASL AUTHENTICATION CONTROLS"
.na
.nf
.ad
.fi
.IP "\fBsmtp_sasl_auth_enable (no)\fR"
Enable SASL authentication in the Postfix SMTP client.
.IP "\fBsmtp_sasl_password_maps (empty)\fR"
Optional Postfix SMTP client lookup tables with one username:password
entry per sender, remote hostname or next\-hop domain.
.IP "\fBsmtp_sasl_security_options (noplaintext, noanonymous)\fR"
Postfix SMTP client SASL security options; as of Postfix 2.3
the list of available
features depends on the SASL client implementation that is selected
with \fBsmtp_sasl_type\fR.
.PP
Available in Postfix version 2.2 and later:
.IP "\fBsmtp_sasl_mechanism_filter (empty)\fR"
If non\-empty, a Postfix SMTP client filter for the remote SMTP
server's list of offered SASL mechanisms.
.PP
Available in Postfix version 2.3 and later:
.IP "\fBsmtp_sender_dependent_authentication (no)\fR"
Enable sender\-dependent authentication in the Postfix SMTP client; this is
available only with SASL authentication, and disables SMTP connection
caching to ensure that mail from different senders will use the
appropriate credentials.
.IP "\fBsmtp_sasl_path (empty)\fR"
Implementation\-specific information that the Postfix SMTP client
passes through to
the SASL plug\-in implementation that is selected with
\fBsmtp_sasl_type\fR.
.IP "\fBsmtp_sasl_type (cyrus)\fR"
The SASL plug\-in type that the Postfix SMTP client should use
for authentication.
.PP
Available in Postfix version 2.5 and later:
.IP "\fBsmtp_sasl_auth_cache_name (empty)\fR"
An optional table to prevent repeated SASL authentication
failures with the same remote SMTP server hostname, username and
password.
.IP "\fBsmtp_sasl_auth_cache_time (90d)\fR"
The maximal age of an smtp_sasl_auth_cache_name entry before it
is removed.
.IP "\fBsmtp_sasl_auth_soft_bounce (yes)\fR"
When a remote SMTP server rejects a SASL authentication request
with a 535 reply code, defer mail delivery instead of returning
mail as undeliverable.
.PP
Available in Postfix version 2.9 and later:
.IP "\fBsmtp_send_dummy_mail_auth (no)\fR"
Whether or not to append the "AUTH=<>" option to the MAIL
FROM command in SASL\-authenticated SMTP sessions.
.SH "STARTTLS SUPPORT CONTROLS"
.na
.nf
.ad
.fi
Detailed information about STARTTLS configuration may be found
in the TLS_README document.
.IP "\fBsmtp_tls_security_level (empty)\fR"
The default SMTP TLS security level for the Postfix SMTP client.
.IP "\fBsmtp_sasl_tls_security_options ($smtp_sasl_security_options)\fR"
The SASL authentication security options that the Postfix SMTP
client uses for TLS encrypted SMTP sessions.
.IP "\fBsmtp_starttls_timeout (300s)\fR"
Time limit for Postfix SMTP client write and read operations
during TLS startup and shutdown handshake procedures.
.IP "\fBsmtp_tls_CAfile (empty)\fR"
A file containing CA certificates of root CAs trusted to sign
either remote SMTP server certificates or intermediate CA certificates.
.IP "\fBsmtp_tls_CApath (empty)\fR"
Directory with PEM format Certification Authority certificates
that the Postfix SMTP client uses to verify a remote SMTP server
certificate.
.IP "\fBsmtp_tls_cert_file (empty)\fR"
File with the Postfix SMTP client RSA certificate in PEM format.
.IP "\fBsmtp_tls_mandatory_ciphers (medium)\fR"
The minimum TLS cipher grade that the Postfix SMTP client will
use with
mandatory TLS encryption.
.IP "\fBsmtp_tls_exclude_ciphers (empty)\fR"
List of ciphers or cipher types to exclude from the Postfix
SMTP client cipher
list at all TLS security levels.
.IP "\fBsmtp_tls_mandatory_exclude_ciphers (empty)\fR"
Additional list of ciphers or cipher types to exclude from the
Postfix SMTP client cipher list at mandatory TLS security levels.
.IP "\fBsmtp_tls_dcert_file (empty)\fR"
File with the Postfix SMTP client DSA certificate in PEM format.
.IP "\fBsmtp_tls_dkey_file ($smtp_tls_dcert_file)\fR"
File with the Postfix SMTP client DSA private key in PEM format.
.IP "\fBsmtp_tls_key_file ($smtp_tls_cert_file)\fR"
File with the Postfix SMTP client RSA private key in PEM format.
.IP "\fBsmtp_tls_loglevel (0)\fR"
Enable additional Postfix SMTP client logging of TLS activity.
.IP "\fBsmtp_tls_note_starttls_offer (no)\fR"
Log the hostname of a remote SMTP server that offers STARTTLS,
when TLS is not already enabled for that server.
.IP "\fBsmtp_tls_policy_maps (empty)\fR"
Optional lookup tables with the Postfix SMTP client TLS security
policy by next\-hop destination; when a non\-empty value is specified,
this overrides the obsolete smtp_tls_per_site parameter.
.IP "\fBsmtp_tls_mandatory_protocols (see 'postconf -d' output)\fR"
TLS protocols that the Postfix SMTP client will use with mandatory
TLS encryption.
.IP "\fBsmtp_tls_scert_verifydepth (9)\fR"
The verification depth for remote SMTP server certificates.
.IP "\fBsmtp_tls_secure_cert_match (nexthop, dot\-nexthop)\fR"
How the Postfix SMTP client verifies the server certificate
peername for the "secure" TLS security level.
.IP "\fBsmtp_tls_session_cache_database (empty)\fR"
Name of the file containing the optional Postfix SMTP client
TLS session cache.
.IP "\fBsmtp_tls_session_cache_timeout (3600s)\fR"
The expiration time of Postfix SMTP client TLS session cache
information.
.IP "\fBsmtp_tls_verify_cert_match (hostname)\fR"
How the Postfix SMTP client verifies the server certificate
peername for the
"verify" TLS security level.
.IP "\fBtls_daemon_random_bytes (32)\fR"
The number of pseudo\-random bytes that an \fBsmtp\fR(8) or \fBsmtpd\fR(8)
process requests from the \fBtlsmgr\fR(8) server in order to seed its
internal pseudo random number generator (PRNG).
.IP "\fBtls_high_cipherlist (see 'postconf -d' output)\fR"
The OpenSSL cipherlist for "high" grade ciphers.
.IP "\fBtls_medium_cipherlist (see 'postconf -d' output)\fR"
The OpenSSL cipherlist for "medium" or higher grade ciphers.
.IP "\fBtls_null_cipherlist (eNULL:!aNULL)\fR"
The OpenSSL cipherlist for "NULL" grade ciphers that provide
authentication without encryption.
.PP
Available in in Postfix version 2.3..3.7:
.IP "\fBtls_low_cipherlist (see 'postconf -d' output)\fR"
The OpenSSL cipherlist for "low" or higher grade ciphers.
.IP "\fBtls_export_cipherlist (see 'postconf -d' output)\fR"
The OpenSSL cipherlist for "export" or higher grade ciphers.
.PP
Available in Postfix version 2.4 and later:
.IP "\fBsmtp_sasl_tls_verified_security_options ($smtp_sasl_tls_security_options)\fR"
The SASL authentication security options that the Postfix SMTP
client uses for TLS encrypted SMTP sessions with a verified server
certificate.
.PP
Available in Postfix version 2.5 and later:
.IP "\fBsmtp_tls_fingerprint_cert_match (empty)\fR"
List of acceptable remote SMTP server certificate fingerprints for
the "fingerprint" TLS security level (\fBsmtp_tls_security_level\fR =
fingerprint).
.IP "\fBsmtp_tls_fingerprint_digest (see 'postconf -d' output)\fR"
The message digest algorithm used to construct remote SMTP server
certificate fingerprints.
.PP
Available in Postfix version 2.6 and later:
.IP "\fBsmtp_tls_protocols (see postconf -d output)\fR"
TLS protocols that the Postfix SMTP client will use with
opportunistic TLS encryption.
.IP "\fBsmtp_tls_ciphers (medium)\fR"
The minimum TLS cipher grade that the Postfix SMTP client
will use with opportunistic TLS encryption.
.IP "\fBsmtp_tls_eccert_file (empty)\fR"
File with the Postfix SMTP client ECDSA certificate in PEM format.
.IP "\fBsmtp_tls_eckey_file ($smtp_tls_eccert_file)\fR"
File with the Postfix SMTP client ECDSA private key in PEM format.
.PP
Available in Postfix version 2.7 and later:
.IP "\fBsmtp_tls_block_early_mail_reply (no)\fR"
Try to detect a mail hijacking attack based on a TLS protocol
vulnerability (CVE\-2009\-3555), where an attacker prepends malicious
HELO, MAIL, RCPT, DATA commands to a Postfix SMTP client TLS session.
.PP
Available in Postfix version 2.8 and later:
.IP "\fBtls_disable_workarounds (see 'postconf -d' output)\fR"
List or bit\-mask of OpenSSL bug work\-arounds to disable.
.PP
Available in Postfix version 2.11\-3.1:
.IP "\fBtls_dane_digest_agility (on)\fR"
Configure RFC7671 DANE TLSA digest algorithm agility.
.IP "\fBtls_dane_trust_anchor_digest_enable (yes)\fR"
Enable support for RFC 6698 (DANE TLSA) DNS records that contain
digests of trust\-anchors with certificate usage "2".
.PP
Available in Postfix version 2.11 and later:
.IP "\fBsmtp_tls_trust_anchor_file (empty)\fR"
Zero or more PEM\-format files with trust\-anchor certificates
and/or public keys.
.IP "\fBsmtp_tls_force_insecure_host_tlsa_lookup (no)\fR"
Lookup the associated DANE TLSA RRset even when a hostname is
not an alias and its address records lie in an unsigned zone.
.IP "\fBtlsmgr_service_name (tlsmgr)\fR"
The name of the \fBtlsmgr\fR(8) service entry in master.cf.
.PP
Available in Postfix version 3.0 and later:
.IP "\fBsmtp_tls_wrappermode (no)\fR"
Request that the Postfix SMTP client connects using the
SUBMISSIONS/SMTPS protocol instead of using the STARTTLS command.
.PP
Available in Postfix version 3.1 and later:
.IP "\fBsmtp_tls_dane_insecure_mx_policy (see 'postconf -d' output)\fR"
The TLS policy for MX hosts with "secure" TLSA records when the
nexthop destination security level is \fBdane\fR, but the MX
record was found via an "insecure" MX lookup.
.PP
Available in Postfix version 3.2 and later:
.IP "\fBtls_eecdh_auto_curves (see 'postconf -d' output)\fR"
The prioritized list of elliptic curves supported by the Postfix
SMTP client and server.
.PP
Available in Postfix version 3.4 and later:
.IP "\fBsmtp_tls_connection_reuse (no)\fR"
Try to make multiple deliveries per TLS\-encrypted connection.
.IP "\fBsmtp_tls_chain_files (empty)\fR"
List of one or more PEM files, each holding one or more private keys
directly followed by a corresponding certificate chain.
.IP "\fBsmtp_tls_servername (empty)\fR"
Optional name to send to the remote SMTP server in the TLS Server
Name Indication (SNI) extension.
.PP
Available in Postfix 3.5, 3.4.6, 3.3.5, 3.2.10, 3.1.13 and later:
.IP "\fBtls_fast_shutdown_enable (yes)\fR"
A workaround for implementations that hang Postfix while shutting
down a TLS session, until Postfix times out.
.PP
Available in Postfix version 3.8 and later:
.IP "\fBtls_ffdhe_auto_groups (see 'postconf -d' output)\fR"
The prioritized list of finite\-field Diffie\-Hellman ephemeral
(FFDHE) key exchange groups supported by the Postfix SMTP client and
server.
.PP
Available in Postfix 3.9, 3.8.1, 3.7.6, 3.6.10, 3.5.20 and later:
.IP "\fBtls_config_file (default)\fR"
Optional configuration file with baseline OpenSSL settings.
.IP "\fBtls_config_name (empty)\fR"
The application name passed by Postfix to OpenSSL library
initialization functions.
.SH "OBSOLETE STARTTLS CONTROLS"
.na
.nf
.ad
.fi
The following configuration parameters exist for compatibility
with Postfix versions before 2.3. Support for these will
be removed in a future release.
.IP "\fBsmtp_use_tls (no)\fR"
Opportunistic mode: use TLS when a remote SMTP server announces
STARTTLS support, otherwise send the mail in the clear.
.IP "\fBsmtp_enforce_tls (no)\fR"
Enforcement mode: require that remote SMTP servers use TLS
encryption, and never send mail in the clear.
.IP "\fBsmtp_tls_enforce_peername (yes)\fR"
With mandatory TLS encryption, require that the remote SMTP
server hostname matches the information in the remote SMTP server
certificate.
.IP "\fBsmtp_tls_per_site (empty)\fR"
Optional lookup tables with the Postfix SMTP client TLS usage
policy by next\-hop destination and by remote SMTP server hostname.
.IP "\fBsmtp_tls_cipherlist (empty)\fR"
Obsolete Postfix < 2.3 control for the Postfix SMTP client TLS
cipher list.
.SH "RESOURCE AND RATE CONTROLS"
.na
.nf
.ad
.fi
.IP "\fBsmtp_connect_timeout (30s)\fR"
The Postfix SMTP client time limit for completing a TCP connection, or
zero (use the operating system built\-in time limit).
.IP "\fBsmtp_helo_timeout (300s)\fR"
The Postfix SMTP client time limit for sending the HELO or EHLO command,
and for receiving the initial remote SMTP server response.
.IP "\fBlmtp_lhlo_timeout (300s)\fR"
The Postfix LMTP client time limit for sending the LHLO command,
and for receiving the initial remote LMTP server response.
.IP "\fBsmtp_xforward_timeout (300s)\fR"
The Postfix SMTP client time limit for sending the XFORWARD command,
and for receiving the remote SMTP server response.
.IP "\fBsmtp_mail_timeout (300s)\fR"
The Postfix SMTP client time limit for sending the MAIL FROM command,
and for receiving the remote SMTP server response.
.IP "\fBsmtp_rcpt_timeout (300s)\fR"
The Postfix SMTP client time limit for sending the SMTP RCPT TO
command, and for receiving the remote SMTP server response.
.IP "\fBsmtp_data_init_timeout (120s)\fR"
The Postfix SMTP client time limit for sending the SMTP DATA command,
and for receiving the remote SMTP server response.
.IP "\fBsmtp_data_xfer_timeout (180s)\fR"
The Postfix SMTP client time limit for sending the SMTP message content.
.IP "\fBsmtp_data_done_timeout (600s)\fR"
The Postfix SMTP client time limit for sending the SMTP ".", and
for receiving the remote SMTP server response.
.IP "\fBsmtp_quit_timeout (300s)\fR"
The Postfix SMTP client time limit for sending the QUIT command,
and for receiving the remote SMTP server response.
.PP
Available in Postfix version 2.1 and later:
.IP "\fBsmtp_mx_address_limit (5)\fR"
The maximal number of MX (mail exchanger) IP addresses that can
result from Postfix SMTP client mail exchanger lookups, or zero (no
limit).
.IP "\fBsmtp_mx_session_limit (2)\fR"
The maximal number of SMTP sessions per delivery request before
the Postfix SMTP client
gives up or delivers to a fall\-back relay host, or zero (no
limit).
.IP "\fBsmtp_rset_timeout (20s)\fR"
The Postfix SMTP client time limit for sending the RSET command,
and for receiving the remote SMTP server response.
.PP
Available in Postfix version 2.2 and earlier:
.IP "\fBlmtp_cache_connection (yes)\fR"
Keep Postfix LMTP client connections open for up to $max_idle
seconds.
.PP
Available in Postfix version 2.2 and later:
.IP "\fBsmtp_connection_cache_destinations (empty)\fR"
Permanently enable SMTP connection caching for the specified
destinations.
.IP "\fBsmtp_connection_cache_on_demand (yes)\fR"
Temporarily enable SMTP connection caching while a destination
has a high volume of mail in the active queue.
.IP "\fBsmtp_connection_reuse_time_limit (300s)\fR"
The amount of time during which Postfix will use an SMTP
connection repeatedly.
.IP "\fBsmtp_connection_cache_time_limit (2s)\fR"
When SMTP connection caching is enabled, the amount of time that
an unused SMTP client socket is kept open before it is closed.
.PP
Available in Postfix version 2.3 and later:
.IP "\fBconnection_cache_protocol_timeout (5s)\fR"
Time limit for connection cache connect, send or receive
operations.
.PP
Available in Postfix version 2.9 \- 3.6:
.IP "\fBsmtp_per_record_deadline (no)\fR"
Change the behavior of the smtp_*_timeout time limits, from a
time limit per read or write system call, to a time limit to send
or receive a complete record (an SMTP command line, SMTP response
line, SMTP message content line, or TLS protocol message).
.PP
Available in Postfix version 2.11 and later:
.IP "\fBsmtp_connection_reuse_count_limit (0)\fR"
When SMTP connection caching is enabled, the number of times
that an SMTP session may be reused before it is closed, or zero (no
limit).
.PP
Available in Postfix version 3.4 and later:
.IP "\fBsmtp_tls_connection_reuse (no)\fR"
Try to make multiple deliveries per TLS\-encrypted connection.
.PP
Available in Postfix version 3.7 and later:
.IP "\fBsmtp_per_request_deadline (no)\fR"
Change the behavior of the smtp_*_timeout time limits, from a
time limit per plaintext or TLS read or write call, to a combined
time limit for sending a complete SMTP request and for receiving a
complete SMTP response.
.IP "\fBsmtp_min_data_rate (500)\fR"
The minimum plaintext data transfer rate in bytes/second for
DATA requests, when deadlines are enabled with smtp_per_request_deadline.
.PP
Implemented in the qmgr(8) daemon:
.IP "\fBtransport_destination_concurrency_limit ($default_destination_concurrency_limit)\fR"
A transport\-specific override for the
default_destination_concurrency_limit parameter value, where
\fItransport\fR is the master.cf name of the message delivery
transport.
.IP "\fBtransport_destination_recipient_limit ($default_destination_recipient_limit)\fR"
A transport\-specific override for the
default_destination_recipient_limit parameter value, where
\fItransport\fR is the master.cf name of the message delivery
transport.
.SH "SMTPUTF8 CONTROLS"
.na
.nf
.ad
.fi
Preliminary SMTPUTF8 support is introduced with Postfix 3.0.
.IP "\fBsmtputf8_enable (yes)\fR"
Enable preliminary SMTPUTF8 support for the protocols described
in RFC 6531, RFC 6532, and RFC 6533.
.IP "\fBsmtputf8_autodetect_classes (sendmail, verify)\fR"
Detect that a message requires SMTPUTF8 support for the specified
mail origin classes.
.PP
Available in Postfix version 3.2 and later:
.IP "\fBenable_idna2003_compatibility (no)\fR"
Enable 'transitional' compatibility between IDNA2003 and IDNA2008,
when converting UTF\-8 domain names to/from the ASCII form that is
used for DNS lookups.
.SH "TROUBLE SHOOTING CONTROLS"
.na
.nf
.ad
.fi
.IP "\fBdebug_peer_level (2)\fR"
The increment in verbose logging level when a nexthop destination,
remote client or server name or network address matches a pattern
given with the debug_peer_list parameter.
.IP "\fBdebug_peer_list (empty)\fR"
Optional list of nexthop destination, remote client or server
name or network address patterns that, if matched, cause the verbose
logging level to increase by the amount specified in $debug_peer_level.
.IP "\fBerror_notice_recipient (postmaster)\fR"
The recipient of postmaster notifications about mail delivery
problems that are caused by policy, resource, software or protocol
errors.
.IP "\fBinternal_mail_filter_classes (empty)\fR"
What categories of Postfix\-generated mail are subject to
before\-queue content inspection by non_smtpd_milters, header_checks
and body_checks.
.IP "\fBnotify_classes (resource, software)\fR"
The list of error classes that are reported to the postmaster.
.SH "MISCELLANEOUS CONTROLS"
.na
.nf
.ad
.fi
.IP "\fBbest_mx_transport (empty)\fR"
Where the Postfix SMTP client should deliver mail when it detects
a "mail loops back to myself" error condition.
.IP "\fBconfig_directory (see 'postconf -d' output)\fR"
The default location of the Postfix main.cf and master.cf
configuration files.
.IP "\fBdaemon_timeout (18000s)\fR"
How much time a Postfix daemon process may take to handle a
request before it is terminated by a built\-in watchdog timer.
.IP "\fBdelay_logging_resolution_limit (2)\fR"
The maximal number of digits after the decimal point when logging
sub\-second delay values.
.IP "\fBdisable_dns_lookups (no)\fR"
Disable DNS lookups in the Postfix SMTP and LMTP clients.
.IP "\fBinet_interfaces (all)\fR"
The local network interface addresses that this mail system receives
mail on.
.IP "\fBinet_protocols (see 'postconf -d output')\fR"
The Internet protocols Postfix will attempt to use when making
or accepting connections.
.IP "\fBipc_timeout (3600s)\fR"
The time limit for sending or receiving information over an internal
communication channel.
.IP "\fBlmtp_assume_final (no)\fR"
When a remote LMTP server announces no DSN support, assume that
the
server performs final delivery, and send "delivered" delivery status
notifications instead of "relayed".
.IP "\fBlmtp_tcp_port (24)\fR"
The default TCP port that the Postfix LMTP client connects to.
.IP "\fBmax_idle (100s)\fR"
The maximum amount of time that an idle Postfix daemon process waits
for an incoming connection before terminating voluntarily.
.IP "\fBmax_use (100)\fR"
The maximal number of incoming connections that a Postfix daemon
process will service before terminating voluntarily.
.IP "\fBprocess_id (read\-only)\fR"
The process ID of a Postfix command or daemon process.
.IP "\fBprocess_name (read\-only)\fR"
The process name of a Postfix command or daemon process.
.IP "\fBproxy_interfaces (empty)\fR"
The remote network interface addresses that this mail system receives mail
on by way of a proxy or network address translation unit.
.IP "\fBsmtp_address_preference (any)\fR"
The address type ("ipv6", "ipv4" or "any") that the Postfix
SMTP client will try first, when a destination has IPv6 and IPv4
addresses with equal MX preference.
.IP "\fBsmtp_bind_address (empty)\fR"
An optional numerical network address that the Postfix SMTP client
should bind to when making an IPv4 connection.
.IP "\fBsmtp_bind_address6 (empty)\fR"
An optional numerical network address that the Postfix SMTP client
should bind to when making an IPv6 connection.
.IP "\fBsmtp_helo_name ($myhostname)\fR"
The hostname to send in the SMTP HELO or EHLO command.
.IP "\fBlmtp_lhlo_name ($myhostname)\fR"
The hostname to send in the LMTP LHLO command.
.IP "\fBsmtp_host_lookup (dns)\fR"
What mechanisms the Postfix SMTP client uses to look up a host's
IP address.
.IP "\fBsmtp_randomize_addresses (yes)\fR"
Randomize the order of equal\-preference MX host addresses.
.IP "\fBsyslog_facility (mail)\fR"
The syslog facility of Postfix logging.
.IP "\fBsyslog_name (see 'postconf -d' output)\fR"
A prefix that is prepended to the process name in syslog
records, so that, for example, "smtpd" becomes "prefix/smtpd".
.PP
Available with Postfix 2.2 and earlier:
.IP "\fBfallback_relay (empty)\fR"
Optional list of relay hosts for SMTP destinations that can't be
found or that are unreachable.
.PP
Available with Postfix 2.3 and later:
.IP "\fBsmtp_fallback_relay ($fallback_relay)\fR"
Optional list of relay destinations that will be used when an
SMTP destination is not found, or when delivery fails due to a
non\-permanent error.
.PP
Available with Postfix 3.0 and later:
.IP "\fBsmtp_address_verify_target (rcpt)\fR"
In the context of email address verification, the SMTP protocol
stage that determines whether an email address is deliverable.
.PP
Available with Postfix 3.1 and later:
.IP "\fBlmtp_fallback_relay (empty)\fR"
Optional list of relay hosts for LMTP destinations that can't be
found or that are unreachable.
.PP
Available with Postfix 3.2 and later:
.IP "\fBsmtp_tcp_port (smtp)\fR"
The default TCP port that the Postfix SMTP client connects to.
.PP
Available in Postfix 3.3 and later:
.IP "\fBservice_name (read\-only)\fR"
The master.cf service name of a Postfix daemon process.
.PP
Available in Postfix 3.7 and later:
.IP "\fBsmtp_bind_address_enforce (no)\fR"
Defer delivery when the Postfix SMTP client cannot apply the
smtp_bind_address or smtp_bind_address6 setting.
.SH "SEE ALSO"
.na
.nf
generic(5), output address rewriting
header_checks(5), message header content inspection
body_checks(5), body parts content inspection
qmgr(8), queue manager
bounce(8), delivery status reports
scache(8), connection cache server
postconf(5), configuration parameters
master(5), generic daemon options
master(8), process manager
tlsmgr(8), TLS session and PRNG management
postlogd(8), Postfix logging
syslogd(8), system logging
.SH "README FILES"
.na
.nf
.ad
.fi
Use "\fBpostconf readme_directory\fR" or
"\fBpostconf html_directory\fR" to locate this information.
.na
.nf
SASL_README, Postfix SASL howto
TLS_README, Postfix STARTTLS howto
.SH "LICENSE"
.na
.nf
.ad
.fi
The Secure Mailer license must be distributed with this software.
.SH "AUTHOR(S)"
.na
.nf
Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA

Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA

Command pipelining in cooperation with:
Jon Ribbens
Oaktree Internet Solutions Ltd.,
Internet House,
Canal Basin,
Coventry,
CV1 4LY, United Kingdom.

SASL support originally by:
Till Franke
SuSE Rhein/Main AG
65760 Eschborn, Germany

TLS support originally by:
Lutz Jaenicke
BTU Cottbus
Allgemeine Elektrotechnik
Universitaetsplatz 3\-4
D\-03044 Cottbus, Germany

Revised TLS and SMTP connection cache support by:
Victor Duchovni
Morgan Stanley