Adding upstream version 3.8.5.upstream/3.8.5

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 15683 insertions, 0 deletions

diff --git a/man/man5/postconf.5 b/man/man5/postconf.5
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+.TH POSTCONF 5 
+.SH NAME
+postconf
+\-
+Postfix configuration parameters
+.SH SYNOPSIS
+.na
+.nf
+\fBpostconf\fR \fIparameter\fR ...
+
+\fBpostconf \-e\fR "\fIparameter=value\fR" ...
+.SH DESCRIPTION
+.ad
+.fi
+The Postfix main.cf configuration file specifies parameters that
+control the operation of the Postfix mail system. Typically the
+file contains only a small subset of all parameters; parameters
+not specified are left at their default values.
+.PP
+The general format of the main.cf file is as follows:
+.IP \(bu
+Each logical line has the form "parameter = value".
+Whitespace around the "=" is ignored, as is whitespace at the
+end of a logical line.
+.IP \(bu
+Empty lines and whitespace-only lines are ignored, as are lines
+whose first non-whitespace character is a `#'.
+.IP \(bu
+A logical line starts with non-whitespace text. A line that starts
+with whitespace continues a logical line.
+.IP \(bu
+A parameter value may refer to other parameters.
+.RS
+.IP \(bu 
+The expressions "$name" and "${name}" are recursively replaced with
+the value of the named parameter. The parameter name must contain
+only characters from the set [a-zA-Z0-9_]. An undefined parameter
+value is replaced with the empty value.
+.IP \(bu
+The expressions "${name?value}" and "${name?{value}}" are replaced
+with "value" when "$name" is non-empty. The parameter name must
+contain only characters from the set [a-zA-Z0-9_]. These forms are
+supported with Postfix versions >= 2.2 and >= 3.0, respectively.
+.IP \(bu
+The expressions "${name:value}" and "${name:{value}}" are replaced
+with "value" when "$name" is empty. The parameter name must contain
+only characters from the set [a-zA-Z0-9_]. These forms are supported
+with Postfix versions >= 2.2 and >= 3.0, respectively.
+.IP \(bu
+The expression "${name?{value1}:{value2}}" is replaced with "value1"
+when "$name" is non-empty, and with "value2" when "$name" is empty.
+The "{}" is required for "value1", optional for "value2". The
+parameter name must contain only characters from the set [a-zA-Z0-9_].
+This form is supported with Postfix versions >= 3.0.
+.IP \(bu
+The first item inside "${...}" may be a relational expression of the
+form: "{value3} == {value4}". Besides the "==" (equality) operator
+Postfix supports "!=" (inequality), "<", "<=", ">=", and ">". The
+comparison is numerical when both operands are all digits, otherwise
+the comparison is lexicographical. These forms are supported with
+Postfix versions >= 3.0.
+.IP \(bu
+Each "value" is subject to recursive named parameter and relational
+expression evaluation, except where noted.
+.IP \(bu
+Whitespace before or after each "{value}" is ignored.
+.IP \(bu
+Specify "$$" to produce a single "$" character.
+.IP \(bu
+The legacy form "$(...)" is equivalent to the preferred form "${...}".
+.RE
+.IP \(bu
+When the same parameter is defined multiple times, only the last
+instance is remembered.
+.IP \(bu
+Otherwise, the order of main.cf parameter definitions does not matter.
+.PP
+The remainder of this document is a description of all Postfix
+configuration parameters. Default values are shown after the 
+parameter name in parentheses, and can be looked up with the
+"\fBpostconf \-d\fR" command. 
+.PP
+Note: this is not an invitation to make changes to Postfix
+configuration parameters. Unnecessary changes can impair the
+operation of the mail system.
+.SH 2bounce_notice_recipient (default: postmaster)
+The recipient of undeliverable mail that cannot be returned to
+the sender.  This feature is enabled with the notify_classes
+parameter.
+.SH access_map_defer_code (default: 450)
+The numerical Postfix SMTP server response code for
+an \fBaccess\fR(5) map "defer" action, including "defer_if_permit"
+or "defer_if_reject". Prior to Postfix 2.6, the response
+is hard\-coded as "450".
+.PP
+Do not change this unless you have a complete understanding of RFC 5321.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH access_map_reject_code (default: 554)
+The numerical Postfix SMTP server response code for
+an \fBaccess\fR(5) map "reject" action.
+.PP
+Do not change this unless you have a complete understanding of RFC 5321.
+.SH address_verify_cache_cleanup_interval (default: 12h)
+The amount of time between \fBverify\fR(8) address verification
+database cleanup runs. This feature requires that the database
+supports the "delete" and "sequence" operators.  Specify a zero
+interval to disable database cleanup.
+.PP
+After each database cleanup run, the \fBverify\fR(8) daemon logs the
+number of entries that were retained and dropped. A cleanup run is
+logged as "partial" when the daemon terminates early after "\fBpostfix
+reload\fR", "\fBpostfix stop\fR", or no requests for $max_idle
+seconds.
+.PP
+Specify a non\-negative time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is h (hours).
+.PP
+This feature is available in Postfix 2.7.
+.SH address_verify_default_transport (default: $default_transport)
+Overrides the default_transport parameter setting for address
+verification probes.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH address_verify_local_transport (default: $local_transport)
+Overrides the local_transport parameter setting for address
+verification probes.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH address_verify_map (default: see "postconf \-d" output)
+Lookup table for persistent address verification status
+storage.  The table is maintained by the \fBverify\fR(8) service, and
+is opened before the process releases privileges.
+.PP
+The lookup table is persistent by default (Postfix 2.7 and later).
+Specify an empty table name to keep the information in volatile
+memory which is lost after "\fBpostfix reload\fR" or "\fBpostfix
+stop\fR". This is the default with Postfix version 2.6 and earlier.
+.PP
+Specify a location in a file system that will not fill up. If the
+database becomes corrupted, the world comes to an end. To recover,
+delete (NOT: truncate) the file and do "\fBpostfix reload\fR".
+.PP
+Postfix daemon processes do not use root privileges when opening
+this file (Postfix 2.5 and later).  The file must therefore be
+stored under a Postfix\-owned directory such as the data_directory.
+As a migration aid, an attempt to open the file under a non\-Postfix
+directory is redirected to the Postfix\-owned data_directory, and a
+warning is logged.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+address_verify_map = hash:/var/lib/postfix/verify
+address_verify_map = btree:/var/lib/postfix/verify
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH address_verify_negative_cache (default: yes)
+Enable caching of failed address verification probe results.  When
+this feature is enabled, the cache may pollute quickly with garbage.
+When this feature is disabled, Postfix will generate an address
+probe for every lookup.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH address_verify_negative_expire_time (default: 3d)
+The time after which a failed probe expires from the address
+verification cache.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is d (days).
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH address_verify_negative_refresh_time (default: 3h)
+The time after which a failed address verification probe needs to
+be refreshed.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is h (hours).
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH address_verify_pending_request_limit (default: see "postconf \-d" output)
+A safety limit that prevents address verification requests from
+overwhelming the Postfix queue. By default, the number of pending
+requests is limited to 1/4 of the active queue maximum size
+(qmgr_message_active_limit). The queue manager enforces the limit
+by tempfailing requests that exceed the limit. This affects only
+unknown addresses and inactive addresses that have expired, because
+the \fBverify\fR(8) daemon automatically refreshes an active address
+before it expires.
+.PP
+This feature is available in Postfix 3.1 and later.
+.SH address_verify_poll_count (default: normal: 3, overload: 1)
+How many times to query the \fBverify\fR(8) service for the completion
+of an address verification request in progress.
+.PP
+By default, the Postfix SMTP server polls the \fBverify\fR(8) service
+up to three times under non\-overload conditions, and only once when
+under overload.  With Postfix version 2.5 and earlier, the SMTP
+server always polls the \fBverify\fR(8) service up to three times by
+default.
+.PP
+Specify 1 to implement a crude form of greylisting, that is, always
+defer the first delivery request for a new address.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+# Postfix <= 2.6 default
+address_verify_poll_count = 3
+# Poor man's greylisting
+address_verify_poll_count = 1
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH address_verify_poll_delay (default: 3s)
+The delay between queries for the completion of an address
+verification request in progress.
+.PP
+The default polling delay is 3 seconds.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH address_verify_positive_expire_time (default: 31d)
+The time after which a successful probe expires from the address
+verification cache.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is d (days).
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH address_verify_positive_refresh_time (default: 7d)
+The time after which a successful address verification probe needs
+to be refreshed.  The address verification status is not updated
+when the probe fails (optimistic caching).
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is d (days).
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH address_verify_relay_transport (default: $relay_transport)
+Overrides the relay_transport parameter setting for address
+verification probes.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH address_verify_relayhost (default: $relayhost)
+Overrides the relayhost parameter setting for address verification
+probes. This information can be overruled with the \fBtransport\fR(5) table.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH address_verify_sender (default: $double_bounce_sender)
+The sender address to use in address verification probes; prior
+to Postfix 2.5 the default was "postmaster". To
+avoid problems with address probes that are sent in response to
+address probes, the Postfix SMTP server excludes the probe sender
+address from all SMTPD access blocks.
+.PP
+Specify an empty value (address_verify_sender =) or <> if you want
+to use the null sender address. Beware, some sites reject mail from
+<>, even though RFCs require that such addresses be accepted.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+address_verify_sender = <>
+address_verify_sender = postmaster@mydomain
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH address_verify_sender_dependent_default_transport_maps (default: $sender_dependent_default_transport_maps)
+Overrides the sender_dependent_default_transport_maps parameter
+setting for address verification probes.
+.PP
+This feature is available in Postfix 2.7 and later.
+.SH address_verify_sender_dependent_relayhost_maps (default: $sender_dependent_relayhost_maps)
+Overrides the sender_dependent_relayhost_maps parameter setting for address
+verification probes.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH address_verify_sender_ttl (default: 0s)
+The time between changes in the time\-dependent portion of address
+verification probe sender addresses. The time\-dependent portion is
+appended to the localpart of the address specified with the
+address_verify_sender parameter. This feature is ignored when the
+probe sender addresses is the null sender, i.e. the address_verify_sender
+value is empty or <>.
+.PP
+Historically, the probe sender address was fixed. This has
+caused such addresses to end up on spammer mailing lists, and has
+resulted in wasted network and processing resources.
+.PP
+To enable time\-dependent probe sender addresses, specify a
+non\-zero time value. Specify a value of at least several hours,
+to avoid problems with senders that use greylisting. Avoid nice
+TTL values, to make the result less predictable.
+.PP
+Specify a non\-negative time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.9 and later.
+.SH address_verify_service_name (default: verify)
+The name of the \fBverify\fR(8) address verification service. This service
+maintains the status of sender and/or recipient address verification
+probes, and generates probes on request by other Postfix processes.
+.SH address_verify_transport_maps (default: $transport_maps)
+Overrides the transport_maps parameter setting for address verification
+probes.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH address_verify_virtual_transport (default: $virtual_transport)
+Overrides the virtual_transport parameter setting for address
+verification probes.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH alias_database (default: see "postconf \-d" output)
+The alias databases for \fBlocal\fR(8) delivery that are updated with
+"\fBnewaliases\fR" or with "\fBsendmail \-bi\fR".
+.PP
+This is a separate configuration parameter because not all the
+tables specified with $alias_maps have to be local files.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+alias_database = hash:/etc/aliases
+alias_database = hash:/etc/mail/aliases
+.fi
+.ad
+.ft R
+.SH alias_maps (default: see "postconf \-d" output)
+The alias databases that are used for \fBlocal\fR(8) delivery. See
+\fBaliases\fR(5) for syntax details.
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+Note: these lookups are recursive.
+.PP
+The default list is system dependent.  On systems with NIS, the
+default is to search the local alias database, then the NIS alias
+database.
+.PP
+If you change the alias database, run "\fBpostalias /etc/aliases\fR"
+(or wherever your system stores the mail alias file), or simply
+run "\fBnewaliases\fR" to build the necessary DBM or DB file.
+.PP
+The \fBlocal\fR(8) delivery agent disallows regular expression substitution
+of $1 etc. in alias_maps, because that would open a security hole.
+.PP
+The \fBlocal\fR(8) delivery agent will silently ignore requests to use
+the \fBproxymap\fR(8) server within alias_maps. Instead it will open the
+table directly. Before Postfix version 2.2, the \fBlocal\fR(8) delivery
+agent will terminate with a fatal error.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+alias_maps = hash:/etc/aliases, nis:mail.aliases
+alias_maps = hash:/etc/aliases
+.fi
+.ad
+.ft R
+.SH allow_mail_to_commands (default: alias, forward)
+Restrict \fBlocal\fR(8) mail delivery to external commands.  The default
+is to disallow delivery to "|command" in :include:  files (see
+\fBaliases\fR(5) for the text that defines this terminology).
+.PP
+Specify zero or more of: \fBalias\fR, \fBforward\fR or \fBinclude\fR,
+in order to allow commands in \fBaliases\fR(5), .forward files or in
+:include:  files, respectively.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+allow_mail_to_commands = alias,forward,include
+.fi
+.ad
+.ft R
+.SH allow_mail_to_files (default: alias, forward)
+Restrict \fBlocal\fR(8) mail delivery to external files. The default is
+to disallow "/file/name" destinations in :include:  files (see
+\fBaliases\fR(5) for the text that defines this terminology).
+.PP
+Specify zero or more of: \fBalias\fR, \fBforward\fR or \fBinclude\fR,
+in order to allow "/file/name" destinations in \fBaliases\fR(5), .forward
+files and in :include:  files, respectively.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+allow_mail_to_files = alias,forward,include
+.fi
+.ad
+.ft R
+.SH allow_min_user (default: no)
+Allow a sender or recipient address to have `\-' as the first
+character.  By
+default, this is not allowed, to avoid accidents with software that
+passes email addresses via the command line. Such software
+would not be able to distinguish a malicious address from a
+bona fide command\-line option. Although this can be prevented by
+inserting a "\-\-" option terminator into the command line, this is
+difficult to enforce consistently and globally.
+.PP
+As of Postfix version 2.5, this feature is implemented by
+trivial\-\fBrewrite\fR(8).  With earlier versions this feature was implemented
+by \fBqmgr\fR(8) and was limited to recipient addresses only.
+.SH allow_percent_hack (default: yes)
+Enable the rewriting of the form "user%domain" to "user@domain".
+This is enabled by default.
+.PP
+Note: as of Postfix version 2.2, message header address rewriting
+happens only when one of the following conditions is true:
+.IP \(bu
+The message is received with the Postfix \fBsendmail\fR(1) command,
+.IP \(bu
+The message is received from a network client that matches
+$local_header_rewrite_clients,
+.IP \(bu
+The message is received from the network, and the
+remote_header_rewrite_domain parameter specifies a non\-empty value.
+.br
+.PP
+To get the behavior before Postfix version 2.2, specify
+"local_header_rewrite_clients = static:all".
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+allow_percent_hack = no
+.fi
+.ad
+.ft R
+.SH allow_srv_lookup_fallback (default: no)
+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.
+.PP
+This feature is available in Postfix 3.8 and later.
+.SH allow_untrusted_routing (default: no)
+Forward mail with sender\-specified routing (user[@%!]remote[@%!]site)
+from untrusted clients to destinations matching $relay_domains.
+.PP
+By default, this feature is turned off.  This closes a nasty open
+relay loophole where a backup MX host can be tricked into forwarding
+junk mail to a primary MX host which then spams it out to the world.
+.PP
+This parameter also controls if non\-local addresses with sender\-specified
+routing can match Postfix access tables. By default, such addresses
+cannot match Postfix access tables, because the address is ambiguous.
+.SH alternate_config_directories (default: empty)
+A list of non\-default Postfix configuration directories that may
+be specified with "\-c config_directory" on the command line (in the
+case of \fBsendmail\fR(1), with the "\-C" option), or via the MAIL_CONFIG
+environment parameter.
+.PP
+This list must be specified in the default Postfix main.cf file,
+and will be used by set\-gid Postfix commands such as \fBpostqueue\fR(1)
+and \fBpostdrop\fR(1).
+.PP
+Specify absolute pathnames, separated by comma or space. Note: $name
+expansion is not supported.
+.SH always_add_missing_headers (default: no)
+Always add (Resent\-) From:, To:, Date: or Message\-ID: headers
+when not present.  Postfix 2.6 and later add these headers only
+when clients match the local_header_rewrite_clients parameter
+setting.  Earlier Postfix versions always add these headers; this
+may break DKIM signatures that cover non\-existent headers.
+The undisclosed_recipients_header parameter setting determines
+whether a To: header will be added.
+.SH always_bcc (default: empty)
+Optional address that receives a "blind carbon copy" of each message
+that is received by the Postfix mail system.
+.PP
+Note: with Postfix 2.3 and later the BCC address is added as if it
+was specified with NOTIFY=NONE. The sender will not be notified
+when the BCC address is undeliverable, as long as all down\-stream
+software implements RFC 3461.
+.PP
+Note: with Postfix 2.2 and earlier the sender will be notified
+when the BCC address is undeliverable.
+.PP
+Note: automatic BCC recipients are produced only for new mail.
+To avoid mailer loops, automatic BCC recipients are not generated
+after Postfix forwards mail internally, or after Postfix generates
+mail itself.
+.SH anvil_rate_time_unit (default: 60s)
+The time unit over which client connection rates and other rates
+are calculated.
+.PP
+This feature is implemented by the \fBanvil\fR(8) service which is available
+in Postfix version 2.2 and later.
+.PP
+The default interval is relatively short. Because of the high
+frequency of updates, the \fBanvil\fR(8) server uses volatile memory
+only. Thus, information is lost whenever the process terminates.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH anvil_status_update_time (default: 600s)
+How frequently the \fBanvil\fR(8) connection and rate limiting server
+logs peak usage information.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH append_at_myorigin (default: yes)
+With locally submitted mail, append the string "@$myorigin" to mail
+addresses without domain information. With remotely submitted mail,
+append the string "@$remote_header_rewrite_domain" instead.
+.PP
+Note 1: this feature is enabled by default and must not be turned off.
+Postfix does not support domain\-less addresses.
+.PP
+Note 2: with Postfix version 2.2, message header address rewriting
+happens only when one of the following conditions is true:
+.IP \(bu
+The message is received with the Postfix \fBsendmail\fR(1) command,
+.IP \(bu
+The message is received from a network client that matches
+$local_header_rewrite_clients,
+.IP \(bu
+The message is received from the network, and the
+remote_header_rewrite_domain parameter specifies a non\-empty value.
+.br
+.PP
+To get the behavior before Postfix version 2.2, specify
+"local_header_rewrite_clients = static:all".
+.SH append_dot_mydomain (default: Postfix >= 3.0: no, Postfix < 3.0: yes)
+With locally submitted mail, append the string ".$mydomain" to
+addresses that have no ".domain" information. With remotely submitted
+mail, append the string ".$remote_header_rewrite_domain"
+instead.
+.PP
+Note 1: When disabled (Postfix 3.0 and later), users will not be
+able to send mail to "user@partialdomainname" but will have to
+specify full domain names instead.
+.PP
+Note 2: with Postfix version 2.2, message header address rewriting
+happens only when one of the following conditions is true:
+.IP \(bu
+The message is received with the Postfix \fBsendmail\fR(1) command,
+.IP \(bu
+The message is received from a network client that matches
+$local_header_rewrite_clients,
+.IP \(bu
+The message is received from the network, and the
+remote_header_rewrite_domain parameter specifies a non\-empty value.
+.br
+.PP
+To get the behavior before Postfix version 2.2, specify
+"local_header_rewrite_clients = static:all".
+.SH application_event_drain_time (default: 100s)
+How long the \fBpostkick\fR(1) command waits for a request to enter the
+Postfix daemon process input buffer before giving up.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH authorized_flush_users (default: static:anyone)
+List of users who are authorized to flush the queue.
+.PP
+By default, all users are allowed to flush the queue.  Access is
+always granted if the invoking user is the super\-user or the
+$mail_owner user.  Otherwise, the real UID of the process is looked
+up in the system password file, and access is granted only if the
+corresponding login name is on the access list.  The username
+"unknown" is used for processes whose real UID is not found in the
+password file.
+.PP
+Specify a list of user names, "/file/name" or "type:table" patterns,
+separated by commas and/or whitespace. The list is matched left to
+right, and the search stops on the first match. A "/file/name"
+pattern is replaced
+by its contents; a "type:table" lookup table is matched when a name
+matches a lookup key (the lookup result is ignored).  Continue long
+lines by starting the next line with whitespace. Specify "!pattern"
+to exclude a name from the list. The form "!/file/name" is supported
+only in Postfix version 2.4 and later.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH authorized_mailq_users (default: static:anyone)
+List of users who are authorized to view the queue.
+.PP
+By default, all users are allowed to view the queue.  Access is
+always granted if the invoking user is the super\-user or the
+$mail_owner user.  Otherwise, the real UID of the process is looked
+up in the system password file, and access is granted only if the
+corresponding login name is on the access list.  The username
+"unknown" is used for processes whose real UID is not found in the
+password file.
+.PP
+Specify a list of user names, "/file/name" or "type:table" patterns,
+separated by commas and/or whitespace. The list is matched left to
+right, and the search stops on the first match. A "/file/name"
+pattern is replaced
+by its contents; a "type:table" lookup table is matched when a name
+matches a lookup key (the lookup result is ignored).  Continue long
+lines by starting the next line with whitespace. Specify "!pattern"
+to exclude a user name from the list. The form "!/file/name" is
+supported only in Postfix version 2.4 and later.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH authorized_submit_users (default: static:anyone)
+List of users who are authorized to submit mail with the \fBsendmail\fR(1)
+command (and with the privileged \fBpostdrop\fR(1) helper command).
+.PP
+By default, all users are allowed to submit mail.  Otherwise, the
+real UID of the process is looked up in the system password file,
+and access is granted only if the corresponding login name is on
+the access list.  The username "unknown" is used for processes
+whose real UID is not found in the password file. To deny mail
+submission access to all users specify an empty list.
+.PP
+Specify a list of user names, "/file/name" or "type:table" patterns,
+separated by commas and/or whitespace. The list is matched left to right,
+and the search stops on the first match. A "/file/name" pattern is
+replaced by its contents;
+a "type:table" lookup table is matched when a name matches a lookup key
+(the lookup result is ignored).  Continue long lines by starting the
+next line with whitespace. Specify "!pattern" to exclude a user
+name from the list. The form "!/file/name" is supported only in
+Postfix version 2.4 and later.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+authorized_submit_users = !www, static:all
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH authorized_verp_clients (default: $mynetworks)
+What remote SMTP clients are allowed to specify the XVERP command.
+This command requests that mail be delivered one recipient at a
+time with a per recipient return address.
+.PP
+By default, only trusted clients are allowed to specify XVERP.
+.PP
+This parameter was introduced with Postfix version 1.1.  Postfix
+version 2.1 renamed this parameter to smtpd_authorized_verp_clients
+and changed the default to none.
+.PP
+Specify a list of network/netmask patterns, separated by commas
+and/or whitespace. The mask specifies the number of bits in the
+network part of a host address. You can also specify hostnames or
+\&.domain names (the initial dot causes the domain to match any name
+below it),  "/file/name" or "type:table" patterns.  A "/file/name"
+pattern is replaced by its contents; a "type:table" lookup table
+is matched when a table entry matches a lookup string (the lookup
+result is ignored).  Continue long lines by starting the next line
+with whitespace. Specify "!pattern" to exclude an address or network
+block from the list. The form "!/file/name" is supported only in
+Postfix version 2.4 and later.
+.PP
+Note: IP version 6 address information must be specified inside
+[] in the authorized_verp_clients value, and in files
+specified with "/file/name".  IP version 6 addresses contain the
+":" character, and would otherwise be confused with a "type:table"
+pattern.
+.SH backwards_bounce_logfile_compatibility (default: yes)
+Produce additional \fBbounce\fR(8) logfile records that can be read by
+Postfix versions before 2.0. The current and more extensible "name =
+value" format is needed in order to implement more sophisticated
+functionality.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH berkeley_db_create_buffer_size (default: 16777216)
+The per\-table I/O buffer size for programs that create Berkeley DB
+hash or btree tables.  Specify a byte count.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH berkeley_db_read_buffer_size (default: 131072)
+The per\-table I/O buffer size for programs that read Berkeley DB
+hash or btree tables.  Specify a byte count.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH best_mx_transport (default: empty)
+Where the Postfix SMTP client should deliver mail when it detects
+a "mail loops back to myself" error condition. This happens when
+the local MTA is the best SMTP mail exchanger for a destination
+not listed in $mydestination, $inet_interfaces, $proxy_interfaces,
+$virtual_alias_domains, or $virtual_mailbox_domains.  By default,
+the Postfix SMTP client returns such mail as undeliverable.
+.PP
+Specify, for example, "best_mx_transport = local" to pass the mail
+from the Postfix SMTP client to the \fBlocal\fR(8) delivery agent. You
+can specify
+any message delivery "transport" or "transport:nexthop" that is
+defined in the master.cf file. See the \fBtransport\fR(5) manual page
+for the syntax and meaning of "transport" or "transport:nexthop".
+.PP
+However, this feature is expensive because it ties up a Postfix
+SMTP client process while the \fBlocal\fR(8) delivery agent is doing its
+work. It is more efficient (for Postfix) to list all hosted domains
+in a table or database.
+.SH biff (default: yes)
+Whether or not to use the local biff service.  This service sends
+"new mail" notifications to users who have requested new mail
+notification with the UNIX command "biff y".
+.PP
+For compatibility reasons this feature is on by default.  On systems
+with lots of interactive users, the biff service can be a performance
+drain.  Specify "biff = no" in main.cf to disable.
+.SH body_checks (default: empty)
+Optional lookup tables for content inspection as specified in
+the \fBbody_checks\fR(5) manual page.
+.PP
+Note: with Postfix versions before 2.0, these rules inspect
+all content after the primary message headers.
+.SH body_checks_size_limit (default: 51200)
+How much text in a message body segment (or attachment, if you
+prefer to use that term) is subjected to body_checks inspection.
+The amount of text is limited to avoid scanning huge attachments.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH bounce_notice_recipient (default: postmaster)
+The recipient of postmaster notifications with the message headers
+of mail that Postfix did not deliver and of SMTP conversation
+transcripts of mail that Postfix did not receive.  This feature is
+enabled with the notify_classes parameter.
+.SH bounce_queue_lifetime (default: 5d)
+Consider a bounce message as undeliverable, when delivery fails
+with a temporary error, and the time in the queue has reached the
+bounce_queue_lifetime limit.  By default, this limit is the same
+as for regular mail.
+.PP
+Specify a non\-negative time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is d (days).
+.PP
+Specify 0 when mail delivery should be tried only once.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH bounce_service_name (default: bounce)
+The name of the \fBbounce\fR(8) service. This service maintains a record
+of failed delivery attempts and generates non\-delivery notifications.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH bounce_size_limit (default: 50000)
+The maximal amount of original message text that is sent in a
+non\-delivery notification. Specify a byte count.  A message is
+returned as either message/rfc822 (the complete original) or as
+text/rfc822\-headers (the headers only).  With Postfix version 2.4
+and earlier, a message is always returned as message/rfc822 and is
+truncated when it exceeds the size limit.
+.PP
+Notes:
+.IP \(bu
+If you increase this limit, then you should increase the
+mime_nesting_limit value proportionally.
+.IP \(bu
+Be careful when making changes.  Excessively large values
+will result in the loss of non\-delivery notifications, when a bounce
+message size exceeds a local or remote MTA's message size limit.
+.br
+.SH bounce_template_file (default: empty)
+Pathname of a configuration file with bounce message templates.
+These override the built\-in templates of delivery status notification
+(DSN) messages for undeliverable mail, delayed mail, successful
+delivery, or delivery verification. The \fBbounce\fR(5) manual page
+describes how to edit and test template files.
+.PP
+Template message body text may contain $name references to
+Postfix configuration parameters. The result of $name expansion can
+be previewed with "\fBpostconf \-b \fIfile_name\fR\fR" before the file
+is placed into the Postfix configuration directory.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH broken_sasl_auth_clients (default: no)
+Enable interoperability with remote SMTP clients that implement an obsolete
+version of the AUTH command (RFC 4954). Examples of such clients
+are MicroSoft Outlook Express version 4 and MicroSoft Exchange
+version 5.0.
+.PP
+Specify "broken_sasl_auth_clients = yes" to have Postfix advertise
+AUTH support in a non\-standard way.
+.SH canonical_classes (default: envelope_sender, envelope_recipient, header_sender, header_recipient)
+What addresses are subject to canonical_maps address mapping.
+By default, canonical_maps address mapping is applied to envelope
+sender and recipient addresses, and to header sender and header
+recipient addresses.
+.PP
+Specify one or more of: envelope_sender, envelope_recipient,
+header_sender, header_recipient
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH canonical_maps (default: empty)
+Optional address mapping lookup tables for message headers and
+envelopes. The mapping is applied to both sender and recipient
+addresses, in both envelopes and in headers, as controlled
+with the canonical_classes parameter. This is typically used
+to clean up dirty addresses from legacy mail systems, or to replace
+login names by Firstname.Lastname.  The table format and lookups
+are documented in \fBcanonical\fR(5). For an overview of Postfix address
+manipulations see the ADDRESS_REWRITING_README document.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+Note: these lookups are recursive.
+.PP
+If you use this feature, run "\fBpostmap /etc/postfix/canonical\fR" to
+build the necessary DBM or DB file after every change. The changes
+will become visible after a minute or so.  Use "\fBpostfix reload\fR"
+to eliminate the delay.
+.PP
+Note: with Postfix version 2.2, message header address mapping
+happens only when message header address rewriting is enabled:
+.IP \(bu
+The message is received with the Postfix \fBsendmail\fR(1) command,
+.IP \(bu
+The message is received from a network client that matches
+$local_header_rewrite_clients,
+.IP \(bu
+The message is received from the network, and the
+remote_header_rewrite_domain parameter specifies a non\-empty value.
+.br
+.PP
+To get the behavior before Postfix version 2.2, specify
+"local_header_rewrite_clients = static:all".
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+canonical_maps = dbm:/etc/postfix/canonical
+canonical_maps = hash:/etc/postfix/canonical
+.fi
+.ad
+.ft R
+.SH cleanup_replace_stray_cr_lf (default: yes)
+Replace each stray <CR> or <LF> character in message
+content with a space character, to prevent outbound SMTP smuggling,
+and to make the evaluation of Postfix\-added DKIM or other signatures
+independent from how a remote mail server handles such characters.
+.PP
+SMTP does not allow such characters unless they are part of a
+<CR><LF> sequence, and different mail systems handle
+such stray characters in an implementation\-dependent manner. Stray
+<CR> or <LF> characters could be used for outbound
+SMTP smuggling, where an attacker uses a Postfix server to send
+message content with a non\-standard End\-of\-DATA sequence that
+triggers inbound SMTP smuggling at a remote SMTP server.
+.PP
+The replacement happens before all other content management,
+and before Postfix may add a DKIM etc. signature; if the signature
+were created first, the replacement could invalidate the signature.
+.PP
+In addition to preventing SMTP smuggling, replacing stray
+<CR> or <LF> characters ensures that the result of
+signature validation by later mail system will not depend on how
+that mail system handles those stray characters in an
+implementation\-dependent manner.
+.PP
+This feature is available in Postfix >= 3.9, 3.8.5, 3.7.10,
+3.6.14, and 3.5.24.
+.SH cleanup_service_name (default: cleanup)
+The name of the \fBcleanup\fR(8) service. This service rewrites addresses
+into the standard form, and performs \fBcanonical\fR(5) address mapping
+and \fBvirtual\fR(5) aliasing.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH command_directory (default: see "postconf \-d" output)
+The location of all postfix administrative commands.
+.SH command_execution_directory (default: empty)
+The \fBlocal\fR(8) delivery agent working directory for delivery to
+external commands.  Failure to change directory causes the delivery
+to be deferred.
+.PP
+The command_execution_directory value is not subject to Postfix
+configuration parameter $name expansion. Instead, the following
+$name expansions are done on command_execution_directory before the
+directory is used. Expansion happens in the context
+of the delivery request.  The result of $name expansion is filtered
+with the character set that is specified with the
+execution_directory_expansion_filter parameter.
+.IP "\fB$user\fR"
+The recipient's username.
+.br
+.IP "\fB$shell\fR"
+The recipient's login shell pathname.
+.br
+.IP "\fB$home\fR"
+The recipient's home directory.
+.br
+.IP "\fB$recipient\fR"
+The full recipient address.
+.br
+.IP "\fB$extension\fR"
+The optional recipient address extension.
+.br
+.IP "\fB$domain\fR"
+The recipient domain.
+.br
+.IP "\fB$local\fR"
+The entire recipient localpart.
+.br
+.IP "\fB$recipient_delimiter\fR"
+The address extension delimiter that was found in the recipient
+address (Postfix 2.11 and later), or the system\-wide recipient
+address extension delimiter (Postfix 2.10 and earlier).
+.br
+.IP "\fB${name?value}\fR"
+.IP "\fB${name?{value}}\fR (Postfix >= 3.0)"
+Expands to \fIvalue\fR when \fI$name\fR is non\-empty.
+.br
+.IP "\fB${name:value}\fR"
+.IP "\fB${name:{value}}\fR (Postfix >= 3.0)"
+Expands to \fIvalue\fR when \fI$name\fR is empty.
+.br
+.IP "\fB${name?{value1}:{value2}}\fR (Postfix >= 3.0)"
+Expands to \fIvalue1\fR when \fI$name\fR is non\-empty,
+\fIvalue2\fR otherwise.
+.br
+.br
+.PP
+Instead of $name you can also specify ${name} or $(name).
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH command_expansion_filter (default: see "postconf \-d" output)
+Restrict the characters that the \fBlocal\fR(8) delivery agent allows in
+$name expansions of $mailbox_command and $command_execution_directory.
+Characters outside the
+allowed set are replaced by underscores.
+.SH command_time_limit (default: 1000s)
+Time limit for delivery to external commands. This limit is used
+by the \fBlocal\fR(8) delivery agent, and is the default time limit for
+delivery by the \fBpipe\fR(8) delivery agent.
+.PP
+Note: if you set this time limit to a large value you must update the
+global ipc_timeout parameter as well.
+.SH compatibility_level (default: 0)
+A safety net that causes Postfix to run with backwards\-compatible
+default settings after an upgrade to a newer Postfix version.
+.PP
+With backwards compatibility turned on (the main.cf compatibility_level
+value is less than the Postfix built\-in value), Postfix looks for
+settings that are left at their implicit default value, and logs a
+message when a backwards\-compatible default setting is required.
+.sp
+.in +4
+.nf
+.na
+.ft C
+using backwards\-compatible default setting \fIname=value\fR
+    to [accept a specific client request]
+.sp
+using backwards\-compatible default setting \fIname=value\fR
+    to [enable specific Postfix behavior]
+.fi
+.ad
+.ft R
+.in -4
+.PP
+See COMPATIBILITY_README for specific message details. If such
+a message is logged in the context of a legitimate request, the
+system administrator should make the backwards\-compatible setting
+permanent in main.cf or master.cf, for example:
+.sp
+.in +4
+.nf
+.na
+.ft C
+# \fBpostconf\fR \fIname=value\fR
+# \fBpostfix reload\fR
+.fi
+.ad
+.ft R
+.in -4
+.PP
+When no more backwards\-compatible settings need to be made
+permanent, the administrator should turn off backwards compatibility
+by updating the compatibility_level setting in main.cf:
+.sp
+.in +4
+.nf
+.na
+.ft C
+# \fBpostconf compatibility_level=\fIN\fR\fR
+# \fBpostfix reload\fR
+.fi
+.ad
+.ft R
+.in -4
+.PP
+For \fIN\fR specify the number that is logged in your \fBpostfix\fR(1)
+warning message:
+.sp
+.in +4
+.nf
+.na
+.ft C
+warning: To disable backwards compatibility use "postconf
+    compatibility_level=\fIN\fR" and "postfix reload"
+.fi
+.ad
+.ft R
+.in -4
+.PP
+Starting with Postfix version 3.6, the compatibility level in
+the above warning message is the Postfix version that introduced
+the last incompatible change. The level is formatted as
+\fImajor.minor.patch\fR, where \fIpatch\fR is usually omitted and
+defaults to zero. Earlier compatibility levels are 0, 1 and 2.
+.PP
+NOTE: this also introduces support for the "<level",
+"<=level", and other operators to compare compatibility levels.
+With the standard operators "<", "<=", etc., compatibility
+level "3.10" would be smaller than "3.9" which is undesirable.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH config_directory (default: see "postconf \-d" output)
+The default location of the Postfix main.cf and master.cf
+configuration files. This can be overruled via the following
+mechanisms:
+.IP \(bu
+The MAIL_CONFIG environment variable (daemon processes
+and commands).
+.IP \(bu
+The "\-c" command\-line option (commands only).
+.br
+.PP
+With Postfix commands that run with set\-gid privileges, a
+config_directory override either requires root privileges, or it
+requires that the directory is listed with the alternate_config_directories
+parameter in the default main.cf file.
+.SH confirm_delay_cleared (default: no)
+After sending a "your message is delayed" notification, inform
+the sender when the delay clears up. This can result in a sudden
+burst of notifications at the end of a prolonged network outage,
+and is therefore disabled by default.
+.PP
+See also: delay_warning_time.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH connection_cache_protocol_timeout (default: 5s)
+Time limit for connection cache connect, send or receive
+operations.  The time limit is enforced in the client.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH connection_cache_service_name (default: scache)
+The name of the \fBscache\fR(8) connection cache service.  This service
+maintains a limited pool of cached sessions.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH connection_cache_status_update_time (default: 600s)
+How frequently the \fBscache\fR(8) server logs usage statistics with
+connection cache hit and miss rates for logical destinations and for
+physical endpoints.
+.SH connection_cache_ttl_limit (default: 2s)
+The maximal time\-to\-live value that the \fBscache\fR(8) connection
+cache server
+allows. Requests that specify a larger TTL will be stored with the
+maximum allowed TTL. The purpose of this additional control is to
+protect the infrastructure against careless people. The cache TTL
+is already bounded by $max_idle.
+.SH content_filter (default: empty)
+After the message is queued, send the entire message to the
+specified \fItransport:destination\fR. The \fItransport\fR name
+specifies the first field of a mail delivery agent definition in
+master.cf; the syntax of the next\-hop \fIdestination\fR is described
+in the manual page of the corresponding delivery agent.  More
+information about external content filters is in the Postfix
+FILTER_README file.
+.PP
+Notes:
+.IP \(bu
+This setting has lower precedence than a FILTER action
+that is specified in an \fBaccess\fR(5), \fBheader_checks\fR(5) or \fBbody_checks\fR(5)
+table.
+.IP \(bu
+The meaning of an empty next\-hop filter \fIdestination\fR
+is version dependent.  Postfix 2.7 and later will use the recipient
+domain; earlier versions will use $myhostname.  Specify
+"default_filter_nexthop = $myhostname" for compatibility with Postfix
+2.6 or earlier, or specify a content_filter value with an explicit
+next\-hop \fIdestination\fR.
+.br
+.SH cyrus_sasl_config_path (default: empty)
+Search path for Cyrus SASL application configuration files,
+currently used only to locate the $smtpd_sasl_path.conf file.
+Specify zero or more directories separated by a colon character,
+or an empty value to use Cyrus SASL's built\-in search path.
+.PP
+This feature is available in Postfix 2.5 and later when compiled
+with Cyrus SASL 2.1.22 or later.
+.SH daemon_directory (default: see "postconf \-d" output)
+The directory with Postfix support programs and daemon programs.
+These should not be invoked directly by humans. The directory must
+be owned by root.
+.SH daemon_table_open_error_is_fatal (default: no)
+How a Postfix daemon process handles errors while opening lookup
+tables: gradual degradation or immediate termination.
+.IP "\fB no \fR (default)"
+Gradual degradation: a
+daemon process logs a message of type "error" and continues execution
+with reduced functionality. Features that do not depend on the
+unavailable table will work normally, while features that depend
+on the table will result in a type "warning" message.
+.br
+When
+the notify_classes parameter value contains the "data" class, the
+Postfix SMTP server and client will report transcripts of sessions
+with an error because a table is unavailable.
+.br
+.IP "\fB yes \fR (historical behavior)"
+Immediate
+termination: a daemon process logs a type "fatal" message and
+terminates immediately.  This option reduces the number of possible
+code paths through Postfix, and may therefore be slightly more
+secure than the default.
+.br
+.br
+.PP
+For the sake of sanity, the number of type "error" messages is
+limited to 13 over the lifetime of a daemon process.
+.PP
+This feature is available in Postfix 2.9 and later.
+.SH daemon_timeout (default: 18000s)
+How much time a Postfix daemon process may take to handle a
+request before it is terminated by a built\-in watchdog timer.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH data_directory (default: see "postconf \-d" output)
+The directory with Postfix\-writable data files (for example:
+caches, pseudo\-random numbers).  This directory must be owned by
+the mail_owner account, and must not be shared with non\-Postfix
+software.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH debug_peer_level (default: 2)
+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.
+.PP
+Per\-nexthop debug logging is available in Postfix 3.6 and later.
+.SH debug_peer_list (default: empty)
+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.
+.PP
+Per\-nexthop debug logging is available in Postfix 3.6 and later.
+.PP
+Specify domain names, network/netmask patterns, "/file/name"
+patterns or "type:table" lookup tables. The right\-hand side result
+from "type:table" lookups is ignored.
+.PP
+Pattern matching of domain names is controlled by the presence
+or absence of "debug_peer_list" in the parent_domain_matches_subdomains
+parameter value.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+debug_peer_list = 127.0.0.1
+debug_peer_list = example.com
+.fi
+.ad
+.ft R
+.SH debugger_command (default: empty)
+The external command to execute when a Postfix daemon program is
+invoked with the \-D option.
+.PP
+Use "command .. & sleep 5" so that the debugger can attach before
+the process marches on. If you use an X\-based debugger, be sure to
+set up your XAUTHORITY environment variable before starting Postfix.
+.PP
+Note: the command is subject to $name expansion, before it is
+passed to the default command interpreter. Specify "$$" to
+produce a single "$" character.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+debugger_command =
+    PATH=/usr/bin:/usr/X11R6/bin
+    ddd $daemon_directory/$process_name $process_id & sleep 5
+.fi
+.ad
+.ft R
+.SH default_database_type (default: see "postconf \-d" output)
+The default database type for use in \fBnewaliases\fR(1), \fBpostalias\fR(1)
+and \fBpostmap\fR(1) commands. On many UNIX systems the default type is
+either \fBdbm\fR or \fBhash\fR. The default setting is frozen
+when the Postfix system is built.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+default_database_type = hash
+default_database_type = dbm
+.fi
+.ad
+.ft R
+.SH default_delivery_slot_cost (default: 5)
+How often the Postfix queue manager's scheduler is allowed to
+preempt delivery of one message with another.
+.PP
+Each transport maintains a so\-called "available delivery slot counter"
+for each message. One message can be preempted by another one when
+the other message can be delivered using no more delivery slots
+(i.e., invocations of delivery agents) than the current message
+counter has accumulated (or will eventually accumulate \- see about
+slot loans below). This parameter controls how often the counter is
+incremented \- it happens after each default_delivery_slot_cost
+recipients have been delivered.
+.PP
+The cost of 0 is used to disable the preempting scheduling completely.
+The minimum value the scheduling algorithm can use is 2 \- use it
+if you want to maximize the message throughput rate. Although there
+is no maximum, it doesn't make much sense to use values above say
+50.
+.PP
+The only reason why the value of 2 is not the default is the way
+this parameter affects the delivery of mailing\-list mail. In the
+worst case, delivery can take somewhere between (cost+1/cost)
+and (cost/cost\-1) times more than if the preemptive scheduler was
+disabled. The default value of 5 turns out to provide reasonable
+message response times while making sure the mailing\-list deliveries
+are not extended by more than 20\-25 percent even in the worst case.
+.PP
+Use \fItransport\fR_delivery_slot_cost to specify a
+transport\-specific override, where \fItransport\fR is the master.cf
+name of the message delivery transport.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+default_delivery_slot_cost = 0
+default_delivery_slot_cost = 2
+.fi
+.ad
+.ft R
+.SH default_delivery_slot_discount (default: 50)
+The default value for transport\-specific _delivery_slot_discount
+settings.
+.PP
+This parameter speeds up the moment when a message preemption can
+happen. Instead of waiting until the full amount of delivery slots
+required is available, the preemption can happen when
+\fItransport\fR_delivery_slot_discount percent of the required amount
+plus \fItransport\fR_delivery_slot_loan still remains to be accumulated.
+Note that the full amount will still have to be accumulated before
+another preemption can take place later.
+.PP
+Use \fItransport\fR_delivery_slot_discount to specify a
+transport\-specific override, where \fItransport\fR is the master.cf
+name of the message delivery transport.
+.SH default_delivery_slot_loan (default: 3)
+The default value for transport\-specific _delivery_slot_loan
+settings.
+.PP
+This parameter speeds up the moment when a message preemption can
+happen. Instead of waiting until the full amount of delivery slots
+required is available, the preemption can happen when
+transport_delivery_slot_discount percent of the required amount
+plus transport_delivery_slot_loan still remains to be accumulated.
+Note that the full amount will still have to be accumulated before
+another preemption can take place later.
+.PP
+Use \fItransport\fR_delivery_slot_loan to specify a
+transport\-specific override, where \fItransport\fR is the master.cf
+name of the message delivery transport.
+.SH default_delivery_status_filter (default: empty)
+Optional filter to replace the delivery status code or explanatory
+text of successful or unsuccessful deliveries.  This does not allow
+the replacement of a successful status code (2.X.X) with an
+unsuccessful status code (4.X.X or 5.X.X) or vice versa.
+.PP
+Note: the (smtp|lmtp)_delivery_status_filter is applied only
+once per recipient: when delivery is successful, when delivery is
+rejected with 5XX, or when there are no more alternate MX or A
+destinations. Use smtp_reply_filter or lmtp_reply_filter to inspect
+responses for all delivery attempts.
+.PP
+The following parameters can be used to implement a filter for
+specific delivery agents: lmtp_delivery_status_filter,
+local_delivery_status_filter, pipe_delivery_status_filter,
+smtp_delivery_status_filter or virtual_delivery_status_filter. These
+parameters support the same filter syntax as described here.
+.PP
+Specify zero or more "type:table" lookup table names, separated
+by comma or whitespace. For each successful or unsuccessful delivery
+to a recipient, the tables are queried in the specified order with
+one line of text that is structured as follows:
+.sp
+.in +4
+enhanced\-status\-code SPACE explanatory\-text
+.in -4
+.PP
+The first table match wins. The lookup result must have the
+same structure as the query, a successful status code (2.X.X) must
+be replaced with a successful status code, an unsuccessful status
+code (4.X.X or 5.X.X) must be replaced with an unsuccessful status
+code, and the explanatory text field must be non\-empty. Other results
+will result in a warning.
+.PP
+Example 1: convert specific soft TLS errors into hard errors,
+by overriding the first number in the enhanced status code.
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    smtp_delivery_status_filter = pcre:/etc/postfix/smtp_dsn_filter
+.fi
+.ad
+.ft R
+.in -4
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/smtp_dsn_filter:
+    /^4(\e.\ed+\e.\ed+ TLS is required, but host \eS+ refused to start TLS: .+)/
+        5$1
+    /^4(\e.\ed+\e.\ed+ TLS is required, but was not offered by host .+)/
+        5$1
+    # Do not change the following into hard bounces. They may
+    # result from a local configuration problem.
+    # 4.\ed+.\ed+ TLS is required, but our TLS engine is unavailable
+    # 4.\ed+.\ed+ TLS is required, but unavailable
+    # 4.\ed+.\ed+ Cannot start TLS: handshake failure
+.fi
+.ad
+.ft R
+.in -4
+.PP
+Example 2: censor the per\-recipient delivery status text so
+that it does not reveal the destination command or filename
+when a remote sender requests confirmation of successful delivery.
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    local_delivery_status_filter = pcre:/etc/postfix/local_dsn_filter
+.fi
+.ad
+.ft R
+.in -4
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/local_dsn_filter:
+    /^(2\eS+ delivered to file).+/    $1
+    /^(2\eS+ delivered to command).+/ $1
+.fi
+.ad
+.ft R
+.in -4
+.PP
+Notes:
+.IP \(bu
+This feature will NOT override the soft_bounce safety net.
+.IP \(bu
+This feature will change the enhanced status code and text
+that is logged to the maillog file, and that is reported to the
+sender in delivery confirmation or non\-delivery notifications.
+.br
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH default_destination_concurrency_failed_cohort_limit (default: 1)
+How many pseudo\-cohorts must suffer connection or handshake
+failure before a specific destination is considered unavailable
+(and further delivery is suspended). Specify zero to disable this
+feature. A destination's pseudo\-cohort failure count is reset each
+time a delivery completes without connection or handshake failure
+for that specific destination.
+.PP
+A pseudo\-cohort is the number of deliveries equal to a destination's
+delivery concurrency.
+.PP
+Use \fItransport\fR_destination_concurrency_failed_cohort_limit to specify
+a transport\-specific override, where \fItransport\fR is the master.cf
+name of the message delivery transport.
+.PP
+This feature is available in Postfix 2.5. The default setting
+is compatible with earlier Postfix versions.
+.SH default_destination_concurrency_limit (default: 20)
+The default maximal number of parallel deliveries to the same
+destination.  This is the default limit for delivery via the \fBlmtp\fR(8),
+\fBpipe\fR(8), \fBsmtp\fR(8) and \fBvirtual\fR(8) delivery agents.
+With a per\-destination recipient limit > 1, a destination is a domain,
+otherwise it is a recipient.
+.PP
+Use \fItransport\fR_destination_concurrency_limit to specify a
+transport\-specific override, where \fItransport\fR is the master.cf
+name of the message delivery transport.
+.SH default_destination_concurrency_negative_feedback (default: 1)
+The per\-destination amount of delivery concurrency negative
+feedback, after a delivery completes with a connection or handshake
+failure. Feedback values are in the range 0..1 inclusive. With
+negative feedback, concurrency is decremented at the beginning of
+a sequence of length 1/feedback. This is unlike positive feedback,
+where concurrency is incremented at the end of a sequence of length
+1/feedback.
+.PP
+As of Postfix version 2.5, negative feedback cannot reduce
+delivery concurrency to zero.  Instead, a destination is marked
+dead (further delivery suspended) after the failed pseudo\-cohort
+count reaches $default_destination_concurrency_failed_cohort_limit
+(or $\fItransport\fR_destination_concurrency_failed_cohort_limit).
+To make the scheduler completely immune to connection or handshake
+failures, specify a zero feedback value and a zero failed pseudo\-cohort
+limit.
+.PP
+Specify one of the following forms:
+.IP "\fB\fInumber\fR \fR"
+.IP "\fB\fInumber\fR / \fInumber\fR \fR"
+Constant feedback. The value must be in the range 0..1 inclusive.
+The default setting of "1" is compatible with Postfix versions
+before 2.5, where a destination's delivery concurrency is throttled
+down to zero (and further delivery suspended) after a single failed
+pseudo\-cohort.
+.br
+.IP "\fB\fInumber\fR / concurrency \fR"
+Variable feedback of "\fInumber\fR / (delivery concurrency)".
+The \fInumber\fR must be in the range 0..1 inclusive. With
+\fInumber\fR equal to "1", a destination's delivery concurrency
+is decremented by 1 after each failed pseudo\-cohort.
+.br
+.br
+.PP
+A pseudo\-cohort is the number of deliveries equal to a destination's
+delivery concurrency.
+.PP
+Use \fItransport\fR_destination_concurrency_negative_feedback
+to specify a transport\-specific override, where \fItransport\fR
+is the master.cf
+name of the message delivery transport.
+.PP
+This feature is available in Postfix 2.5. The default setting
+is compatible with earlier Postfix versions.
+.SH default_destination_concurrency_positive_feedback (default: 1)
+The per\-destination amount of delivery concurrency positive
+feedback, after a delivery completes without connection or handshake
+failure. Feedback values are in the range 0..1 inclusive.  The
+concurrency increases until it reaches the per\-destination maximal
+concurrency limit. With positive feedback, concurrency is incremented
+at the end of a sequence with length 1/feedback. This is unlike
+negative feedback, where concurrency is decremented at the start
+of a sequence of length 1/feedback.
+.PP
+Specify one of the following forms:
+.IP "\fB\fInumber\fR \fR"
+.IP "\fB\fInumber\fR / \fInumber\fR \fR"
+Constant feedback.  The value must be in the range 0..1
+inclusive. The default setting of "1" is compatible with Postfix
+versions before 2.5, where a destination's delivery concurrency
+doubles after each successful pseudo\-cohort.
+.br
+.IP "\fB\fInumber\fR / concurrency \fR"
+Variable feedback of "\fInumber\fR / (delivery concurrency)".
+The \fInumber\fR must be in the range 0..1 inclusive. With
+\fInumber\fR equal to "1", a destination's delivery concurrency
+is incremented by 1 after each successful pseudo\-cohort.
+.br
+.br
+.PP
+A pseudo\-cohort is the number of deliveries equal to a destination's
+delivery concurrency.
+.PP
+Use \fItransport\fR_destination_concurrency_positive_feedback
+to specify a transport\-specific override, where \fItransport\fR
+is the master.cf name of the message delivery transport.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH default_destination_rate_delay (default: 0s)
+The default amount of delay that is inserted between individual
+message deliveries to the same destination and over the same message
+delivery transport. Specify a non\-zero value to rate\-limit those
+message deliveries to at most one per $default_destination_rate_delay.
+.PP
+The resulting behavior depends on the value of the corresponding
+per\-destination recipient limit.
+.IP \(bu
+With a corresponding per\-destination recipient limit >
+1, the rate delay specifies the time between deliveries to the
+\fIsame domain\fR.  Different domains are delivered in parallel,
+subject to the process limits specified in master.cf.
+.IP \(bu
+With a corresponding per\-destination recipient limit equal
+to 1, the rate delay specifies the time between deliveries to the
+\fIsame recipient\fR. Different recipients are delivered in
+parallel, subject to the process limits specified in master.cf.
+.br
+.PP
+To enable the delay, specify a non\-zero time value (an integral
+value plus an optional one\-letter suffix that specifies the time
+unit).
+.PP
+Time units: s (seconds), m (minutes), h (hours), d (days), w
+(weeks). The default time unit is s (seconds).
+.PP
+NOTE: the delay is enforced by the queue manager. The delay
+timer state does not survive "\fBpostfix reload\fR" or "\fBpostfix
+stop\fR".
+.PP
+Use \fItransport\fR_destination_rate_delay to specify a
+transport\-specific override, where \fItransport\fR is the master.cf
+name of the message delivery transport.
+.PP
+NOTE: with a non\-zero _destination_rate_delay, specify a
+\fItransport\fR_destination_concurrency_failed_cohort_limit of 10
+or more to prevent Postfix from deferring all mail for the same
+destination after only one connection or handshake error.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH default_destination_recipient_limit (default: 50)
+The default maximal number of recipients per message delivery.
+This is the default limit for delivery via the \fBlmtp\fR(8), \fBpipe\fR(8),
+\fBsmtp\fR(8) and \fBvirtual\fR(8) delivery agents.
+.PP
+Setting this parameter to a value of 1 affects email deliveries
+as follows:
+.IP \(bu
+It changes the meaning of the corresponding per\-destination
+concurrency limit, from concurrency of deliveries to the \fIsame
+domain\fR into concurrency of deliveries to the \fIsame recipient\fR.
+Different recipients are delivered in parallel, subject to the
+process limits specified in master.cf.
+.IP \(bu
+It changes the meaning of the corresponding per\-destination
+rate delay, from the delay between deliveries to the \fIsame
+domain\fR into the delay between deliveries to the \fIsame
+recipient\fR.  Again, different recipients are delivered in parallel,
+subject to the process limits specified in master.cf.
+.IP \(bu
+It changes the meaning of other corresponding per\-destination
+settings in a similar manner, from settings for delivery to the
+\fIsame domain\fR into settings for delivery to the \fIsame
+recipient\fR.
+.br
+.PP
+Use \fItransport\fR_destination_recipient_limit to specify a
+transport\-specific override, where \fItransport\fR is the master.cf
+name of the message delivery transport.
+.SH default_extra_recipient_limit (default: 1000)
+The default value for the extra per\-transport limit imposed on the
+number of in\-memory recipients.  This extra recipient space is
+reserved for the cases when the Postfix queue manager's scheduler
+preempts one message with another and suddenly needs some extra
+recipient slots for the chosen message in order to avoid performance
+degradation.
+.PP
+Use \fItransport\fR_extra_recipient_limit to specify a
+transport\-specific override, where \fItransport\fR is the master.cf
+name of the message delivery transport.
+.SH default_filter_nexthop (default: empty)
+When a content_filter or FILTER request specifies no explicit
+next\-hop destination, use $default_filter_nexthop instead; when
+that value is empty, use the domain in the recipient address.
+Specify "default_filter_nexthop = $myhostname" for compatibility
+with Postfix version 2.6 and earlier, or specify an explicit next\-hop
+destination with each content_filter value or FILTER action.
+.PP
+This feature is available in Postfix 2.7 and later.
+.SH default_minimum_delivery_slots (default: 3)
+How many recipients a message must have in order to invoke the
+Postfix queue manager's scheduling algorithm at all.  Messages
+which would never accumulate at least this many delivery slots
+(subject to slot cost parameter as well) are never preempted.
+.PP
+Use \fItransport\fR_minimum_delivery_slots to specify a
+transport\-specific override, where \fItransport\fR is the master.cf
+name of the message delivery transport.
+.SH default_privs (default: nobody)
+The default rights used by the \fBlocal\fR(8) delivery agent for delivery
+to an external file or command.  These rights are used when delivery
+is requested from an \fBaliases\fR(5) file that is owned by \fBroot\fR, or
+when delivery is done on behalf of \fBroot\fR. \fBDO NOT SPECIFY A
+PRIVILEGED USER OR THE POSTFIX OWNER\fR.
+.SH default_process_limit (default: 100)
+The default maximal number of Postfix child processes that provide
+a given service. This limit can be overruled for specific services
+in the master.cf file.
+.SH default_rbl_reply (default: see "postconf \-d" output)
+The default Postfix SMTP server response template for a request that is
+rejected by an RBL\-based restriction. This template can be overruled
+by specific entries in the optional rbl_reply_maps lookup table.
+.PP
+This feature is available in Postfix 2.0 and later.
+.PP
+The template does not support Postfix configuration parameter $name
+substitution. Instead, it supports exactly one level of $name
+substitution for the following attributes:
+.IP "\fB$client\fR"
+The client hostname and IP address, formatted as name[address].
+.br
+.IP "\fB$client_address\fR"
+The client IP address.
+.br
+.IP "\fB$client_name\fR"
+The client hostname or "unknown". See reject_unknown_client_hostname
+for more details.
+.br
+.IP "\fB$reverse_client_name\fR"
+The client hostname from address\->name lookup, or "unknown".
+See reject_unknown_reverse_client_hostname for more details.
+.br
+.IP "\fB$helo_name\fR"
+The hostname given in HELO or EHLO command or empty string.
+.br
+.IP "\fB$rbl_class\fR"
+The denylisted entity type: Client host, Helo command, Sender
+address, or Recipient address.
+.br
+.IP "\fB$rbl_code\fR"
+The numerical SMTP response code, as specified with the
+maps_rbl_reject_code configuration parameter. Note: The numerical
+SMTP response code is required, and must appear at the start of the
+reply. With Postfix version 2.3 and later this information may be followed
+by an RFC 3463 enhanced status code.
+.br
+.IP "\fB$rbl_domain\fR"
+The RBL domain where $rbl_what is denylisted.
+.br
+.IP "\fB$rbl_reason\fR"
+The reason why $rbl_what is denylisted, or an empty string.
+.br
+.IP "\fB$rbl_what\fR"
+The entity that is denylisted (an IP address, a hostname, a domain
+name, or an email address whose domain was denylisted).
+.br
+.IP "\fB$recipient\fR"
+The recipient address or <> in case of the null address.
+.br
+.IP "\fB$recipient_domain\fR"
+The recipient domain or empty string.
+.br
+.IP "\fB$recipient_name\fR"
+The recipient address localpart or <> in case of null address.
+.br
+.IP "\fB$sender\fR"
+The sender address or <> in case of the null address.
+.br
+.IP "\fB$sender_domain\fR"
+The sender domain or empty string.
+.br
+.IP "\fB$sender_name\fR"
+The sender address localpart or <> in case of the null address.
+.br
+.IP "\fB${name?value}\fR"
+.IP "\fB${name?{value}}\fR (Postfix >= 3.0)"
+Expands to \fIvalue\fR when \fI$name\fR is non\-empty.
+.br
+.IP "\fB${name:value}\fR"
+.IP "\fB${name:{value}}\fR (Postfix >= 3.0)"
+Expands to \fIvalue\fR when \fI$name\fR is empty.
+.br
+.IP "\fB${name?{value1}:{value2}}\fR (Postfix >= 3.0)"
+Expands to \fIvalue1\fR when \fI$name\fR is non\-empty,
+\fIvalue2\fR otherwise.
+.br
+.br
+.PP
+Instead of $name you can also specify ${name} or $(name).
+.PP
+Note: when an enhanced status code is specified in an RBL reply
+template, it is subject to modification.  The following transformations
+are needed when the same RBL reply template is used for client,
+helo, sender, or recipient access restrictions.
+.IP \(bu
+When rejecting a sender address, the Postfix SMTP server
+will transform a recipient DSN status (e.g., 4.1.1\-4.1.6) into the
+corresponding sender DSN status, and vice versa.
+.IP \(bu
+When rejecting non\-address information (such as the HELO
+command argument or the client hostname/address), the Postfix SMTP
+server will transform a sender or recipient DSN status into a generic
+non\-address DSN status (e.g., 4.0.0).
+.br
+.SH default_recipient_limit (default: 20000)
+The default per\-transport upper limit on the number of in\-memory
+recipients.  These limits take priority over the global
+qmgr_message_recipient_limit after the message has been assigned
+to the respective transports.  See also default_extra_recipient_limit
+and qmgr_message_recipient_minimum.
+.PP
+Use \fItransport\fR_recipient_limit to specify a
+transport\-specific override, where \fItransport\fR is the master.cf
+name of the message delivery transport.
+.SH default_recipient_refill_delay (default: 5s)
+The default per\-transport maximum delay between refilling recipients.
+When not all message recipients fit into memory at once, keep loading
+more of them at least once every this many seconds.  This is used to
+make sure the recipients are refilled in a timely manner even when
+$default_recipient_refill_limit is too high for too slow deliveries.
+.PP
+Use \fItransport\fR_recipient_refill_delay to specify a
+transport\-specific override, where \fItransport\fR is the master.cf
+name of the message delivery transport.
+.PP
+This feature is available in Postfix 2.4 and later.
+.SH default_recipient_refill_limit (default: 100)
+The default per\-transport limit on the number of recipients refilled at
+once.  When not all message recipients fit into memory at once, keep
+loading more of them in batches of at least this many at a time.  See also
+$default_recipient_refill_delay, which may result in recipient batches
+lower than this when this limit is too high for too slow deliveries.
+.PP
+Use \fItransport\fR_recipient_refill_limit to specify a
+transport\-specific override, where \fItransport\fR is the master.cf
+name of the message delivery transport.
+.PP
+This feature is available in Postfix 2.4 and later.
+.SH default_transport (default: smtp)
+The default mail delivery transport and next\-hop destination for
+destinations that do not match $mydestination, $inet_interfaces,
+$proxy_interfaces, $virtual_alias_domains, $virtual_mailbox_domains,
+or $relay_domains.  This information can be overruled with the
+sender_dependent_default_transport_maps parameter and with the
+\fBtransport\fR(5) table.
+.PP
+In order of decreasing precedence, the nexthop destination is taken
+from $sender_dependent_default_transport_maps, $default_transport,
+$sender_dependent_relayhost_maps, $relayhost, or from the recipient
+domain.
+.PP
+Specify a string of the form \fItransport:nexthop\fR, where \fItransport\fR
+is the name of a mail delivery transport defined in master.cf.
+The \fI:nexthop\fR destination is optional; its syntax is documented
+in the manual page of the corresponding delivery agent. In the case of
+SMTP or LMTP, specify one or more destinations separated by comma or
+whitespace (with Postfix 3.5 and later).
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+default_transport = uucp:relayhostname
+.fi
+.ad
+.ft R
+.SH default_transport_rate_delay (default: 0s)
+The default amount of delay that is inserted between individual
+message deliveries over the same message delivery transport,
+regardless of destination. Specify a non\-zero value to rate\-limit
+those message deliveries to at most one per $default_transport_rate_delay.
+.PP
+Use \fItransport\fR_transport_rate_delay to specify a
+transport\-specific override, where the initial \fItransport\fR is
+the master.cf name of the message delivery transport.
+.PP
+Example: throttle outbound SMTP mail to at most 3 deliveries
+per minute.
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    smtp_transport_rate_delay = 20s
+.fi
+.ad
+.ft R
+.PP
+To enable the delay, specify a non\-zero time value (an integral
+value plus an optional one\-letter suffix that specifies the time
+unit).
+.PP
+Time units: s (seconds), m (minutes), h (hours), d (days), w
+(weeks). The default time unit is s (seconds).
+.PP
+NOTE: the delay is enforced by the queue manager.
+.PP
+This feature is available in Postfix 3.1 and later.
+.SH default_verp_delimiters (default: +=)
+The two default VERP delimiter characters. These are used when
+no explicit delimiters are specified with the SMTP XVERP command
+or with the "\fBsendmail \-XV\fR" command\-line option (Postfix 2.2
+and earlier: \fB\-V\fR). Specify characters that are allowed by the
+verp_delimiter_filter setting.
+.PP
+This feature is available in Postfix 1.1 and later.
+.SH defer_code (default: 450)
+The numerical Postfix SMTP server response code when a remote SMTP
+client request is rejected by the "defer" restriction.
+.PP
+Do not change this unless you have a complete understanding of RFC 5321.
+.SH defer_service_name (default: defer)
+The name of the defer service. This service is implemented by the
+\fBbounce\fR(8) daemon and maintains a record
+of failed delivery attempts and generates non\-delivery notifications.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH defer_transports (default: empty)
+The names of message delivery transports that should not deliver mail
+unless someone issues "\fBsendmail \-q\fR" or equivalent. Specify zero
+or more mail delivery transport names that appear in the
+first field of master.cf.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+defer_transports = smtp
+.fi
+.ad
+.ft R
+.SH delay_logging_resolution_limit (default: 2)
+The maximal number of digits after the decimal point when logging
+sub\-second delay values.  Specify a number in the range 0..6.
+.PP
+Large delay values are rounded off to an integral number of seconds;
+delay values below the delay_logging_resolution_limit are logged
+as "0", and delay values under 100s are logged with at most two\-digit
+precision.
+.PP
+The format of the "delays=a/b/c/d" logging is as follows:
+.IP \(bu
+a = time from message arrival to last active queue entry
+.IP \(bu
+b = time from last active queue entry to connection setup
+.IP \(bu
+c = time in connection setup, including DNS, EHLO and STARTTLS
+.IP \(bu
+d = time in message transmission
+.br
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH delay_notice_recipient (default: postmaster)
+The recipient of postmaster notifications with the message headers
+of mail that cannot be delivered within $delay_warning_time time
+units.
+.PP
+See also: delay_warning_time, notify_classes.
+.SH delay_warning_time (default: 0h)
+The time after which the sender receives a copy of the message
+headers of mail that is still queued. The confirm_delay_cleared
+parameter controls sender notification when the delay clears up.
+.PP
+To enable this feature, specify a non\-zero time value (an integral
+value plus an optional one\-letter suffix that specifies the time
+unit).
+.PP
+Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is h (hours).
+.PP
+See also: delay_notice_recipient, notify_classes, confirm_delay_cleared.
+.SH deliver_lock_attempts (default: 20)
+The maximal number of attempts to acquire an exclusive lock on a
+mailbox file or \fBbounce\fR(8) logfile.
+.SH deliver_lock_delay (default: 1s)
+The time between attempts to acquire an exclusive lock on a mailbox
+file or \fBbounce\fR(8) logfile.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH destination_concurrency_feedback_debug (default: no)
+Make the queue manager's feedback algorithm verbose for performance
+analysis purposes.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH detect_8bit_encoding_header (default: yes)
+Automatically detect 8BITMIME body content by looking at
+Content\-Transfer\-Encoding: message headers; historically, this
+behavior was hard\-coded to be "always on".
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH disable_dns_lookups (default: no)
+Disable DNS lookups in the Postfix SMTP and LMTP clients. When
+disabled, hosts are looked up with the getaddrinfo() system
+library routine which normally also looks in /etc/hosts.  As of
+Postfix 2.11, this parameter is deprecated; use smtp_dns_support_level
+instead.
+.PP
+DNS lookups are enabled by default.
+.SH disable_mime_input_processing (default: no)
+Turn off MIME processing while receiving mail. This means that no
+special treatment is given to Content\-Type: message headers, and
+that all text after the initial message headers is considered to
+be part of the message body.
+.PP
+This feature is available in Postfix 2.0 and later.
+.PP
+Mime input processing is enabled by default, and is needed in order
+to recognize MIME headers in message content.
+.SH disable_mime_output_conversion (default: no)
+Disable the conversion of 8BITMIME format to 7BIT format.  Mime
+output conversion is needed when the destination does not advertise
+8BITMIME support.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH disable_verp_bounces (default: no)
+Disable sending one bounce report per recipient.
+.PP
+The default, one per recipient, is what ezmlm needs.
+.PP
+This feature is available in Postfix 1.1 and later.
+.SH disable_vrfy_command (default: no)
+Disable the SMTP VRFY command. This stops some techniques used to
+harvest email addresses.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+disable_vrfy_command = no
+.fi
+.ad
+.ft R
+.SH dns_ncache_ttl_fix_enable (default: no)
+Enable a workaround for future libc incompatibility. The Postfix
+implementation of RFC 2308 negative reply caching relies on the
+promise that res_query() and res_search() invoke res_send(), which
+returns the server response in an application buffer even if the
+requested record does not exist. If this promise is broken, specify
+"yes" to enable a  workaround for DNS reputation lookups.
+.PP
+This feature is available in Postfix 3.1 and later.
+.SH dnsblog_reply_delay (default: 0s)
+A debugging aid to artificially delay DNS responses.
+.PP
+This feature is available in Postfix 2.8.
+.SH dnsblog_service_name (default: dnsblog)
+The name of the \fBdnsblog\fR(8) service entry in master.cf. This
+service performs DNS allow/denylist lookups.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH dnssec_probe (default: ns:.)
+The DNS query type (default: "ns") and DNS query name (default:
+".") that Postfix may use to determine whether DNSSEC validation
+is available.
+.PP
+Background: DNSSEC validation is needed for Postfix DANE support;
+this ensures that Postfix receives TLSA records with secure TLS
+server certificate info. When DNSSEC validation is unavailable,
+mail deliveries using \fIopportunistic\fR DANE will not be protected
+by server certificate info in TLSA records, and mail deliveries
+using \fImandatory\fR DANE will not be made at all.
+.PP
+By default, a Postfix process will send a DNSSEC probe after
+1) the process made a DNS query that requested DNSSEC validation,
+2) the process did not receive a DNSSEC validated response to this
+query or to an earlier query, and 3) the process did not already
+send a DNSSEC probe.
+.PP
+When the DNSSEC probe has no response, or when the response is
+not DNSSEC validated, Postfix logs a warning that DNSSEC validation
+may be unavailable.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+warning: DNSSEC validation may be unavailable
+warning: reason: dnssec_probe 'ns:.' received a response that is not DNSSEC validated
+warning: reason: dnssec_probe 'ns:.' received no response: Server failure
+.fi
+.ad
+.ft R
+.PP
+Possible reasons why DNSSEC validation may be unavailable:
+.IP \(bu
+The local /etc/resolv.conf file specifies a DNS resolver that
+does not validate DNSSEC signatures (that's
+$queue_directory/etc/resolv.conf when a Postfix daemon runs in a
+chroot jail).
+.IP \(bu
+The local system library does not pass on the "DNSSEC validated"
+bit to Postfix, or Postfix does not know how to ask the library to
+do that.
+.br
+.PP
+By default, the DNSSEC probe asks for the DNS root zone NS
+records, because resolvers should always have that information
+cached. If Postfix runs on a network where the DNS root zone is not
+reachable, specify a different probe, or specify an empty dnssec_probe
+value to disable the feature.
+.PP
+This feature is available in Postfix 3.6 and later. It was backported
+to Postfix versions 3.5.9, 3.4.19, 3.3.16. 3.2.21.
+.SH dont_remove (default: 0)
+Don't remove queue files and save them to the "saved" mail queue.
+This is a debugging aid.  To inspect the envelope information and
+content of a Postfix queue file, use the \fBpostcat\fR(1) command.
+.SH double_bounce_sender (default: double\-bounce)
+The sender address of postmaster notifications that are generated
+by the mail system. All mail to this address is silently discarded,
+in order to terminate mail bounce loops.
+.SH duplicate_filter_limit (default: 1000)
+The maximal number of addresses remembered by the address
+duplicate filter for \fBaliases\fR(5) or \fBvirtual\fR(5) alias expansion, or
+for \fBshowq\fR(8) queue displays.
+.SH empty_address_default_transport_maps_lookup_key (default: <>)
+The sender_dependent_default_transport_maps search string that
+will be used instead of the null sender address.
+.PP
+This feature is available in Postfix 2.7 and later.
+.SH empty_address_local_login_sender_maps_lookup_key (default: <>)
+The lookup key to be used in local_login_sender_maps tables, instead
+of the null sender address.
+.PP
+This feature is available in Postfix 3.6 and later.
+.SH empty_address_recipient (default: MAILER\-DAEMON)
+The recipient of mail addressed to the null address.  Postfix does
+not accept such addresses in SMTP commands, but they may still be
+created locally as the result of configuration or software error.
+.SH empty_address_relayhost_maps_lookup_key (default: <>)
+The sender_dependent_relayhost_maps search string that will be
+used instead of the null sender address.
+.PP
+This feature is available in Postfix 2.5 and later. With
+earlier versions, sender_dependent_relayhost_maps lookups were
+skipped for the null sender address.
+.SH enable_errors_to (default: no)
+Report mail delivery errors to the address specified with the
+non\-standard Errors\-To: message header, instead of the envelope
+sender address (this feature is removed with Postfix version 2.2, is
+turned off by default with Postfix version 2.1, and is always turned on
+with older Postfix versions).
+.SH enable_idna2003_compatibility (default: no)
+Enable 'transitional' compatibility between IDNA2003 and IDNA2008,
+when converting UTF\-8 domain names to/from the ASCII form that is
+used for DNS lookups. Specify "yes" for compatibility with Postfix
+<= 3.1 (not recommended). This affects the conversion of domain
+names that contain for example the German sz and the Greek zeta.
+See http://unicode.org/cldr/utility/idna.jsp for more examples.
+.PP
+This feature is available in Postfix 3.2 and later.
+.SH enable_long_queue_ids (default: no)
+Enable long, non\-repeating, queue IDs (queue file names).  The
+benefit of non\-repeating names is simpler logfile analysis and
+easier queue migration (there is no need to run "postsuper" to
+change queue file names that don't match their message file inode
+number).
+.PP
+Note: see below for how to convert long queue file names to
+Postfix <= 2.8.
+.PP
+Changing the parameter value to "yes" has the following effects:
+.IP \(bu
+Existing queue file names are not affected.
+.IP \(bu
+New queue files are created with names such as 3Pt2mN2VXxznjll.
+These are encoded in a 52\-character alphabet that contains digits
+(0\-9), upper\-case letters (B\-Z) and lower\-case letters (b\-z). For
+safety reasons the vowels (AEIOUaeiou) are excluded from the alphabet.
+The name format is: 6 or more characters for the time in seconds,
+4 characters for the time in microseconds, the 'z'; the remainder
+is the file inode number encoded in the first 51 characters of the
+52\-character alphabet.
+.IP \(bu
+New messages have a Message\-ID header with
+\fIqueueID\fR@\fImyhostname\fR.
+.IP \(bu
+The mailq (postqueue \-p) output has a wider Queue ID column.
+The number of whitespace\-separated fields is not changed.
+.IP \(bu
+The hash_queue_depth algorithm uses the first characters
+of the queue file creation time in microseconds, after conversion
+into hexadecimal representation. This produces the same queue hashing
+behavior as if the queue file name was created with "enable_long_queue_ids
+= no".
+.br
+.PP
+Changing the parameter value to "no" has the following effects:
+.IP \(bu
+Existing long queue file names are renamed to the short
+form (while running "postfix reload" or "postsuper").
+.IP \(bu
+New queue files are created with names such as C3CD21F3E90
+from a hexadecimal alphabet that contains digits (0\-9) and upper\-case
+letters (A\-F). The name format is: 5 characters for the time in
+microseconds; the remainder is the file inode number.
+.IP \(bu
+New messages have a Message\-ID header with
+\fIYYYYMMDDHHMMSS.queueid\fR@\fImyhostname\fR, where
+\fIYYYYMMDDHHMMSS\fR are the year, month, day, hour, minute and
+second.
+.IP \(bu
+The mailq (postqueue \-p) output has the same format as
+with Postfix <= 2.8.
+.IP \(bu
+The hash_queue_depth algorithm uses the first characters
+of the queue file name, with the hexadecimal representation of the
+file creation time in microseconds.
+.br
+.PP
+Before migration to Postfix <= 2.8, the following commands
+are required to convert long queue file names into short names:
+.PP
+.nf
+.na
+.ft C
+# postfix stop
+# postconf enable_long_queue_ids=no
+# postsuper
+.fi
+.ad
+.ft R
+.PP
+Repeat the postsuper command until it reports no more queue file
+name changes.
+.PP
+This feature is available in Postfix 2.9 and later.
+.SH enable_original_recipient (default: yes)
+Enable support for the original recipient address after an
+address is rewritten to a different address (for example with
+aliasing or with canonical mapping).
+.PP
+The original recipient address is used as follows:
+.IP "Final delivery"
+With "enable_original_recipient =
+yes", the original recipient address is stored in the \fBX\-Original\-To\fR
+message header. This header may be used to distinguish between
+different recipients that share the same mailbox.
+.br
+.IP "Recipient deduplication"
+With "enable_original_recipient
+= yes", the \fBcleanup\fR(8) daemon performs duplicate recipient elimination
+based on the content of (original recipient, maybe\-rewritten
+recipient) pairs.  Otherwise, the \fBcleanup\fR(8) daemon performs duplicate
+recipient elimination based only on the maybe\-rewritten recipient
+address.
+.br
+.br
+.PP
+Note: with Postfix <= 3.2 the "setting enable_original_recipient
+= \fBno\fR" breaks address verification for addresses that are
+aliased or otherwise rewritten (Postfix is unable to store the
+address verification result under the original probe destination
+address; instead, it can store the result only under the rewritten
+address).
+.PP
+This feature is available in Postfix 2.1 and later. Postfix
+version 2.0 behaves as if this parameter is always set to \fByes\fR.
+Postfix versions before 2.0 have no support for the original recipient
+address.
+.SH enable_threaded_bounces (default: no)
+Enable non\-delivery, success, and delay notifications that link
+to the original message by including a References: and In\-Reply\-To:
+header with the original Message\-ID value. There are advantages and
+disadvantages to consider.
+.IP "\fB advantage \fR"
+This allows mail readers to present
+a delivery status notification in the same email thread as the original
+message.
+.br
+.IP "\fB disadvantage \fR"
+This makes it easy for users to
+mistakenly delete the whole email thread (all related messages),
+instead of deleting only the non\-delivery notification.
+.br
+.br
+.PP
+This feature is available in Postfix 3.6 and later.
+.SH error_notice_recipient (default: postmaster)
+The recipient of postmaster notifications about mail delivery
+problems that are caused by policy, resource, software or protocol
+errors.  These notifications are enabled with the notify_classes
+parameter.
+.SH error_service_name (default: error)
+The name of the \fBerror\fR(8) pseudo delivery agent. This service always
+returns mail as undeliverable.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH execution_directory_expansion_filter (default: see "postconf \-d" output)
+Restrict the characters that the \fBlocal\fR(8) delivery agent allows
+in $name expansions of $command_execution_directory.  Characters
+outside the allowed set are replaced by underscores.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH expand_owner_alias (default: no)
+When delivering to an alias "\fIaliasname\fR" that has an
+"owner\-\fIaliasname\fR" companion alias, set the envelope sender
+address to the expansion of the "owner\-\fIaliasname\fR" alias.
+Normally, Postfix sets the envelope sender address to the name of
+the "owner\-\fIaliasname\fR" alias.
+.SH export_environment (default: see "postconf \-d" output)
+The list of environment variables that a Postfix process will export
+to non\-Postfix processes. The TZ variable is needed for sane
+time keeping on System\-V\-ish systems.
+.PP
+Specify a list of names and/or name=value pairs, separated by
+whitespace or comma. Specify "{ name=value }" to protect whitespace
+or comma in parameter values (whitespace after the opening "{" and
+before the closing "}"
+is ignored). The form name=value is supported with Postfix version
+2.1 and later; the use of {} is supported with Postfix 3.0 and
+later.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+export_environment = TZ PATH=/bin:/usr/bin
+.fi
+.ad
+.ft R
+.SH extract_recipient_limit (default: 10240)
+The maximal number of recipient addresses that Postfix will extract
+from message headers when mail is submitted with "\fBsendmail \-t\fR".
+.PP
+This feature was removed in Postfix version 2.1.
+.SH fallback_relay (default: empty)
+Optional list of relay hosts for SMTP destinations that can't be
+found or that are unreachable. With Postfix 2.3 this parameter
+is renamed to smtp_fallback_relay.
+.PP
+By default, mail is returned to the sender when a destination is
+not found, and delivery is deferred when a destination is unreachable.
+.PP
+The fallback relays must be SMTP destinations. Specify a domain,
+host, host:port, [host]:port, [address] or [address]:port; the form
+[host] turns off MX lookups.  If you specify multiple SMTP
+destinations, Postfix will try them in the specified order.
+.PP
+Note: before Postfix 2.2, do not use the fallback_relay feature
+when relaying mail
+for a backup or primary MX domain. Mail would loop between the
+Postfix MX host and the fallback_relay host when the final destination
+is unavailable.
+.IP \(bu
+In main.cf specify "relay_transport = relay",
+.IP \(bu
+In master.cf specify "\-o fallback_relay =" (i.e., empty) at
+the end of the relay entry.
+.IP \(bu
+In transport maps, specify "relay:\fInexthop...\fR"
+as the right\-hand side for backup or primary MX domain entries.
+.br
+.PP
+Postfix version 2.2 and later will not use the fallback_relay feature
+for destinations that it is MX host for.
+.SH fallback_transport (default: empty)
+Optional message delivery transport that the \fBlocal\fR(8) delivery
+agent should use for names that are not found in the \fBaliases\fR(5)
+or UNIX password database.
+.PP
+The precedence of \fBlocal\fR(8) delivery features from high to low
+is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
+mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
+fallback_transport_maps, fallback_transport and luser_relay.
+.SH fallback_transport_maps (default: empty)
+Optional lookup tables with per\-recipient message delivery
+transports for recipients that the \fBlocal\fR(8) delivery agent could
+not find in the \fBaliases\fR(5) or UNIX password database.
+.PP
+The precedence of \fBlocal\fR(8) delivery features from high to low
+is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
+mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
+fallback_transport_maps, fallback_transport and luser_relay.
+.PP
+For safety reasons, this feature does not allow $number
+substitutions in regular expression maps.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH fast_flush_domains (default: $relay_domains)
+Optional list of destinations that are eligible for per\-destination
+logfiles with mail that is queued to those destinations.
+.PP
+By default, Postfix maintains "fast flush" logfiles only for
+destinations that the Postfix SMTP server is willing to relay to
+(i.e. the default is: "fast_flush_domains = $relay_domains"; see
+the relay_domains parameter in the \fBpostconf\fR(5) manual).
+.PP
+Specify a list of hosts or domains, "/file/name" patterns or
+"type:table" lookup tables, separated by commas and/or whitespace.
+Continue long lines by starting the next line with whitespace. A
+"/file/name" pattern is replaced by its contents; a "type:table"
+lookup table is matched when the domain or its parent domain appears
+as lookup key.
+.PP
+Pattern matching of domain names is controlled by the presence
+or absence of "fast_flush_domains" in the parent_domain_matches_subdomains
+parameter value.
+.PP
+Specify "fast_flush_domains =" (i.e., empty) to disable the feature
+altogether.
+.SH fast_flush_purge_time (default: 7d)
+The time after which an empty per\-destination "fast flush" logfile
+is deleted.
+.PP
+You can specify the time as a number, or as a number followed by
+a letter that indicates the time unit: s=seconds, m=minutes, h=hours,
+d=days, w=weeks.  The default time unit is days.
+.SH fast_flush_refresh_time (default: 12h)
+The time after which a non\-empty but unread per\-destination "fast
+flush" logfile needs to be refreshed.  The contents of a logfile
+are refreshed by requesting delivery of all messages listed in the
+logfile.
+.PP
+You can specify the time as a number, or as a number followed by
+a letter that indicates the time unit: s=seconds, m=minutes, h=hours,
+d=days, w=weeks.  The default time unit is hours.
+.SH fault_injection_code (default: 0)
+Force specific internal tests to fail, to test the handling of
+errors that are difficult to reproduce otherwise.
+.SH flush_service_name (default: flush)
+The name of the \fBflush\fR(8) service. This service maintains per\-destination
+logfiles with the queue file names of mail that is queued for those
+destinations.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH fork_attempts (default: 5)
+The maximal number of attempts to fork() a child process.
+.SH fork_delay (default: 1s)
+The delay between attempts to fork() a child process.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH forward_expansion_filter (default: see "postconf \-d" output)
+Restrict the characters that the \fBlocal\fR(8) delivery agent allows in
+$name expansions of $forward_path.  Characters outside the
+allowed set are replaced by underscores.
+.SH forward_path (default: see "postconf \-d" output)
+The \fBlocal\fR(8) delivery agent search list for finding a .forward
+file with user\-specified delivery methods. The first file that is
+found is used.
+.PP
+The forward_path value is not subject to Postfix configuration
+parameter $name expansion. Instead, the following $name expansions
+are done on forward_path before the search actually happens.
+The result of $name expansion is
+filtered with the character set that is specified with the
+forward_expansion_filter parameter.
+.IP "\fB$user\fR"
+The recipient's username.
+.br
+.IP "\fB$shell\fR"
+The recipient's login shell pathname.
+.br
+.IP "\fB$home\fR"
+The recipient's home directory.
+.br
+.IP "\fB$recipient\fR"
+The full recipient address.
+.br
+.IP "\fB$extension\fR"
+The optional recipient address extension.
+.br
+.IP "\fB$domain\fR"
+The recipient domain.
+.br
+.IP "\fB$local\fR"
+The entire recipient localpart.
+.br
+.IP "\fB$recipient_delimiter\fR"
+The address extension delimiter that was found in the recipient
+address (Postfix 2.11 and later), or the 'first' delimiter specified
+with the system\-wide recipient address extension delimiter (Postfix
+3.5.22, 3.5.12, 3.7.8, 3.8.3 and later). Historically, this was
+always the system\-wide recipient
+address extension delimiter (Postfix 2.10 and earlier).
+.br
+.IP "\fB${name?value}\fR"
+.IP "\fB${name?{value}}\fR (Postfix >= 3.0)"
+Expands to \fIvalue\fR when \fI$name\fR is non\-empty.
+.br
+.IP "\fB${name:value}\fR"
+.IP "\fB${name:{value}}\fR (Postfix >= 3.0)"
+Expands to \fIvalue\fR when \fI$name\fR is empty.
+.br
+.IP "\fB${name?{value1}:{value2}}\fR (Postfix >= 3.0)"
+Expands to \fIvalue1\fR when \fI$name\fR is non\-empty,
+\fIvalue2\fR otherwise.
+.br
+.br
+.PP
+Instead of $name you can also specify ${name} or $(name).
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+forward_path = /var/forward/$user
+forward_path =
+    /var/forward/$user/.forward$recipient_delimiter$extension,
+    /var/forward/$user/.forward
+.fi
+.ad
+.ft R
+.SH frozen_delivered_to (default: yes)
+Update the \fBlocal\fR(8) delivery agent's idea of the Delivered\-To:
+address (see prepend_delivered_header) only once, at the start of
+a delivery attempt; do not update the Delivered\-To: address while
+expanding aliases or .forward files.
+.PP
+This feature is available in Postfix 2.3 and later. With older
+Postfix releases, the behavior is as if this parameter is set to
+"no". The old setting can be expensive with deeply nested aliases
+or .forward files. When an alias or .forward file changes the
+Delivered\-To: address, it ties up one queue file and one cleanup
+process instance while mail is being forwarded.
+.SH hash_queue_depth (default: 1)
+The number of subdirectory levels for queue directories listed with
+the hash_queue_names parameter. Queue hashing is implemented by
+creating one or more levels of directories with one\-character names.
+Originally, these directory names were equal to the first characters
+of the queue file name, with the hexadecimal representation of the
+file creation time in microseconds.
+.PP
+With long queue file names, queue hashing produces the same
+results as with short names. The file creation time in microseconds
+is converted into hexadecimal form before the result is used for
+queue hashing.  The base 16 encoding gives finer control over the
+number of subdirectories than is possible with the base 52 encoding
+of long queue file names.
+.PP
+After changing the hash_queue_names or hash_queue_depth parameter,
+execute the command "\fBpostfix reload\fR".
+.SH hash_queue_names (default: deferred, defer)
+The names of queue directories that are split across multiple
+subdirectory levels.
+.PP
+Before Postfix version 2.2, the default list of hashed queues
+was significantly larger. Claims about improvements in file system
+technology suggest that hashing of the incoming and active queues
+is no longer needed. Fewer hashed directories speed up the time
+needed to restart Postfix.
+.PP
+After changing the hash_queue_names or hash_queue_depth parameter,
+execute the command "\fBpostfix reload\fR".
+.SH header_address_token_limit (default: 10240)
+The maximal number of address tokens are allowed in an address
+message header. Information that exceeds the limit is discarded.
+The limit is enforced by the \fBcleanup\fR(8) server.
+.SH header_checks (default: empty)
+Optional lookup tables for content inspection of primary non\-MIME
+message headers, as specified in the \fBheader_checks\fR(5) manual page.
+.SH header_from_format (default: standard)
+The format of the Postfix\-generated \fBFrom:\fR header. This
+setting affects the appearance of 'full name' information when a
+local program such as /bin/mail submits a message without a From:
+header through the Postfix \fBsendmail\fR(1) command.
+.PP
+Specify one of the following:
+.IP "\fBstandard\fR (default)"
+Produce a header formatted
+as "\fBFrom:\fR \fIname\fR\fB <\fR\fIaddress\fR\fB>\fR".
+This is the default as of Postfix 3.3.
+.br
+.IP "\fBobsolete\fR"
+Produce a header formatted as "\fBFrom:\fR
+\fIaddress\fR \fB(\fR\fIname\fR\fB)\fR". This is the behavior
+prior to Postfix 3.3.
+.br
+.br
+.PP
+Notes:
+.IP \(bu
+Postfix generates the format "\fBFrom:\fR \fIaddress\fR"
+when \fIname\fR information is unavailable or the envelope sender
+address is empty. This is the same behavior as prior to Postfix
+3.3.
+.IP \(bu
+In the \fBstandard\fR form, the \fIname\fR will be quoted
+if it contains \fBspecials\fR as defined in RFC 5322, or the "!%"
+address operators.
+.IP \(bu
+The Postfix \fBsendmail\fR(1) command gets \fIname\fR information
+from the \fB\-F\fR command\-line option, from the \fBNAME\fR
+environment variable, or from the UNIX password file.
+.br
+.PP
+This feature is available in Postfix 3.3 and later.
+.SH header_size_limit (default: 102400)
+The maximal amount of memory in bytes for storing a message header.
+If a header is larger, the excess is discarded.  The limit is
+enforced by the \fBcleanup\fR(8) server.
+.SH helpful_warnings (default: yes)
+Log warnings about problematic configuration settings, and provide
+helpful suggestions.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH home_mailbox (default: empty)
+Optional pathname of a mailbox file relative to a \fBlocal\fR(8) user's
+home directory.
+.PP
+Specify a pathname ending in "/" for qmail\-style delivery.
+.PP
+The precedence of \fBlocal\fR(8) delivery features from high to low
+is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
+mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
+fallback_transport_maps, fallback_transport and luser_relay.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+home_mailbox = Mailbox
+home_mailbox = Maildir/
+.fi
+.ad
+.ft R
+.SH hopcount_limit (default: 50)
+The maximal number of Received:  message headers that is allowed
+in the primary message headers. A message that exceeds the limit
+is bounced, in order to stop a mailer loop.
+.SH html_directory (default: see "postconf \-d" output)
+The location of Postfix HTML files that describe how to build,
+configure or operate a specific Postfix subsystem or feature.
+.SH ignore_mx_lookup_error (default: no)
+Ignore DNS MX lookups that produce no response.  By default,
+the Postfix SMTP client defers delivery and tries again after some
+delay.  This behavior is required by the SMTP standard.
+.PP
+Specify "ignore_mx_lookup_error = yes" to force a DNS A record
+lookup instead. This violates the SMTP standard and can result in
+mis\-delivery of mail.
+.SH ignore_srv_lookup_error (default: no)
+When SRV record lookup fails, fall back to MX or IP address
+lookup as if SRV record lookup was not enabled.
+.PP
+This feature is available in Postfix 3.8 and later.
+.SH import_environment (default: see "postconf \-d" output)
+The list of environment variables that a privileged Postfix
+process will import from a non\-Postfix parent process, or name=value
+environment overrides.  Unprivileged utilities will enforce the
+name=value overrides, but otherwise will not change their process
+environment.  Examples of relevant environment variables:
+.IP "\fBTZ\fR"
+May be needed for sane time keeping on most System\-V\-ish systems.
+.br
+.IP "\fBDISPLAY\fR"
+Needed for debugging Postfix daemons with an X\-windows debugger.
+.br
+.IP "\fBXAUTHORITY\fR"
+Needed for debugging Postfix daemons with an X\-windows debugger.
+.br
+.IP "\fBMAIL_CONFIG\fR"
+Needed to make "\fBpostfix \-c\fR" work.
+.br
+.IP "\fBPOSTLOG_SERVICE\fR"
+Needed to make "\fBmaillog_file\fR" work during daemon
+process initialization.
+.br
+.IP "\fBPOSTLOG_HOSTNAME\fR"
+Needed to make "\fBmaillog_file\fR" work during daemon
+process initialization.
+.br
+.br
+.PP
+Specify a list of names and/or name=value pairs, separated by
+whitespace or comma. Specify "{ name=value }" to protect whitespace
+or comma in environment variable values (whitespace after the opening "{" and
+before the closing "}"
+is ignored). The form name=value is supported with Postfix version
+2.1 and later; the use of {} is supported with Postfix 3.0 and
+later.
+.SH in_flow_delay (default: 1s)
+Time to pause before accepting a new message, when the message
+arrival rate exceeds the message delivery rate. This feature is
+turned on by default (it's disabled on SCO UNIX due to an SCO bug).
+.PP
+With the default 100 Postfix SMTP server process limit, "in_flow_delay
+= 1s" limits the mail inflow to 100 messages per second above the
+number of messages delivered per second.
+.PP
+Specify 0 to disable the feature. Valid delays are 0..10.
+.SH inet_interfaces (default: all)
+The local network interface addresses that this mail system receives
+mail on. Specify "all" to receive mail on all network
+interfaces (default), and "loopback\-only" to receive mail
+on loopback network interfaces only (Postfix version 2.2 and later).  The
+parameter also controls delivery of mail to user@[ip.address].
+.PP
+Note 1: you need to stop and start Postfix when this parameter changes.
+.PP
+Note 2: address information may be enclosed inside [],
+but this form is not required here.
+.PP
+When inet_interfaces specifies just one IPv4 and/or IPv6 address
+that is not a loopback address, the Postfix SMTP client will use
+this address as the IP source address for outbound mail. Support
+for IPv6 is available in Postfix version 2.2 and later.
+.PP
+On a multi\-homed firewall with separate Postfix instances listening on the
+"inside" and "outside" interfaces, this can prevent each instance from
+being able to reach remote SMTP servers on the "other side" of the
+firewall. Setting
+smtp_bind_address to 0.0.0.0 avoids the potential problem for
+IPv4, and setting smtp_bind_address6 to :: solves the problem
+for IPv6.
+.PP
+A better solution for multi\-homed firewalls is to leave inet_interfaces
+at the default value and instead use explicit IP addresses in
+the master.cf SMTP server definitions.  This preserves the Postfix
+SMTP client's
+loop detection, by ensuring that each side of the firewall knows that the
+other IP address is still the same host. Setting $inet_interfaces to a
+single IPv4 and/or IPV6 address is primarily useful with virtual
+hosting of domains on
+secondary IP addresses, when each IP address serves a different domain
+(and has a different $myhostname setting).
+.PP
+See also the proxy_interfaces parameter, for network addresses that
+are forwarded to Postfix by way of a proxy or address translator.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+inet_interfaces = all (DEFAULT)
+inet_interfaces = loopback\-only (Postfix version 2.2 and later)
+inet_interfaces = 127.0.0.1
+inet_interfaces = 127.0.0.1, [::1] (Postfix version 2.2 and later)
+inet_interfaces = 192.168.1.2, 127.0.0.1
+.fi
+.ad
+.ft R
+.SH inet_protocols (default: see 'postconf \-d output')
+The Internet protocols Postfix will attempt to use when making
+or accepting connections. Specify one or more of "ipv4"
+or "ipv6", separated by whitespace or commas. The form
+"all" is equivalent to "ipv4, ipv6" or "ipv4", depending
+on whether the operating system implements IPv6.
+.PP
+With Postfix 2.8 and earlier the default is "ipv4". For backwards
+compatibility with these releases, the Postfix 2.9 and later upgrade
+procedure appends an explicit "inet_protocols = ipv4" setting to
+main.cf when no explicit setting is present. This compatibility
+workaround will be phased out as IPv6 deployment becomes more common.
+.PP
+This feature is available in Postfix 2.2 and later.
+.PP
+Note: you MUST stop and start Postfix after changing this
+parameter.
+.PP
+On systems that pre\-date IPV6_V6ONLY support (RFC 3493), an
+IPv6 server will also accept IPv4 connections, even when IPv4 is
+turned off with the inet_protocols parameter.  On systems with
+IPV6_V6ONLY support, Postfix will use separate server sockets for
+IPv6 and IPv4, and each will accept only connections for the
+corresponding protocol.
+.PP
+When IPv4 support is enabled via the inet_protocols parameter,
+Postfix will look up DNS type A records, and will convert
+IPv4\-in\-IPv6 client IP addresses (::ffff:1.2.3.4) to their original
+IPv4 form (1.2.3.4).  The latter is needed on hosts that pre\-date
+IPV6_V6ONLY support (RFC 3493).
+.PP
+When IPv6 support is enabled via the inet_protocols parameter,
+Postfix will do DNS type AAAA record lookups.
+.PP
+When both IPv4 and IPv6 support are enabled, the Postfix SMTP
+client will choose the protocol as specified with the
+smtp_address_preference parameter. Postfix versions before 2.8
+attempt to connect via IPv6 before attempting to use IPv4.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+inet_protocols = ipv4
+inet_protocols = all (DEFAULT)
+inet_protocols = ipv6
+inet_protocols = ipv4, ipv6
+.fi
+.ad
+.ft R
+.SH info_log_address_format (default: external)
+The email address form that will be used in non\-debug logging
+(info, warning, etc.). As of Postfix 3.5 when an address localpart
+contains spaces or other special characters, the localpart will be
+quoted, for example:
+.sp
+.in +4
+.nf
+.na
+.ft C
+    from=<"name with spaces"@example.com>
+.fi
+.ad
+.ft R
+.in -4
+.PP
+Older Postfix versions would log the internal (unquoted) form:
+.sp
+.in +4
+.nf
+.na
+.ft C
+    from=<name with spaces@example.com>
+.fi
+.ad
+.ft R
+.in -4
+.PP
+The external and internal forms are identical for the vast
+majority of email addresses that contain no spaces or other special
+characters in the localpart.
+.PP
+The logging in external form is consistent with the address
+form that Postfix 3.2 and later prefer for most table lookups. This
+is therefore the more useful form for non\-debug logging.
+.PP
+Specify "\fBinfo_log_address_format = internal\fR" for backwards
+compatibility.
+.PP
+Postfix uses the unquoted form internally, because an attacker
+can specify an email address in different forms by playing games
+with quotes and backslashes. An attacker should not be able to use
+such games to circumvent Postfix access policies.
+.PP
+This feature is available in Postfix 3.5 and later.
+.SH initial_destination_concurrency (default: 5)
+The initial per\-destination concurrency level for parallel delivery
+to the same destination.
+With per\-destination recipient limit > 1, a destination is a domain,
+otherwise it is a recipient.
+.PP
+Use \fItransport\fR_initial_destination_concurrency to specify
+a transport\-specific override, where \fItransport\fR is the master.cf
+name of the message delivery transport (Postfix 2.5 and later).
+.PP
+Warning: with concurrency of 1, one bad message can be enough to
+block all mail to a site.
+.SH internal_mail_filter_classes (default: empty)
+What categories of Postfix\-generated mail are subject to
+before\-queue content inspection by non_smtpd_milters, header_checks
+and body_checks.  Specify zero or more of the following, separated
+by whitespace or comma.
+.IP "\fBbounce\fR"
+Inspect the content of delivery
+status notifications.
+.br
+.IP "\fBnotify\fR"
+Inspect the content of postmaster
+notifications by the \fBsmtp\fR(8) and \fBsmtpd\fR(8) processes.
+.br
+.br
+.PP
+NOTE: It's generally not safe to enable content inspection of
+Postfix\-generated email messages. The user is warned.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH invalid_hostname_reject_code (default: 501)
+The numerical Postfix SMTP server response code when the client
+HELO or EHLO command parameter is rejected by the reject_invalid_helo_hostname
+restriction.
+.PP
+Do not change this unless you have a complete understanding of RFC 5321.
+.SH ipc_idle (default: version dependent)
+The time after which a client closes an idle internal communication
+channel.  The purpose is to allow Postfix daemon processes to
+terminate voluntarily after they become idle. This is used, for
+example, by the Postfix address resolving and rewriting clients.
+.PP
+With Postfix 2.4 the default value was reduced from 100s to 5s.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH ipc_timeout (default: 3600s)
+The time limit for sending or receiving information over an internal
+communication channel.  The purpose is to break out of deadlock
+situations. If the time limit is exceeded the software aborts with a
+fatal error.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH ipc_ttl (default: 1000s)
+The time after which a client closes an active internal communication
+channel.  The purpose is to allow Postfix daemon processes to
+terminate voluntarily
+after reaching their client limit.  This is used, for example, by
+the Postfix address resolving and rewriting clients.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH known_tcp_ports (default: lmtp=24, smtp=25, smtps=submissions=465, submission=587)
+Optional setting that avoids lookups in the \fBservices\fR(5) database.
+This feature was implemented to address inconsistencies in the name
+of the port "465" service. The ABNF is:
+.sp
+.in +4
+known_tcp_ports = empty | name\-to\-port *("," name\-to\-port)
+.br
+name\-to\-port = 1*(service\-name "=') port\-number
+.in -4
+.PP
+The comma is required. Whitespace is optional but it cannot appear
+inside a service name or port number.
+.PP
+This feature is available in Postfix 3.6 and later.
+.SH line_length_limit (default: 2048)
+Upon input, long lines are chopped up into pieces of at most
+this length; upon delivery, long lines are reconstructed.
+.SH lmdb_map_size (default: 16777216)
+The initial OpenLDAP LMDB database size limit in bytes.  Each time
+a database becomes full, its size limit is doubled.
+.PP
+This feature is available in Postfix 2.11 and later.
+.SH lmtp_address_preference (default: ipv6)
+The LMTP\-specific version of the smtp_address_preference
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH lmtp_address_verify_target (default: rcpt)
+The LMTP\-specific version of the smtp_address_verify_target
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH lmtp_assume_final (default: no)
+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". The default setting is backwards
+compatible to avoid the infinitesimal possibility of breaking
+existing LMTP\-based content filters.
+.SH lmtp_balance_inet_protocols (default: yes)
+The LMTP\-specific version of the smtp_balance_inet_protocols
+configuration parameter. See there for details.
+.PP
+This feature is available in Postfix 3.3 and later.
+.SH lmtp_bind_address (default: empty)
+The LMTP\-specific version of the smtp_bind_address configuration
+parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_bind_address6 (default: empty)
+The LMTP\-specific version of the smtp_bind_address6 configuration
+parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_bind_address_enforce (default: empty)
+The LMTP\-specific version of the smtp_bind_address_enforce
+configuration parameter. See there for details.
+.PP
+This feature is available in Postfix 3.7 and later.
+.SH lmtp_body_checks (default: empty)
+The LMTP\-specific version of the smtp_body_checks configuration
+parameter. See there for details.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH lmtp_cache_connection (default: yes)
+Keep Postfix LMTP client connections open for up to $max_idle
+seconds. When the LMTP client receives a request for the same
+connection the connection is reused.
+.PP
+This parameter is available in Postfix version 2.2 and earlier.
+With Postfix version 2.3 and later, see lmtp_connection_cache_on_demand,
+lmtp_connection_cache_destinations, or lmtp_connection_reuse_time_limit.
+.PP
+The effectiveness of cached connections will be determined by the
+number of remote LMTP servers in use, and the concurrency limit specified
+for the Postfix LMTP client. Cached connections are closed under any of
+the following conditions:
+.IP \(bu
+The Postfix LMTP client idle time limit is reached.  This limit is
+specified with the Postfix max_idle configuration parameter.
+.IP \(bu
+A delivery request specifies a different destination than the
+one currently cached.
+.IP \(bu
+The per\-process limit on the number of delivery requests is
+reached.  This limit is specified with the Postfix max_use
+configuration parameter.
+.IP \(bu
+Upon the onset of another delivery request, the remote LMTP server
+associated with the current session does not respond to the RSET
+command.
+.br
+.PP
+Most of these limitations have been with the Postfix
+connection cache that is shared among multiple LMTP client
+programs.
+.SH lmtp_cname_overrides_servername (default: yes)
+The LMTP\-specific version of the smtp_cname_overrides_servername
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_connect_timeout (default: 0s)
+The Postfix LMTP client time limit for completing a TCP connection, or
+zero (use the operating system built\-in time limit).  When no
+connection can be made within the deadline, the LMTP client tries
+the next address on the mail exchanger list.
+.PP
+Specify a non\-negative time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+lmtp_connect_timeout = 30s
+.fi
+.ad
+.ft R
+.SH lmtp_connection_cache_destinations (default: empty)
+The LMTP\-specific version of the smtp_connection_cache_destinations
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_connection_cache_on_demand (default: yes)
+The LMTP\-specific version of the smtp_connection_cache_on_demand
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_connection_cache_time_limit (default: 2s)
+The LMTP\-specific version of the
+smtp_connection_cache_time_limit configuration parameter.
+See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_connection_reuse_count_limit (default: 0)
+The LMTP\-specific version of the smtp_connection_reuse_count_limit
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.11 and later.
+.SH lmtp_connection_reuse_time_limit (default: 300s)
+The LMTP\-specific version of the smtp_connection_reuse_time_limit
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_data_done_timeout (default: 600s)
+The Postfix LMTP client time limit for sending the LMTP ".",
+and for receiving the remote LMTP server response.  When no response
+is received within the deadline, a warning is logged that the mail
+may be delivered multiple times.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH lmtp_data_init_timeout (default: 120s)
+The Postfix LMTP client time limit for sending the LMTP DATA command,
+and
+for receiving the remote LMTP server response.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH lmtp_data_xfer_timeout (default: 180s)
+The Postfix LMTP client time limit for sending the LMTP message
+content.
+When the connection stalls for more than $lmtp_data_xfer_timeout
+the LMTP client terminates the transfer.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH lmtp_defer_if_no_mx_address_found (default: no)
+The LMTP\-specific version of the smtp_defer_if_no_mx_address_found
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_delivery_status_filter (default: empty)
+The LMTP\-specific version of the smtp_delivery_status_filter
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH lmtp_destination_concurrency_limit (default: $default_destination_concurrency_limit)
+The maximal number of parallel deliveries to the same destination
+via the lmtp message delivery transport. This limit is enforced by
+the queue manager. The message delivery transport name is the first
+field in the entry in the master.cf file.
+.SH lmtp_destination_recipient_limit (default: $default_destination_recipient_limit)
+The maximal number of recipients per message for the lmtp
+message delivery transport. This limit is enforced by the queue
+manager. The message delivery transport name is the first field in
+the entry in the master.cf file.
+.PP
+Setting this parameter to a value of 1 changes the meaning of
+lmtp_destination_concurrency_limit from concurrency per domain into
+concurrency per recipient.
+.SH lmtp_discard_lhlo_keyword_address_maps (default: empty)
+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. See lmtp_discard_lhlo_keywords for
+details. The table is not indexed by hostname for consistency with
+smtpd_discard_ehlo_keyword_address_maps.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_discard_lhlo_keywords (default: empty)
+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
+This feature is available in Postfix 2.3 and later.
+.PP
+Notes:
+.IP \(bu
+Specify the \fBsilent\-discard\fR pseudo keyword to prevent
+this action from being logged.
+.IP \(bu
+Use the lmtp_discard_lhlo_keyword_address_maps feature to
+discard LHLO keywords selectively.
+.br
+.SH lmtp_dns_reply_filter (default: empty)
+Optional filter for Postfix LMTP client DNS lookup results.
+See smtp_dns_reply_filter for details including an example.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH lmtp_dns_resolver_options (default: empty)
+The LMTP\-specific version of the smtp_dns_resolver_options
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH lmtp_dns_support_level (default: empty)
+The LMTP\-specific version of the smtp_dns_support_level
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.11 and later.
+.SH lmtp_enforce_tls (default: no)
+The LMTP\-specific version of the smtp_enforce_tls configuration
+parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_fallback_relay (default: empty)
+Optional list of relay hosts for LMTP destinations that can't be
+found or that are unreachable.  In main.cf elements are separated by
+whitespace or commas.
+.PP
+By default, mail is returned to the sender when a destination is not
+found, and delivery is deferred when a destination is unreachable.
+.PP
+The fallback relays must be TCP destinations, specified without
+a leading "inet:" prefix.  Specify a host or host:port.  Since MX
+lookups do not apply with LMTP, there is no need to use the "[host]" or
+"[host]:port" forms.  If you specify multiple LMTP destinations, Postfix
+will try them in the specified order.
+.PP
+This feature is available in Postfix 3.1 and later.
+.SH lmtp_generic_maps (default: empty)
+The LMTP\-specific version of the smtp_generic_maps configuration
+parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_header_checks (default: empty)
+The LMTP\-specific version of the smtp_header_checks configuration
+parameter. See there for details.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH lmtp_host_lookup (default: dns)
+The LMTP\-specific version of the smtp_host_lookup configuration
+parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_lhlo_name (default: $myhostname)
+The hostname to send in the LMTP LHLO command.
+.PP
+The default value is the machine hostname.  Specify a hostname or
+[ip.add.re.ss] or [ip:v6:add:re::ss].
+.PP
+This information can be specified in the main.cf file for all LMTP
+clients, or it can be specified in the master.cf file for a specific
+client, for example:
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/master.cf:
+    mylmtp ... lmtp \-o lmtp_lhlo_name=foo.bar.com
+.fi
+.ad
+.ft R
+.in -4
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_lhlo_timeout (default: 300s)
+The Postfix LMTP client time limit for sending the LHLO command,
+and for receiving the initial remote LMTP server response.
+.PP
+Time units: s (seconds), m (minutes), h (hours), d (days), w
+(weeks).  The default time unit is s (seconds).
+.SH lmtp_line_length_limit (default: 998)
+The LMTP\-specific version of the smtp_line_length_limit
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_mail_timeout (default: 300s)
+The Postfix LMTP client time limit for sending the MAIL FROM command,
+and for receiving the remote LMTP server response.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH lmtp_mime_header_checks (default: empty)
+The LMTP\-specific version of the smtp_mime_header_checks
+configuration parameter. See there for details.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH lmtp_min_data_rate (default: 500)
+The LMTP\-specific version of the smtp_min_data_rate configuration
+parameter. See there for details.
+.PP
+This feature is available in Postfix 3.7 and later.
+.SH lmtp_mx_address_limit (default: 5)
+The LMTP\-specific version of the smtp_mx_address_limit configuration
+parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_mx_session_limit (default: 2)
+The LMTP\-specific version of the smtp_mx_session_limit configuration
+parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_nested_header_checks (default: empty)
+The LMTP\-specific version of the smtp_nested_header_checks
+configuration parameter. See there for details.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH lmtp_per_record_deadline (default: no)
+The LMTP\-specific version of the smtp_per_record_deadline
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.9 and later.
+.SH lmtp_per_request_deadline (default: no)
+The LMTP\-specific version of the smtp_per_request_deadline
+configuration parameter. See there for details.
+.PP
+This feature is available in Postfix 3.7 and later.
+.SH lmtp_pix_workaround_delay_time (default: 10s)
+The LMTP\-specific version of the smtp_pix_workaround_delay_time
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_pix_workaround_maps (default: empty)
+The LMTP\-specific version of the smtp_pix_workaround_maps
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.4 and later.
+.SH lmtp_pix_workaround_threshold_time (default: 500s)
+The LMTP\-specific version of the smtp_pix_workaround_threshold_time
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_pix_workarounds (default: empty)
+The LMTP\-specific version of the smtp_pix_workaround
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.4 and later.
+.SH lmtp_quit_timeout (default: 300s)
+The Postfix LMTP client time limit for sending the QUIT command,
+and for receiving the remote LMTP server response.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH lmtp_quote_rfc821_envelope (default: yes)
+The LMTP\-specific version of the smtp_quote_rfc821_envelope
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_randomize_addresses (default: yes)
+The LMTP\-specific version of the smtp_randomize_addresses
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_rcpt_timeout (default: 300s)
+The Postfix LMTP client time limit for sending the RCPT TO command,
+and for receiving the remote LMTP server response.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH lmtp_reply_filter (default: empty)
+The LMTP\-specific version of the smtp_reply_filter
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.7 and later.
+.SH lmtp_rset_timeout (default: 20s)
+The Postfix LMTP client time limit for sending the RSET command,
+and for receiving the remote LMTP server response. The LMTP client
+sends RSET in
+order to finish a recipient address probe, or to verify that a
+cached connection is still alive.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH lmtp_sasl_auth_cache_name (default: empty)
+The LMTP\-specific version of the smtp_sasl_auth_cache_name
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH lmtp_sasl_auth_cache_time (default: 90d)
+The LMTP\-specific version of the smtp_sasl_auth_cache_time
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH lmtp_sasl_auth_enable (default: no)
+Enable SASL authentication in the Postfix LMTP client.
+.SH lmtp_sasl_auth_soft_bounce (default: yes)
+The LMTP\-specific version of the smtp_sasl_auth_soft_bounce
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH lmtp_sasl_mechanism_filter (default: empty)
+The LMTP\-specific version of the smtp_sasl_mechanism_filter
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_sasl_password_maps (default: empty)
+Optional Postfix LMTP client lookup tables with one username:password entry
+per host or domain.  If a remote host or domain has no username:password
+entry, then the Postfix LMTP client will not attempt to authenticate
+to the remote host.
+.SH lmtp_sasl_path (default: empty)
+Implementation\-specific information that is passed through to
+the SASL plug\-in implementation that is selected with
+\fBlmtp_sasl_type\fR.  Typically this specifies the name of a
+configuration file or rendezvous point.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_sasl_security_options (default: noplaintext, noanonymous)
+SASL security options; as of Postfix 2.3 the list of available
+features depends on the SASL client implementation that is selected
+with \fBlmtp_sasl_type\fR.
+.PP
+The following security features are defined for the \fBcyrus\fR
+client SASL implementation:
+.IP "\fBnoplaintext\fR"
+Disallow authentication methods that use plaintext passwords.
+.br
+.IP "\fBnoactive\fR"
+Disallow authentication methods that are vulnerable to non\-dictionary
+active attacks.
+.br
+.IP "\fBnodictionary\fR"
+Disallow authentication methods that are vulnerable to passive
+dictionary attacks.
+.br
+.IP "\fBnoanonymous\fR"
+Disallow anonymous logins.
+.br
+.br
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+lmtp_sasl_security_options = noplaintext
+.fi
+.ad
+.ft R
+.SH lmtp_sasl_tls_security_options (default: $lmtp_sasl_security_options)
+The LMTP\-specific version of the smtp_sasl_tls_security_options
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_sasl_tls_verified_security_options (default: $lmtp_sasl_tls_security_options)
+The LMTP\-specific version of the
+smtp_sasl_tls_verified_security_options configuration parameter.
+See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_sasl_type (default: cyrus)
+The SASL plug\-in type that the Postfix LMTP client should use
+for authentication.  The available types are listed with the
+"\fBpostconf \-A\fR" command.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_send_dummy_mail_auth (default: no)
+The LMTP\-specific version of the smtp_send_dummy_mail_auth
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.9 and later.
+.SH lmtp_send_xforward_command (default: no)
+Send an XFORWARD command to the remote LMTP server when the LMTP LHLO
+server response announces XFORWARD support.  This allows an \fBlmtp\fR(8)
+delivery agent, used for content filter message injection, to
+forward the name, address, protocol and HELO name of the original
+client to the content filter and downstream LMTP server.
+Before you change the value to yes, it is best to make sure that
+your content filter supports this command.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH lmtp_sender_dependent_authentication (default: no)
+The LMTP\-specific version of the smtp_sender_dependent_authentication
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_skip_5xx_greeting (default: yes)
+The LMTP\-specific version of the smtp_skip_5xx_greeting
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_skip_quit_response (default: no)
+Wait for the response to the LMTP QUIT command.
+.SH lmtp_starttls_timeout (default: 300s)
+The LMTP\-specific version of the smtp_starttls_timeout configuration
+parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tcp_port (default: 24)
+The default TCP port that the Postfix LMTP client connects to.
+Specify a symbolic name (see \fBservices\fR(5)) or a numeric port.
+.SH lmtp_tls_CAfile (default: empty)
+The LMTP\-specific version of the smtp_tls_CAfile
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_CApath (default: empty)
+The LMTP\-specific version of the smtp_tls_CApath
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_block_early_mail_reply (default: empty)
+The LMTP\-specific version of the smtp_tls_block_early_mail_reply
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.7 and later.
+.SH lmtp_tls_cert_file (default: empty)
+The LMTP\-specific version of the smtp_tls_cert_file
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_chain_files (default: empty)
+The LMTP\-specific version of the smtp_tls_chain_files configuration
+parameter. See there for details.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH lmtp_tls_ciphers (default: medium)
+The LMTP\-specific version of the smtp_tls_ciphers configuration
+parameter. See there for details.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH lmtp_tls_connection_reuse (default: no)
+The LMTP\-specific version of the smtp_tls_connection_reuse configuration
+parameter. See there for details.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH lmtp_tls_dcert_file (default: empty)
+The LMTP\-specific version of the smtp_tls_dcert_file
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_dkey_file (default: $lmtp_tls_dcert_file)
+The LMTP\-specific version of the smtp_tls_dkey_file
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_eccert_file (default: empty)
+The LMTP\-specific version of the smtp_tls_eccert_file configuration
+parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.6 and later, when Postfix is
+compiled and linked with OpenSSL 1.0.0 or later.
+.SH lmtp_tls_eckey_file (default: empty)
+The LMTP\-specific version of the smtp_tls_eckey_file configuration
+parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.6 and later, when Postfix is
+compiled and linked with OpenSSL 1.0.0 or later.
+.SH lmtp_tls_enforce_peername (default: yes)
+The LMTP\-specific version of the smtp_tls_enforce_peername
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_exclude_ciphers (default: empty)
+The LMTP\-specific version of the smtp_tls_exclude_ciphers
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_fingerprint_cert_match (default: empty)
+The LMTP\-specific version of the smtp_tls_fingerprint_cert_match
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH lmtp_tls_fingerprint_digest (default: see "postconf \-d" output)
+The LMTP\-specific version of the smtp_tls_fingerprint_digest
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH lmtp_tls_force_insecure_host_tlsa_lookup (default: no)
+The LMTP\-specific version of the smtp_tls_force_insecure_host_tlsa_lookup
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.11 and later.
+.SH lmtp_tls_key_file (default: $lmtp_tls_cert_file)
+The LMTP\-specific version of the smtp_tls_key_file
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_loglevel (default: 0)
+The LMTP\-specific version of the smtp_tls_loglevel
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_mandatory_ciphers (default: medium)
+The LMTP\-specific version of the smtp_tls_mandatory_ciphers
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_mandatory_exclude_ciphers (default: empty)
+The LMTP\-specific version of the smtp_tls_mandatory_exclude_ciphers
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_mandatory_protocols (default: see postconf \-d output)
+The LMTP\-specific version of the smtp_tls_mandatory_protocols
+configuration parameter. See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_note_starttls_offer (default: no)
+The LMTP\-specific version of the smtp_tls_note_starttls_offer
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_per_site (default: empty)
+The LMTP\-specific version of the smtp_tls_per_site configuration
+parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_policy_maps (default: empty)
+The LMTP\-specific version of the smtp_tls_policy_maps
+configuration parameter. See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_protocols (default: see postconf \-d output)
+The LMTP\-specific version of the smtp_tls_protocols configuration
+parameter. See there for details.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH lmtp_tls_scert_verifydepth (default: 9)
+The LMTP\-specific version of the smtp_tls_scert_verifydepth
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_secure_cert_match (default: nexthop)
+The LMTP\-specific version of the smtp_tls_secure_cert_match
+configuration parameter. See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_security_level (default: empty)
+The LMTP\-specific version of the smtp_tls_security_level configuration
+parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_servername (default: empty)
+The LMTP\-specific version of the smtp_tls_servername configuration
+parameter. See there for details.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH lmtp_tls_session_cache_database (default: empty)
+The LMTP\-specific version of the smtp_tls_session_cache_database
+configuration parameter. See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_session_cache_timeout (default: 3600s)
+The LMTP\-specific version of the smtp_tls_session_cache_timeout
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_trust_anchor_file (default: empty)
+The LMTP\-specific version of the smtp_tls_trust_anchor_file
+configuration parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.11 and later.
+.SH lmtp_tls_verify_cert_match (default: hostname)
+The LMTP\-specific version of the smtp_tls_verify_cert_match
+configuration parameter. See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_tls_wrappermode (default: no)
+The LMTP\-specific version of the smtp_tls_wrappermode configuration
+parameter. See there for details.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH lmtp_use_tls (default: no)
+The LMTP\-specific version of the smtp_use_tls configuration
+parameter.  See there for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH lmtp_xforward_timeout (default: 300s)
+The Postfix LMTP client time limit for sending the XFORWARD command,
+and for receiving the remote LMTP server response.
+.PP
+In case of problems the client does NOT try the next address on
+the mail exchanger list.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH local_command_shell (default: empty)
+Optional shell program for \fBlocal\fR(8) delivery to non\-Postfix commands.
+By default, non\-Postfix commands are executed directly; commands
+are given to the default shell (typically, /bin/sh) only when they
+contain shell meta characters or shell built\-in commands.
+.PP
+"sendmail's restricted shell" (smrsh) is what most people will
+use in order to restrict what programs can be run from e.g. .forward
+files (smrsh is part of the Sendmail distribution).
+.PP
+Note: when a shell program is specified, it is invoked even
+when the command contains no shell built\-in commands or meta
+characters.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+local_command_shell = /some/where/smrsh \-c
+local_command_shell = /bin/bash \-c
+.fi
+.ad
+.ft R
+.SH local_delivery_status_filter (default: $default_delivery_status_filter)
+Optional filter for the \fBlocal\fR(8) delivery agent to change the
+status code or explanatory text of successful or unsuccessful
+deliveries.  See default_delivery_status_filter for details.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH local_destination_concurrency_limit (default: 2)
+The maximal number of parallel deliveries via the local mail
+delivery transport to the same recipient (when
+"local_destination_recipient_limit = 1") or the maximal number of
+parallel deliveries to the same local domain (when
+"local_destination_recipient_limit > 1"). This limit is enforced by
+the queue manager. The message delivery transport name is the first
+field in the entry in the master.cf file.
+.PP
+A low limit of 2 is recommended, just in case someone has an
+expensive shell command in a .forward file or in an alias (e.g.,
+a mailing list manager).  You don't want to run lots of those at
+the same time.
+.SH local_destination_recipient_limit (default: 1)
+The maximal number of recipients per message delivery via the
+local mail delivery transport. This limit is enforced by the queue
+manager. The message delivery transport name is the first field in
+the entry in the master.cf file.
+.PP
+Setting this parameter to a value > 1 changes the meaning of
+local_destination_concurrency_limit from concurrency per recipient
+into concurrency per domain.
+.SH local_header_rewrite_clients (default: permit_inet_interfaces)
+Rewrite or add message headers in mail from these clients,
+updating incomplete addresses with the domain name in $myorigin or
+$mydomain, and adding missing headers.
+.PP
+See the append_at_myorigin and append_dot_mydomain parameters
+for details of how domain names are appended to incomplete addresses.
+.PP
+See remote_header_rewrite_domain to optionally rewrite or add
+message headers in mail from other clients.
+.PP
+Specify a list of zero or more of the following:
+.IP "\fBpermit_inet_interfaces\fR"
+Append the domain name in $myorigin or $mydomain when the
+client IP address matches $inet_interfaces. This is enabled by
+default.
+.br
+.IP "\fBpermit_mynetworks\fR"
+Append the domain name in $myorigin or $mydomain when the
+client IP address matches any network or network address listed in
+$mynetworks. This setting will not prevent remote mail header
+address rewriting when mail from a remote client is forwarded by
+a neighboring system.
+.br
+.IP "\fBpermit_sasl_authenticated \fR"
+Append the domain name in $myorigin or $mydomain when the
+client is successfully authenticated via the RFC 4954 (AUTH)
+protocol.
+.br
+.IP "\fBpermit_tls_clientcerts \fR"
+Append the domain name in $myorigin or $mydomain when the
+remote SMTP client TLS certificate fingerprint or public key fingerprint
+(Postfix 2.9 and later) is listed in $relay_clientcerts.
+The fingerprint digest algorithm is configurable via the
+smtpd_tls_fingerprint_digest parameter (hard\-coded as md5 prior to
+Postfix version 2.5).
+.br
+The default algorithm is \fBsha256\fR with Postfix >= 3.6
+and the \fBcompatibility_level\fR set to 3.6 or higher. With Postfix
+<= 3.5, the default algorithm is \fBmd5\fR.  The best\-practice
+algorithm is now \fBsha256\fR. Recent advances in hash function
+cryptanalysis have led to md5 and sha1 being deprecated in favor of
+sha256.  However, as long as there are no known "second pre\-image"
+attacks against the older algorithms, their use in this context, though
+not recommended, is still likely safe.
+.br
+.IP "\fBpermit_tls_all_clientcerts \fR"
+Append the domain name in $myorigin or $mydomain when the
+remote SMTP client TLS certificate is successfully verified, regardless of
+whether it is listed on the server, and regardless of the certifying
+authority.
+.br
+.IP "\fBcheck_address_map \fItype:table\fR \fR"
+.IP "\fB\fItype:table\fR \fR"
+Append the domain name in $myorigin or $mydomain when the
+client IP address matches the specified lookup table.
+The lookup result is ignored, and no subnet lookup is done. This
+is suitable for, e.g., pop\-before\-smtp lookup tables.
+.br
+.br
+.PP
+Examples:
+.PP
+The Postfix < 2.2 backwards compatible setting: always rewrite
+message headers, and always append my own domain to incomplete
+header addresses.
+.sp
+.in +4
+.nf
+.na
+.ft C
+local_header_rewrite_clients = static:all
+.fi
+.ad
+.ft R
+.in -4
+.PP
+The purist (and default) setting: rewrite headers only in mail
+from Postfix sendmail and in SMTP mail from this machine.
+.sp
+.in +4
+.nf
+.na
+.ft C
+local_header_rewrite_clients = permit_inet_interfaces
+.fi
+.ad
+.ft R
+.in -4
+.PP
+The intermediate setting: rewrite header addresses and append
+$myorigin or $mydomain information only with mail from Postfix
+sendmail, from local clients, or from authorized SMTP clients.
+.PP
+Note: this setting will not prevent remote mail header address
+rewriting when mail from a remote client is forwarded by a neighboring
+system.
+.sp
+.in +4
+.nf
+.na
+.ft C
+local_header_rewrite_clients = permit_mynetworks,
+    permit_sasl_authenticated permit_tls_clientcerts
+    check_address_map hash:/etc/postfix/pop\-before\-smtp
+.fi
+.ad
+.ft R
+.in -4
+.SH local_login_sender_maps (default: static:*)
+A list of lookup tables that are searched by the UNIX login name,
+and that return a list of allowed envelope sender patterns separated
+by space or comma. These sender patterns are enforced by the Postfix
+\fBpostdrop\fR(1) command. The default is backwards\-compatible:
+every user may specify any sender envelope address.
+.PP
+When no UNIX login name is available, the \fBpostdrop\fR(1) command will
+prepend "\fBuid:\fR" to the numerical UID and use that instead.
+.PP
+This feature ignores address extensions in the user\-specified
+envelope sender address.
+.PP
+The following sender patterns are special; these cannot be used
+as part of a longer pattern.
+.IP "\fB * \fR
+This pattern allows any envelope sender address.
+.br
+.IP "\fB <> \fR"
+This pattern allows the empty
+envelope sender address. See the
+empty_address_local_login_sender_maps_lookup_key configuration
+parameter.
+.br
+.IP "\fB @\fR\fIdomain\fR"
+This pattern allows an
+envelope sender address when the '\fB@\fR' and \fIdomain\fR part
+match.
+.br
+.br
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    # Allow root and postfix full control, anyone else can only
+    # send mail as themselves. Use "uid:" followed by the numerical
+    # UID when the UID has no entry in the UNIX password file.
+    local_login_sender_maps =
+        inline:{ { root = * }, { postfix = * } },
+        pcre:/etc/postfix/login_senders
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/login_senders:
+   # Allow both the bare username and the user@domain forms.
+    /(.+)/ $1 $1@example.com
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 3.6 and later.
+.SH local_recipient_maps (default: proxy:unix:passwd.byname $alias_maps)
+Lookup tables with all names or addresses of local recipients:
+a recipient address is local when its domain matches $mydestination,
+$inet_interfaces or $proxy_interfaces.  Specify @domain as a
+wild\-card for domains that do not have a valid recipient list.
+Technically, tables listed with $local_recipient_maps are used as
+lists: Postfix needs to know only if a lookup string is found or
+not, but it does not use the result from table lookup.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.PP
+If this parameter is non\-empty (the default), then the Postfix SMTP
+server will reject mail for unknown local users.
+.PP
+To turn off local recipient checking in the Postfix SMTP server,
+specify "local_recipient_maps =" (i.e. empty).
+.PP
+The default setting assumes that you use the default Postfix local
+delivery agent for local delivery. You need to update the
+local_recipient_maps setting if:
+.IP \(bu
+You redefine the local delivery agent in master.cf.
+.IP \(bu
+You redefine the "local_transport" setting in main.cf.
+.IP \(bu
+You use the "luser_relay", "mailbox_transport", or "fallback_transport"
+feature of the Postfix \fBlocal\fR(8) delivery agent.
+.br
+.PP
+Details are described in the LOCAL_RECIPIENT_README file.
+.PP
+Beware: if the Postfix SMTP server runs chrooted, you need to access
+the passwd file via the \fBproxymap\fR(8) service, in order to overcome
+chroot access restrictions. The alternative, maintaining a copy of
+the system password file in the chroot jail is not practical.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+local_recipient_maps =
+.fi
+.ad
+.ft R
+.SH local_transport (default: local:$myhostname)
+The default mail delivery transport and next\-hop destination
+for final delivery to domains listed with mydestination, and for
+[ipaddress] destinations that match $inet_interfaces or $proxy_interfaces.
+This information can be overruled with the \fBtransport\fR(5) table.
+.PP
+By default, local mail is delivered to the transport called "local",
+which is just the name of a service that is defined the master.cf file.
+.PP
+Specify a string of the form \fItransport:nexthop\fR, where \fItransport\fR
+is the name of a mail delivery transport defined in master.cf.
+The \fI:nexthop\fR destination is optional; its syntax is documented
+in the manual page of the corresponding delivery agent.
+.PP
+Beware: if you override the default local delivery agent then you
+need to review the LOCAL_RECIPIENT_README document, otherwise the
+SMTP server may reject mail for local recipients.
+.SH luser_relay (default: empty)
+Optional catch\-all destination for unknown \fBlocal\fR(8) recipients.
+By default, mail for unknown recipients in domains that match
+$mydestination, $inet_interfaces or $proxy_interfaces is returned
+as undeliverable.
+.PP
+The luser_relay value is not subject to Postfix configuration
+parameter $name expansion. Instead, the following $name expansions
+are done:
+.IP "\fB$domain\fR"
+The recipient domain.
+.br
+.IP "\fB$extension\fR"
+The recipient address extension.
+.br
+.IP "\fB$home\fR"
+The recipient's home directory.
+.br
+.IP "\fB$local\fR"
+The entire recipient address localpart.
+.br
+.IP "\fB$recipient\fR"
+The full recipient address.
+.br
+.IP "\fB$recipient_delimiter\fR"
+The address extension delimiter that was found in the recipient
+address (Postfix 2.11 and later), or the system\-wide recipient
+address extension delimiter (Postfix 2.10 and earlier).
+.br
+.IP "\fB$shell\fR"
+The recipient's login shell.
+.br
+.IP "\fB$user\fR"
+The recipient username.
+.br
+.IP "\fB${name?value}\fR"
+.IP "\fB${name?{value}}\fR (Postfix >= 3.0)"
+Expands to \fIvalue\fR when \fI$name\fR is non\-empty.
+.br
+.IP "\fB${name:value}\fR"
+.IP "\fB${name:{value}}\fR (Postfix >= 3.0)"
+Expands to \fIvalue\fR when \fI$name\fR is empty.
+.br
+.IP "\fB${name?{value1}:{value2}}\fR (Postfix >= 3.0)"
+Expands to \fIvalue1\fR when \fI$name\fR is non\-empty,
+\fIvalue2\fR otherwise.
+.br
+.br
+.PP
+Instead of $name you can also specify ${name} or $(name).
+.PP
+Note: luser_relay works only for the Postfix \fBlocal\fR(8) delivery agent.
+.PP
+Note: if you use this feature for accounts not in the UNIX password
+file, then you must specify "local_recipient_maps =" (i.e. empty)
+in the main.cf file, otherwise the Postfix SMTP server will reject mail
+for non\-UNIX accounts with "User unknown in local recipient table".
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+luser_relay = $user@other.host
+luser_relay = $local@other.host
+luser_relay = admin+$local
+.fi
+.ad
+.ft R
+.SH mail_name (default: Postfix)
+The mail system name that is displayed in Received: headers, in
+the SMTP greeting banner, and in bounced mail.
+.SH mail_owner (default: postfix)
+The UNIX system account that owns the Postfix queue and most Postfix
+daemon processes.  Specify the name of an unprivileged user account
+that does not share a user or group ID with other accounts, and that
+owns no other files
+or processes on the system.  In particular, don't specify nobody
+or daemon.  PLEASE USE A DEDICATED USER ID AND GROUP ID.
+.PP
+When this parameter value is changed you need to re\-run "\fBpostfix
+set\-permissions\fR" (with Postfix version 2.0 and earlier:
+"\fB/etc/postfix/post\-install set\-permissions\fR".
+.SH mail_release_date (default: see "postconf \-d" output)
+The Postfix release date, in "YYYYMMDD" format.
+.SH mail_spool_directory (default: see "postconf \-d" output)
+The directory where \fBlocal\fR(8) UNIX\-style mailboxes are kept. The
+default setting depends on the system type. Specify a name ending
+in / for maildir\-style delivery.
+.PP
+Note: maildir delivery is done with the privileges of the recipient.
+If you use the mail_spool_directory setting for maildir style
+delivery, then you must create the top\-level maildir directory in
+advance. Postfix will not create it.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+mail_spool_directory = /var/mail
+mail_spool_directory = /var/spool/mail
+.fi
+.ad
+.ft R
+.SH mail_version (default: see "postconf \-d" output)
+The version of the mail system. Stable releases are named
+\fImajor\fR.\fIminor\fR.\fIpatchlevel\fR. Experimental releases
+also include the release date. The version string can be used in,
+for example, the SMTP greeting banner.
+.SH mailbox_command (default: empty)
+Optional external command that the \fBlocal\fR(8) delivery agent should
+use for mailbox delivery.  The command is run with the user ID and
+the primary group ID privileges of the recipient.  Exception:
+command delivery for root executes with $default_privs privileges.
+This is not a problem, because 1) mail for root should always be
+aliased to a real user and 2) don't log in as root, use "su" instead.
+.PP
+The following environment variables are exported to the command:
+.IP "\fBCLIENT_ADDRESS\fR"
+Remote client network address. Available in Postfix version 2.2 and
+later.
+.br
+.IP "\fBCLIENT_HELO\fR"
+Remote client EHLO command parameter. Available in Postfix version 2.2
+and later.
+.br
+.IP "\fBCLIENT_HOSTNAME\fR"
+Remote client hostname. Available in Postfix version 2.2 and later.
+.br
+.IP "\fBCLIENT_PROTOCOL\fR"
+Remote client protocol. Available in Postfix version 2.2 and later.
+.br
+.IP "\fBDOMAIN\fR"
+The domain part of the recipient address.
+.br
+.IP "\fBEXTENSION\fR"
+The optional address extension.
+.br
+.IP "\fBHOME\fR"
+The recipient home directory.
+.br
+.IP "\fBLOCAL\fR"
+The recipient address localpart.
+.br
+.IP "\fBLOGNAME\fR"
+The recipient's username.
+.br
+.IP "\fBORIGINAL_RECIPIENT\fR"
+The entire recipient address, before any address rewriting or
+aliasing.
+.br
+.IP "\fBRECIPIENT\fR"
+The full recipient address.
+.br
+.IP "\fBSASL_METHOD\fR"
+SASL authentication method specified in the remote client AUTH
+command. Available in Postfix version 2.2 and later.
+.br
+.IP "\fBSASL_SENDER\fR"
+SASL sender address specified in the remote client MAIL FROM
+command. Available in Postfix version 2.2 and later.
+.br
+.IP "\fBSASL_USER\fR"
+SASL username specified in the remote client AUTH command.
+Available in Postfix version 2.2 and later.
+.br
+.IP "\fBSENDER\fR"
+The full sender address.
+.br
+.IP "\fBSHELL\fR"
+The recipient's login shell.
+.br
+.IP "\fBUSER\fR"
+The recipient username.
+.br
+.br
+.PP
+Unlike other Postfix configuration parameters, the mailbox_command
+parameter is not subjected to $name substitutions. This is to make
+it easier to specify shell syntax (see example below).
+.PP
+If you can, avoid shell meta characters because they will force
+Postfix to run an expensive shell process. If you're delivering
+via "procmail" then running a shell won't make a noticeable difference
+in the total cost.
+.PP
+Note: if you use the mailbox_command feature to deliver mail
+system\-wide, you must set up an alias that forwards mail for root
+to a real user.
+.PP
+The precedence of \fBlocal\fR(8) delivery features from high to low
+is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
+mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
+fallback_transport_maps, fallback_transport and luser_relay.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+mailbox_command = /some/where/procmail
+mailbox_command = /some/where/procmail \-a "$EXTENSION"
+mailbox_command = /some/where/maildrop \-d "$USER"
+        \-f "$SENDER" "$EXTENSION"
+.fi
+.ad
+.ft R
+.SH mailbox_command_maps (default: empty)
+Optional lookup tables with per\-recipient external commands to use
+for \fBlocal\fR(8) mailbox delivery.  Behavior is as with mailbox_command.
+.PP
+The precedence of \fBlocal\fR(8) delivery features from high to low
+is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
+mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
+fallback_transport_maps, fallback_transport and luser_relay.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.SH mailbox_delivery_lock (default: see "postconf \-d" output)
+How to lock a UNIX\-style \fBlocal\fR(8) mailbox before attempting delivery.
+For a list of available file locking methods, use the "\fBpostconf
+\-l\fR" command.
+.PP
+This setting is ignored with \fBmaildir\fR style delivery,
+because such deliveries are safe without explicit locks.
+.PP
+Note: The \fBdotlock\fR method requires that the recipient UID or
+GID has write access to the parent directory of the mailbox file.
+.PP
+Note: the default setting of this parameter is system dependent.
+.SH mailbox_size_limit (default: 51200000)
+The maximal size of any \fBlocal\fR(8) individual mailbox or maildir
+file, or zero (no limit).  In fact, this limits the size of any
+file that is written to upon local delivery, including files written
+by external commands that are executed by the \fBlocal\fR(8) delivery
+agent. The value cannot exceed LONG_MAX (typically, a 32\-bit or
+64\-bit signed integer).
+.PP
+This limit must not be smaller than the message size limit.
+.SH mailbox_transport (default: empty)
+Optional message delivery transport that the \fBlocal\fR(8) delivery
+agent should use for mailbox delivery to all local recipients,
+whether or not they are found in the UNIX passwd database.
+.PP
+The precedence of \fBlocal\fR(8) delivery features from high to low
+is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
+mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
+fallback_transport_maps, fallback_transport and luser_relay.
+.SH mailbox_transport_maps (default: empty)
+Optional lookup tables with per\-recipient message delivery
+transports to use for \fBlocal\fR(8) mailbox delivery, whether or not the
+recipients are found in the UNIX passwd database.
+.PP
+The precedence of \fBlocal\fR(8) delivery features from high to low
+is: aliases, .forward files, mailbox_transport_maps, mailbox_transport,
+mailbox_command_maps, mailbox_command, home_mailbox, mail_spool_directory,
+fallback_transport_maps, fallback_transport and luser_relay.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.PP
+For safety reasons, this feature does not allow $number
+substitutions in regular expression maps.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH maillog_file (default: empty)
+The name of an optional logfile that is written by the Postfix
+\fBpostlogd\fR(8) service. An empty value selects logging to \fBsyslogd\fR(8).
+Specify "/dev/stdout" to select logging to standard output. Stdout
+logging requires that Postfix is started with "postfix start\-fg".
+.PP
+Note 1: The maillog_file parameter value must contain a prefix
+that is specified with the maillog_file_prefixes parameter.
+.PP
+Note 2: Some Postfix non\-daemon programs may still log information
+to \fBsyslogd\fR(8), before they have processed their configuration
+parameters and command\-line options.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH maillog_file_compressor (default: gzip)
+The program to run after rotating $maillog_file with "postfix
+logrotate". The command is run with the rotated logfile name as its
+first argument.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH maillog_file_prefixes (default: /var, /dev/stdout)
+A list of allowed prefixes for a maillog_file value. This is a
+safety feature to contain the damage from a single configuration
+mistake. Specify one or more prefix strings, separated by comma or
+whitespace.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH maillog_file_rotate_suffix (default: %Y%m%d\-%H%M%S)
+The format of the suffix to append to $maillog_file while rotating
+the file with "postfix logrotate". See \fBstrftime\fR(3) for syntax. The
+default suffix, YYYYMMDD\-HHMMSS, allows logs to be rotated frequently.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH mailq_path (default: see "postconf \-d" output)
+Sendmail compatibility feature that specifies where the Postfix
+\fBmailq\fR(1) command is installed. This command can be used to
+list the Postfix mail queue.
+.SH manpage_directory (default: see "postconf \-d" output)
+Where the Postfix manual pages are installed.
+.SH maps_rbl_domains (default: empty)
+Obsolete feature: use the reject_rbl_client feature instead.
+.SH maps_rbl_reject_code (default: 554)
+The numerical Postfix SMTP server response code when a remote SMTP
+client request is blocked by the reject_rbl_client, reject_rhsbl_client,
+reject_rhsbl_reverse_client, reject_rhsbl_sender or
+reject_rhsbl_recipient restriction.
+.PP
+Do not change this unless you have a complete understanding of RFC 5321.
+.SH masquerade_classes (default: envelope_sender, header_sender, header_recipient)
+What addresses are subject to address masquerading.
+.PP
+By default, address masquerading is limited to envelope sender
+addresses, and to header sender and header recipient addresses.
+This allows you to use address masquerading on a mail gateway while
+still being able to forward mail to users on individual machines.
+.PP
+Specify zero or more of: envelope_sender, envelope_recipient,
+header_sender, header_recipient
+.SH masquerade_domains (default: empty)
+Optional list of domains whose subdomain structure will be stripped
+off in email addresses.
+.PP
+The list is processed left to right, and processing stops at the
+first match.  Thus,
+.sp
+.in +4
+.nf
+.na
+.ft C
+masquerade_domains = foo.example.com example.com
+.fi
+.ad
+.ft R
+.in -4
+.PP
+strips "user@any.thing.foo.example.com" to "user@foo.example.com",
+but strips "user@any.thing.else.example.com" to "user@example.com".
+.PP
+A domain name prefixed with ! means do not masquerade this domain
+or its subdomains. Thus,
+.sp
+.in +4
+.nf
+.na
+.ft C
+masquerade_domains = !foo.example.com example.com
+.fi
+.ad
+.ft R
+.in -4
+.PP
+does not change "user@any.thing.foo.example.com" or "user@foo.example.com",
+but strips "user@any.thing.else.example.com" to "user@example.com".
+.PP
+Note: with Postfix version 2.2, message header address masquerading
+happens only when message header address rewriting is enabled:
+.IP \(bu
+The message is received with the Postfix \fBsendmail\fR(1) command,
+.IP \(bu
+The message is received from a network client that matches
+$local_header_rewrite_clients,
+.IP \(bu
+The message is received from the network, and the
+remote_header_rewrite_domain parameter specifies a non\-empty value.
+.br
+.PP
+To get the behavior before Postfix version 2.2, specify
+"local_header_rewrite_clients = static:all".
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+masquerade_domains = $mydomain
+.fi
+.ad
+.ft R
+.SH masquerade_exceptions (default: empty)
+Optional list of user names that are not subjected to address
+masquerading, even when their addresses match $masquerade_domains.
+.PP
+By default, address masquerading makes no exceptions.
+.PP
+Specify a list of user names, "/file/name" or "type:table" patterns,
+separated by commas and/or whitespace. The list is matched left to
+right, and the search stops on the first match. A "/file/name"
+pattern is replaced
+by its contents; a "type:table" lookup table is matched when a name
+matches a lookup key (the lookup result is ignored).  Continue long
+lines by starting the next line with whitespace. Specify "!pattern"
+to exclude a name from the list. The form "!/file/name" is supported
+only in Postfix version 2.4 and later.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+masquerade_exceptions = root, mailer\-daemon
+masquerade_exceptions = root
+.fi
+.ad
+.ft R
+.SH master_service_disable (default: empty)
+Selectively disable \fBmaster\fR(8) listener ports by service type
+or by service name and type.  Specify a list of service types
+("inet", "unix", "fifo", or "pass") or "name/type" tuples, where
+"name" is the first field of a master.cf entry and "type" is a
+service type. As with other Postfix matchlists, a search stops at
+the first match.  Specify "!pattern" to exclude a service from the
+list. By default, all \fBmaster\fR(8) listener ports are enabled.
+.PP
+Note: this feature does not support "/file/name" or "type:table"
+patterns, nor does it support wildcards such as "*" or "all". This
+is intentional.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+# With Postfix 2.6..2.10 use '.' instead of '/'.
+# Turn on all \fBmaster\fR(8) listener ports (the default).
+master_service_disable =
+# Turn off only the main SMTP listener port.
+master_service_disable = smtp/inet
+# Turn off all TCP/IP listener ports.
+master_service_disable = inet
+# Turn off all TCP/IP listener ports except "foo".
+master_service_disable = !foo/inet, inet
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH max_idle (default: 100s)
+The maximum amount of time that an idle Postfix daemon process waits
+for an incoming connection before terminating voluntarily.  This
+parameter
+is ignored by the Postfix queue manager and by other long\-lived
+Postfix daemon processes.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH max_use (default: 100)
+The maximal number of incoming connections that a Postfix daemon
+process will service before terminating voluntarily.  This parameter
+is ignored by the Postfix queue
+manager and by other long\-lived Postfix daemon processes.
+.SH maximal_backoff_time (default: 4000s)
+The maximal time between attempts to deliver a deferred message.
+.PP
+This parameter should be set to a value greater than or equal
+to $minimal_backoff_time. See also $queue_run_delay.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH maximal_queue_lifetime (default: 5d)
+Consider a message as undeliverable, when delivery fails with a
+temporary error, and the time in the queue has reached the
+maximal_queue_lifetime limit.
+.PP
+Specify a non\-negative time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is d (days).
+.PP
+Specify 0 when mail delivery should be tried only once.
+.SH message_drop_headers (default: bcc, content\-length, resent\-bcc, return\-path)
+Names of message headers that the \fBcleanup\fR(8) daemon will remove
+after applying \fBheader_checks\fR(5) and before invoking Milter applications.
+The default setting is compatible with Postfix < 3.0.
+.PP
+Specify a list of header names, separated by comma or space.
+Names are matched in a case\-insensitive manner.  The list of supported
+header names is limited only by available memory.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH message_reject_characters (default: empty)
+The set of characters that Postfix will reject in message
+content.  The usual C\-like escape sequences are recognized: \ea
+\eb \ef \en \er \et \ev \e\fIddd\fR (up to three octal digits) and
+\e\e.
+.PP
+Note 1: this feature does not recognize text that requires MIME
+decoding. It inspects raw message content, just like header_checks
+and body_checks.
+.PP
+Note 2: this feature is disabled with "receive_override_options
+= no_header_body_checks".
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+message_reject_characters = \e0
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH message_size_limit (default: 10240000)
+The maximal size in bytes of a message, including envelope information.
+The value cannot exceed LONG_MAX (typically, a 32\-bit or 64\-bit
+signed integer).
+.PP
+Note: be careful when making changes.  Excessively small values
+will result in the loss of non\-delivery notifications, when a bounce
+message size exceeds the local or remote MTA's message size limit.
+.SH message_strip_characters (default: empty)
+The set of characters that Postfix will remove from message
+content.  The usual C\-like escape sequences are recognized: \ea
+\eb \ef \en \er \et \ev \e\fIddd\fR (up to three octal digits) and
+\e\e.
+.PP
+Note 1: this feature does not recognize text that requires MIME
+decoding. It inspects raw message content, just like header_checks
+and body_checks.
+.PP
+Note 2: this feature is disabled with "receive_override_options
+= no_header_body_checks".
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+message_strip_characters = \e0
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH meta_directory (default: see 'postconf \-d' output)
+The location of non\-executable files that are shared among
+multiple Postfix instances, such as postfix\-files, dynamicmaps.cf,
+and the multi\-instance template files main.cf.proto and master.cf.proto.
+This directory should contain only Postfix\-related files.  Typically,
+the meta_directory parameter has the same default as the config_directory
+parameter (/etc/postfix or /usr/local/etc/postfix).
+.PP
+For backwards compatibility with Postfix versions 2.6..2.11,
+specify "meta_directory = $daemon_directory" in main.cf before
+installing or upgrading Postfix, or specify "meta_directory =
+/path/name" on the "make makefiles", "make install" or "make upgrade"
+command line.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH milter_command_timeout (default: 30s)
+The time limit for sending an SMTP command to a Milter (mail
+filter) application, and for receiving the response.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH milter_connect_macros (default: see "postconf \-d" output)
+The macros that are sent to Milter (mail filter) applications
+after completion of an SMTP connection. See MILTER_README
+for a list of available macro names and their meanings.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH milter_connect_timeout (default: 30s)
+The time limit for connecting to a Milter (mail filter)
+application, and for negotiating protocol options.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH milter_content_timeout (default: 300s)
+The time limit for sending message content to a Milter (mail
+filter) application, and for receiving the response.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH milter_data_macros (default: see "postconf \-d" output)
+The macros that are sent to version 4 or higher Milter (mail
+filter) applications after the SMTP DATA command. See MILTER_README
+for a list of available macro names and their meanings.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH milter_default_action (default: tempfail)
+The default action when a Milter (mail filter) response is
+unavailable (for example, bad Postfix configuration or Milter
+failure). Specify one of the following:
+.IP "accept"
+Proceed as if the mail filter was not present.
+.br
+.IP "reject"
+Reject all further commands in this session
+with a permanent status code.
+.br
+.IP "tempfail"
+Reject all further commands in this session
+with a temporary status code.
+.br
+.IP "quarantine"
+Like "accept", but freeze the message in
+the "hold" queue. Available with Postfix 2.6 and later.
+.br
+.br
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH milter_end_of_data_macros (default: see "postconf \-d" output)
+The macros that are sent to Milter (mail filter) applications
+after the message end\-of\-data. See MILTER_README for a list of
+available macro names and their meanings.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH milter_end_of_header_macros (default: see "postconf \-d" output)
+The macros that are sent to Milter (mail filter) applications
+after the end of the message header. See MILTER_README for a list
+of available macro names and their meanings.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH milter_header_checks (default: empty)
+Optional lookup tables for content inspection of message headers
+that are produced by Milter applications.  See the \fBheader_checks\fR(5)
+manual page available actions. Currently, PREPEND is not implemented.
+.PP
+The following example sends all mail that is marked as SPAM to
+a spam handling machine. Note that matches are case\-insensitive
+by default.
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    milter_header_checks = pcre:/etc/postfix/milter_header_checks
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/milter_header_checks:
+    /^X\-SPAM\-FLAG:\es+YES/ FILTER mysmtp:sanitizer.example.com:25
+.fi
+.ad
+.ft R
+.PP
+The milter_header_checks mechanism could also be used for
+allowlisting. For example it could be used to skip heavy content
+inspection for DKIM\-signed mail from known friendly domains.
+.PP
+This feature is available in Postfix 2.7, and as an optional
+patch for Postfix 2.6.
+.SH milter_helo_macros (default: see "postconf \-d" output)
+The macros that are sent to Milter (mail filter) applications
+after the SMTP HELO or EHLO command. See
+MILTER_README for a list of available macro names and their meanings.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH milter_macro_daemon_name (default: $myhostname)
+The {daemon_name} macro value for Milter (mail filter) applications.
+See MILTER_README for a list of available macro names and their
+meanings.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH milter_macro_defaults (default: empty)
+Optional list of \fIname=value\fR pairs that specify default
+values for arbitrary macros that Postfix may send to Milter
+applications.  These defaults are used when there is no corresponding
+information from the message delivery context.
+.PP
+Specify \fIname=value\fR or \fI{name=value}\fR pairs separated
+by comma or whitespace.  Enclose a pair in "{}" when a value contains
+comma or whitespace (this form ignores whitespace after the enclosing
+"{", around the "=", and before the enclosing "}").
+.PP
+This feature is available in Postfix 3.1 and later.
+.SH milter_macro_v (default: $mail_name $mail_version)
+The {v} macro value for Milter (mail filter) applications.
+See MILTER_README for a list of available macro names and their
+meanings.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH milter_mail_macros (default: see "postconf \-d" output)
+The macros that are sent to Milter (mail filter) applications
+after the SMTP MAIL FROM command. See MILTER_README
+for a list of available macro names and their meanings.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH milter_protocol (default: 6)
+The mail filter protocol version and optional protocol extensions
+for communication with a Milter application; prior to Postfix 2.6
+the default protocol is 2. Postfix
+sends this version number during the initial protocol handshake.
+It should match the version number that is expected by the mail
+filter application (or by its Milter library).
+.PP
+Protocol versions:
+.IP "2"
+Use Sendmail 8 mail filter protocol version 2 (default
+with Sendmail version 8.11 .. 8.13 and Postfix version 2.3 ..
+2.5).
+.br
+.IP "3"
+Use Sendmail 8 mail filter protocol version 3.
+.br
+.IP "4"
+Use Sendmail 8 mail filter protocol version 4.
+.br
+.IP "6"
+Use Sendmail 8 mail filter protocol version 6 (default
+with Sendmail version 8.14 and Postfix version 2.6).
+.br
+.br
+.PP
+Protocol extensions:
+.IP "no_header_reply"
+Specify this when the Milter application
+will not reply for each individual message header.
+.br
+.br
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH milter_rcpt_macros (default: see "postconf \-d" output)
+The macros that are sent to Milter (mail filter) applications
+after the SMTP RCPT TO command. See MILTER_README
+for a list of available macro names and their meanings.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH milter_unknown_command_macros (default: see "postconf \-d" output)
+The macros that are sent to version 3 or higher Milter (mail
+filter) applications after an unknown SMTP command.  See MILTER_README
+for a list of available macro names and their meanings.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH mime_boundary_length_limit (default: 2048)
+The maximal length of MIME multipart boundary strings. The MIME
+processor is unable to distinguish between boundary strings that
+do not differ in the first $mime_boundary_length_limit characters.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH mime_header_checks (default: $header_checks)
+Optional lookup tables for content inspection of MIME related
+message headers, as described in the \fBheader_checks\fR(5) manual page.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH mime_nesting_limit (default: 100)
+The maximal recursion level that the MIME processor will handle.
+Postfix refuses mail that is nested deeper than the specified limit.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH minimal_backoff_time (default: 300s)
+The minimal time between attempts to deliver a deferred message;
+prior to Postfix 2.4 the default value was 1000s.
+.PP
+This parameter also limits the time an unreachable destination is
+kept in the short\-term, in\-memory, destination status cache.
+.PP
+This parameter should be set greater than or equal to
+$queue_run_delay. See also $maximal_backoff_time.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH multi_instance_directories (default: empty)
+An optional list of non\-default Postfix configuration directories;
+these directories belong to additional Postfix instances that share
+the Postfix executable files and documentation with the default
+Postfix instance, and that are started, stopped, etc., together
+with the default Postfix instance.  Specify a list of pathnames
+separated by comma or whitespace.
+.PP
+When $multi_instance_directories is empty, the \fBpostfix\fR(1) command
+runs in single\-instance mode and operates on a single Postfix
+instance only. Otherwise, the \fBpostfix\fR(1) command runs in multi\-instance
+mode and invokes the multi\-instance manager specified with the
+multi_instance_wrapper parameter. The multi\-instance manager in
+turn executes \fBpostfix\fR(1) commands for the default instance and for
+all Postfix instances in $multi_instance_directories.
+.PP
+Currently, this parameter setting is ignored except for the
+default main.cf file.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH multi_instance_enable (default: no)
+Allow this Postfix instance to be started, stopped, etc., by a
+multi\-instance manager.  By default, new instances are created in
+a safe state that prevents them from being started inadvertently.
+This parameter is reserved for the multi\-instance manager.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH multi_instance_group (default: empty)
+The optional instance group name of this Postfix instance. A
+group identifies closely\-related Postfix instances that the
+multi\-instance manager can start, stop, etc., as a unit.  This
+parameter is reserved for the multi\-instance manager.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH multi_instance_name (default: empty)
+The optional instance name of this Postfix instance. This name
+becomes also the default value for the syslog_name parameter.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH multi_instance_wrapper (default: empty)
+The pathname of a multi\-instance manager command that the
+\fBpostfix\fR(1) command invokes when the multi_instance_directories
+parameter value is non\-empty. The pathname may be followed by
+initial command arguments separated by whitespace; shell
+metacharacters such as quotes are not supported in this context.
+.PP
+The \fBpostfix\fR(1) command invokes the manager command with the
+\fBpostfix\fR(1) non\-option command arguments on the manager command line,
+and with all installation configuration parameters exported into
+the manager command process environment. The manager command in
+turn invokes the \fBpostfix\fR(1) command for individual Postfix instances
+as "postfix \-c \fIconfig_directory\fR \fIcommand\fR".
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH multi_recipient_bounce_reject_code (default: 550)
+The numerical Postfix SMTP server response code when a remote SMTP
+client request is blocked by the reject_multi_recipient_bounce
+restriction.
+.PP
+Do not change this unless you have a complete understanding of RFC 5321.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH mydestination (default: $myhostname, localhost.$mydomain, localhost)
+The list of domains that are delivered via the $local_transport
+mail delivery transport. By default this is the Postfix \fBlocal\fR(8)
+delivery agent which looks up all recipients in /etc/passwd and
+/etc/aliases. The SMTP server validates recipient addresses with
+$local_recipient_maps and rejects non\-existent recipients. See also
+the local domain class in the ADDRESS_CLASS_README file.
+.PP
+The default mydestination value specifies names for the local
+machine only.  On a mail domain gateway, you should also include
+$mydomain.
+.PP
+The $local_transport delivery method is also selected for mail
+addressed to user@[the.net.work.address] of the mail system (the
+IP addresses specified with the inet_interfaces and proxy_interfaces
+parameters).
+.PP
+Warnings:
+.IP \(bu
+Do not specify the names of virtual domains \- those domains
+are specified elsewhere. See VIRTUAL_README for more information.
+.IP \(bu
+Do not specify the names of domains that this machine is
+backup MX host for. See STANDARD_CONFIGURATION_README for how to
+set up backup MX hosts.
+.IP \(bu
+By default, the Postfix SMTP server rejects mail for recipients
+not listed with the local_recipient_maps parameter.  See the
+\fBpostconf\fR(5) manual for a description of the local_recipient_maps
+and unknown_local_recipient_reject_code parameters.
+.br
+.PP
+Specify a list of host or domain names, "/file/name" or "type:table"
+patterns, separated by commas and/or whitespace. A "/file/name"
+pattern is replaced by its contents; a "type:table" lookup table
+is matched when a name matches a lookup key (the lookup result is
+ignored).  Continue long lines by starting the next line with
+whitespace.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+mydestination = $myhostname, localhost.$mydomain $mydomain
+mydestination = $myhostname, localhost.$mydomain www.$mydomain, ftp.$mydomain
+.fi
+.ad
+.ft R
+.SH mydomain (default: see "postconf \-d" output)
+The internet domain name of this mail system.  The default is to
+use $myhostname minus the first component, or "localdomain" (Postfix
+2.3 and later).  $mydomain is used as
+a default value for many other configuration parameters.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+mydomain = domain.tld
+.fi
+.ad
+.ft R
+.SH myhostname (default: see "postconf \-d" output)
+The internet hostname of this mail system. The default is to use
+the fully\-qualified domain name (FQDN) from gethostname(), or to
+use the non\-FQDN result from gethostname() and append ".$mydomain".
+$myhostname is used as a default value for many other configuration
+parameters.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+myhostname = host.example.com
+.fi
+.ad
+.ft R
+.SH mynetworks (default: see "postconf \-d" output)
+The list of "trusted" remote SMTP clients that have more privileges than
+"strangers".
+.PP
+In particular, "trusted" SMTP clients are allowed to relay mail
+through Postfix.  See the smtpd_relay_restrictions parameter
+description in the \fBpostconf\fR(5) manual.
+.PP
+You can specify the list of "trusted" network addresses by hand
+or you can let Postfix do it for you (which is the default).
+See the description of the mynetworks_style parameter for more
+information.
+.PP
+If you specify the mynetworks list by hand,
+Postfix ignores the mynetworks_style setting.
+.PP
+Specify a list of network addresses or network/netmask patterns,
+separated by commas and/or whitespace. Continue long lines by
+starting the next line with whitespace.
+.PP
+The netmask specifies the number of bits in the network part
+of a host address.  You can also specify "/file/name" or "type:table"
+patterns.  A "/file/name" pattern is replaced by its contents; a
+"type:table" lookup table is matched when a table entry matches a
+lookup string (the lookup result is ignored).
+.PP
+The list is matched left to right, and the search stops on the
+first match.  Specify "!pattern" to exclude an address or network
+block from the list. The form "!/file/name" is supported only
+in Postfix version 2.4 and later.
+.PP
+Note 1: Pattern matching of domain names is controlled by the
+presence or absence of "mynetworks" in the parent_domain_matches_subdomains
+parameter value.
+.PP
+Note 2: IP version 6 address information must be specified inside
+[] in the mynetworks value, and in files specified with
+"/file/name".  IP version 6 addresses contain the ":" character,
+and would otherwise be confused with a "type:table" pattern.
+.PP
+Note 3: CIDR ranges cannot be specified in hash tables.  Use cidr
+tables if CIDR ranges are used.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+mynetworks = 127.0.0.0/8 168.100.189.0/28
+mynetworks = !192.168.0.1, 192.168.0.0/28
+mynetworks = 127.0.0.0/8 168.100.189.0/28 [::1]/128 [2001:240:587::]/64
+mynetworks = $config_directory/mynetworks
+mynetworks = hash:/etc/postfix/network_table
+mynetworks = cidr:/etc/postfix/network_table.cidr
+.fi
+.ad
+.ft R
+.SH mynetworks_style (default: Postfix >= 3.0: host, Postfix < 3.0: subnet)
+The method to generate the default value for the mynetworks parameter.
+This is the list of trusted networks for relay access control etc.
+.IP \(bu
+Specify "mynetworks_style = host" when Postfix should
+"trust" only the local machine.
+.IP \(bu
+Specify "mynetworks_style = subnet" when Postfix
+should "trust" remote SMTP clients in the same IP subnetworks as the local
+machine.  On Linux, this works correctly only with interfaces
+specified with the "ifconfig" or "ip" command.
+.IP \(bu
+Specify "mynetworks_style = class" when Postfix should
+"trust" remote SMTP clients in the same IP class A/B/C networks as the
+local machine.  Caution: this may cause
+Postfix to "trust" your entire provider's network.  Instead, specify
+an explicit mynetworks list by hand, as described with the mynetworks
+configuration parameter.
+.br
+.SH myorigin (default: $myhostname)
+The domain name that locally\-posted mail appears to come
+from, and that locally posted mail is delivered to. The default,
+$myhostname, is adequate for small sites.  If you run a domain with
+multiple machines, you should (1) change this to $mydomain and (2)
+set up a domain\-wide alias database that aliases each user to
+user@that.users.mailhost.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+myorigin = $mydomain
+.fi
+.ad
+.ft R
+.SH nested_header_checks (default: $header_checks)
+Optional lookup tables for content inspection of non\-MIME message
+headers in attached messages, as described in the \fBheader_checks\fR(5)
+manual page.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH newaliases_path (default: see "postconf \-d" output)
+Sendmail compatibility feature that specifies the location of the
+\fBnewaliases\fR(1) command. This command can be used to rebuild the
+\fBlocal\fR(8) \fBaliases\fR(5) database.
+.SH non_fqdn_reject_code (default: 504)
+The numerical Postfix SMTP server reply code when a client request
+is rejected by the reject_non_fqdn_helo_hostname, reject_non_fqdn_sender
+or reject_non_fqdn_recipient restriction.
+.SH non_smtpd_milters (default: empty)
+A list of Milter (mail filter) applications for new mail that
+does not arrive via the Postfix \fBsmtpd\fR(8) server. This includes local
+submission via the \fBsendmail\fR(1) command line, new mail that arrives
+via the Postfix \fBqmqpd\fR(8) server, and old mail that is re\-injected
+into the queue with "postsuper \-r".  Specify space or comma as a
+separator. See the MILTER_README document for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH notify_classes (default: resource, software)
+The list of error classes that are reported to the postmaster. These
+postmaster notifications do not replace user notifications. The
+default is to report only the most serious problems. The paranoid
+may wish to turn on the policy (UCE and mail relaying) and protocol
+error (broken mail software) reports.
+.PP
+NOTE: postmaster notifications may contain confidential information
+such as SASL passwords or message content.  It is the system
+administrator's responsibility to treat such information with care.
+.PP
+The error classes are:
+.IP "\fBbounce\fR (also implies \fB2bounce\fR)"
+Send the postmaster copies of the headers of bounced mail, and
+send transcripts of SMTP sessions when Postfix rejects mail. The
+notification is sent to the address specified with the
+bounce_notice_recipient configuration parameter (default: postmaster).
+.br
+.IP "\fB2bounce\fR"
+Send undeliverable bounced mail to the postmaster. The notification
+is sent to the address specified with the 2bounce_notice_recipient
+configuration parameter (default: postmaster).
+.br
+.IP "\fBdata\fR"
+Send the postmaster a transcript of the SMTP session with an
+error because a critical data file was unavailable. The notification
+is sent to the address specified with the error_notice_recipient
+configuration parameter (default: postmaster).
+.br
+This feature
+is available in Postfix 2.9 and later.
+.br
+.IP "\fBdelay\fR"
+Send the postmaster copies of the headers of delayed mail (see
+delay_warning_time). The
+notification is sent to the address specified with the
+delay_notice_recipient configuration parameter (default: postmaster).
+.br
+.IP "\fBpolicy\fR"
+Send the postmaster a transcript of the SMTP session when a
+client request was rejected because of (UCE) policy. The notification
+is sent to the address specified with the error_notice_recipient
+configuration parameter (default: postmaster).
+.br
+.IP "\fBprotocol\fR"
+Send the postmaster a transcript of the SMTP session in case
+of client or server protocol errors. The notification is sent to
+the address specified with the error_notice_recipient configuration
+parameter (default: postmaster).
+.br
+.IP "\fBresource\fR"
+Inform the postmaster of mail not delivered due to resource
+problems.  The notification is sent to the address specified with
+the error_notice_recipient configuration parameter (default:
+postmaster).
+.br
+.IP "\fBsoftware\fR"
+Inform the postmaster of mail not delivered due to software
+problems.  The notification is sent to the address specified with
+the error_notice_recipient configuration parameter (default:
+postmaster).
+.br
+.br
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+notify_classes = bounce, delay, policy, protocol, resource, software
+notify_classes = 2bounce, resource, software
+.fi
+.ad
+.ft R
+.SH openssl_path (default: openssl)
+The location of the OpenSSL command line program \fBopenssl\fR(1).  This
+is used by the "\fBpostfix tls\fR" command to create private keys,
+certificate signing requests, self\-signed certificates, and to
+compute public key digests for DANE TLSA records.  In multi\-instance
+environments, this parameter is always determined from the configuration
+of the default Postfix instance.
+.PP
+Example:
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    # NetBSD pkgsrc:
+    openssl_path = /usr/pkg/bin/openssl
+    # Local build:
+    openssl_path = /usr/local/bin/openssl
+.fi
+.ad
+.ft R
+.in -4
+.PP
+This feature is available in Postfix 3.1 and later.
+.SH owner_request_special (default: yes)
+Enable special treatment for owner\-\fIlistname\fR entries in the
+\fBaliases\fR(5) file, and don't split owner\-\fIlistname\fR and
+\fIlistname\fR\-request address localparts when the recipient_delimiter
+is set to "\-".  This feature is useful for mailing lists.
+.SH parent_domain_matches_subdomains (default: see "postconf \-d" output)
+A list of Postfix features where the pattern "example.com" also
+matches subdomains of example.com,
+instead of requiring an explicit ".example.com" pattern.  This is
+planned backwards compatibility:  eventually, all Postfix features
+are expected to require explicit ".example.com" style patterns when
+you really want to match subdomains.
+.PP
+The following Postfix feature names are supported.
+.IP "Postfix version 1.0 and later"
+debug_peer_list,
+fast_flush_domains,
+mynetworks,
+permit_mx_backup_networks,
+relay_domains,
+transport_maps
+.br
+.IP "Postfix version 1.1 and later"
+qmqpd_authorized_clients,
+smtpd_access_maps,
+.br
+.IP "Postfix version 2.8 and later"
+postscreen_access_list
+.br
+.IP "Postfix version 3.0 and later"
+smtpd_client_event_limit_exceptions
+.br
+.br
+.SH permit_mx_backup_networks (default: empty)
+Restrict the use of the permit_mx_backup SMTP access feature to
+only domains whose primary MX hosts match the listed networks.
+The parameter value syntax is the same as with the mynetworks
+parameter; note, however, that the default value is empty.
+.PP
+Pattern matching of domain names is controlled by the presence
+or absence of "permit_mx_backup_networks" in the
+parent_domain_matches_subdomains parameter value.
+.SH pickup_service_name (default: pickup)
+The name of the \fBpickup\fR(8) service. This service picks up local mail
+submissions from the Postfix maildrop queue.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH pipe_delivery_status_filter (default: $default_delivery_status_filter)
+Optional filter for the \fBpipe\fR(8) delivery agent to change the
+delivery status code or explanatory text of successful or unsuccessful
+deliveries.  See default_delivery_status_filter for details.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH plaintext_reject_code (default: 450)
+The numerical Postfix SMTP server response code when a request
+is rejected by the \fBreject_plaintext_session\fR restriction.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH postlog_service_name (default: postlog)
+The name of the \fBpostlogd\fR(8) service entry in master.cf.
+This service appends logfile records to the file specified
+with the maillog_file parameter.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH postlogd_watchdog_timeout (default: 10s)
+How much time a \fBpostlogd\fR(8) process may take to process a request
+before it is terminated by a built\-in watchdog timer. This is a
+safety mechanism that prevents \fBpostlogd\fR(8) from becoming non\-responsive
+due to a bug in Postfix itself or in system software. This limit
+cannot be set under 10s.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH postmulti_control_commands (default: reload flush)
+The \fBpostfix\fR(1) commands that the \fBpostmulti\fR(1) instance manager
+treats as "control" commands, that operate on running instances. For
+these commands, disabled instances are skipped.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH postmulti_start_commands (default: start)
+The \fBpostfix\fR(1) commands that the \fBpostmulti\fR(1) instance manager treats
+as "start" commands. For these commands, disabled instances are "checked"
+rather than "started", and failure to "start" a member instance of an
+instance group will abort the start\-up of later instances.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH postmulti_stop_commands (default: see "postconf \-d" output)
+The \fBpostfix\fR(1) commands that the \fBpostmulti\fR(1) instance manager treats
+as "stop" commands. For these commands, disabled instances are skipped,
+and enabled instances are processed in reverse order.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH postscreen_access_list (default: permit_mynetworks)
+Permanent allow/denylist for remote SMTP client IP addresses.
+\fBpostscreen\fR(8) searches this list immediately after a remote SMTP
+client connects.  Specify a comma\- or whitespace\-separated list of
+commands (in upper or lower case) or lookup tables. The search stops
+upon the first command that fires for the client IP address.
+.IP "\fB permit_mynetworks \fR"
+Allowlist the client and
+terminate the search if the client IP address matches $mynetworks.
+Do not subject the client to any before/after 220 greeting tests.
+Pass the connection immediately to a Postfix SMTP server process.
+.br
+Pattern matching of domain names is controlled by the presence
+or absence of "postscreen_access_list" in the
+parent_domain_matches_subdomains parameter value.
+.br
+.IP "\fB type:table \fR"
+Query the specified lookup
+table. Each table lookup result is an access list, except that
+access lists inside a table cannot specify type:table entries.
+.br
+To discourage the use of hash, btree, etc. tables, there is no
+support for substring matching like \fBsmtpd\fR(8). Use CIDR tables
+instead.
+.br
+.IP "\fB permit \fR"
+Allowlist the client and terminate
+the search. Do not subject the client to any before/after 220
+greeting tests. Pass the connection immediately to a Postfix SMTP
+server process.
+.br
+.IP "\fB reject \fR"
+Denylist the client and terminate
+the search. Subject the client to the action configured with the
+postscreen_denylist_action configuration parameter.
+.br
+.IP "\fB dunno \fR"
+All \fBpostscreen\fR(8) access lists
+implicitly have this command at the end.
+.br
+When \fB dunno \fR
+is executed inside a lookup table, return from the lookup table and
+evaluate the next command.
+.br
+When \fB dunno \fR is executed
+outside a lookup table, terminate the search, and subject the client
+to the configured before/after 220 greeting tests.
+.br
+.br
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    postscreen_access_list = permit_mynetworks,
+        cidr:/etc/postfix/postscreen_access.cidr
+    # Postfix < 3.6 use postscreen_blacklist_action.
+    postscreen_denylist_action = enforce
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/postscreen_access.cidr:
+    # Rules are evaluated in the order as specified.
+    # Denylist 192.168.* except 192.168.0.1.
+    192.168.0.1         dunno
+    192.168.0.0/16      reject
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_allowlist_interfaces (default: static:all)
+A list of local \fBpostscreen\fR(8) server IP addresses where a
+non\-allowlisted remote SMTP client can obtain \fBpostscreen\fR(8)'s temporary
+allowlist status. This status is required before the client can
+talk to a Postfix SMTP server process.  By default, a client can
+obtain \fBpostscreen\fR(8)'s allowlist status on any local \fBpostscreen\fR(8)
+server IP address.
+.PP
+When \fBpostscreen\fR(8) listens on both primary and backup MX
+addresses, the postscreen_allowlist_interfaces parameter can be
+configured to give the temporary allowlist status only when a client
+connects to a primary MX address. Once a client is allowlisted it
+can talk to a Postfix SMTP server on any address. Thus, clients
+that connect only to backup MX addresses will never become allowlisted,
+and will never be allowed to talk to a Postfix SMTP server process.
+.PP
+Specify a list of network addresses or network/netmask patterns,
+separated by commas and/or whitespace. The netmask specifies the
+number of bits in the network part of a host address. Continue long
+lines by starting the next line with whitespace.
+.PP
+You can also specify "/file/name" or "type:table" patterns.  A
+"/file/name" pattern is replaced by its contents; a "type:table"
+lookup table is matched when a table entry matches a lookup string
+(the lookup result is ignored).
+.PP
+The list is matched left to right, and the search stops on the
+first match. Specify "!pattern" to exclude an address or network
+block from the list.
+.PP
+Note: IP version 6 address information must be specified inside
+[] in the postscreen_allowlist_interfaces value, and in files
+specified with "/file/name".  IP version 6 addresses contain the
+":" character, and would otherwise be confused with a "type:table"
+pattern.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    # Don't allowlist connections to the backup IP address.
+    # Postfix < 3.6 use postscreen_whitelist_interfaces.
+    postscreen_allowlist_interfaces = !168.100.189.8, static:all
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 3.6 and later.
+.PP
+Available as postscreen_whitelist_interfaces in Postfix 2.9 \- 3.5.
+.SH postscreen_bare_newline_action (default: ignore)
+The action that \fBpostscreen\fR(8) takes when a remote SMTP client sends
+a bare newline character, that is, a newline not preceded by carriage
+return.  Specify one of the following:
+.IP "\fBignore\fR"
+Ignore the failure of this test. Allow other tests to complete.
+Do \fInot\fR repeat this test before the result from some
+other test expires.
+This option is useful for testing and collecting statistics
+without blocking mail permanently.
+.br
+.IP "\fBenforce\fR"
+Allow other tests to complete. Reject attempts to deliver mail
+with a 550 SMTP reply, and log the helo/sender/recipient information.
+Repeat this test the next time the client connects.
+.br
+.IP "\fBdrop\fR"
+Drop the connection immediately with a 521 SMTP reply. Repeat
+this test the next time the client connects.
+.br
+.br
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_bare_newline_enable (default: no)
+Enable "bare newline" SMTP protocol tests in the \fBpostscreen\fR(8)
+server. These tests are expensive: a remote SMTP client must
+disconnect after
+it passes the test, before it can talk to a real Postfix SMTP server.
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_bare_newline_ttl (default: 30d)
+The amount of time that \fBpostscreen\fR(8) will use the result from
+a successful "bare newline" SMTP protocol test. During this
+time, the client IP address is excluded from this test. The default
+is long because a remote SMTP client must disconnect after it passes
+the test,
+before it can talk to a real Postfix SMTP server.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is d (days).
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_blacklist_action (default: ignore)
+Renamed to postscreen_denylist_action in Postfix 3.6.
+.PP
+This feature is available in Postfix 2.8 \- 3.5.
+.SH postscreen_cache_cleanup_interval (default: 12h)
+The amount of time between \fBpostscreen\fR(8) cache cleanup runs.
+Cache cleanup increases the load on the cache database and should
+therefore not be run frequently. This feature requires that the
+cache database supports the "delete" and "sequence" operators.
+Specify a zero interval to disable cache cleanup.
+.PP
+After each cache cleanup run, the \fBpostscreen\fR(8) daemon logs the
+number of entries that were retained and dropped. A cleanup run is
+logged as "partial" when the daemon terminates early after "\fBpostfix
+reload\fR", "\fBpostfix stop\fR", or no requests for $max_idle
+seconds.
+.PP
+Specify a non\-negative time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is h (hours).
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_cache_map (default: btree:$data_directory/postscreen_cache)
+Persistent storage for the \fBpostscreen\fR(8) server decisions.
+.PP
+To share a \fBpostscreen\fR(8) cache between multiple \fBpostscreen\fR(8)
+instances, use "postscreen_cache_map = proxy:btree:/path/to/file".
+This requires Postfix version 2.9 or later; earlier \fBproxymap\fR(8)
+implementations don't support cache cleanup. For an alternative
+approach see the \fBmemcache_table\fR(5) manpage.
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_cache_retention_time (default: 7d)
+The amount of time that \fBpostscreen\fR(8) will cache an expired
+temporary allowlist entry before it is removed. This prevents clients
+from being logged as "NEW" just because their cache entry expired
+an hour ago. It also prevents the cache from filling up with clients
+that passed some deep protocol test once and never came back.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is d (days).
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_client_connection_count_limit (default: $smtpd_client_connection_count_limit)
+How many simultaneous connections any remote SMTP client is
+allowed to have
+with the \fBpostscreen\fR(8) daemon. By default, this limit is the same
+as with the Postfix SMTP server. Note that the triage process can
+take several seconds, with the time spent in postscreen_greet_wait
+delay, and with the time spent talking to the \fBpostscreen\fR(8) built\-in
+dummy SMTP protocol engine.
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_command_count_limit (default: 20)
+The limit on the total number of commands per SMTP session for
+\fBpostscreen\fR(8)'s built\-in SMTP protocol engine.  This SMTP engine
+defers or rejects all attempts to deliver mail, therefore there is
+no need to enforce separate limits on the number of junk commands
+and error commands.
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_command_filter (default: $smtpd_command_filter)
+A mechanism to transform commands from remote SMTP clients.
+See smtpd_command_filter for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH postscreen_command_time_limit (default: normal: 300s, overload: 10s)
+The time limit to read an entire command line with \fBpostscreen\fR(8)'s
+built\-in SMTP protocol engine.
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_denylist_action (default: ignore)
+The action that \fBpostscreen\fR(8) takes when a remote SMTP client is
+permanently denylisted with the postscreen_access_list parameter.
+Specify one of the following:
+.IP "\fBignore\fR (default)"
+Ignore  this result. Allow other tests to complete.  Repeat
+this test the next time the client connects.
+This option is useful for testing and collecting statistics
+without blocking mail.
+.br
+.IP "\fBenforce\fR"
+Allow other tests to complete. Reject attempts to deliver mail
+with a 550 SMTP reply, and log the helo/sender/recipient information.
+Repeat this test the next time the client connects.
+.br
+.IP "\fBdrop\fR"
+Drop the connection immediately with a 521 SMTP reply. Repeat
+this test the next time the client connects.
+.br
+.br
+.PP
+This feature is available in Postfix 3.6 and later.
+.PP
+Available as postscreen_blacklist_action in Postfix 2.8 \- 3.5.
+.SH postscreen_disable_vrfy_command (default: $disable_vrfy_command)
+Disable the SMTP VRFY command in the \fBpostscreen\fR(8) daemon.  See
+disable_vrfy_command for details.
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_discard_ehlo_keyword_address_maps (default: $smtpd_discard_ehlo_keyword_address_maps)
+Lookup tables, indexed by the remote SMTP client address, with
+case insensitive lists of EHLO keywords (pipelining, starttls, auth,
+etc.) that the \fBpostscreen\fR(8) server will not send in the EHLO response
+to a remote SMTP client. See smtpd_discard_ehlo_keywords for details.
+The table is not searched by hostname for robustness reasons.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH postscreen_discard_ehlo_keywords (default: $smtpd_discard_ehlo_keywords)
+A case insensitive list of EHLO keywords (pipelining, starttls,
+auth, etc.) that the \fBpostscreen\fR(8) server will not send in the EHLO
+response to a remote SMTP client. See smtpd_discard_ehlo_keywords
+for details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH postscreen_dnsbl_action (default: ignore)
+The action that \fBpostscreen\fR(8) takes when a remote SMTP client's combined
+DNSBL score is equal to or greater than a threshold (as defined
+with the postscreen_dnsbl_sites and postscreen_dnsbl_threshold
+parameters).  Specify one of the following:
+.IP "\fBignore\fR (default)"
+Ignore the failure of this test. Allow other tests to complete.
+Repeat this test the next time the client connects.
+This option is useful for testing and collecting statistics
+without blocking mail.
+.br
+.IP "\fBenforce\fR"
+Allow other tests to complete. Reject attempts to deliver mail
+with a 550 SMTP reply, and log the helo/sender/recipient information.
+Repeat this test the next time the client connects.
+.br
+.IP "\fBdrop\fR"
+Drop the connection immediately with a 521 SMTP reply. Repeat
+this test the next time the client connects.
+.br
+.br
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_dnsbl_allowlist_threshold (default: 0)
+Allow a remote SMTP client to skip "before" and "after 220
+greeting" protocol tests, based on its combined DNSBL score as
+defined with the postscreen_dnsbl_sites parameter.
+.PP
+Specify a negative value to enable this feature. When a client
+passes the postscreen_dnsbl_allowlist_threshold without having
+failed other tests, all pending or disabled tests are flagged as
+completed with a time\-to\-live value equal to postscreen_dnsbl_ttl.
+When a test was already completed, its time\-to\-live value is updated
+if it was less than postscreen_dnsbl_ttl.
+.PP
+This feature is available in Postfix 3.6 and later.
+.PP
+Available as postscreen_dnsbl_whitelist_threshold in Postfix 2.11
+\- 3.5.
+.SH postscreen_dnsbl_max_ttl (default: ${postscreen_dnsbl_ttl?{$postscreen_dnsbl_ttl}:{1}}h)
+The maximum amount of time that \fBpostscreen\fR(8) will use the
+result from a successful DNS\-based reputation test before a
+client IP address is required to pass that test again. If the DNS
+reply specifies a shorter TTL value, that value will be used unless
+it would be smaller than postscreen_dnsbl_min_ttl.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is h (hours).
+.PP
+This feature is available in Postfix 3.1. The default setting
+is backwards\-compatible with older Postfix versions.
+.SH postscreen_dnsbl_min_ttl (default: 60s)
+The minimum amount of time that \fBpostscreen\fR(8) will use the
+result from a successful DNS\-based reputation test before a
+client IP address is required to pass that test again. If the DNS
+reply specifies a larger TTL value, that value will be used unless
+it would be larger than postscreen_dnsbl_max_ttl.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 3.1.
+.SH postscreen_dnsbl_reply_map (default: empty)
+A mapping from an actual DNSBL domain name which includes a secret
+password, to the DNSBL domain name that postscreen will reply with
+when it rejects mail.  When no mapping is found, the actual DNSBL
+domain will be used.
+.PP
+For maximal stability it is best to use a file that is read
+into memory such as pcre:, regexp: or texthash: (texthash: is similar
+to hash:, except a) there is no need to run \fBpostmap\fR(1) before the
+file can be used, and b) texthash: does not detect changes after
+the file is read).
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    postscreen_dnsbl_reply_map = texthash:/etc/postfix/dnsbl_reply
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/dnsbl_reply:
+   secret.zen.spamhaus.org      zen.spamhaus.org
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_dnsbl_sites (default: empty)
+Optional list of patterns with DNS allow/denylist domains, filters
+and weight
+factors. When the list is non\-empty, the \fBdnsblog\fR(8) daemon will
+query these domains with the reversed IP addresses of remote SMTP
+clients,
+and \fBpostscreen\fR(8) will update an SMTP client's DNSBL score with
+each non\-error reply as described below.
+.PP
+Caution: when postscreen rejects mail, its SMTP response contains
+the DNSBL
+domain name. Use the postscreen_dnsbl_reply_map feature to hide
+"password" information in DNSBL domain names.
+.PP
+When a client's score is equal to or greater than the threshold
+specified with postscreen_dnsbl_threshold, \fBpostscreen\fR(8) can drop
+the connection with the remote SMTP client.
+.PP
+Specify a list of domain=filter*weight patterns, separated by
+comma or whitespace.
+.IP \(bu
+When a pattern specifies no "=filter", \fBpostscreen\fR(8) will
+use any non\-error DNSBL query result.  Otherwise, \fBpostscreen\fR(8)
+will use only DNSBL
+query results that match the filter. The filter has the form d.d.d.d,
+where each d is a number, or a pattern inside [] that contains one
+or more ";"\-separated numbers or number..number ranges.
+.IP \(bu
+When a pattern specifies no "*weight", the weight of the
+pattern is 1.  Otherwise, the weight must be an integral number.
+Specify a negative number for allowlisting.
+.IP \(bu
+When a pattern matches one or more DNSBL query results,
+\fBpostscreen\fR(8) adds that pattern's weight once to the remote SMTP
+client's DNSBL score.
+.br
+.PP
+Examples:
+.PP
+To use example.com as a high\-confidence blocklist, and to
+block mail with example.net and example.org only when both agree:
+.PP
+.nf
+.na
+.ft C
+postscreen_dnsbl_threshold = 2
+postscreen_dnsbl_sites = example.com*2, example.net, example.org
+.fi
+.ad
+.ft R
+.PP
+To filter only DNSBL replies containing 127.0.0.4:
+.PP
+.nf
+.na
+.ft C
+postscreen_dnsbl_sites = example.com=127.0.0.4
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_dnsbl_threshold (default: 1)
+The inclusive lower bound for blocking a remote SMTP client, based on
+its combined DNSBL score as defined with the postscreen_dnsbl_sites
+parameter.
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_dnsbl_timeout (default: 10s)
+The time limit for DNSBL or DNSWL lookups. This is separate from
+the timeouts in the \fBdnsblog\fR(8) daemon which are defined by system
+\fBresolver\fR(3) routines.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 3.0.
+.SH postscreen_dnsbl_ttl (default: 1h)
+The amount of time that \fBpostscreen\fR(8) will use the result from
+a successful DNS\-based reputation test before a client
+IP address is required to pass that test again.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is h (hours).
+.PP
+This feature is available in Postfix 2.8\-3.0. It was
+replaced by postscreen_dnsbl_max_ttl in Postfix 3.1.
+.SH postscreen_dnsbl_whitelist_threshold (default: 0)
+Renamed to postscreen_dnsbl_allowlist_threshold in Postfix 3.6.
+.PP
+This feature is available in Postfix 2.11 \- 3.5.
+.SH postscreen_enforce_tls (default: $smtpd_enforce_tls)
+Mandatory TLS: announce STARTTLS support to remote SMTP clients, and
+require that clients use TLS encryption.  See smtpd_postscreen_enforce_tls
+for details.
+.PP
+This feature is available in Postfix 2.8 and later.
+Preferably, use postscreen_tls_security_level instead.
+.SH postscreen_expansion_filter (default: see "postconf \-d" output)
+List of characters that are permitted in postscreen_reject_footer
+attribute expansions.  See smtpd_expansion_filter for further
+details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH postscreen_forbidden_commands (default: $smtpd_forbidden_commands)
+List of commands that the \fBpostscreen\fR(8) server considers in
+violation of the SMTP protocol. See smtpd_forbidden_commands for
+syntax, and postscreen_non_smtp_command_action for possible actions.
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_greet_action (default: ignore)
+The action that \fBpostscreen\fR(8) takes when a remote SMTP client speaks
+before its turn within the time specified with the postscreen_greet_wait
+parameter.  Specify one of the following:
+.IP "\fBignore\fR (default)"
+Ignore the failure of this test. Allow other tests to complete.
+Repeat this test the next time the client connects.
+This option is useful for testing and collecting statistics
+without blocking mail.
+.br
+.IP "\fBenforce\fR"
+Allow other tests to complete. Reject attempts to deliver mail
+with a 550 SMTP reply, and log the helo/sender/recipient information.
+Repeat this test the next time the client connects.
+.br
+.IP "\fBdrop\fR"
+Drop the connection immediately with a 521 SMTP reply. Repeat
+this test the next time the client connects.
+.br
+.br
+.PP
+In either case, \fBpostscreen\fR(8) will not allowlist the remote SMTP client
+IP address.
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_greet_banner (default: $smtpd_banner)
+The \fItext\fR in the optional "220\-\fItext\fR..." server
+response that
+\fBpostscreen\fR(8) sends ahead of the real Postfix SMTP server's "220
+text..." response, in an attempt to confuse bad SMTP clients so
+that they speak before their turn (pre\-greet).  Specify an empty
+value to disable this feature.
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_greet_ttl (default: 1d)
+The amount of time that \fBpostscreen\fR(8) will use the result from
+a successful PREGREET test. During this time, the client IP address
+is excluded from this test. The default is relatively short, because
+a good client can immediately talk to a real Postfix SMTP server.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is d (days).
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_greet_wait (default: normal: 6s, overload: 2s)
+The amount of time that \fBpostscreen\fR(8) will wait for an SMTP
+client to send a command before its turn, and for DNS blocklist
+lookup results to arrive (default: up to 2 seconds under stress,
+up to 6 seconds otherwise).
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_helo_required (default: $smtpd_helo_required)
+Require that a remote SMTP client sends HELO or EHLO before
+commencing a MAIL transaction.
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_non_smtp_command_action (default: drop)
+The action that \fBpostscreen\fR(8) takes when a remote SMTP client sends
+non\-SMTP commands as specified with the postscreen_forbidden_commands
+parameter.  Specify one of the following:
+.IP "\fBignore\fR"
+Ignore the failure of this test. Allow other tests to complete.
+Do \fInot\fR repeat this test before the result from some
+other test expires.
+This option is useful for testing and collecting statistics
+without blocking mail permanently.
+.br
+.IP "\fBenforce\fR"
+Allow other tests to complete. Reject attempts to deliver mail
+with a 550 SMTP reply, and log the helo/sender/recipient information.
+Repeat this test the next time the client connects.
+.br
+.IP "\fBdrop\fR"
+Drop the connection immediately with a 521 SMTP reply. Repeat
+this test the next time the client connects. This action is the
+same as with the Postfix SMTP server's smtpd_forbidden_commands
+feature.
+.br
+.br
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_non_smtp_command_enable (default: no)
+Enable "non\-SMTP command" tests in the \fBpostscreen\fR(8) server. These
+tests are expensive: a client must disconnect after it passes the
+test, before it can talk to a real Postfix SMTP server.
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_non_smtp_command_ttl (default: 30d)
+The amount of time that \fBpostscreen\fR(8) will use the result from
+a successful "non_smtp_command" SMTP protocol test. During this
+time, the client IP address is excluded from this test. The default
+is long because a client must disconnect after it passes the test,
+before it can talk to a real Postfix SMTP server.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is d (days).
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_pipelining_action (default: enforce)
+The action that \fBpostscreen\fR(8) takes when a remote SMTP client
+sends
+multiple commands instead of sending one command and waiting for
+the server to respond.  Specify one of the following:
+.IP "\fBignore\fR"
+Ignore the failure of this test. Allow other tests to complete.
+Do \fInot\fR repeat this test before the result from some
+other test expires.
+This option is useful for testing and collecting statistics
+without blocking mail permanently.
+.br
+.IP "\fBenforce\fR"
+Allow other tests to complete. Reject attempts to deliver mail
+with a 550 SMTP reply, and log the helo/sender/recipient information.
+Repeat this test the next time the client connects.
+.br
+.IP "\fBdrop\fR"
+Drop the connection immediately with a 521 SMTP reply. Repeat
+this test the next time the client connects.
+.br
+.br
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_pipelining_enable (default: no)
+Enable "pipelining" SMTP protocol tests in the \fBpostscreen\fR(8)
+server. These tests are expensive: a good client must disconnect
+after it passes the test, before it can talk to a real Postfix SMTP
+server.
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_pipelining_ttl (default: 30d)
+The amount of time that \fBpostscreen\fR(8) will use the result from
+a successful "pipelining" SMTP protocol test. During this time, the
+client IP address is excluded from this test. The default is
+long because a good client must disconnect after it passes the test,
+before it can talk to a real Postfix SMTP server.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is d (days).
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_post_queue_limit (default: $default_process_limit)
+The number of clients that can be waiting for service from a
+real Postfix SMTP server process. When this queue is full, all
+clients will
+receive a 421 response.
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_pre_queue_limit (default: $default_process_limit)
+The number of non\-allowlisted clients that can be waiting for
+a decision whether they will receive service from a real Postfix
+SMTP server
+process. When this queue is full, all non\-allowlisted clients will
+receive a 421 response.
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_reject_footer (default: $smtpd_reject_footer)
+Optional information that is appended after a 4XX or 5XX
+\fBpostscreen\fR(8) server
+response. See smtpd_reject_footer for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH postscreen_reject_footer_maps (default: $smtpd_reject_footer_maps)
+Optional lookup table for information that is appended after a 4XX
+or 5XX \fBpostscreen\fR(8) server response. See smtpd_reject_footer_maps for
+further details.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH postscreen_tls_security_level (default: $smtpd_tls_security_level)
+The SMTP TLS security level for the \fBpostscreen\fR(8) server; when
+a non\-empty value is specified, this overrides the obsolete parameters
+postscreen_use_tls and postscreen_enforce_tls. See smtpd_tls_security_level
+for details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH postscreen_upstream_proxy_protocol (default: empty)
+The name of the proxy protocol used by an optional before\-postscreen
+proxy agent. When a proxy agent is used, this protocol conveys local
+and remote address and port information. Specify
+"postscreen_upstream_proxy_protocol = haproxy" to enable the haproxy
+protocol; version 2 is supported with Postfix 3.5 and later.
+.PP
+This feature is available in Postfix 2.10 and later.
+.SH postscreen_upstream_proxy_timeout (default: 5s)
+The time limit for the proxy protocol specified with the
+postscreen_upstream_proxy_protocol parameter.
+.PP
+This feature is available in Postfix 2.10 and later.
+.SH postscreen_use_tls (default: $smtpd_use_tls)
+Opportunistic TLS: announce STARTTLS support to remote SMTP clients,
+but do not require that clients use TLS encryption.
+.PP
+This feature is available in Postfix 2.8 and later.
+Preferably, use postscreen_tls_security_level instead.
+.SH postscreen_watchdog_timeout (default: 10s)
+How much time a \fBpostscreen\fR(8) process may take to respond to
+a remote SMTP client command or to perform a cache operation before it
+is terminated by a built\-in watchdog timer.  This is a safety
+mechanism that prevents \fBpostscreen\fR(8) from becoming non\-responsive
+due to a bug in Postfix itself or in system software.  To avoid
+false alarms and unnecessary cache corruption this limit cannot be
+set under 10s.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.8.
+.SH postscreen_whitelist_interfaces (default: static:all)
+Renamed to postscreen_allowlist_interfaces in Postfix 3.6.
+.PP
+This feature is available in Postfix 2.9 \- 3.5.
+.SH prepend_delivered_header (default: command, file, forward)
+The message delivery contexts where the Postfix \fBlocal\fR(8) delivery
+agent prepends a Delivered\-To:  message header with the address
+that the mail was delivered to. This information is used for mail
+delivery loop detection.
+.PP
+By default, the Postfix local delivery agent prepends a Delivered\-To:
+header when forwarding mail and when delivering to file (mailbox)
+and command. Turning off the Delivered\-To: header when forwarding
+mail is not recommended.
+.PP
+Specify zero or more of \fBforward\fR, \fBfile\fR, or \fBcommand\fR.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+prepend_delivered_header = forward
+.fi
+.ad
+.ft R
+.SH process_id (read\-only)
+The process ID of a Postfix command or daemon process.
+.SH process_id_directory (default: pid)
+The location of Postfix PID files relative to $queue_directory.
+This is a read\-only parameter.
+.SH process_name (read\-only)
+The process name of a Postfix command or daemon process.
+.SH propagate_unmatched_extensions (default: canonical, virtual)
+What address lookup tables copy an address extension from the lookup
+key to the lookup result.
+.PP
+For example, with a \fBvirtual\fR(5) mapping of "\fIjoe@example.com =>
+joe.user@example.net\fR", the address "\fIjoe+foo@example.com\fR"
+would rewrite to "\fIjoe.user+foo@example.net\fR".
+.PP
+Specify zero or more of \fBcanonical\fR, \fBvirtual\fR, \fBalias\fR,
+\fBforward\fR, \fBinclude\fR or \fBgeneric\fR. These cause
+address extension
+propagation with \fBcanonical\fR(5), \fBvirtual\fR(5), and \fBaliases\fR(5) maps,
+with \fBlocal\fR(8) .forward and :include: file lookups, and with \fBsmtp\fR(8)
+generic maps, respectively.
+.PP
+Note: enabling this feature for types other than \fBcanonical\fR
+and \fBvirtual\fR is likely to cause problems when mail is forwarded
+to other sites, especially with mail that is sent to a mailing list
+exploder address.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+propagate_unmatched_extensions = canonical, virtual, alias,
+        forward, include
+propagate_unmatched_extensions = canonical, virtual
+.fi
+.ad
+.ft R
+.SH proxy_interfaces (default: empty)
+The remote network interface addresses that this mail system receives mail
+on by way of a proxy or network address translation unit.
+.PP
+This feature is available in Postfix 2.0 and later.
+.PP
+You must specify your "outside" proxy/NAT addresses when your
+system is a backup MX host for other domains, otherwise mail delivery
+loops will happen when the primary MX host is down.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+proxy_interfaces = 1.2.3.4
+.fi
+.ad
+.ft R
+.SH proxy_read_maps (default: see "postconf \-d" output)
+The lookup tables that the \fBproxymap\fR(8) server is allowed to
+access for the read\-only service.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma.
+Table references that don't begin with proxy: are ignored.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH proxy_write_maps (default: see "postconf \-d" output)
+The lookup tables that the \fBproxymap\fR(8) server is allowed to
+access for the read\-write service. Postfix\-owned local database
+files should be stored under the Postfix\-owned data_directory.
+Table references that don't begin with proxy: are ignored.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH proxymap_service_name (default: proxymap)
+The name of the proxymap read\-only table lookup service.  This
+service is normally implemented by the \fBproxymap\fR(8) daemon.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH proxywrite_service_name (default: proxywrite)
+The name of the proxywrite read\-write table lookup service.
+This service is normally implemented by the \fBproxymap\fR(8) daemon.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH qmgr_clog_warn_time (default: 300s)
+The minimal delay between warnings that a specific destination is
+clogging up the Postfix active queue. Specify 0 to disable.
+.PP
+Specify a non\-negative time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is enabled with the helpful_warnings parameter.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH qmgr_daemon_timeout (default: 1000s)
+How much time a Postfix queue manager process may take to handle
+a request before it is terminated by a built\-in watchdog timer.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH qmgr_fudge_factor (default: 100)
+Obsolete feature: the percentage of delivery resources that a busy
+mail system will use up for delivery of a large mailing  list
+message.
+.PP
+This feature exists only in the \fBoqmgr\fR(8) old queue manager. The
+current queue manager solves the problem in a better way.
+.SH qmgr_ipc_timeout (default: 60s)
+The time limit for the queue manager to send or receive information
+over an internal communication channel.  The purpose is to break
+out of deadlock situations. If the time limit is exceeded the
+software either retries or aborts the operation.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH qmgr_message_active_limit (default: 20000)
+The maximal number of messages in the active queue.
+.SH qmgr_message_recipient_limit (default: 20000)
+The maximal number of recipients held in memory by the Postfix
+queue manager, and the maximal size of the short\-term,
+in\-memory "dead" destination status cache.
+.SH qmgr_message_recipient_minimum (default: 10)
+The minimal number of in\-memory recipients for any message. This
+takes priority over any other in\-memory recipient limits (i.e.,
+the global qmgr_message_recipient_limit and the per transport
+_recipient_limit) if necessary. The minimum value allowed for this
+parameter is 1.
+.SH qmqpd_authorized_clients (default: empty)
+What remote QMQP clients are allowed to connect to the Postfix QMQP
+server port.
+.PP
+By default, no client is allowed to use the service. This is
+because the QMQP server will relay mail to any destination.
+.PP
+Specify a list of client patterns. A list pattern specifies a host
+name, a domain name, an internet address, or a network/mask pattern,
+where the mask specifies the number of bits in the network part.
+When a pattern specifies a file name, its contents are substituted
+for the file name; when a pattern is a "type:table" table specification,
+table lookup is used instead.
+.PP
+Patterns are separated by whitespace and/or commas. In order to
+reverse the result, precede a pattern with an
+exclamation point (!). The form "!/file/name" is supported only
+in Postfix version 2.4 and later.
+.PP
+Pattern matching of domain names is controlled by the presence
+or absence of "qmqpd_authorized_clients" in the
+parent_domain_matches_subdomains parameter value.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+qmqpd_authorized_clients = !192.168.0.1, 192.168.0.0/24
+.fi
+.ad
+.ft R
+.SH qmqpd_client_port_logging (default: no)
+Enable logging of the remote QMQP client port in addition to
+the hostname and IP address. The logging format is "host[address]:port".
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH qmqpd_error_delay (default: 1s)
+How long the Postfix QMQP server will pause before sending a negative
+reply to the remote QMQP client. The purpose is to slow down confused
+or malicious clients.
+.PP
+Specify a non\-negative time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH qmqpd_timeout (default: 300s)
+The time limit for sending or receiving information over the network.
+If a read or write operation blocks for more than $qmqpd_timeout
+seconds the Postfix QMQP server gives up and disconnects.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH queue_directory (default: see "postconf \-d" output)
+The location of the Postfix top\-level queue directory. This is the
+root directory of Postfix daemon processes that run chrooted.
+.SH queue_file_attribute_count_limit (default: 100)
+The maximal number of (name=value) attributes that may be stored
+in a Postfix queue file. The limit is enforced by the \fBcleanup\fR(8)
+server.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH queue_minfree (default: 0)
+The minimal amount of free space in bytes in the queue file system
+that is needed to receive mail.  This is currently used by the
+Postfix SMTP server to decide if it will accept any mail at all.
+.PP
+By default, the Postfix SMTP server rejects MAIL FROM commands when
+the amount of free space is less than 1.5*$message_size_limit
+(Postfix version 2.1 and later).
+To specify a higher minimum free space limit, specify a queue_minfree
+value that is at least 1.5*$message_size_limit.
+.PP
+With Postfix versions 2.0 and earlier, a queue_minfree value of
+zero means there is no minimum required amount of free space.
+.SH queue_run_delay (default: 300s)
+The time between deferred queue scans by the queue manager;
+prior to Postfix 2.4 the default value was 1000s.
+.PP
+This parameter should be set less than or equal to
+$minimal_backoff_time. See also $maximal_backoff_time.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH queue_service_name (default: qmgr)
+The name of the \fBqmgr\fR(8) service. This service manages the Postfix
+queue and schedules delivery requests.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH rbl_reply_maps (default: empty)
+Optional lookup tables with RBL response templates. The tables are
+indexed by the RBL domain name. By default, Postfix uses the default
+template as specified with the default_rbl_reply configuration
+parameter. See there for a discussion of the syntax of RBL reply
+templates.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH readme_directory (default: see "postconf \-d" output)
+The location of Postfix README files that describe how to build,
+configure or operate a specific Postfix subsystem or feature.
+.SH receive_override_options (default: empty)
+Enable or disable recipient validation, built\-in content
+filtering, or address mapping. Typically, these are specified in
+master.cf as command\-line arguments for the \fBsmtpd\fR(8), \fBqmqpd\fR(8) or
+\fBpickup\fR(8) daemons.
+.PP
+Specify zero or more of the following options.  The options
+override main.cf settings and are either implemented by \fBsmtpd\fR(8),
+\fBqmqpd\fR(8), or \fBpickup\fR(8) themselves, or they are forwarded to the
+cleanup server.
+.IP "\fBno_unknown_recipient_checks\fR"
+Do not try to reject unknown recipients (SMTP server only).
+This is typically specified AFTER an external content filter.
+.br
+.IP "\fBno_address_mappings\fR"
+Disable canonical address mapping, virtual alias map expansion,
+address masquerading, and automatic BCC (blind carbon\-copy)
+recipients. This is typically specified BEFORE an external content
+filter.
+.br
+.IP "\fBno_header_body_checks\fR"
+Disable header/body_checks. This is typically specified AFTER
+an external content filter.
+.br
+.IP "\fBno_milters\fR"
+Disable Milter (mail filter) applications. This is typically
+specified AFTER an external content filter.
+.br
+.br
+.PP
+Note: when the "BEFORE content filter" receive_override_options
+setting is specified in the main.cf file, specify the "AFTER content
+filter" receive_override_options setting in master.cf (and vice
+versa).
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+receive_override_options =
+    no_unknown_recipient_checks, no_header_body_checks
+receive_override_options = no_address_mappings
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH recipient_bcc_maps (default: empty)
+Optional BCC (blind carbon\-copy) address lookup tables, indexed by
+envelope recipient address.  The BCC address (multiple results are not
+supported) is added when mail enters from outside of Postfix.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.PP
+The table search order is as follows:
+.IP \(bu
+Look up the "user+extension@domain.tld" address including the
+optional address extension.
+.IP \(bu
+Look up the "user@domain.tld" address without the optional
+address extension.
+.IP \(bu
+Look up the "user+extension" address local part when the
+recipient domain equals $myorigin, $mydestination, $inet_interfaces
+or $proxy_interfaces.
+.IP \(bu
+Look up the "user" address local part when the recipient domain
+equals $myorigin, $mydestination, $inet_interfaces or $proxy_interfaces.
+.IP \(bu
+Look up the "@domain.tld" part.
+.br
+.PP
+Note: with Postfix 2.3 and later the BCC address is added as if it
+was specified with NOTIFY=NONE. The sender will not be notified
+when the BCC address is undeliverable, as long as all down\-stream
+software implements RFC 3461.
+.PP
+Note: with Postfix 2.2 and earlier the sender will unconditionally
+be notified when the BCC address is undeliverable.
+.PP
+Note: automatic BCC recipients are produced only for new mail.
+To avoid mailer loops, automatic BCC recipients are not generated
+after Postfix forwards mail internally, or after Postfix generates
+mail itself.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+recipient_bcc_maps = hash:/etc/postfix/recipient_bcc
+.fi
+.ad
+.ft R
+.PP
+After a change, run "\fBpostmap /etc/postfix/recipient_bcc\fR".
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH recipient_canonical_classes (default: envelope_recipient, header_recipient)
+What addresses are subject to recipient_canonical_maps address
+mapping.  By default, recipient_canonical_maps address mapping is
+applied to envelope recipient addresses, and to header recipient
+addresses.
+.PP
+Specify one or more of: envelope_recipient, header_recipient
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH recipient_canonical_maps (default: empty)
+Optional address mapping lookup tables for envelope and header
+recipient addresses.
+The table format and lookups are documented in \fBcanonical\fR(5).
+.PP
+Note: $recipient_canonical_maps is processed before $canonical_maps.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+recipient_canonical_maps = hash:/etc/postfix/recipient_canonical
+.fi
+.ad
+.ft R
+.SH recipient_delimiter (default: empty)
+The set of characters that can separate an email address
+localpart, user name, or a .forward file name from its extension.
+For example, with "recipient_delimiter = +", the software tries
+user+foo@example.com before trying user@example.com, user+foo before
+trying user, and .forward+foo before trying .forward.
+.PP
+More formally, an email address localpart or user name is
+separated from its extension by the first character that matches
+the recipient_delimiter set. The delimiter character and extension
+may then be used to generate an extended .forward file name. This
+implementation recognizes one delimiter character and one extension
+per email address localpart or email address. With Postfix 2.10 and
+earlier, the recipient_delimiter specifies a single character.
+.PP
+See \fBcanonical\fR(5), \fBlocal\fR(8), \fBrelocated\fR(5) and \fBvirtual\fR(5) for the
+effects of recipient_delimiter on lookups in aliases, canonical,
+virtual, and relocated maps, and see the propagate_unmatched_extensions
+parameter for propagating an extension from one email address to
+another.
+.PP
+When used in command_execution_directory, forward_path, or
+luser_relay, ${recipient_delimiter} is replaced with the actual
+recipient delimiter that was found in the recipient email address
+(Postfix 2.11 and later), or it is replaced with the main.cf
+recipient_delimiter parameter value (Postfix 2.10 and earlier).
+.PP
+The recipient_delimiter is not applied to the mailer\-daemon
+address, the postmaster address, or the double\-bounce address. With
+the default "owner_request_special = yes" setting, the recipient_delimiter
+is also not applied to addresses with the special "owner\-" prefix
+or the special "\-request" suffix.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+# Handle Postfix\-style extensions.
+recipient_delimiter = +
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+# Handle both Postfix and qmail extensions (Postfix 2.11 and later).
+recipient_delimiter = +\-
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+# Use .forward for mail without address extension, and for mail with
+# an unrecognized address extension.
+forward_path = $home/.forward${recipient_delimiter}${extension},
+    $home/.forward
+.fi
+.ad
+.ft R
+.SH reject_code (default: 554)
+The numerical Postfix SMTP server response code when a remote SMTP
+client request is rejected by the "reject" restriction.
+.PP
+Do not change this unless you have a complete understanding of RFC 5321.
+.SH reject_tempfail_action (default: defer_if_permit)
+The Postfix SMTP server's action when a reject\-type restriction
+fails due to a temporary error condition. Specify "defer" to defer
+the remote SMTP client request immediately. With the default
+"defer_if_permit" action, the Postfix SMTP server continues to look
+for opportunities to reject mail, and defers the client request
+only if it would otherwise be accepted.
+.PP
+For finer control, see: unverified_recipient_tempfail_action,
+unverified_sender_tempfail_action, unknown_address_tempfail_action,
+and unknown_helo_hostname_tempfail_action.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH relay_clientcerts (default: empty)
+List of tables with remote SMTP client\-certificate fingerprints or
+public key fingerprints (Postfix 2.9 and later) for which the Postfix
+SMTP server will allow access with the permit_tls_clientcerts
+feature.  The fingerprint digest algorithm is configurable via the
+smtpd_tls_fingerprint_digest parameter (hard\-coded as md5 prior to
+Postfix version 2.5).
+.PP
+The default algorithm is \fBsha256\fR with Postfix >= 3.6
+and the \fBcompatibility_level\fR set to 3.6 or higher. With Postfix
+<= 3.5, the default algorithm is \fBmd5\fR.  The best\-practice
+algorithm is now \fBsha256\fR. Recent advances in hash function
+cryptanalysis have led to md5 and sha1 being deprecated in favor of
+sha256.  However, as long as there are no known "second pre\-image"
+attacks against the older algorithms, their use in this context, though
+not recommended, is still likely safe.
+.PP
+Postfix lookup tables are in the form of (key, value) pairs.
+Since we only need the key, the value can be chosen freely, e.g.
+the name of the user or host:
+D7:04:2F:A7:0B:8C:A5:21:FA:31:77:E1:41:8A:EE:80 lutzpc.at.home
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+relay_clientcerts = hash:/etc/postfix/relay_clientcerts
+.fi
+.ad
+.ft R
+.PP
+For more fine\-grained control, use check_ccert_access to select
+an appropriate \fBaccess\fR(5) policy for each client.
+See RESTRICTION_CLASS_README.
+.PP
+This feature is available with Postfix version 2.2.
+.SH relay_destination_concurrency_limit (default: $default_destination_concurrency_limit)
+The maximal number of parallel deliveries to the same destination
+via the relay message delivery transport. This limit is enforced
+by the queue manager. The message delivery transport name is the
+first field in the entry in the master.cf file.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH relay_destination_recipient_limit (default: $default_destination_recipient_limit)
+The maximal number of recipients per message for the relay
+message delivery transport. This limit is enforced by the queue
+manager. The message delivery transport name is the first field in
+the entry in the master.cf file.
+.PP
+Setting this parameter to a value of 1 changes the meaning of
+relay_destination_concurrency_limit from concurrency per domain
+into concurrency per recipient.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH relay_domains (default: Postfix >= 3.0: empty, Postfix < 3.0: $mydestination)
+What destination domains (and subdomains thereof) this system
+will relay mail to. For details about how
+the relay_domains value is used, see the description of the
+permit_auth_destination and reject_unauth_destination SMTP recipient
+restrictions.
+.PP
+Domains that match $relay_domains are delivered with the
+$relay_transport mail delivery transport. The SMTP server validates
+recipient addresses with $relay_recipient_maps and rejects non\-existent
+recipients. See also the relay domains address class in the
+ADDRESS_CLASS_README file.
+.PP
+Note: Postfix will not automatically forward mail for domains
+that list this system as their primary or backup MX host. See the
+permit_mx_backup restriction in the \fBpostconf\fR(5) manual page.
+.PP
+Specify a list of host or domain names, "/file/name" patterns
+or "type:table" lookup tables, separated by commas and/or whitespace.
+Continue long lines by starting the next line with whitespace. A
+"/file/name" pattern is replaced by its contents; a "type:table"
+lookup table is matched when a (parent) domain appears as lookup
+key. Specify "!pattern" to exclude a domain from the list. The form
+"!/file/name" is supported only in Postfix version 2.4 and later.
+.PP
+Pattern matching of domain names is controlled by the presence
+or absence of "relay_domains" in the parent_domain_matches_subdomains
+parameter value.
+.SH relay_domains_reject_code (default: 554)
+The numerical Postfix SMTP server response code when a client
+request is rejected by the reject_unauth_destination recipient
+restriction.
+.PP
+Do not change this unless you have a complete understanding of RFC 5321.
+.SH relay_recipient_maps (default: empty)
+Optional lookup tables with all valid addresses in the domains
+that match $relay_domains. Specify @domain as a wild\-card for
+domains that have no valid recipient list, and become a source of
+backscatter mail: Postfix accepts spam for non\-existent recipients
+and then floods innocent people with undeliverable mail.  Technically,
+tables
+listed with $relay_recipient_maps are used as lists: Postfix needs
+to know only if a lookup string is found or not, but it does not
+use the result from the table lookup.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.PP
+If this parameter is non\-empty, then the Postfix SMTP server will reject
+mail to unknown relay users. This feature is off by default.
+.PP
+See also the relay domains address class in the ADDRESS_CLASS_README
+file.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+relay_recipient_maps = hash:/etc/postfix/relay_recipients
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH relay_transport (default: relay)
+The default mail delivery transport and next\-hop destination for
+remote delivery to domains listed with $relay_domains. In order of
+decreasing precedence, the nexthop destination is taken from
+$relay_transport, $sender_dependent_relayhost_maps, $relayhost, or
+from the recipient domain. This information can be overruled with
+the \fBtransport\fR(5) table.
+.PP
+Specify a string of the form \fItransport:nexthop\fR, where \fItransport\fR
+is the name of a mail delivery transport defined in master.cf.
+The \fI:nexthop\fR destination is optional; its syntax is documented
+in the manual page of the corresponding delivery agent.
+.PP
+See also the relay domains address class in the ADDRESS_CLASS_README
+file.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH relayhost (default: empty)
+The next\-hop destination(s) for non\-local mail; overrides non\-local
+domains in recipient addresses. This information is overruled with
+relay_transport, sender_dependent_default_transport_maps,
+default_transport, sender_dependent_relayhost_maps
+and with the \fBtransport\fR(5) table.
+.PP
+On an intranet, specify the organizational domain name. If your
+internal DNS uses no MX records, specify the name of the intranet
+gateway host instead.
+.PP
+In the case of SMTP or LMTP delivery, specify one or more destinations
+in the form of a domain name, hostname, hostname:port, [hostname]:port,
+[hostaddress] or [hostaddress]:port, separated by comma or whitespace.
+The form [hostname] turns off MX lookups. Multiple destinations are
+supported in Postfix 3.5 and later.
+.PP
+If you're connected via UUCP, see the UUCP_README file for useful
+information.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+relayhost = $mydomain
+relayhost = [gateway.example.com]
+relayhost = mail1.example:587, mail2.example:587
+relayhost = [an.ip.add.ress]
+.fi
+.ad
+.ft R
+.SH relocated_maps (default: empty)
+Optional lookup tables with new contact information for users or
+domains that no longer exist.  The table format and lookups are
+documented in \fBrelocated\fR(5).
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.PP
+If you use this feature, run "\fBpostmap /etc/postfix/relocated\fR" to
+build the necessary DBM or DB file after change, then "\fBpostfix
+reload\fR" to make the changes visible.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+relocated_maps = dbm:/etc/postfix/relocated
+relocated_maps = hash:/etc/postfix/relocated
+.fi
+.ad
+.ft R
+.SH remote_header_rewrite_domain (default: empty)
+Rewrite or add message headers in mail from remote clients if
+the remote_header_rewrite_domain parameter value is non\-empty,
+updating incomplete addresses with the domain specified in the
+remote_header_rewrite_domain parameter, and adding missing headers.
+.PP
+The
+local_header_rewrite_clients parameter controls what clients Postfix
+considers local.
+.PP
+Examples:
+.PP
+The safe setting: append "domain.invalid" to incomplete header
+addresses from remote SMTP clients, so that those addresses cannot
+be confused with local addresses.
+.sp
+.in +4
+.nf
+.na
+.ft C
+remote_header_rewrite_domain = domain.invalid
+.fi
+.ad
+.ft R
+.in -4
+.PP
+The default, purist, setting: don't rewrite headers from remote
+clients at all.
+.sp
+.in +4
+.nf
+.na
+.ft C
+remote_header_rewrite_domain =
+.fi
+.ad
+.ft R
+.in -4
+.SH require_home_directory (default: no)
+Require that a \fBlocal\fR(8) recipient's home directory exists
+before mail delivery is attempted. By default this test is disabled.
+It can be useful for environments that import home directories to
+the mail server (IMPORTING HOME DIRECTORIES IS NOT RECOMMENDED).
+.SH reset_owner_alias (default: no)
+Reset the \fBlocal\fR(8) delivery agent's idea of the owner\-alias
+attribute, when delivering mail to a child alias that does not have
+its own owner alias.
+.PP
+This feature is available in Postfix 2.8 and later. With older
+Postfix releases, the behavior is as if this parameter is set to
+"yes".
+.PP
+As documented in \fBaliases\fR(5), when an alias \fIname\fR has a
+companion alias named owner\-\fIname\fR, this will replace the
+envelope sender address, so that delivery errors will be
+reported to the owner alias instead of the sender. This configuration
+is recommended for mailing lists.
+.PP
+A less known property of the owner alias is that it also forces
+the \fBlocal\fR(8) delivery agent to write local and remote addresses
+from alias expansion to a new queue file, instead of attempting to
+deliver mail to local addresses as soon as they come out of alias
+expansion.
+.PP
+Writing local addresses from alias expansion to a new queue
+file allows for robust handling of temporary delivery errors: errors
+with one local member have no effect on deliveries to other members
+of the list.  On the other hand, delivery to local addresses as
+soon as they come out of alias expansion is fragile: a temporary
+error with one local address from alias expansion will cause the
+entire alias to be expanded repeatedly until the error goes away,
+or until the message expires in the queue.  In that case, a problem
+with one list member results in multiple message deliveries to other
+list members.
+.PP
+The default behavior of Postfix 2.8 and later is to keep the
+owner\-alias attribute of the parent alias, when delivering mail to
+a child alias that does not have its own owner alias. Then, local
+addresses from that child alias will be written to a new queue file,
+and a temporary error with one local address will not affect delivery
+to other mailing list members.
+.PP
+Unfortunately, older Postfix releases reset the owner\-alias
+attribute when delivering mail to a child alias that does not have
+its own owner alias. To be precise, this resets only the decision
+to create a new queue file, not the decision to override the envelope
+sender address. The \fBlocal\fR(8) delivery agent then attempts to
+deliver local addresses as soon as they come out of child alias
+expansion.  If delivery to any address from child alias expansion
+fails with a temporary error condition, the entire mailing list may
+be expanded repeatedly until the mail expires in the queue, resulting
+in multiple deliveries of the same message to mailing list members.
+.SH resolve_dequoted_address (default: yes)
+Resolve a recipient address safely instead of correctly, by
+looking inside quotes.
+.PP
+By default, the Postfix address resolver does not quote the
+address localpart as per RFC 822, so that additional @ or % or !
+operators remain visible. This behavior is safe but it is also
+technically incorrect.
+.PP
+If you specify "resolve_dequoted_address = no", then
+the Postfix
+resolver will not know about additional @ etc. operators in the
+address localpart. This opens opportunities for obscure mail relay
+attacks with user@domain@domain addresses when Postfix provides
+backup MX service for Sendmail systems.
+.SH resolve_null_domain (default: no)
+Resolve an address that ends in the "@" null domain as if the
+local hostname were specified, instead of rejecting the address as
+invalid.
+.PP
+This feature is available in Postfix 2.1 and later.
+Earlier versions always resolve the null domain as the local
+hostname.
+.PP
+The Postfix SMTP server uses this feature to reject mail from
+or to addresses that end in the "@" null domain, and from addresses
+that rewrite into a form that ends in the "@" null domain.
+.SH resolve_numeric_domain (default: no)
+Resolve "user@ipaddress" as "user@[ipaddress]", instead of
+rejecting the address as invalid.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH respectful_logging (default: see 'postconf \-d' output)
+Avoid logging that implies white is better than black. Instead
+use 'allowlist', 'denylist', and variations of those words.
+.PP
+This feature is available in Postfix 3.6 and later.
+.SH rewrite_service_name (default: rewrite)
+The name of the address rewriting service. This service rewrites
+addresses to standard form and resolves them to a (delivery method,
+next\-hop host, recipient) triple.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH sample_directory (default: /etc/postfix)
+The name of the directory with example Postfix configuration files.
+Starting with Postfix 2.1, these files have been replaced with the
+\fBpostconf\fR(5) manual page.
+.SH send_cyrus_sasl_authzid (default: no)
+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
+The non\-default setting "yes" enables the behavior of older
+Postfix versions.  These always send a SASL authzid that is equal
+to the SASL authcid, but this causes interoperability problems
+with some SMTP servers.
+.PP
+This feature is available in Postfix 2.4.4 and later.
+.SH sender_based_routing (default: no)
+This parameter should not be used. It was replaced by sender_dependent_relayhost_maps
+in Postfix version 2.3.
+.SH sender_bcc_maps (default: empty)
+Optional BCC (blind carbon\-copy) address lookup tables, indexed
+by envelope sender address.  The BCC address (multiple results are not
+supported) is added when mail enters from outside of Postfix.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.PP
+The table search order is as follows:
+.IP \(bu
+Look up the "user+extension@domain.tld" address including the
+optional address extension.
+.IP \(bu
+Look up the "user@domain.tld" address without the optional
+address extension.
+.IP \(bu
+Look up the "user+extension" address local part when the
+sender domain equals $myorigin, $mydestination, $inet_interfaces
+or $proxy_interfaces.
+.IP \(bu
+Look up the "user" address local part when the sender domain
+equals $myorigin, $mydestination, $inet_interfaces or $proxy_interfaces.
+.IP \(bu
+Look up the "@domain.tld" part.
+.br
+.PP
+Note: with Postfix 2.3 and later the BCC address is added as if it
+was specified with NOTIFY=NONE. The sender will not be notified
+when the BCC address is undeliverable, as long as all down\-stream
+software implements RFC 3461.
+.PP
+Note: with Postfix 2.2 and earlier the sender will be notified
+when the BCC address is undeliverable.
+.PP
+Note: automatic BCC recipients are produced only for new mail.
+To avoid mailer loops, automatic BCC recipients are not generated
+after Postfix forwards mail internally, or after Postfix generates
+mail itself.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+sender_bcc_maps = hash:/etc/postfix/sender_bcc
+.fi
+.ad
+.ft R
+.PP
+After a change, run "\fBpostmap /etc/postfix/sender_bcc\fR".
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH sender_canonical_classes (default: envelope_sender, header_sender)
+What addresses are subject to sender_canonical_maps address
+mapping.  By default, sender_canonical_maps address mapping is
+applied to envelope sender addresses, and to header sender addresses.
+.PP
+Specify one or more of: envelope_sender, header_sender
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH sender_canonical_maps (default: empty)
+Optional address mapping lookup tables for envelope and header
+sender addresses.
+The table format and lookups are documented in \fBcanonical\fR(5).
+.PP
+Example: you want to rewrite the SENDER address "user@ugly.example"
+to "user@pretty.example", while still being able to send mail to
+the RECIPIENT address "user@ugly.example".
+.PP
+Note: $sender_canonical_maps is processed before $canonical_maps.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+sender_canonical_maps = hash:/etc/postfix/sender_canonical
+.fi
+.ad
+.ft R
+.SH sender_dependent_default_transport_maps (default: empty)
+A sender\-dependent override for the global default_transport
+parameter setting. The tables are searched by the envelope sender
+address and @domain. A lookup result of DUNNO terminates the search
+without overriding the global default_transport parameter setting.
+This information is overruled with the \fBtransport\fR(5) table.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.PP
+Note: this overrides default_transport, not transport_maps, and
+therefore the expected syntax is that of default_transport, not the
+syntax of transport_maps.  Specifically, this does not support the
+transport_maps syntax for null transport, null nexthop, or null
+email addresses.
+.PP
+For safety reasons, this feature does not allow $number
+substitutions in regular expression maps.
+.PP
+This feature is available in Postfix 2.7 and later.
+.SH sender_dependent_relayhost_maps (default: empty)
+A sender\-dependent override for the global relayhost parameter
+setting. The tables are searched by the envelope sender address and
+@domain. A lookup result of DUNNO terminates the search without
+overriding the global relayhost parameter setting (Postfix 2.6 and
+later). This information is overruled with relay_transport,
+sender_dependent_default_transport_maps, default_transport and with
+the \fBtransport\fR(5) table.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.PP
+For safety reasons, this feature does not allow $number
+substitutions in regular expression maps.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH sendmail_fix_line_endings (default: always)
+Controls how the Postfix sendmail command converts email message
+line endings from <CR><LF> into UNIX format (<LF>).
+.IP "\fBalways\fR"
+Always convert message lines ending
+in <CR><LF>. This setting is the default with Postfix
+2.9 and later.
+.br
+.IP "\fBstrict\fR"
+Convert message lines ending in
+<CR><LF> only if the first input line ends in
+<CR><LF>. This setting is backwards\-compatible with
+Postfix 2.8 and earlier.
+.br
+.IP "\fBnever\fR"
+Never convert message lines ending in
+<CR><LF>. This setting exists for completeness only.
+.br
+.br
+.PP
+This feature is available in Postfix 2.9 and later.
+.SH sendmail_path (default: see "postconf \-d" output)
+A Sendmail compatibility feature that specifies the location of
+the Postfix \fBsendmail\fR(1) command. This command can be used to
+submit mail into the Postfix queue.
+.SH service_name (read\-only)
+The master.cf service name of a Postfix daemon process. This
+can be used to distinguish the logging from different services that
+use the same program name.
+.PP
+Example master.cf entries:
+.PP
+.nf
+.na
+.ft C
+# Distinguish inbound MTA logging from submission and smtps logging.
+smtp      inet  n       \-       n       \-       \-       smtpd
+submission inet n       \-       n       \-       \-       smtpd
+    \-o syslog_name=postfix/$service_name
+smtps     inet  n       \-       n       \-       \-       smtpd
+    \-o syslog_name=postfix/$service_name
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+# Distinguish outbound MTA logging from inbound relay logging.
+smtp      unix  \-       \-       n       \-       \-       smtp
+relay     unix  \-       \-       n       \-       \-       smtp
+    \-o syslog_name=postfix/$service_name
+.fi
+.ad
+.ft R
+.SH service_throttle_time (default: 60s)
+How long the Postfix \fBmaster\fR(8) waits before forking a server that
+appears to be malfunctioning.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH setgid_group (default: postdrop)
+The group ownership of set\-gid Postfix commands and of group\-writable
+Postfix directories. When this parameter value is changed you need
+to re\-run "\fBpostfix set\-permissions\fR" (with Postfix version 2.0 and
+earlier: "\fB/etc/postfix/post\-install set\-permissions\fR".
+.SH shlib_directory (default: see 'postconf \-d' output)
+The location of Postfix dynamically\-linked libraries
+(libpostfix\-*.so), and the default location of Postfix database
+plugins (postfix\-*.so) that have a relative pathname in the
+dynamicmaps.cf file.  The shlib_directory parameter defaults to
+"no" when Postfix dynamically\-linked libraries and database plugins
+are disabled at compile time, otherwise it typically defaults to
+/usr/lib/postfix or /usr/local/lib/postfix.
+.PP
+Notes:
+.IP \(bu
+The directory specified with shlib_directory should contain
+only Postfix\-related files. Postfix dynamically\-linked libraries
+and database plugins should not be installed in a "public" system
+directory such as /usr/lib or /usr/local/lib. Linking Postfix
+dynamically\-linked library files or database plugins into non\-Postfix
+programs is not supported.  Postfix dynamically\-linked libraries
+and database plugins implement a Postfix\-internal API that changes
+without maintaining compatibility.
+.IP \(bu
+You can change the shlib_directory value after Postfix is
+built. However, you may have to run ldconfig or equivalent to prevent
+Postfix programs from failing because the libpostfix\-*.so files are
+not found.  No ldconfig command is needed if you keep the libpostfix\-*.so
+files in the compiled\-in default $shlib_directory location.
+.br
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH show_user_unknown_table_name (default: yes)
+Display the name of the recipient table in the "User unknown"
+responses.  The extra detail makes troubleshooting easier but also
+reveals information that is nobody else's business.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH showq_service_name (default: showq)
+The name of the \fBshowq\fR(8) service. This service produces mail queue
+status reports.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH smtp_address_preference (default: any)
+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. This feature has no effect
+unless the inet_protocols setting enables both IPv4 and IPv6.
+.PP
+Postfix SMTP client address preference has evolved. With Postfix
+2.8 the default is "ipv6"; earlier implementations are hard\-coded
+to prefer IPv6 over IPv4.
+.PP
+Notes for mail delivery between sites that have both IPv4 and
+IPv6 connectivity:
+.IP \(bu
+The setting "smtp_address_preference = ipv6" is unsafe.
+It can fail to deliver mail when there is an outage that affects
+IPv6, while the destination is still reachable over IPv4.
+.IP \(bu
+The setting "smtp_address_preference = any" is safe. With
+this, mail will eventually be delivered even if there is an outage
+that affects IPv6 or IPv4, as long as it does not affect both.
+.br
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH smtp_address_verify_target (default: rcpt)
+In the context of email address verification, the SMTP protocol
+stage that determines whether an email address is deliverable.
+Specify one of "rcpt" or "data".  The latter is needed with remote
+SMTP servers that reject recipients after the DATA command. Use
+transport_maps to apply this feature selectively:
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    transport_maps = hash:/etc/postfix/transport
+.fi
+.ad
+.ft R
+.in -4
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/transport:
+    smtp\-domain\-that\-verifies\-after\-data    smtp\-data\-target:
+    lmtp\-domain\-that\-verifies\-after\-data    lmtp\-data\-target:
+.fi
+.ad
+.ft R
+.in -4
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/master.cf:
+    smtp\-data\-target    unix    \-    \-    n    \-    \-    smtp
+        \-o smtp_address_verify_target=data
+    lmtp\-data\-target    unix    \-    \-    n    \-    \-    lmtp
+        \-o lmtp_address_verify_target=data
+.fi
+.ad
+.ft R
+.in -4
+.PP
+Unselective use of the "data" target does no harm, but will
+result in unnecessary "lost connection after DATA" events at remote
+SMTP/LMTP servers.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH smtp_always_send_ehlo (default: yes)
+Always send EHLO at the start of an SMTP session.
+.PP
+With "smtp_always_send_ehlo = no", the Postfix SMTP client sends
+EHLO only when
+the word "ESMTP" appears in the server greeting banner (example:
+220 spike.porcupine.org ESMTP Postfix).
+.SH smtp_balance_inet_protocols (default: yes)
+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
+This avoids an interoperability problem when a destination resolves
+to primarily IPv6 addresses, the smtp_address_limit feature eliminates
+most or all IPv4 addresses, and the destination is not reachable over
+IPv6.
+.PP
+This feature is available in Postfix 3.3 and later.
+.SH smtp_bind_address (default: empty)
+An optional numerical network address that the Postfix SMTP client
+should bind to when making an IPv4 connection.
+.PP
+This can be specified in the main.cf file for all SMTP clients, or
+it can be specified in the master.cf file for a specific client,
+for example:
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/master.cf:
+    smtp ... smtp \-o smtp_bind_address=11.22.33.44
+.fi
+.ad
+.ft R
+.in -4
+.PP
+See smtp_bind_address_enforce for how Postfix should handle
+errors (Postfix 3.7 and later).
+.PP
+Note 1: when inet_interfaces specifies no more than one IPv4
+address, and that address is a non\-loopback address, it is
+automatically used as the smtp_bind_address.  This supports virtual
+IP hosting, but can be a problem on multi\-homed firewalls. See the
+inet_interfaces documentation for more detail.
+.PP
+Note 2: address information may be enclosed inside [],
+but this form is not required here.
+.SH smtp_bind_address6 (default: empty)
+An optional numerical network address that the Postfix SMTP client
+should bind to when making an IPv6 connection.
+.PP
+This feature is available in Postfix 2.2 and later.
+.PP
+This can be specified in the main.cf file for all SMTP clients, or
+it can be specified in the master.cf file for a specific client,
+for example:
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/master.cf:
+    smtp ... smtp \-o smtp_bind_address6=1:2:3:4:5:6:7:8
+.fi
+.ad
+.ft R
+.in -4
+.PP
+See smtp_bind_address_enforce for how Postfix should handle
+errors (Postfix 3.7 and later).
+.PP
+Note 1: when inet_interfaces specifies no more than one IPv6
+address, and that address is a non\-loopback address, it is
+automatically used as the smtp_bind_address6.  This supports virtual
+IP hosting, but can be a problem on multi\-homed firewalls. See the
+inet_interfaces documentation for more detail.
+.PP
+Note 2: address information may be enclosed inside [],
+but this form is not recommended here.
+.SH smtp_bind_address_enforce (default: no)
+Defer delivery when the Postfix SMTP client cannot apply the
+smtp_bind_address or smtp_bind_address6 setting. By default, the
+Postfix SMTP client will continue delivery after logging a warning.
+.PP
+This feature is available in Postfix 3.7 and later.
+.SH smtp_body_checks (default: empty)
+Restricted \fBbody_checks\fR(5) tables for the Postfix SMTP client.
+These tables are searched while mail is being delivered.  Actions
+that change the delivery time or destination are not available.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH smtp_cname_overrides_servername (default: version dependent)
+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. The value "no"
+hardens Postfix smtp_tls_per_site hostname\-based policies against
+false hostname information in DNS CNAME records, and makes SASL
+password file lookups more predictable. This is the default setting
+as of Postfix 2.3.
+.PP
+When DNS CNAME records are validated with secure DNS lookups
+(smtp_dns_support_level = dnssec), they are always allowed to
+override the above servername (Postfix 2.11 and later).
+.PP
+This feature is available in Postfix 2.2.9 and later.
+.SH smtp_connect_timeout (default: 30s)
+The Postfix SMTP client time limit for completing a TCP connection, or
+zero (use the operating system built\-in time limit).
+.PP
+When no connection can be made within the deadline, the Postfix
+SMTP client
+tries the next address on the mail exchanger list. Specify 0 to
+disable the time limit (i.e. use whatever timeout is implemented by
+the operating system).
+.PP
+Specify a non\-negative time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH smtp_connection_cache_destinations (default: empty)
+Permanently enable SMTP connection caching for the specified
+destinations.  With SMTP connection caching, a connection is not
+closed immediately after completion of a mail transaction.  Instead,
+the connection is kept open for up to $smtp_connection_cache_time_limit
+seconds.  This allows connections to be reused for other deliveries,
+and can improve mail delivery performance.
+.PP
+Specify a comma or white space separated list of destinations
+or pseudo\-destinations:
+.IP \(bu
+if mail is sent without a relay host: a domain name (the
+right\-hand side of an email address, without the [] around a numeric
+IP address),
+.IP \(bu
+if mail is sent via a relay host: a relay host name (without
+[] or non\-default TCP port), as specified in main.cf or in the
+transport map,
+.IP \(bu
+if mail is sent via a UNIX\-domain socket: a pathname (without
+the unix: prefix),
+.IP \(bu
+a /file/name with domain names and/or relay host names as
+defined above,
+.IP \(bu
+a "type:table" with domain names and/or relay host names on
+the left\-hand side.  The right\-hand side result from "type:table"
+lookups is ignored.
+.br
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtp_connection_cache_on_demand (default: yes)
+Temporarily enable SMTP connection caching while a destination
+has a high volume of mail in the active queue.  With SMTP connection
+caching, a connection is not closed immediately after completion
+of a mail transaction.  Instead, the connection is kept open for
+up to $smtp_connection_cache_time_limit seconds.  This allows
+connections to be reused for other deliveries, and can improve mail
+delivery performance.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtp_connection_cache_time_limit (default: 2s)
+When SMTP connection caching is enabled, the amount of time that
+an unused SMTP client socket is kept open before it is closed.  Do
+not specify larger values without permission from the remote sites.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtp_connection_reuse_count_limit (default: 0)
+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).  With a reuse count limit of N, a connection is used up to
+N+1 times.
+.PP
+NOTE: This feature is unsafe. When a high\-volume destination
+has multiple inbound MTAs, then the slowest inbound MTA will attract
+the most connections to that destination.  This limitation does not
+exist with the smtp_connection_reuse_time_limit feature.
+.PP
+This feature is available in Postfix 2.11.
+.SH smtp_connection_reuse_time_limit (default: 300s)
+The amount of time during which Postfix will use an SMTP
+connection repeatedly.  The timer starts when the connection is
+initiated (i.e. it includes the connect, greeting and helo latency,
+in addition to the latencies of subsequent mail delivery transactions).
+.PP
+This feature addresses a performance stability problem with
+remote SMTP servers. This problem is not specific to Postfix: it
+can happen when any MTA sends large amounts of SMTP email to a site
+that has multiple MX hosts.
+.PP
+The problem starts when one of a set of MX hosts becomes slower
+than the rest.  Even though SMTP clients connect to fast and slow
+MX hosts with equal probability, the slow MX host ends up with more
+simultaneous inbound connections than the faster MX hosts, because
+the slow MX host needs more time to serve each client request.
+.PP
+The slow MX host becomes a connection attractor.  If one MX
+host becomes N times slower than the rest, it dominates mail delivery
+latency unless there are more than N fast MX hosts to counter the
+effect. And if the number of MX hosts is smaller than N, the mail
+delivery latency becomes effectively that of the slowest MX host
+divided by the total number of MX hosts.
+.PP
+The solution uses connection caching in a way that differs from
+Postfix version 2.2.  By limiting the amount of time during which a connection
+can be used repeatedly (instead of limiting the number of deliveries
+over that connection), Postfix not only restores fairness in the
+distribution of simultaneous connections across a set of MX hosts,
+it also favors deliveries over connections that perform well, which
+is exactly what we want.
+.PP
+The default reuse time limit, 300s, is comparable to the various
+smtp transaction timeouts which are fair estimates of maximum excess
+latency for a slow delivery.  Note that hosts may accept thousands
+of messages over a single connection within the default connection
+reuse time limit. This number is much larger than the default Postfix
+version 2.2 limit of 10 messages per cached connection. It may prove necessary
+to lower the limit to avoid interoperability issues with MTAs that
+exhibit bugs when many messages are delivered via a single connection.
+A lower reuse time limit risks losing the benefit of connection
+reuse when the average connection and mail delivery latency exceeds
+the reuse time limit.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtp_data_done_timeout (default: 600s)
+The Postfix SMTP client time limit for sending the SMTP ".", and
+for receiving the remote SMTP server response.
+.PP
+When no response is received within the deadline, a warning is
+logged that the mail may be delivered multiple times.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH smtp_data_init_timeout (default: 120s)
+The Postfix SMTP client time limit for sending the SMTP DATA command,
+and for receiving the remote SMTP server response.
+.PP
+Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH smtp_data_xfer_timeout (default: 180s)
+The Postfix SMTP client time limit for sending the SMTP message content.
+When the connection makes no progress for more than $smtp_data_xfer_timeout
+seconds the Postfix SMTP client terminates the transfer.
+.PP
+Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH smtp_defer_if_no_mx_address_found (default: no)
+Defer mail delivery when no MX record resolves to an IP address.
+.PP
+The default (no) is to return the mail as undeliverable. With older
+Postfix versions the default was to keep trying to deliver the mail
+until someone fixed the MX record or until the mail was too old.
+.PP
+Note: the Postfix SMTP client always ignores MX records with equal
+or worse preference
+than the local MTA itself.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH smtp_delivery_status_filter (default: $default_delivery_status_filter)
+Optional filter for the \fBsmtp\fR(8) delivery agent to change the
+delivery status code or explanatory text of successful or unsuccessful
+deliveries.  See default_delivery_status_filter for details.
+.PP
+NOTE: This feature modifies Postfix SMTP client error or non\-error
+messages that may or may not be derived from remote SMTP server
+responses.  In contrast, the smtp_reply_filter feature modifies
+remote SMTP server responses only.
+.SH smtp_destination_concurrency_limit (default: $default_destination_concurrency_limit)
+The maximal number of parallel deliveries to the same destination
+via the smtp message delivery transport. This limit is enforced by
+the queue manager. The message delivery transport name is the first
+field in the entry in the master.cf file.
+.SH smtp_destination_recipient_limit (default: $default_destination_recipient_limit)
+The maximal number of recipients per message for the smtp
+message delivery transport. This limit is enforced by the queue
+manager. The message delivery transport name is the first field in
+the entry in the master.cf file.
+.PP
+Setting this parameter to a value of 1 changes the meaning of
+smtp_destination_concurrency_limit from concurrency per domain
+into concurrency per recipient.
+.SH smtp_discard_ehlo_keyword_address_maps (default: empty)
+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. See smtp_discard_ehlo_keywords for details. The
+table is not indexed by hostname for consistency with
+smtpd_discard_ehlo_keyword_address_maps.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtp_discard_ehlo_keywords (default: empty)
+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.
+.PP
+This feature is available in Postfix 2.2 and later.
+.PP
+Notes:
+.IP \(bu
+Specify the \fBsilent\-discard\fR pseudo keyword to prevent
+this action from being logged.
+.IP \(bu
+Use the smtp_discard_ehlo_keyword_address_maps feature to
+discard EHLO keywords selectively.
+.br
+.SH smtp_dns_reply_filter (default: empty)
+Optional filter for Postfix SMTP client DNS lookup results.
+Specify zero or more lookup tables.  The lookup tables are searched
+in the given order for a match with the DNS lookup result, converted
+to the following form:
+.PP
+.nf
+.na
+.ft C
+    \fIname ttl class type preference value\fR
+.fi
+.ad
+.ft R
+.PP
+The \fIclass\fR field is always "IN", the \fIpreference\fR
+field exists only for MX records, the names of hosts, domains, etc.
+end in ".", and those names are in ASCII form (xn\-\-mumble form in
+the case of UTF8 names).
+.PP
+When a match is found, the table lookup result specifies an
+action.  By default, the table query and the action name are
+case\-insensitive.  Currently, only the \fBIGNORE\fR action is
+implemented.
+.PP
+Notes:
+.IP \(bu
+Postfix DNS reply filters have no effect on implicit DNS
+lookups through nsswitch.conf or equivalent mechanisms.
+.IP \(bu
+The Postfix SMTP/LMTP client uses smtp_dns_reply_filter
+and lmtp_dns_reply_filter only to discover a remote SMTP or LMTP
+service (record types MX, A, AAAA, and TLSA).  These lookups are
+also made to implement the features reject_unverified_sender and
+reject_unverified_recipient.
+.IP \(bu
+The Postfix SMTP/LMTP client defers mail delivery when
+a filter removes all lookup results from a successful query.
+.IP \(bu
+Postfix SMTP server uses smtpd_dns_reply_filter only to
+look up MX, A, AAAA, and TXT records to implement the features
+reject_unknown_helo_hostname, reject_unknown_sender_domain,
+reject_unknown_recipient_domain, reject_rbl_*, and reject_rhsbl_*.
+.IP \(bu
+The Postfix SMTP server logs a warning or defers mail
+delivery when a filter removes all lookup results from a successful
+query.
+.br
+.PP
+Example: ignore Google AAAA records in Postfix SMTP client DNS
+lookups, because Google sometimes hard\-rejects mail from IPv6 clients
+with valid PTR etc. records.
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    smtp_dns_reply_filter = pcre:/etc/postfix/smtp_dns_reply_filter
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/smtp_dns_reply_filter:
+    # /domain ttl IN AAAA address/ action, all case\-insensitive.
+    # Note: the domain name ends in ".".
+    /^\eS+\e.google\e.com\e.\es+\eS+\es+\eS+\es+AAAA\es+/ IGNORE
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH smtp_dns_resolver_options (default: empty)
+DNS Resolver options for the Postfix SMTP client.  Specify zero
+or more of the following options, separated by comma or whitespace.
+Option names are case\-sensitive. Some options refer to domain names
+that are specified in the file /etc/resolv.conf or equivalent.
+.IP "\fBres_defnames\fR"
+Append the current domain name to single\-component names (those
+that do not contain a "." character). This can produce incorrect
+results, and is the hard\-coded behavior prior to Postfix 2.8.
+.br
+.IP "\fBres_dnsrch\fR"
+Search for host names in the current domain and in parent
+domains. This can produce incorrect results and is therefore not
+recommended.
+.br
+.br
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH smtp_dns_support_level (default: empty)
+Level of DNS support in the Postfix SMTP client.  With
+"smtp_dns_support_level" left at its empty default value, the legacy
+"disable_dns_lookups" parameter controls whether DNS is enabled in
+the Postfix SMTP client, otherwise the legacy parameter is ignored.
+.PP
+Specify one of the following:
+.IP "\fBdisabled\fR"
+Disable DNS lookups.  No MX lookups are performed and hostname
+to address lookups are unconditionally "native".  This setting is
+not appropriate for hosts that deliver mail to the public Internet.
+Some obsolete how\-to documents recommend disabling DNS lookups in
+some configurations with content_filters.  This is no longer required
+and strongly discouraged.
+.br
+.IP "\fBenabled\fR"
+Enable DNS lookups.  Nexthop destination domains not enclosed
+in "[]" will be subject to MX lookups.  If "dns" and "native" are
+included in the "smtp_host_lookup" parameter value, DNS will be
+queried first to resolve MX\-host A records, followed by "native"
+lookups if no answer is found in DNS.
+.br
+.IP "\fBdnssec\fR"
+Enable DNSSEC
+lookups.  The "dnssec" setting differs from the "enabled" setting
+above in the following ways:
+.IP \(bu
+Any MX lookups will set
+RES_USE_DNSSEC and RES_USE_EDNS0 to request DNSSEC\-validated
+responses. If the MX response is DNSSEC\-validated the corresponding
+hostnames are considered validated.
+.IP \(bu
+The address lookups of
+validated hostnames are also validated, (provided of course
+"smtp_host_lookup" includes "dns", see below).
+.IP \(bu
+Temporary
+failures in DNSSEC\-enabled hostname\-to\-address resolution block any
+"native" lookups.  Additional "native" lookups only happen when
+DNSSEC lookups hard\-fail (NODATA or NXDOMAIN).
+.br
+.br
+.br
+.PP
+The Postfix SMTP client considers non\-MX "[nexthop]" and
+"[nexthop]:port" destinations equivalent to statically\-validated
+MX records of the form "nexthop.  IN MX 0 nexthop."  Therefore,
+with "dnssec" support turned on, validated hostname\-to\-address
+lookups apply to the nexthop domain of any "[nexthop]" or
+"[nexthop]:port" destination.  This is also true for LMTP "inet:host"
+and "inet:host:port" destinations, as LMTP hostnames are never
+subject to MX lookups.
+.PP
+The "dnssec" setting is recommended only if you plan to use the
+dane or dane\-only TLS security
+level, otherwise enabling DNSSEC support in Postfix offers no
+additional security.  Postfix DNSSEC support relies on an upstream
+recursive nameserver that validates DNSSEC signatures.  Such a DNS
+server will always filter out forged DNS responses, even when Postfix
+itself is not configured to use DNSSEC.
+.PP
+When using Postfix DANE support the "smtp_host_lookup" parameter
+should include "dns", as DANE is not applicable
+to hosts resolved via "native" lookups.
+.PP
+As mentioned above, Postfix is not a validating stub
+resolver; it relies on the system's configured DNSSEC\-validating
+recursive
+nameserver to perform all DNSSEC validation.  Since this
+nameserver's DNSSEC\-validated responses will be fully trusted, it
+is strongly recommended that the MTA host have a local DNSSEC\-validating
+recursive caching nameserver listening on a loopback address, and
+be configured to use only this nameserver for all lookups.  Otherwise,
+Postfix may remain subject to man\-in\-the\-middle attacks that forge
+responses from the recursive nameserver
+.PP
+DNSSEC support requires a version of Postfix compiled against a
+reasonably\-modern DNS \fBresolver\fR(3) library that implements the
+RES_USE_DNSSEC and RES_USE_EDNS0 resolver options.
+.PP
+This feature is available in Postfix 2.11 and later.
+.SH smtp_enforce_tls (default: no)
+Enforcement mode: require that remote SMTP servers use TLS
+encryption, and never send mail in the clear.  This also requires
+that the remote SMTP server hostname matches the information in
+the remote server certificate, and that the remote SMTP server
+certificate was issued by a CA that is trusted by the Postfix SMTP
+client. If the certificate doesn't verify or the hostname doesn't
+match, delivery is deferred and mail stays in the queue.
+.PP
+The server hostname is matched against all names provided as
+dNSNames in the SubjectAlternativeName.  If no dNSNames are specified,
+the CommonName is checked.  The behavior may be changed with the
+smtp_tls_enforce_peername option.
+.PP
+This option is useful only if you are definitely sure that you
+will only connect to servers that support RFC 2487 _and_ that
+provide valid server certificates.  Typical use is for clients that
+send all their email to a dedicated mailhub.
+.PP
+This feature is available in Postfix 2.2 and later. With
+Postfix 2.3 and later use smtp_tls_security_level instead.
+.SH smtp_fallback_relay (default: $fallback_relay)
+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. With Postfix 2.2 and earlier this parameter
+is called fallback_relay.
+.PP
+By default, smtp_fallback_relay is empty, mail is returned to
+the sender when a destination is not found, and delivery is deferred
+after it fails due to a non\-permanent error.
+.PP
+With bulk email deliveries, it can be beneficial to run the
+fallback relay MTA on the same host, so that it can reuse the sender
+IP address.  This speeds up deliveries that are delayed by IP\-based
+reputation systems (greylist, etc.).
+.PP
+The fallback relays must be SMTP destinations. Specify a domain,
+host, host:port, [host]:port, [address] or [address]:port; the form
+[host] turns off MX lookups.  If you specify multiple SMTP
+destinations, Postfix will try them in the specified order.
+.PP
+To prevent mailer loops between MX hosts and fall\-back hosts,
+Postfix version 2.2 and later will not use the fallback relays for
+destinations that it is MX host for (assuming DNS lookup is turned on).
+.SH smtp_generic_maps (default: empty)
+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.
+This is needed when the local machine does not have its own Internet
+domain name, but uses something like \fIlocaldomain.local\fR
+instead.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.PP
+The table format and lookups are documented in \fBgeneric\fR(5);
+examples are shown in the ADDRESS_REWRITING_README and
+STANDARD_CONFIGURATION_README documents.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtp_header_checks (default: empty)
+Restricted \fBheader_checks\fR(5) tables for the Postfix SMTP client.
+These tables are searched while mail is being delivered.  Actions
+that change the delivery time or destination are not available.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH smtp_helo_name (default: $myhostname)
+The hostname to send in the SMTP HELO or EHLO command.
+.PP
+The default value is the machine hostname.  Specify a hostname or
+[ip.add.re.ss].
+.PP
+This information can be specified in the main.cf file for all SMTP
+clients, or it can be specified in the master.cf file for a specific
+client, for example:
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/master.cf:
+    mysmtp ... smtp \-o smtp_helo_name=foo.bar.com
+.fi
+.ad
+.ft R
+.in -4
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH smtp_helo_timeout (default: 300s)
+The Postfix SMTP client time limit for sending the HELO or EHLO command,
+and for receiving the initial remote SMTP server response.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH smtp_host_lookup (default: dns)
+What mechanisms the Postfix SMTP client uses to look up a host's
+IP address.  This parameter is ignored when DNS lookups are disabled
+(see: disable_dns_lookups and smtp_dns_support_level).  The "dns"
+mechanism is always tried before "native" if both are listed.
+.PP
+Specify one of the following:
+.IP "\fBdns\fR"
+Hosts can be found in the DNS (preferred).
+.br
+.IP "\fBnative\fR"
+Use the native naming service only (nsswitch.conf, or equivalent
+mechanism).
+.br
+.IP "\fBdns, native\fR"
+Use the native service for hosts not found in the DNS.
+.br
+.br
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH smtp_line_length_limit (default: 998)
+The maximal length of message header and body lines that Postfix
+will send via SMTP. This limit does not include the <CR><LF>
+at the end of each line.  Longer lines are broken by inserting
+"<CR><LF><SPACE>", to minimize the damage to MIME
+formatted mail. Specify zero to disable this limit.
+.PP
+The Postfix limit of 998 characters not including <CR><LF>
+is consistent with the SMTP limit of 1000 characters including
+<CR><LF>.  The Postfix limit was 990 with Postfix 2.8
+and earlier.
+.SH smtp_mail_timeout (default: 300s)
+The Postfix SMTP client time limit for sending the MAIL FROM command,
+and for receiving the remote SMTP server response.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH smtp_mime_header_checks (default: empty)
+Restricted \fBmime_header_checks\fR(5) tables for the Postfix SMTP
+client. These tables are searched while mail is being delivered.
+Actions that change the delivery time or destination are not
+available.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH smtp_min_data_rate (default: 500)
+The minimum plaintext data transfer rate in bytes/second for
+DATA requests, when deadlines are enabled with smtp_per_request_deadline.
+After a write operation transfers N plaintext message bytes (possibly
+after TLS encryption), and after the DATA request deadline is
+decremented by the elapsed time of that write operation, the DATA
+request deadline is incremented by N/smtp_min_data_rate seconds.
+However, the deadline will never be incremented beyond the time
+limit specified with smtp_data_xfer_timeout.
+.PP
+This feature is available in Postfix 3.7 and later.
+.SH smtp_mx_address_limit (default: 5)
+The maximal number of MX (mail exchanger) IP addresses that can
+result from Postfix SMTP client mail exchanger lookups, or zero (no
+limit). Prior to
+Postfix version 2.3, this limit was disabled by default.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH smtp_mx_session_limit (default: 2)
+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). This restriction ignores sessions that fail to complete the
+SMTP initial handshake (Postfix version 2.2 and earlier) or that fail to
+complete the EHLO and TLS handshake (Postfix version 2.3 and later).
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH smtp_nested_header_checks (default: empty)
+Restricted \fBnested_header_checks\fR(5) tables for the Postfix SMTP
+client. These tables are searched while mail is being delivered.
+Actions that change the delivery time or destination are not
+available.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH smtp_never_send_ehlo (default: no)
+Never send EHLO at the start of an SMTP session. See also the
+smtp_always_send_ehlo parameter.
+.SH smtp_per_record_deadline (default: no)
+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).  This
+limits the impact from hostile peers that trickle data one byte at
+a time.
+.PP
+Note: when per\-record deadlines are enabled, a short timeout
+may cause problems with TLS over very slow network connections.
+The reasons are that a TLS protocol message can be up to 16 kbytes
+long (with TLSv1), and that an entire TLS protocol message must be
+sent or received within the per\-record deadline.
+.PP
+This feature is available in Postfix 2.9\-3.6. With older
+Postfix releases, the behavior is as if this parameter is set to
+"no". Postfix 3.7 and later use smtp_per_request_deadline.
+.SH smtp_per_request_deadline (default: no)
+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. The deadline limits only the time spent
+waiting for plaintext or TLS read or write calls, not time spent
+elsewhere. The per\-request deadline limits the impact from hostile
+peers that trickle data one byte at a time.
+.PP
+See smtp_min_data_rate for how the per\-request deadline is
+managed during the DATA phase.
+.PP
+Note: when per\-request deadlines are enabled, a short time limit
+may cause problems with TLS over very slow network connections. The
+reason is that a TLS protocol message can be up to 16 kbytes long
+(with TLSv1), and that an entire TLS protocol message must be
+transferred within the per\-request deadline.
+.PP
+This feature is available in Postfix 3.7 and later. A weaker
+feature, called smtp_per_record_deadline, is available with Postfix
+2.9\-3.6.
+.PP
+This feature is available in Postfix 3.7 and later.
+.SH smtp_pix_workaround_delay_time (default: 10s)
+How long the Postfix SMTP client pauses before sending
+".<CR><LF>" in order to work around the PIX firewall
+"<CR><LF>.<CR><LF>" bug.
+.PP
+Choosing too short a time makes this workaround ineffective when
+sending large messages over slow network connections.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH smtp_pix_workaround_maps (default: empty)
+Lookup tables, indexed by the remote SMTP server address, with
+per\-destination workarounds for CISCO PIX firewall bugs.  The table
+is not indexed by hostname for consistency with
+smtp_discard_ehlo_keyword_address_maps.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.PP
+This feature is available in Postfix 2.4 and later.
+.SH smtp_pix_workaround_threshold_time (default: 500s)
+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.
+.PP
+Specify a non\-negative time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+By default, the workaround is turned off for mail that is queued
+for less than 500 seconds. In other words, the workaround is normally
+turned off for the first delivery attempt.
+.PP
+Specify 0 to enable the PIX firewall
+"<CR><LF>.<CR><LF>" bug workaround upon the
+first delivery attempt.
+.SH smtp_pix_workarounds (default: disable_esmtp, delay_dotcrlf)
+A list that specifies zero or more workarounds for CISCO PIX
+firewall bugs. These workarounds are implemented by the Postfix
+SMTP client. Workaround names are separated by comma or space, and
+are case insensitive.  This parameter setting can be overruled with
+per\-destination smtp_pix_workaround_maps settings.
+.IP "\fBdelay_dotcrlf\fR
+Insert a delay before sending
+".<CR><LF>" after the end of the message content.  The
+delay is subject to the smtp_pix_workaround_delay_time and
+smtp_pix_workaround_threshold_time parameter settings.
+.br
+.IP "\fBdisable_esmtp\fR
+Disable all extended SMTP commands:
+send HELO instead of EHLO.
+.br
+.br
+.PP
+This feature is available in Postfix 2.4 and later. The default
+settings are backwards compatible with earlier Postfix versions.
+.SH smtp_quit_timeout (default: 300s)
+The Postfix SMTP client time limit for sending the QUIT command,
+and for receiving the remote SMTP server response.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH smtp_quote_rfc821_envelope (default: yes)
+Quote addresses in Postfix SMTP client MAIL FROM and RCPT TO commands
+as required
+by RFC 5321. This includes putting quotes around an address localpart
+that ends in ".".
+.PP
+The default is to comply with RFC 5321. If you have to send mail to
+a broken SMTP server, configure a special SMTP client in master.cf:
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/master.cf:
+    broken\-smtp . . . smtp \-o smtp_quote_rfc821_envelope=no
+.fi
+.ad
+.ft R
+.in -4
+.PP
+and route mail for the destination in question to the "broken\-smtp"
+message delivery with a \fBtransport\fR(5) table.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH smtp_randomize_addresses (default: yes)
+Randomize the order of equal\-preference MX host addresses.  This
+is a performance feature of the Postfix SMTP client.
+.SH smtp_rcpt_timeout (default: 300s)
+The Postfix SMTP client time limit for sending the SMTP RCPT TO
+command, and for receiving the remote SMTP server response.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH smtp_reply_filter (default: empty)
+A mechanism to transform replies from remote SMTP servers one
+line at a time.  This is a last\-resort tool to work around server
+replies that break interoperability with the Postfix SMTP client.
+Other uses involve fault injection to test Postfix's handling of
+invalid responses.
+.PP
+Notes:
+.IP \(bu
+In the case of a multi\-line reply, the Postfix SMTP client
+uses the final reply line's numerical SMTP reply code and enhanced
+status code.
+.IP \(bu
+The numerical SMTP reply code (XYZ) takes precedence over
+the enhanced status code (X.Y.Z).  When the enhanced status code
+initial digit differs from the SMTP reply code initial digit, or
+when no enhanced status code is present, the Postfix SMTP client
+uses a generic enhanced status code (X.0.0) instead.
+.br
+.PP
+Specify the name of a "type:table" lookup table. The search
+string is a single SMTP reply line as received from the remote SMTP
+server, except that the trailing <CR><LF> are removed.
+When the lookup succeeds, the result replaces the single SMTP reply
+line.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    smtp_reply_filter = pcre:/etc/postfix/reply_filter
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/reply_filter:
+    # Transform garbage into "250\-filler..." so that it looks like
+    # one line from a multi\-line reply. It does not matter what we
+    # substitute here as long it has the right syntax.  The Postfix
+    # SMTP client will use the final line's numerical SMTP reply
+    # code and enhanced status code.
+    !/^([2\-5][0\-9][0\-9]($|[\- ]))/ 250\-filler for garbage
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.7.
+.SH smtp_rset_timeout (default: 20s)
+The Postfix SMTP client time limit for sending the RSET command,
+and for receiving the remote SMTP server response. The SMTP client
+sends RSET in
+order to finish a recipient address probe, or to verify that a
+cached session is still usable.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH smtp_sasl_auth_cache_name (default: empty)
+An optional table to prevent repeated SASL authentication
+failures with the same remote SMTP server hostname, username and
+password. Each table (key, value) pair contains a server name, a
+username and password, and the full server response. This information
+is stored when a remote SMTP server rejects an authentication attempt
+with a 535 reply code.  As long as the smtp_sasl_password_maps
+information does not change, and as long as the smtp_sasl_auth_cache_name
+information does not expire (see smtp_sasl_auth_cache_time) the
+Postfix SMTP client avoids SASL authentication attempts with the
+same server, username and password, and instead bounces or defers
+mail as controlled with the smtp_sasl_auth_soft_bounce configuration
+parameter.
+.PP
+Use a per\-destination delivery concurrency of 1 (for example,
+"smtp_destination_concurrency_limit = 1",
+"relay_destination_concurrency_limit = 1", etc.), otherwise multiple
+delivery agents may experience a login failure at the same time.
+.PP
+The table must be accessed via the proxywrite service, i.e. the
+map name must start with "proxy:". The table should be stored under
+the directory specified with the data_directory parameter.
+.PP
+This feature uses cryptographic hashing to protect plain\-text
+passwords, and requires that Postfix is compiled with TLS support.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtp_sasl_auth_cache_name = proxy:btree:/var/lib/postfix/sasl_auth_cache
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH smtp_sasl_auth_cache_time (default: 90d)
+The maximal age of an smtp_sasl_auth_cache_name entry before it
+is removed.
+.PP
+Specify a non\-negative time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is d (days).
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH smtp_sasl_auth_enable (default: no)
+Enable SASL authentication in the Postfix SMTP client.  By default,
+the Postfix SMTP client uses no authentication.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtp_sasl_auth_enable = yes
+.fi
+.ad
+.ft R
+.SH smtp_sasl_auth_soft_bounce (default: yes)
+When a remote SMTP server rejects a SASL authentication request
+with a 535 reply code, defer mail delivery instead of returning
+mail as undeliverable. The latter behavior was hard\-coded prior to
+Postfix version 2.5.
+.PP
+Note: the setting "yes" overrides the global soft_bounce
+parameter, but the setting "no" does not.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+# Default as of Postfix 2.5
+smtp_sasl_auth_soft_bounce = yes
+# The old hard\-coded default
+smtp_sasl_auth_soft_bounce = no
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH smtp_sasl_mechanism_filter (default: empty)
+If non\-empty, a Postfix SMTP client filter for the remote SMTP
+server's list of offered SASL mechanisms.  Different client and
+server implementations may support different mechanism lists; by
+default, the Postfix SMTP client will use the intersection of the
+two. smtp_sasl_mechanism_filter specifies an optional third mechanism
+list to intersect with.
+.PP
+Specify mechanism names, "/file/name" patterns or "type:table"
+lookup tables. The right\-hand side result from "type:table" lookups
+is ignored. Specify "!pattern" to exclude a mechanism name from the
+list. The form "!/file/name" is supported only in Postfix version
+2.4 and later.
+.PP
+This feature is available in Postfix 2.2 and later.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+smtp_sasl_mechanism_filter = plain, login
+smtp_sasl_mechanism_filter = /etc/postfix/smtp_mechs
+smtp_sasl_mechanism_filter = !gssapi, !login, static:rest
+.fi
+.ad
+.ft R
+.SH smtp_sasl_password_maps (default: empty)
+Optional Postfix SMTP client lookup tables with one username:password
+entry per sender, remote hostname or next\-hop domain. Per\-sender
+lookup is done only when sender\-dependent authentication is enabled.
+If no username:password entry is found, then the Postfix SMTP client
+will not attempt to authenticate to the remote host.
+.PP
+The Postfix SMTP client opens the lookup table before going to
+chroot jail, so you can leave the password file in /etc/postfix.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.SH smtp_sasl_path (default: empty)
+Implementation\-specific information that the Postfix SMTP client
+passes through to
+the SASL plug\-in implementation that is selected with
+\fBsmtp_sasl_type\fR.  Typically this specifies the name of a
+configuration file or rendezvous point.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtp_sasl_security_options (default: noplaintext, noanonymous)
+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
+The following security features are defined for the \fBcyrus\fR
+client SASL implementation:
+.PP
+Specify zero or more of the following:
+.IP "\fBnoplaintext\fR"
+Disallow methods that use plaintext passwords.
+.br
+.IP "\fBnoactive\fR"
+Disallow methods subject to active (non\-dictionary) attack.
+.br
+.IP "\fBnodictionary\fR"
+Disallow methods subject to passive (dictionary) attack.
+.br
+.IP "\fBnoanonymous\fR"
+Disallow methods that allow anonymous authentication.
+.br
+.IP "\fBmutual_auth\fR"
+Only allow methods that provide mutual authentication (not
+available with SASL version 1).
+.br
+.br
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtp_sasl_security_options = noplaintext
+.fi
+.ad
+.ft R
+.SH smtp_sasl_tls_security_options (default: $smtp_sasl_security_options)
+The SASL authentication security options that the Postfix SMTP
+client uses for TLS encrypted SMTP sessions.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtp_sasl_tls_verified_security_options (default: $smtp_sasl_tls_security_options)
+The SASL authentication security options that the Postfix SMTP
+client uses for TLS encrypted SMTP sessions with a verified server
+certificate.
+.PP
+When mail is sent to the public MX host for the recipient's
+domain, server certificates are by default optional, and delivery
+proceeds even if certificate verification fails. For delivery via
+a submission service that requires SASL authentication, it may be
+appropriate to send plaintext passwords only when the connection
+to the server is strongly encrypted \fBand\fR the server identity
+is verified.
+.PP
+The smtp_sasl_tls_verified_security_options parameter makes it
+possible to only enable plaintext mechanisms when a secure connection
+to the server is available. Submission servers subject to this
+policy must either have verifiable certificates or offer suitable
+non\-plaintext SASL mechanisms.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH smtp_sasl_type (default: cyrus)
+The SASL plug\-in type that the Postfix SMTP client should use
+for authentication.  The available types are listed with the
+"\fBpostconf \-A\fR" command.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtp_send_dummy_mail_auth (default: no)
+Whether or not to append the "AUTH=<>" option to the MAIL
+FROM command in SASL\-authenticated SMTP sessions. The default is
+not to send this, to avoid problems with broken remote SMTP servers.
+Before Postfix 2.9 the behavior is as if "smtp_send_dummy_mail_auth
+= yes".
+.PP
+This feature is available in Postfix 2.9 and later.
+.SH smtp_send_xforward_command (default: no)
+Send the non\-standard XFORWARD command when the Postfix SMTP server
+EHLO response announces XFORWARD support.
+.PP
+This allows a Postfix SMTP delivery agent, used for injecting mail
+into
+a content filter, to forward the name, address, protocol and HELO
+name of the original client to the content filter and downstream
+queuing SMTP server. This can produce more useful logging than
+localhost[127.0.0.1] etc.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH smtp_sender_dependent_authentication (default: no)
+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.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtp_skip_4xx_greeting (default: yes)
+Skip SMTP servers that greet with a 4XX status code (go away, try
+again later).
+.PP
+By default, the Postfix SMTP client moves on the next mail exchanger.
+Specify
+"smtp_skip_4xx_greeting = no" if Postfix should defer delivery
+immediately.
+.PP
+This feature is available in Postfix 2.0 and earlier.
+Later Postfix versions always skip remote SMTP servers that greet
+with a
+4XX status code.
+.SH smtp_skip_5xx_greeting (default: yes)
+Skip remote SMTP servers that greet with a 5XX status code.
+.PP
+By default, the Postfix SMTP client moves on the next mail
+exchanger. Specify "smtp_skip_5xx_greeting = no" if Postfix should
+bounce the mail immediately. Caution: the latter behavior appears
+to contradict RFC 2821.
+.SH smtp_skip_quit_response (default: yes)
+Do not wait for the response to the SMTP QUIT command.
+.SH smtp_starttls_timeout (default: 300s)
+Time limit for Postfix SMTP client write and read operations
+during TLS startup and shutdown handshake procedures.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtp_tcp_port (default: smtp)
+The default TCP port that the Postfix SMTP client connects to.
+Specify a symbolic name (see \fBservices\fR(5)) or a numeric port.
+.SH smtp_tls_CAfile (default: empty)
+A file containing CA certificates of root CAs trusted to sign
+either remote SMTP server certificates or intermediate CA certificates.
+These are loaded into memory before the \fBsmtp\fR(8) client enters the
+chroot jail. If the number of trusted roots is large, consider using
+smtp_tls_CApath instead, but note that the latter directory must be
+present in the chroot jail if the \fBsmtp\fR(8) client is chrooted. This
+file may also be used to augment the client certificate trust chain,
+but it is best to include all the required certificates directly in
+$smtp_tls_cert_file (or, Postfix >= 3.4 $smtp_tls_chain_files).
+.PP
+Specify "smtp_tls_CAfile = /path/to/system_CA_file" to use
+ONLY the system\-supplied default Certification Authority certificates.
+.PP
+Specify "tls_append_default_CA = no" to prevent Postfix from
+appending the system\-supplied default CAs and trusting third\-party
+certificates.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtp_tls_CAfile = /etc/postfix/CAcert.pem
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtp_tls_CApath (default: empty)
+Directory with PEM format Certification Authority certificates
+that the Postfix SMTP client uses to verify a remote SMTP server
+certificate.  Don't forget to create the necessary "hash" links
+with, for example, "$OPENSSL_HOME/bin/c_rehash /etc/postfix/certs".
+.PP
+To use this option in chroot mode, this directory (or a copy)
+must be inside the chroot jail.
+.PP
+Specify "smtp_tls_CApath = /path/to/system_CA_directory" to
+use ONLY the system\-supplied default Certification Authority certificates.
+.PP
+Specify "tls_append_default_CA = no" to prevent Postfix from
+appending the system\-supplied default CAs and trusting third\-party
+certificates.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtp_tls_CApath = /etc/postfix/certs
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtp_tls_block_early_mail_reply (default: no)
+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.
+The attack would succeed with non\-Postfix SMTP servers that reply
+to the malicious HELO, MAIL, RCPT, DATA commands after negotiating
+the Postfix SMTP client TLS session.
+.PP
+This feature is available in Postfix 2.7.
+.SH smtp_tls_cert_file (default: empty)
+File with the Postfix SMTP client RSA certificate in PEM format.
+This file may also contain the Postfix SMTP client private RSA key, and
+these may be the same as the Postfix SMTP server RSA certificate and key
+file.  With Postfix >= 3.4 the preferred way to configure client keys
+and certificates is via the "smtp_tls_chain_files" parameter.
+.PP
+Do not configure client certificates unless you \fBmust\fR present
+client TLS certificates to one or more servers. Client certificates are
+not usually needed, and can cause problems in configurations that work
+well without them. The recommended setting is to let the defaults stand:
+.sp
+.in +4
+.nf
+.na
+.ft C
+smtp_tls_cert_file =
+smtp_tls_key_file =
+smtp_tls_eccert_file =
+smtp_tls_eckey_file =
+# Obsolete DSA parameters
+smtp_tls_dcert_file =
+smtp_tls_dkey_file =
+# Postfix >= 3.4 interface
+smtp_tls_chain_files =
+.fi
+.ad
+.ft R
+.in -4
+.PP
+The best way to use the default settings is to comment out the above
+parameters in main.cf if present.
+.PP
+To enable remote SMTP servers to verify the Postfix SMTP client
+certificate, the issuing CA certificates must be made available to the
+server. You should include the required certificates in the client
+certificate file, the client certificate first, then the issuing
+CA(s) (bottom\-up order).
+.PP
+Example: the certificate for "client.example.com" was issued by
+"intermediate CA" which itself has a certificate issued by "root CA".
+As the "root" super\-user create the client.pem file with:
+.sp
+.in +4
+.nf
+.na
+.ft C
+# \fBumask 077\fR
+# \fBcat client_key.pem client_cert.pem intermediate_CA.pem > chain.pem \fR
+.fi
+.ad
+.ft R
+.in -4
+.PP
+If you also want to verify remote SMTP server certificates issued by
+these CAs, you can add the CA certificates to the smtp_tls_CAfile, in
+which case it is not necessary to have them in the smtp_tls_cert_file,
+smtp_tls_dcert_file (obsolete) or smtp_tls_eccert_file.
+.PP
+A certificate supplied here must be usable as an SSL client certificate
+and hence pass the "openssl verify \-purpose sslclient ..." test.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtp_tls_cert_file = /etc/postfix/chain.pem
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtp_tls_chain_files (default: empty)
+List of one or more PEM files, each holding one or more private keys
+directly followed by a corresponding certificate chain.  The file names
+are separated by commas and/or whitespace.  This parameter obsoletes the
+legacy algorithm\-specific key and certificate file settings.  When this
+parameter is non\-empty, the legacy parameters are ignored, and a warning
+is logged if any are also non\-empty.
+.PP
+With the proliferation of multiple private key algorithms-which,
+as of OpenSSL 1.1.1, include DSA (obsolete), RSA, ECDSA, Ed25519
+and Ed448-it is increasingly impractical to use separate
+parameters to configure the key and certificate chain for each
+algorithm.  Therefore, Postfix now supports storing multiple keys and
+corresponding certificate chains in a single file or in a set of files.
+.PP
+Each key must appear \fBimmediately before\fR the corresponding
+certificate, optionally followed by additional issuer certificates that
+complete the certificate chain for that key.  When multiple files are
+specified, they are equivalent to a single file that is concatenated
+from those files in the given order.  Thus, while a key must always
+precede its certificate and issuer chain, it can be in a separate file,
+so long as that file is listed immediately before the file that holds
+the corresponding certificate chain.  Once all the files are
+concatenated, the sequence of PEM objects must be: \fIkey1, cert1,
+[chain1], key2, cert2, [chain2], ..., keyN, certN, [chainN].\fR
+.PP
+Storing the private key in the same file as the corresponding
+certificate is more reliable.  With the key and certificate in separate
+files, there is a chance that during key rollover a Postfix process
+might load a private key and certificate from separate files that don't
+match.  Various operational errors may even result in a persistent
+broken configuration in which the certificate does not match the private
+key.
+.PP
+The file or files must contain at most one key of each type.  If,
+for example, two or more RSA keys and corresponding chains are listed,
+depending on the version of OpenSSL either only the last one will be
+used or a configuration error may be detected.  Note that while
+"Ed25519" and "Ed448" are considered separate algorithms, the various
+ECDSA curves (typically one of prime256v1, secp384r1 or secp521r1) are
+considered as different parameters of a single "ECDSA" algorithm, so it
+is not presently possible to configure keys for more than one ECDSA
+curve.
+.PP
+Example (separate files for each key and corresponding certificate chain):
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    smtp_tls_chain_files =
+        ${config_directory}/ed25519.pem,
+        ${config_directory}/ed448.pem,
+        ${config_directory}/rsa.pem
+.fi
+.ad
+.ft R
+.in -4
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/ed25519.pem:
+    \-\-\-\-\-BEGIN PRIVATE KEY\-\-\-\-\-
+    MC4CAQAwBQYDK2VwBCIEIEJfbbO4BgBQGBg9NAbIJaDBqZb4bC4cOkjtAH+Efbz3
+    \-\-\-\-\-END PRIVATE KEY\-\-\-\-\-
+    \-\-\-\-\-BEGIN CERTIFICATE\-\-\-\-\-
+    MIIBKzCB3qADAgECAhQaw+rflRreYuUZBp0HuNn/e5rMZDAFBgMrZXAwFDESMBAG
+    ...
+    nC0egv51YPDWxEHom4QA
+    \-\-\-\-\-END CERTIFICATE\-\-\-\-\-
+.fi
+.ad
+.ft R
+.in -4
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/ed448.pem:
+    \-\-\-\-\-BEGIN PRIVATE KEY\-\-\-\-\-
+    MEcCAQAwBQYDK2VxBDsEOQf+m0P+G0qi+NZ0RolyeiE5zdlPQR8h8y4jByBifpIe
+    LNler7nzHQJ1SLcOiXFHXlxp/84VZuh32A==
+    \-\-\-\-\-END PRIVATE KEY\-\-\-\-\-
+    \-\-\-\-\-BEGIN CERTIFICATE\-\-\-\-\-
+    MIIBdjCB96ADAgECAhQSv4oP972KypOZPNPF4fmsiQoRHzAFBgMrZXEwFDESMBAG
+    ...
+    pQcWsx+4J29e6YWH3Cy/CdUaexKP4RPCZDrPX7bk5C2BQ+eeYOxyThMA
+    \-\-\-\-\-END CERTIFICATE\-\-\-\-\-
+.fi
+.ad
+.ft R
+.in -4
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/rsa.pem:
+    \-\-\-\-\-BEGIN PRIVATE KEY\-\-\-\-\-
+    MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQDc4QusgkahH9rL
+    ...
+    ahQkZ3+krcaJvDSMgvu0tDc=
+    \-\-\-\-\-END PRIVATE KEY\-\-\-\-\-
+    \-\-\-\-\-BEGIN CERTIFICATE\-\-\-\-\-
+    MIIC+DCCAeCgAwIBAgIUIUkrbk1GAemPCT8i9wKsTGDH7HswDQYJKoZIhvcNAQEL
+    ...
+    Rirz15HGVNTK8wzFd+nulPzwUo6dH2IU8KazmyRi7OGvpyrMlm15TRE2oyE=
+    \-\-\-\-\-END CERTIFICATE\-\-\-\-\-
+.fi
+.ad
+.ft R
+.in -4
+.PP
+Example (all keys and certificates in a single file):
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    smtp_tls_chain_files = ${config_directory}/chains.pem
+.fi
+.ad
+.ft R
+.in -4
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/chains.pem:
+    \-\-\-\-\-BEGIN PRIVATE KEY\-\-\-\-\-
+    MC4CAQAwBQYDK2VwBCIEIEJfbbO4BgBQGBg9NAbIJaDBqZb4bC4cOkjtAH+Efbz3
+    \-\-\-\-\-END PRIVATE KEY\-\-\-\-\-
+    \-\-\-\-\-BEGIN CERTIFICATE\-\-\-\-\-
+    MIIBKzCB3qADAgECAhQaw+rflRreYuUZBp0HuNn/e5rMZDAFBgMrZXAwFDESMBAG
+    ...
+    nC0egv51YPDWxEHom4QA
+    \-\-\-\-\-END CERTIFICATE\-\-\-\-\-
+    \-\-\-\-\-BEGIN PRIVATE KEY\-\-\-\-\-
+    MEcCAQAwBQYDK2VxBDsEOQf+m0P+G0qi+NZ0RolyeiE5zdlPQR8h8y4jByBifpIe
+    LNler7nzHQJ1SLcOiXFHXlxp/84VZuh32A==
+    \-\-\-\-\-END PRIVATE KEY\-\-\-\-\-
+    \-\-\-\-\-BEGIN CERTIFICATE\-\-\-\-\-
+    MIIBdjCB96ADAgECAhQSv4oP972KypOZPNPF4fmsiQoRHzAFBgMrZXEwFDESMBAG
+    ...
+    pQcWsx+4J29e6YWH3Cy/CdUaexKP4RPCZDrPX7bk5C2BQ+eeYOxyThMA
+    \-\-\-\-\-END CERTIFICATE\-\-\-\-\-
+    \-\-\-\-\-BEGIN PRIVATE KEY\-\-\-\-\-
+    MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQDc4QusgkahH9rL
+    ...
+    ahQkZ3+krcaJvDSMgvu0tDc=
+    \-\-\-\-\-END PRIVATE KEY\-\-\-\-\-
+    \-\-\-\-\-BEGIN CERTIFICATE\-\-\-\-\-
+    MIIC+DCCAeCgAwIBAgIUIUkrbk1GAemPCT8i9wKsTGDH7HswDQYJKoZIhvcNAQEL
+    ...
+    Rirz15HGVNTK8wzFd+nulPzwUo6dH2IU8KazmyRi7OGvpyrMlm15TRE2oyE=
+    \-\-\-\-\-END CERTIFICATE\-\-\-\-\-
+.fi
+.ad
+.ft R
+.in -4
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH smtp_tls_cipherlist (default: empty)
+Obsolete Postfix < 2.3 control for the Postfix SMTP client TLS
+cipher list. As this feature applies to all TLS security levels, it is easy
+to create interoperability problems by choosing a non\-default cipher
+list. Do not use a non\-default TLS cipher list on hosts that deliver email
+to the public Internet: you will be unable to send email to servers that
+only support the ciphers you exclude. Using a restricted cipher list
+may be more appropriate for an internal MTA, where one can exert some
+control over the TLS software and settings of the peer servers.
+.PP
+\fBNote:\fR do not use "" quotes around the parameter value.
+.PP
+This feature is available in Postfix version 2.2. It is not used with
+Postfix 2.3 and later; use smtp_tls_mandatory_ciphers instead.
+.SH smtp_tls_ciphers (default: medium)
+The minimum TLS cipher grade that the Postfix SMTP client
+will use with opportunistic TLS encryption. Cipher types listed in
+smtp_tls_exclude_ciphers are excluded from the base definition of
+the selected cipher grade.   The default value is "medium" for
+Postfix releases after the middle of 2015, "export" for older
+releases.
+.PP
+When TLS is mandatory the cipher grade is chosen via the
+smtp_tls_mandatory_ciphers configuration parameter, see there for syntax
+details. See smtp_tls_policy_maps for information on how to configure
+ciphers on a per\-destination basis.
+.PP
+This feature is available in Postfix 2.6 and later. With earlier Postfix
+releases only the smtp_tls_mandatory_ciphers parameter is implemented,
+and opportunistic TLS always uses "export" or better (i.e. all) ciphers.
+.SH smtp_tls_connection_reuse (default: no)
+Try to make multiple deliveries per TLS\-encrypted connection.
+This uses the \fBtlsproxy\fR(8) service to encrypt an SMTP connection,
+uses the \fBscache\fR(8) service to save that connection, and relies on
+hints from the \fBqmgr\fR(8) daemon.
+.PP
+See "Client\-side
+TLS connection reuse" for background details.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH smtp_tls_dane_insecure_mx_policy (default: see "postconf \-d" output)
+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.  The choices are:
+.IP "\fBmay\fR"
+The TLSA records will be ignored and TLS will be optional.  If
+the MX host does not appear to support STARTTLS, or the STARTTLS
+handshake fails, mail may be sent in the clear.
+.br
+.IP "\fBencrypt\fR"
+The TLSA records will signal a requirement to use TLS.  While
+TLS encryption will be required, authentication will not be performed.
+.br
+.IP "\fBdane\fR"
+The TLSA records will be used just as with "secure" MX records.
+TLS encryption will be required, and, if at least one of the TLSA
+records is "usable", authentication will be required.  When
+authentication succeeds, it will be logged only as "Trusted", not
+"Verified", because the MX host name could have been forged.
+.br
+.br
+The default setting for Postfix >= 3.6 is "dane" with
+"smtp_tls_security_level = dane", otherwise "may". This behavior
+was backported to Postfix versions 3.5.9, 3.4.19, 3.3.16. 3.2.21.
+With earlier Postfix versions the default setting was always "dane".
+.PP
+Though with "insecure" MX records an active attacker can
+compromise SMTP transport security by returning forged MX records,
+such attacks are "tamper\-evident" since any forged MX hostnames
+will be recorded in the mail logs.  Attackers who place a high value
+on staying hidden may be deterred from forging MX records.
+.PP
+This feature is available in Postfix 3.1 and later. The \fBmay\fR
+policy is backwards\-compatible with earlier Postfix versions.
+.SH smtp_tls_dcert_file (default: empty)
+File with the Postfix SMTP client DSA certificate in PEM format.
+This file may also contain the Postfix SMTP client private DSA key.
+The DSA algorithm is obsolete and should not be used.
+.PP
+See the discussion under smtp_tls_cert_file for more details.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtp_tls_dcert_file = /etc/postfix/client\-dsa.pem
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtp_tls_dkey_file (default: $smtp_tls_dcert_file)
+File with the Postfix SMTP client DSA private key in PEM format.
+This file may be combined with the Postfix SMTP client DSA certificate
+file specified with $smtp_tls_dcert_file. The DSA algorithm is obsolete
+and should not be used.
+.PP
+The private key must be accessible without a pass\-phrase, i.e. it
+must not be encrypted. File permissions should grant read\-only
+access to the system superuser account ("root"), and no access
+to anyone else.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtp_tls_eccert_file (default: empty)
+File with the Postfix SMTP client ECDSA certificate in PEM format.
+This file may also contain the Postfix SMTP client ECDSA private key.
+With Postfix >= 3.4 the preferred way to configure client keys and
+certificates is via the "smtp_tls_chain_files" parameter.
+.PP
+See the discussion under smtp_tls_cert_file for more details.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtp_tls_eccert_file = /etc/postfix/ecdsa\-ccert.pem
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.6 and later, when Postfix is
+compiled and linked with OpenSSL 1.0.0 or later.
+.SH smtp_tls_eckey_file (default: $smtp_tls_eccert_file)
+File with the Postfix SMTP client ECDSA private key in PEM format.
+This file may be combined with the Postfix SMTP client ECDSA certificate
+file specified with $smtp_tls_eccert_file.  With Postfix >= 3.4 the
+preferred way to configure client keys and certificates is via the
+"smtp_tls_chain_files" parameter.
+.PP
+The private key must be accessible without a pass\-phrase, i.e. it
+must not be encrypted. File permissions should grant read\-only
+access to the system superuser account ("root"), and no access
+to anyone else.
+.PP
+This feature is available in Postfix 2.6 and later, when Postfix is
+compiled and linked with OpenSSL 1.0.0 or later.
+.SH smtp_tls_enforce_peername (default: yes)
+With mandatory TLS encryption, require that the remote SMTP
+server hostname matches the information in the remote SMTP server
+certificate.  As of RFC 2487 the requirements for hostname checking
+for MTA clients are not specified.
+.PP
+This option can be set to "no" to disable strict peer name
+checking. This setting has no effect on sessions that are controlled
+via the smtp_tls_per_site table.
+.PP
+Disabling the hostname verification can make sense in a closed
+environment where special CAs are created.  If not used carefully,
+this option opens the danger of a "man\-in\-the\-middle" attack (the
+CommonName of this attacker will be logged).
+.PP
+This feature is available in Postfix 2.2 and later. With
+Postfix 2.3 and later use smtp_tls_security_level instead.
+.SH smtp_tls_exclude_ciphers (default: empty)
+List of ciphers or cipher types to exclude from the Postfix
+SMTP client cipher
+list at all TLS security levels. This is not an OpenSSL cipherlist, it is
+a simple list separated by whitespace and/or commas. The elements are a
+single cipher, or one or more "+" separated cipher properties, in which
+case only ciphers matching \fBall\fR the properties are excluded.
+.PP
+Examples (some of these will cause problems):
+.sp
+.in +4
+.nf
+.na
+.ft C
+smtp_tls_exclude_ciphers = aNULL
+smtp_tls_exclude_ciphers = MD5, DES
+smtp_tls_exclude_ciphers = DES+MD5
+smtp_tls_exclude_ciphers = AES256\-SHA, DES\-CBC3\-MD5
+smtp_tls_exclude_ciphers = kEDH+aRSA
+.fi
+.ad
+.ft R
+.in -4
+.PP
+The first setting disables anonymous ciphers. The next setting
+disables ciphers that use the MD5 digest algorithm or the (single) DES
+encryption algorithm. The next setting disables ciphers that use MD5 and
+DES together.  The next setting disables the two ciphers "AES256\-SHA"
+and "DES\-CBC3\-MD5". The last setting disables ciphers that use "EDH"
+key exchange with RSA authentication.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtp_tls_fingerprint_cert_match (default: empty)
+List of acceptable remote SMTP server certificate fingerprints for
+the "fingerprint" TLS security level (\fBsmtp_tls_security_level\fR =
+fingerprint). At this security level, Certification Authorities are not
+used, and certificate expiration times are ignored. Instead, server
+certificates are verified directly via their certificate fingerprint
+or public key fingerprint (Postfix 2.9 and later). The fingerprint
+is a message digest of the server certificate (or public key). The
+digest algorithm is selected via the \fBsmtp_tls_fingerprint_digest\fR
+parameter.
+.PP
+The colons between each pair of nibbles in the fingerprint value
+are optional (Postfix >= 3.6). These were required in earlier
+Postfix releases.
+.PP
+When an \fBsmtp_tls_policy_maps\fR table entry specifies the
+"fingerprint" security level, any "match" attributes in that entry specify
+the list of valid fingerprints for the corresponding destination. Multiple
+fingerprints can be combined with a "|" delimiter in a single match
+attribute, or multiple match attributes can be employed.
+.PP
+Example: Certificate fingerprint verification with internal mailhub.
+Two matching fingerprints are listed. The relayhost may be multiple
+physical hosts behind a load\-balancer, each with its own private/public
+key and self\-signed certificate. Alternatively, a single relayhost may
+be in the process of switching from one set of private/public keys to
+another, and both keys are trusted just prior to the transition.
+.sp
+.in +4
+.nf
+.na
+.ft C
+relayhost = [mailhub.example.com]
+smtp_tls_security_level = fingerprint
+smtp_tls_fingerprint_digest = sha256
+smtp_tls_fingerprint_cert_match =
+    cd:fc:d8:db:f8:c4:82:96:6c:...:28:71:e8:f5:8d:a5:0d:9b:d4:a6
+    dd:5c:ef:f5:c3:bc:64:25:36:...:99:36:06:ce:40:ef:de:2e:ad:a4
+.fi
+.ad
+.ft R
+.in -4
+.PP
+Example: Certificate fingerprint verification with selected destinations.
+As in the example above, we show two matching fingerprints:
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
+    smtp_tls_fingerprint_digest = sha256
+.fi
+.ad
+.ft R
+.in -4
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/tls_policy:
+    example.com fingerprint
+        match=51:e9:af:2e:1e:40:1f:...:64:0a:30:35:2d:09:16:31:5a:eb:82:76
+        match=b6:b4:72:34:e2:59:cd:...:c2:ca:63:0d:4d:cc:2c:7d:84:de:e6:2f
+.fi
+.ad
+.ft R
+.in -4
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH smtp_tls_fingerprint_digest (default: see "postconf \-d" output)
+The message digest algorithm used to construct remote SMTP server
+certificate fingerprints. At the "fingerprint" TLS security level
+(\fBsmtp_tls_security_level\fR = fingerprint), the server certificate is
+verified by directly matching its certificate fingerprint or its public
+key fingerprint (Postfix 2.9 and later). The fingerprint is the
+message digest of the server certificate (or its public key)
+using the selected
+algorithm. With a digest algorithm resistant to "second pre\-image"
+attacks, it is not feasible to create a new public key and a matching
+certificate (or public/private key\-pair) that has the same fingerprint.
+.PP
+The default algorithm is \fBsha256\fR with Postfix >= 3.6
+and the \fBcompatibility_level\fR set to 3.6 or higher. With Postfix
+<= 3.5, the default algorithm is \fBmd5\fR.
+.PP
+The best\-practice algorithm is now \fBsha256\fR. Recent advances in hash
+function cryptanalysis have led to md5 and sha1 being deprecated in favor of
+sha256.  However, as long as there are no known "second pre\-image" attacks
+against the older algorithms, their use in this context, though not
+recommended, is still likely safe.
+.PP
+While additional digest algorithms are often available with OpenSSL's
+libcrypto, only those used by libssl in SSL cipher suites are available to
+Postfix.  You'll likely find support for md5, sha1, sha256 and sha512.
+.PP
+To find the fingerprint of a specific certificate file, with a
+specific digest algorithm, run:
+.sp
+.in +4
+.nf
+.na
+.ft C
+$ openssl x509 \-noout \-fingerprint \-\fIdigest\fR \-in \fIcertfile\fR.pem
+.fi
+.ad
+.ft R
+.in -4
+.PP
+The text to the right of the "=" sign is the desired fingerprint.
+For example:
+.sp
+.in +4
+.nf
+.na
+.ft C
+$ openssl x509 \-noout \-fingerprint \-sha256 \-in cert.pem
+SHA256 Fingerprint=D4:6A:AB:19:24:...:BB:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A
+.fi
+.ad
+.ft R
+.in -4
+.PP
+To extract the public key fingerprint from an X.509 certificate,
+you need to extract the public key from the certificate and compute
+the appropriate digest of its DER (ASN.1) encoding. With OpenSSL
+the "\-pubkey" option of the "x509" command extracts the public
+key always in "PEM" format. We pipe the result to another OpenSSL
+command that converts the key to DER and then to the "dgst" command
+to compute the fingerprint.
+.PP
+The actual command to transform the key to DER format depends on the
+version of OpenSSL used. As of OpenSSL 1.0.0, the "pkey" command supports
+all key types.
+.sp
+.in +4
+.nf
+.na
+.ft C
+# OpenSSL >= 1.0 with SHA\-256 fingerprints.
+$ openssl x509 \-in cert.pem \-noout \-pubkey |
+    openssl pkey \-pubin \-outform DER |
+    openssl dgst \-sha256 \-c
+(stdin)= 64:3f:1f:f6:e5:1e:d4:2a:56:...:fc:09:1a:61:98:b5:bc:7c:60:58
+.fi
+.ad
+.ft R
+.in -4
+.PP
+The Postfix SMTP server and client log the peer (leaf) certificate
+fingerprint and the public key fingerprint when the TLS loglevel is 2 or
+higher.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH smtp_tls_force_insecure_host_tlsa_lookup (default: no)
+Lookup the associated DANE TLSA RRset even when a hostname is
+not an alias and its address records lie in an unsigned zone.  This
+is unlikely to ever yield DNSSEC validated results, since child
+zones of unsigned zones are also unsigned in the absence of DLV or
+locally configured non\-root trust\-anchors.  We anticipate that such
+mechanisms will not be used for just the "_tcp" subdomain of a host.
+Suppressing the TLSA RRset lookup reduces latency and avoids potential
+interoperability problems with nameservers for unsigned zones that
+are not prepared to handle the new TLSA RRset.
+.PP
+This feature is available in Postfix 2.11.
+.SH smtp_tls_key_file (default: $smtp_tls_cert_file)
+File with the Postfix SMTP client RSA private key in PEM format.
+This file may be combined with the Postfix SMTP client RSA certificate
+file specified with $smtp_tls_cert_file.  With Postfix >= 3.4 the
+preferred way to configure client keys and certificates is via the
+"smtp_tls_chain_files" parameter.
+.PP
+The private key must be accessible without a pass\-phrase, i.e. it
+must not be encrypted. File permissions should grant read\-only
+access to the system superuser account ("root"), and no access
+to anyone else.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtp_tls_key_file = $smtp_tls_cert_file
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtp_tls_loglevel (default: 0)
+Enable additional Postfix SMTP client logging of TLS activity.
+Each logging level also includes the information that is logged at
+a lower logging level.
+.IP ""
+0 Disable logging of TLS activity.
+.br
+.IP ""
+1 Log only a summary message on TLS handshake completion
+- no logging of remote SMTP server certificate trust\-chain
+verification errors if server certificate verification is not required.
+With Postfix 2.8 and earlier, log the summary message and unconditionally
+log trust\-chain verification errors.
+.br
+.IP ""
+2 Also log levels during TLS negotiation.
+.br
+.IP ""
+3 Also log the hexadecimal and ASCII dump of the
+TLS negotiation process.
+.br
+.IP ""
+4 Also log the hexadecimal and ASCII dump of complete
+transmission after STARTTLS.
+.br
+.br
+.PP
+Do not use "smtp_tls_loglevel = 2" or higher except in case of
+problems. Use of loglevel 4 is strongly discouraged.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtp_tls_mandatory_ciphers (default: medium)
+The minimum TLS cipher grade that the Postfix SMTP client will
+use with
+mandatory TLS encryption.  The default value "medium" is suitable
+for most destinations with which you may want to enforce TLS, and
+is beyond the reach of today's cryptanalytic methods. See
+smtp_tls_policy_maps for information on how to configure ciphers
+on a per\-destination basis.
+.PP
+The following cipher grades are supported:
+.IP "\fBhigh\fR"
+Enable only "HIGH" grade OpenSSL ciphers.  This setting may
+be appropriate when all mandatory TLS destinations (e.g. when all
+mail is routed to a suitably capable relayhost) support at least one
+"HIGH" grade cipher. The underlying cipherlist is specified via the
+tls_high_cipherlist configuration parameter, which you are strongly
+encouraged not to change.
+.br
+.IP "\fBmedium\fR"
+Enable "MEDIUM" grade or better OpenSSL ciphers.
+The underlying cipherlist is specified via the tls_medium_cipherlist
+configuration parameter, which you are strongly encouraged not to change.
+.br
+.IP "\fBnull\fR"
+Enable only the "NULL" OpenSSL ciphers, these provide authentication
+without encryption.  This setting is only appropriate in the rare case
+that all servers are prepared to use NULL ciphers (not normally enabled
+in TLS servers). A plausible use\-case is an LMTP server listening on a
+UNIX\-domain socket that is configured to support "NULL" ciphers. The
+underlying cipherlist is specified via the tls_null_cipherlist
+configuration parameter, which you are strongly encouraged not to
+change.
+.br
+.IP "\fBlow\fR"
+Enable "LOW" grade or stronger OpenSSL ciphers.  In Postfix
+>= 3.8 this cipher grade is always identical to "medium".  Recent
+versions of OpenSSL do not support any "LOW" grade ciphers.  In
+earlier Postfix releases the underlying cipherlist was specified
+via the tls_low_cipherlist configuration parameter, which you are
+strongly encouraged not to change.  This obsolete cipher grade
+SHOULD NOT be used.
+.br
+.IP "\fBexport\fR"
+Enable "EXPORT" grade or stronger OpenSSL ciphers.  In Postfix
+>= 3.8 this cipher grade is always identical to "medium".  Recent
+versions of OpenSSL do not support any "EXPORT" grade ciphers.  In
+earlier Postfix releases the underlying cipherlist was specified
+via the tls_export_cipherlist configuration parameter, which you are
+strongly encouraged not to change.  This obsolete cipher grade
+SHOULD NOT be used.
+.br
+.br
+.PP
+The underlying cipherlists for grades other than "null" include
+anonymous ciphers, but these are automatically filtered out if the
+Postfix SMTP client is configured to verify server certificates.
+You are very unlikely to need to take any steps to exclude anonymous
+ciphers, they are excluded automatically as necessary.  If you must
+exclude anonymous ciphers at the "may" or "encrypt" security levels,
+when the Postfix SMTP client does not need or use peer certificates, set
+"smtp_tls_exclude_ciphers = aNULL". To exclude anonymous ciphers only when
+TLS is enforced, set "smtp_tls_mandatory_exclude_ciphers = aNULL".
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtp_tls_mandatory_exclude_ciphers (default: empty)
+Additional list of ciphers or cipher types to exclude from the
+Postfix SMTP client cipher list at mandatory TLS security levels. This list
+works in addition to the exclusions listed with smtp_tls_exclude_ciphers
+(see there for syntax details).
+.PP
+Starting with Postfix 2.6, the mandatory cipher exclusions can be
+specified on a per\-destination basis via the TLS policy "exclude"
+attribute. See smtp_tls_policy_maps for notes and examples.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtp_tls_mandatory_protocols (default: see "postconf \-d" output)
+TLS protocols that the Postfix SMTP client will use with mandatory
+TLS encryption.  In main.cf the values are separated by whitespace,
+commas or colons. In the policy table "protocols" attribute (see
+smtp_tls_policy_maps) the only valid separator is colon. An empty value
+means allow all protocols.
+.PP
+The valid protocol names (see \fBSSL_get_version\fR(3)) are "SSLv2",
+"SSLv3", "TLSv1", "TLSv1.1", "TLSv1.2" and "TLSv1.3".  Starting with
+Postfix 3.6, the default value is ">=TLSv1", which sets TLS 1.0 as
+the lowest supported TLS protocol version (see below).  Older releases
+use the "!" exclusion syntax, also described below.
+.PP
+As of Postfix 3.6, the preferred way to limit the range of
+acceptable protocols is to set a lowest acceptable TLS protocol version
+and/or a highest acceptable TLS protocol version.  To set the lower
+bound include an element of the form: ">=\fIversion\fR" where
+\fIversion\fR is a either one of the TLS protocol names listed above,
+or a hexadecimal number corresponding to the desired TLS protocol
+version (0301 for TLS 1.0, 0302 for TLS 1.1, etc.).  For the upper
+bound, use "<=\fIversion\fR".  There must be no whitespace between
+the ">=" or "<=" symbols and the protocol name or number.
+.PP
+Hexadecimal protocol numbers make it possible to specify protocol
+bounds for TLS versions that are known to OpenSSL, but might not be
+known to Postfix.  They cannot be used with the legacy exclusion syntax.
+Leading "0" or "0x" prefixes are supported, but not required.
+Therefore, "301", "0301", "0x301" and "0x0301" are all equivalent to
+"TLSv1".  Hexadecimal versions unknown to OpenSSL will fail to set the
+upper or lower bound, and a warning will be logged.  Hexadecimal
+versions should only be used when Postfix is linked with some future
+version of OpenSSL that supports TLS 1.4 or later, but Postfix does not
+yet support a symbolic name for that protocol version.
+.PP
+Hexadecimal example (Postfix >= 3.6):
+.sp
+.in +4
+.nf
+.na
+.ft C
+# Allow only TLS 1.2 through (hypothetical) TLS 1.4, once supported
+# in some future version of OpenSSL (presently a warning is logged).
+smtp_tls_mandatory_protocols = >=TLSv1.2, <=0305
+# Allow only TLS 1.2 and up:
+smtp_tls_mandatory_protocols = >=0x0303
+.fi
+.ad
+.ft R
+.in -4
+.PP
+With Postfix < 3.6 there is no support for a minimum or maximum
+version, and the protocol range is configured via protocol exclusions.
+To require at least TLS 1.0, set "smtp_tls_mandatory_protocols = !SSLv2,
+!SSLv3". Listing the protocols to include, rather than the protocols to
+exclude, is supported, but not recommended.  The exclusion syntax more
+accurately matches the underlying OpenSSL interface.
+.PP
+When using the exclusion syntax, take care to ensure that the range
+of protocols supported by the Postfix SMTP client is contiguous.  When
+a protocol version is enabled, disabling any higher version implicitly
+disables all versions above that higher version.  Thus, for example:
+.sp
+.in +4
+.nf
+.na
+.ft C
+smtp_tls_mandatory_protocols = !SSLv2, !SSLv3, !TLSv1.1
+.fi
+.ad
+.ft R
+.in -4
+.PP
+also disables any protocol versions higher than TLSv1.1 leaving
+only "TLSv1" enabled.
+.PP
+Support for "TLSv1.3" was introduced in OpenSSL 1.1.1.  Disabling
+this protocol via "!TLSv1.3" is supported since Postfix 3.4 (or patch
+releases >= 3.0.14, 3.1.10, 3.2.7 and 3.3.2).
+.PP
+While the vast majority of SMTP servers with DANE TLSA records now
+support at least TLS 1.2, a few still only support TLS 1.0.  If you use
+"dane" or "dane\-only" it is best not to disable TLSv1, except perhaps
+via the policy table for destinations which you are sure will support
+"TLSv1.2".
+.PP
+See the documentation of the smtp_tls_policy_maps parameter and
+TLS_README for more information about security levels.
+.PP
+Example:
+.nf
+.na
+.ft C
+# Preferred syntax with Postfix >= 3.6:
+smtp_tls_mandatory_protocols = >=TLSv1.2, <=TLSv1.3
+# Legacy syntax:
+smtp_tls_mandatory_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtp_tls_note_starttls_offer (default: no)
+Log the hostname of a remote SMTP server that offers STARTTLS,
+when TLS is not already enabled for that server.
+.PP
+The logfile record looks like:
+.PP
+.nf
+.na
+.ft C
+postfix/smtp[pid]:  Host offered STARTTLS: [name.of.host]
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtp_tls_per_site (default: empty)
+Optional lookup tables with the Postfix SMTP client TLS usage
+policy by next\-hop destination and by remote SMTP server hostname.
+When both lookups succeed, the more specific per\-site policy (NONE,
+MUST, etc.) overrides the less specific one (MAY), and the more secure
+per\-site policy (MUST, etc.) overrides the less secure one (NONE).
+With Postfix 2.3 and later smtp_tls_per_site is strongly discouraged:
+use smtp_tls_policy_maps instead.
+.PP
+Use of the bare hostname as the per\-site table lookup key is
+discouraged. Always use the full destination nexthop (enclosed in
+[] with a possible ":port" suffix). A recipient domain or MX\-enabled
+transport next\-hop with no port suffix may look like a bare hostname,
+but is still a suitable \fIdestination\fR.
+.PP
+Specify a next\-hop destination or server hostname on the left\-hand
+side; no wildcards are allowed. The next\-hop destination is either
+the recipient domain, or the destination specified with a \fBtransport\fR(5)
+table, the relayhost parameter, or the relay_transport parameter.
+On the right hand side specify one of the following keywords:
+.IP "NONE"
+Don't use TLS at all. This overrides a less
+specific \fBMAY\fR lookup result from the alternate host or next\-hop
+lookup key, and overrides the global smtp_use_tls, smtp_enforce_tls,
+and smtp_tls_enforce_peername settings.
+.br
+.IP "MAY"
+Try to use TLS if the server announces support,
+otherwise use an unencrypted connection. This has less precedence
+than a more specific result (including \fBNONE\fR) from the alternate
+host or next\-hop lookup key, and has less precedence than the more
+specific global "smtp_enforce_tls = yes" or "smtp_tls_enforce_peername
+= yes".
+.br
+.IP "MUST_NOPEERMATCH"
+Require TLS encryption, but do not
+require that the remote SMTP server hostname matches the information
+in the remote SMTP server certificate, or that the server certificate
+was issued by a trusted CA. This overrides a less secure \fBNONE\fR
+or a less specific \fBMAY\fR lookup result from the alternate host
+or next\-hop lookup key, and overrides the global smtp_use_tls,
+smtp_enforce_tls and smtp_tls_enforce_peername settings.
+.br
+.IP "MUST"
+Require TLS encryption, require that the remote
+SMTP server hostname matches the information in the remote SMTP
+server certificate, and require that the remote SMTP server certificate
+was issued by a trusted CA. This overrides a less secure \fBNONE\fR
+or \fBMUST_NOPEERMATCH\fR or a less specific \fBMAY\fR lookup
+result from the alternate host or next\-hop lookup key, and overrides
+the global smtp_use_tls, smtp_enforce_tls and smtp_tls_enforce_peername
+settings.
+.br
+.br
+.PP
+The above keywords correspond to the "none", "may", "encrypt" and
+"verify" security levels for the new smtp_tls_security_level parameter
+introduced in Postfix 2.3. Starting with Postfix 2.3, and independently
+of how the policy is specified, the smtp_tls_mandatory_ciphers and
+smtp_tls_mandatory_protocols parameters apply when TLS encryption
+is mandatory. Connections for which encryption is optional typically
+enable all "export" grade and better ciphers (see smtp_tls_ciphers
+and smtp_tls_protocols).
+.PP
+As long as no secure DNS lookup mechanism is available, false
+hostnames in MX or CNAME responses can change the server hostname
+that Postfix uses for TLS policy lookup and server certificate
+verification. Even with a perfect match between the server hostname and
+the server certificate, there is no guarantee that Postfix is connected
+to the right server.  See TLS_README (Closing a DNS loophole with obsolete
+per\-site TLS policies) for a possible work\-around.
+.PP
+This feature is available in Postfix 2.2 and later. With
+Postfix 2.3 and later use smtp_tls_policy_maps instead.
+.SH smtp_tls_policy_maps (default: empty)
+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.  See
+TLS_README for a more detailed discussion of TLS security levels.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.PP
+The TLS policy table is indexed by the full next\-hop destination,
+which is either the recipient domain, or the verbatim next\-hop
+specified in the transport table, $local_transport, $virtual_transport,
+$relay_transport or $default_transport. This includes any enclosing
+square brackets and any non\-default destination server port suffix. The
+LMTP socket type prefix (inet: or unix:) is not included in the lookup
+key.
+.PP
+Only the next\-hop domain, or $myhostname with LMTP over UNIX\-domain
+sockets, is used as the nexthop name for certificate verification. The
+port and any enclosing square brackets are used in the table lookup key,
+but are not used for server name verification.
+.PP
+When the lookup key is a domain name without enclosing square brackets
+or any \fI:port\fR suffix (typically the recipient domain), and the full
+domain is not found in the table, just as with the \fBtransport\fR(5) table,
+the parent domain starting with a leading "." is matched recursively. This
+allows one to specify a security policy for a recipient domain and all
+its sub\-domains.
+.PP
+The lookup result is a security level, followed by an optional list
+of whitespace and/or comma separated name=value attributes that override
+related main.cf settings. The TLS security levels in order of increasing
+security are:
+.IP "\fBnone\fR"
+No TLS. No additional attributes are supported at this level.
+.br
+.IP "\fBmay\fR"
+Opportunistic TLS. Since sending in the clear is acceptable,
+demanding stronger than default TLS security merely reduces
+interoperability. The optional "ciphers", "exclude", and "protocols"
+attributes (available for opportunistic TLS with Postfix >= 2.6)
+and "connection_reuse" attribute (Postfix >= 3.4) override the
+"smtp_tls_ciphers", "smtp_tls_exclude_ciphers", "smtp_tls_protocols",
+and
+"smtp_tls_connection_reuse" configuration parameters. In the policy table,
+multiple ciphers, protocols or excluded ciphers must be separated by colons,
+as attribute values may not contain whitespace or commas. When opportunistic
+TLS handshakes fail, Postfix retries the connection with TLS disabled.
+This allows mail delivery to sites with non\-interoperable TLS
+implementations.
+.br
+.IP "\fBencrypt\fR"
+Mandatory TLS encryption. At this level
+and higher, the optional "protocols" attribute overrides the main.cf
+smtp_tls_mandatory_protocols parameter, the optional "ciphers" attribute
+overrides the main.cf smtp_tls_mandatory_ciphers parameter, the
+optional "exclude" attribute (Postfix >= 2.6) overrides the main.cf
+smtp_tls_mandatory_exclude_ciphers parameter, and the optional
+"connection_reuse" attribute (Postfix >= 3.4) overrides the
+main.cf smtp_tls_connection_reuse parameter. In the policy table,
+multiple ciphers, protocols or excluded ciphers must be separated by colons,
+as attribute values may not contain whitespace or commas.
+.br
+.IP "\fBdane\fR"
+Opportunistic DANE TLS.  The TLS policy for the destination is
+obtained via TLSA records in DNSSEC.  If no TLSA records are found,
+the effective security level used is may.  If TLSA records are
+found, but none are usable, the effective security level is encrypt.  When usable
+TLSA records are obtained for the remote SMTP server, the
+server certificate must match the TLSA records.  RFC 7672 (DANE)
+TLS authentication and DNSSEC support is available with Postfix
+2.11 and later. The optional "connection_reuse" attribute (Postfix
+>= 3.4) overrides the main.cf smtp_tls_connection_reuse parameter.
+When the effective security level used is may, the optional "ciphers",
+"exclude", and "protocols" attributes (Postfix >= 2.6) override the
+"smtp_tls_ciphers", "smtp_tls_exclude_ciphers", and "smtp_tls_protocols"
+configuration parameters.
+When the effective security level used is encrypt, the optional "ciphers",
+"exclude", and "protocols" attributes (Postfix >= 2.6) override the
+"smtp_tls_mandatory_ciphers", "smtp_tls_mandatory_exclude_ciphers", and
+"smtp_tls_mandatory_protocols" configuration parameters.
+.br
+.IP "\fBdane\-only\fR"
+Mandatory DANE TLS.  The TLS policy for the destination is
+obtained via TLSA records in DNSSEC.  If no TLSA records are found,
+or none are usable, no connection is made to the server.  When
+usable TLSA records are obtained for the remote SMTP server, the
+server certificate must match the TLSA records.  RFC 7672 (DANE) TLS
+authentication and DNSSEC support is available with Postfix 2.11
+and later. The optional "ciphers", "exclude", and "protocols" attributes
+(Postfix >= 2.6) override the "smtp_tls_mandatory_ciphers",
+"smtp_tls_mandatory_exclude_ciphers", and "smtp_tls_mandatory_protocols"
+configuration parameters. The optional "connection_reuse" attribute
+(Postfix >= 3.4) overrides the main.cf smtp_tls_connection_reuse parameter.
+.br
+.IP "\fBfingerprint\fR"
+Certificate fingerprint
+verification. Available with Postfix 2.5 and later. At this security
+level, there are no trusted Certification Authorities. The certificate
+trust chain, expiration date, ... are not checked. Instead,
+the optional "match" attribute, or else the main.cf
+\fBsmtp_tls_fingerprint_cert_match\fR parameter, lists the certificate
+fingerprints or the public key fingerprint (Postfix 2.9 and later)
+of the valid server certificate. The digest
+algorithm used to calculate the fingerprint is selected by the
+\fBsmtp_tls_fingerprint_digest\fR parameter. Multiple fingerprints can
+be combined with a "|" delimiter in a single match attribute, or multiple
+match attributes can be employed. The ":" character is not used as a
+delimiter as it occurs between each pair of fingerprint (hexadecimal)
+digits. The optional "ciphers", "exclude", and "protocols" attributes
+(Postfix >= 2.6) override the "smtp_tls_mandatory_ciphers",
+"smtp_tls_mandatory_exclude_ciphers", and "smtp_tls_mandatory_protocols"
+configuration parameters. The optional "connection_reuse" attribute
+(Postfix >= 3.4) overrides the main.cf smtp_tls_connection_reuse
+parameter.
+.br
+.IP "\fBverify\fR"
+Mandatory TLS verification.  At this security
+level, DNS MX lookups are trusted to be secure enough, and the name
+verified in the server certificate is usually obtained indirectly via
+unauthenticated DNS MX lookups.  The optional "match" attribute overrides
+the main.cf smtp_tls_verify_cert_match parameter. In the policy table,
+multiple match patterns and strategies must be separated by colons.
+In practice explicit control over matching is more common with the
+"secure" policy, described below. The optional "ciphers", "exclude",
+and "protocols" attributes (Postfix >= 2.6) override the
+"smtp_tls_mandatory_ciphers", "smtp_tls_mandatory_exclude_ciphers", and
+"smtp_tls_mandatory_protocols" configuration parameters. The optional
+"connection_reuse" attribute (Postfix >= 3.4) overrides the main.cf
+smtp_tls_connection_reuse parameter.
+.br
+.IP "\fBsecure\fR"
+Secure\-channel TLS. At this security level, DNS
+MX lookups, though potentially used to determine the candidate next\-hop
+gateway IP addresses, are \fBnot\fR trusted to be secure enough for TLS
+peername verification. Instead, the default name verified in the server
+certificate is obtained directly from the next\-hop, or is explicitly
+specified via the optional "match" attribute which overrides the
+main.cf smtp_tls_secure_cert_match parameter. In the policy table,
+multiple match patterns and strategies must be separated by colons.
+The match attribute is most useful when multiple domains are supported by
+a common server: the policy entries for additional domains specify matching
+rules for the primary domain certificate. While transport table overrides
+that route the secondary domains to the primary nexthop also allow secure
+verification, they risk delivery to the wrong destination when domains
+change hands or are re\-assigned to new gateways. With the "match"
+attribute approach, routing is not perturbed, and mail is deferred if
+verification of a new MX host fails. The optional "ciphers", "exclude",
+and "protocols" attributes (Postfix >= 2.6) override the
+"smtp_tls_mandatory_ciphers", "smtp_tls_mandatory_exclude_ciphers", and
+"smtp_tls_mandatory_protocols" configuration parameters. The optional
+"connection_reuse" attribute (Postfix >= 3.4) overrides the main.cf
+smtp_tls_connection_reuse parameter.
+.br
+.br
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
+    # Postfix 2.5 and later.
+    #
+    # The default digest is sha256 with Postfix >= 3.6 and
+    # compatibility level >= 3.
+    #
+    smtp_tls_fingerprint_digest = sha256
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/tls_policy:
+    example.edu                 none
+    example.mil                 may
+    example.gov                 encrypt protocols=TLSv1
+    example.com                 verify ciphers=high
+    example.net                 secure
+    .example.net                secure match=.example.net:example.net
+    [mail.example.org]:587      secure match=nexthop
+    # Postfix 2.5 and later
+    [thumb.example.org]          fingerprint
+        match=b6:b4:72:34:e2:59:cd:...:c2:ca:63:0d:4d:cc:2c:7d:84:de:e6:2f
+        match=51:e9:af:2e:1e:40:1f:...:64:0a:30:35:2d:09:16:31:5a:eb:82:76
+.fi
+.ad
+.ft R
+.PP
+\fBNote:\fR The "hostname" strategy if listed in a non\-default
+setting of smtp_tls_secure_cert_match or in the "match" attribute
+in the policy table can render the "secure" level vulnerable to
+DNS forgery. Do not use the "hostname" strategy for secure\-channel
+configurations in environments where DNS security is not assured.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtp_tls_protocols (default: see postconf \-d output)
+TLS protocols that the Postfix SMTP client will use with
+opportunistic TLS encryption.  In main.cf the values are separated by
+whitespace, commas or colons. In the policy table "protocols" attribute
+(see smtp_tls_policy_maps) the only valid separator is colon.  An empty
+value means allow all protocols.
+.PP
+The valid protocol names (see \fBSSL_get_version\fR(3)) are "SSLv2",
+"SSLv3", "TLSv1", "TLSv1.1", "TLSv1.2" and "TLSv1.3".  Starting with
+Postfix 3.6, the default value is ">=TLSv1", which sets TLS 1.0 as
+the lowest supported TLS protocol version (see below).  Older releases
+use the "!" exclusion syntax, also described below.
+.PP
+As of Postfix 3.6, the preferred way to limit the range of
+acceptable protocols is to set the lowest acceptable TLS protocol
+version and/or the highest acceptable TLS protocol version.  To set the
+lower bound include an element of the form: ">=\fIversion\fR" where
+\fIversion\fR is either one of the TLS protocol names listed above,
+or a hexadecimal number corresponding to the desired TLS protocol
+version (0301 for TLS 1.0, 0302 for TLS 1.1, etc.).  For the upper
+bound, use "<=\fIversion\fR".  There must be no whitespace between
+the ">=" or "<=" symbols and the protocol name or number.
+.PP
+Hexadecimal protocol numbers make it possible to specify protocol
+bounds for TLS versions that are known to OpenSSL, but might not be
+known to Postfix.  They cannot be used with the legacy exclusion syntax.
+Leading "0" or "0x" prefixes are supported, but not required.
+Therefore, "301", "0301", "0x301" and "0x0301" are all equivalent to
+"TLSv1".  Hexadecimal versions unknown to OpenSSL will fail to set the
+upper or lower bound, and a warning will be logged.  Hexadecimal
+versions should only be used when Postfix is linked with some future
+version of OpenSSL that supports TLS 1.4 or later, but Postfix does not
+yet support a symbolic name for that protocol version.
+.PP
+Hexadecimal example (Postfix >= 3.6):
+.sp
+.in +4
+.nf
+.na
+.ft C
+# Allow only TLS 1.0 through (hypothetical) TLS 1.4, once supported
+# in some future version of OpenSSL (presently a warning is logged).
+smtp_tls_protocols = >=TLSv1, <=0305
+# Allow only TLS 1.0 and up:
+smtp_tls_protocols = >=0x0301
+.fi
+.ad
+.ft R
+.in -4
+.PP
+With Postfix < 3.6 there is no support for a minimum or maximum
+version, and the protocol range is configured via protocol exclusions.
+To require at least TLS 1.0, set "smtp_tls_protocols = !SSLv2, !SSLv3".
+Listing the protocols to include, rather than protocols to exclude, is
+supported, but not recommended.  The exclusion form more accurately
+matches the underlying OpenSSL interface.
+.PP
+When using the exclusion syntax, take care to ensure that the range of
+protocols advertised by an SSL/TLS client is contiguous.  When a protocol
+version is enabled, disabling any higher version implicitly disables all
+versions above that higher version.  Thus, for example:
+.sp
+.in +4
+.nf
+.na
+.ft C
+smtp_tls_protocols = !SSLv2, !SSLv3, !TLSv1.1
+.fi
+.ad
+.ft R
+.in -4
+also disables any protocols version higher than TLSv1.1 leaving
+only "TLSv1" enabled.
+.PP
+Support for "TLSv1.3" was introduced in OpenSSL 1.1.1.  Disabling
+this protocol via "!TLSv1.3" is supported since Postfix 3.4 (or patch
+releases >= 3.0.14, 3.1.10, 3.2.7 and 3.3.2).
+.PP
+Example:
+.nf
+.na
+.ft C
+# Preferred syntax with Postfix >= 3.6:
+smtp_tls_protocols = >=TLSv1, <=TLSv1.3
+# Legacy syntax:
+smtp_tls_protocols = !SSLv2, !SSLv3
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH smtp_tls_scert_verifydepth (default: 9)
+The verification depth for remote SMTP server certificates. A depth
+of 1 is sufficient if the issuing CA is listed in a local CA file.
+.PP
+The default verification depth is 9 (the OpenSSL default) for
+compatibility with earlier Postfix behavior. Prior to Postfix 2.5,
+the default value was 5, but the limit was not actually enforced. If
+you have set this to a lower non\-default value, certificates with longer
+trust chains may now fail to verify. Certificate chains with 1 or 2
+CAs are common, deeper chains are more rare and any number between 5
+and 9 should suffice in practice. You can choose a lower number if,
+for example, you trust certificates directly signed by an issuing CA
+but not any CAs it delegates to.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtp_tls_secure_cert_match (default: nexthop, dot\-nexthop)
+How the Postfix SMTP client verifies the server certificate
+peername for the "secure" TLS security level. In a "secure" TLS policy table
+($smtp_tls_policy_maps) entry the optional "match" attribute
+overrides this main.cf setting.
+.PP
+This parameter specifies one or more patterns or strategies separated
+by commas, whitespace or colons.  In the policy table the only valid
+separator is the colon character.
+.PP
+For a description of the pattern and strategy syntax see the
+smtp_tls_verify_cert_match parameter. The "hostname" strategy should
+be avoided in this context, as in the absence of a secure global DNS, using
+the results of MX lookups in certificate verification is not immune to active
+(man\-in\-the\-middle) attacks on DNS.
+.PP
+Sample main.cf setting:
+.sp
+.in +4
+.nf
+.na
+.ft C
+smtp_tls_secure_cert_match = nexthop
+.fi
+.ad
+.ft R
+.in -4
+.PP
+Sample policy table override:
+.sp
+.in +4
+.nf
+.na
+.ft C
+example.net     secure match=example.com:.example.com
+\&.example.net    secure match=example.com:.example.com
+.fi
+.ad
+.ft R
+.in -4
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtp_tls_security_level (default: empty)
+The default SMTP TLS security level for the Postfix SMTP client.
+When a non\-empty value is specified, this overrides the obsolete
+parameters smtp_use_tls, smtp_enforce_tls, and smtp_tls_enforce_peername;
+when no value is specified for smtp_tls_enforce_peername or the obsolete
+parameters, the default SMTP TLS security level is
+none.
+.PP
+Specify one of the following security levels:
+.IP "\fBnone\fR"
+No TLS. TLS will not be used unless enabled for specific
+destinations via smtp_tls_policy_maps.
+.br
+.IP "\fBmay\fR"
+Opportunistic TLS. Use TLS if this is supported by the remote
+SMTP server, otherwise use plaintext. Since
+sending in the clear is acceptable, demanding stronger than default TLS
+security merely reduces interoperability.
+The "smtp_tls_ciphers" and "smtp_tls_protocols" (Postfix >= 2.6)
+configuration parameters provide control over the protocols and
+cipher grade used with opportunistic TLS.  With earlier releases the
+opportunistic TLS cipher grade is always "export" and no protocols
+are disabled.
+When TLS handshakes fail, the connection is retried with TLS disabled.
+This allows mail delivery to sites with non\-interoperable TLS
+implementations.
+.br
+.IP "\fBencrypt\fR"
+Mandatory TLS encryption. Since a minimum
+level of security is intended, it is reasonable to be specific about
+sufficiently secure protocol versions and ciphers. At this security level
+and higher, the main.cf parameters smtp_tls_mandatory_protocols and
+smtp_tls_mandatory_ciphers specify the TLS protocols and minimum
+cipher grade which the administrator considers secure enough for
+mandatory encrypted sessions. This security level is not an appropriate
+default for systems delivering mail to the Internet.
+.br
+.IP "\fBdane\fR"
+Opportunistic DANE TLS.  At this security level, the TLS policy
+for the destination is obtained via DNSSEC.  For TLSA policy to be
+in effect, the destination domain's containing DNS zone must be
+signed and the Postfix SMTP client's operating system must be
+configured to send its DNS queries to a recursive DNS nameserver
+that is able to validate the signed records.  Each MX host's DNS
+zone should also be signed, and should publish DANE TLSA (RFC 7672)
+records that specify how that MX host's TLS certificate is to be
+verified.  TLSA records do not preempt the normal SMTP MX host
+selection algorithm, if some MX hosts support TLSA and others do
+not, TLS security will vary from delivery to delivery.  It is up
+to the domain owner to configure their MX hosts and their DNS
+sensibly.  To configure the Postfix SMTP client for DNSSEC lookups
+see the documentation for the smtp_dns_support_level main.cf
+parameter.  When DNSSEC\-validated TLSA records are not found the
+effective tls security level is "may".  When TLSA records are found,
+but are all unusable the effective security level is "encrypt".  For
+purposes of protocol and cipher selection, the "dane" security level
+is treated like a "mandatory" TLS security level, and weak ciphers
+and protocols are disabled.  Since DANE authenticates server
+certificates the "aNULL" cipher\-suites are transparently excluded
+at this level, no need to configure this manually.  RFC 7672 (DANE)
+TLS authentication is available with Postfix 2.11 and later.
+.br
+.IP "\fBdane\-only\fR"
+Mandatory DANE TLS.  This is just like "dane" above, but DANE
+TLSA authentication is required.  There is no fallback to "may" or
+"encrypt" when TLSA records are missing or unusable.  RFC 7672
+(DANE) TLS authentication is available with Postfix 2.11 and later.
+.br
+.IP "\fBfingerprint\fR"
+Certificate fingerprint verification.
+At this security level, there are no trusted Certification Authorities.
+The certificate trust chain, expiration date, etc., are
+not checked. Instead, the \fBsmtp_tls_fingerprint_cert_match\fR
+parameter lists the certificate fingerprint or public key fingerprint
+(Postfix 2.9 and later) of the valid server certificate. The digest
+algorithm used to calculate the fingerprint is selected by the
+\fBsmtp_tls_fingerprint_digest\fR parameter. Available with Postfix
+2.5 and later.
+.br
+.IP "\fBverify\fR"
+Mandatory TLS verification. At this security
+level, DNS MX lookups are trusted to be secure enough, and the name
+verified in the server certificate is usually obtained indirectly
+via unauthenticated DNS MX lookups. The smtp_tls_verify_cert_match
+parameter controls how the server name is verified. In practice explicit
+control over matching is more common at the "secure" level, described
+below. This security level is not an appropriate default for systems
+delivering mail to the Internet.
+.br
+.IP "\fBsecure\fR"
+Secure\-channel TLS.  At this security level,
+DNS MX lookups, though potentially used to determine the candidate
+next\-hop gateway IP addresses, are \fBnot\fR trusted to be secure enough
+for TLS peername verification. Instead, the default name verified in
+the server certificate is obtained from the next\-hop domain as specified
+in the smtp_tls_secure_cert_match configuration parameter. The default
+matching rule is that a server certificate matches when its name is equal
+to or is a sub\-domain of the nexthop domain. This security level is not
+an appropriate default for systems delivering mail to the Internet.
+.br
+.br
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+# No TLS. Formerly: smtp_use_tls=no and smtp_enforce_tls=no.
+smtp_tls_security_level = none
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+# Opportunistic TLS.
+smtp_tls_security_level = may
+# Do not tweak opportunistic ciphers or protocols unless it is essential
+# to do so (if a security vulnerability is found in the SSL library that
+# can be mitigated by disabling a particular protocol or raising the
+# cipher grade).
+smtp_tls_ciphers = medium
+smtp_tls_protocols = >=TLSv1
+# Legacy (Postfix < 3.6) syntax:
+smtp_tls_protocols = !SSLv2, !SSLv3
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+# Mandatory (high\-grade) TLS encryption.
+smtp_tls_security_level = encrypt
+smtp_tls_mandatory_ciphers = high
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+# Authenticated TLS 1.2 or better matching the nexthop domain or a
+# subdomain.
+smtp_tls_security_level = secure
+smtp_tls_mandatory_ciphers = high
+smtp_tls_mandatory_protocols = >=TLSv1.2
+smtp_tls_secure_cert_match = nexthop, dot\-nexthop
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+# Certificate fingerprint verification (Postfix >= 2.5).
+# The CA\-less "fingerprint" security level only scales to a limited
+# number of destinations. As a global default rather than a per\-site
+# setting, this is practical only when mail for all recipients is sent
+# to a central mail hub.
+relayhost = [mailhub.example.com]
+smtp_tls_security_level = fingerprint
+smtp_tls_mandatory_protocols = >=TLSv1.2
+smtp_tls_mandatory_ciphers = high
+smtp_tls_fingerprint_cert_match =
+    3D:95:34:51:...:40:99:C0:C1
+    EC:3B:2D:B0:...:A3:9D:72:F6
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtp_tls_servername (default: empty)
+Optional name to send to the remote SMTP server in the TLS Server
+Name Indication (SNI) extension.  The SNI extension is always on when
+DANE is used to authenticate the server, and in that case the SNI name
+sent is the one required by RFC7672 and this parameter is ignored.
+.PP
+Some SMTP servers use the received SNI name to select an appropriate
+certificate chain to present to the client.  While this may improve
+interoperability with such servers, it may reduce interoperability with
+other servers that choose to abort the connection when they don't have a
+certificate chain configured for the requested name.  Such servers
+should select a default certificate chain and continue the handshake,
+but some may not.  Therefore, absent DANE, no SNI name is sent by
+default.
+.PP
+The SNI name must be either a valid DNS hostname, or else one of the
+special values \fBhostname\fR or \fBnexthop\fR, which select either the
+remote hostname or the nexthop domain respectively.  DNS names for SNI must be
+in A\-label (punycode) form.  Invalid DNS names log a configuration error
+warning and mail delivery is deferred.
+.PP
+Except when using a relayhost to forward all email, the only
+sensible non\-empty main.cf setting for this parameter is
+\fBhostname\fR.  Other non\-empty values are only practical on a
+per\-destination basis via the \fBservername\fR attribute of the Postfix
+TLS policy table.  When
+in doubt, leave this parameter empty, and configure per\-destination SNI
+as needed.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH smtp_tls_session_cache_database (default: empty)
+Name of the file containing the optional Postfix SMTP client
+TLS session cache. Specify a database type that supports enumeration,
+such as \fBbtree\fR or \fBsdbm\fR; there is no need to support
+concurrent access.  The file is created if it does not exist. The \fBsmtp\fR(8)
+daemon does not use this parameter directly, rather the cache is
+implemented indirectly in the \fBtlsmgr\fR(8) daemon. This means that
+per\-smtp\-instance master.cf overrides of this parameter are not effective.
+Note that each of the cache databases supported by \fBtlsmgr\fR(8) daemon:
+$smtpd_tls_session_cache_database, $smtp_tls_session_cache_database
+(and with Postfix 2.3 and later $lmtp_tls_session_cache_database), needs to
+be stored separately. It is not at this time possible to store multiple
+caches in a single database.
+.PP
+Note: \fBdbm\fR databases are not suitable. TLS
+session objects are too large.
+.PP
+As of version 2.5, Postfix no longer uses root privileges when
+opening this file. The file should now be stored under the Postfix\-owned
+data_directory. As a migration aid, an attempt to open the file
+under a non\-Postfix directory is redirected to the Postfix\-owned
+data_directory, and a warning is logged.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtp_tls_session_cache_database = btree:/var/lib/postfix/smtp_scache
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtp_tls_session_cache_timeout (default: 3600s)
+The expiration time of Postfix SMTP client TLS session cache
+information.  A cache cleanup is performed periodically
+every $smtp_tls_session_cache_timeout seconds. As with
+$smtp_tls_session_cache_database, this parameter is implemented in the
+\fBtlsmgr\fR(8) daemon and therefore per\-smtp\-instance master.cf overrides
+are not possible.
+.PP
+As of Postfix 2.11 this setting cannot exceed 100 days.  If set
+<= 0, session caching is disabled.  If set to a positive value
+less than 2 minutes, the minimum value of 2 minutes is used instead.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtp_tls_trust_anchor_file (default: empty)
+Zero or more PEM\-format files with trust\-anchor certificates
+and/or public keys.  If the parameter is not empty the root CAs in
+CAfile and CApath are no longer trusted.  Rather, the Postfix SMTP
+client will only trust certificate\-chains signed by one of the
+trust\-anchors contained in the chosen files.  The specified
+trust\-anchor certificates and public keys are not subject to
+expiration, and need not be (self\-signed) root CAs.  They may, if
+desired, be intermediate certificates. Therefore, these certificates
+also may be found "in the middle" of the trust chain presented by
+the remote SMTP server, and any untrusted issuing parent certificates
+will be ignored.  Specify a list of pathnames separated by comma
+or whitespace.
+.PP
+Whether specified in main.cf, or on a per\-destination basis,
+the trust\-anchor PEM file must be accessible to the Postfix SMTP
+client in the chroot jail if applicable.  The trust\-anchor file
+should contain only certificates and public keys, no private key
+material, and must be readable by the non\-privileged $mail_owner
+user.  This allows destinations to be bound to a set of specific
+CAs or public keys without trusting the same CAs for all destinations.
+.PP
+The main.cf parameter supports single\-purpose Postfix installations
+that send mail to a fixed set of SMTP peers.  At most sites, if
+trust\-anchor files are used at all, they will be specified on a
+per\-destination basis via the "tafile" attribute of the "verify"
+and "secure" levels in smtp_tls_policy_maps.
+.PP
+The underlying mechanism is in support of RFC 7672 (DANE TLSA),
+which defines mechanisms for an SMTP client MTA to securely determine
+server TLS certificates via DNS.
+.PP
+If you want your trust anchors to be public keys, with OpenSSL
+you can extract a single PEM public key from a PEM X.509 file
+containing a single certificate, as follows:
+.sp
+.in +4
+.nf
+.na
+.ft C
+$ openssl x509 \-in cert.pem \-out ta\-key.pem \-noout \-pubkey
+.fi
+.ad
+.ft R
+.in -4
+.PP
+This feature is available in Postfix 2.11 and later.
+.SH smtp_tls_verify_cert_match (default: hostname)
+How the Postfix SMTP client verifies the server certificate
+peername for the
+"verify" TLS security level. In a "verify" TLS policy table
+($smtp_tls_policy_maps) entry the optional "match" attribute
+overrides this main.cf setting.
+.PP
+This parameter specifies one or more patterns or strategies separated
+by commas, whitespace or colons.  In the policy table the only valid
+separator is the colon character.
+.PP
+Patterns specify domain names, or domain name suffixes:
+.IP "\fIexample.com\fR"
+Match the \fIexample.com\fR domain,
+i.e. one of the names in the server certificate must be \fIexample.com\fR.
+Upper and lower case distinctions are ignored.
+.br
+.IP "\fI.example.com\fR"
+Match subdomains of the \fIexample.com\fR domain, i.e. match
+a name in the server certificate that consists of a non\-zero number of
+labels followed by a \fI.example.com\fR suffix. Case distinctions are
+ignored.
+.br
+.br
+.PP
+Strategies specify a transformation from the next\-hop domain
+to the expected name in the server certificate:
+.IP "nexthop"
+Match against the next\-hop domain, which is either the recipient
+domain, or the transport next\-hop configured for the domain stripped of
+any optional socket type prefix, enclosing square brackets and trailing
+port. When MX lookups are not suppressed, this is the original nexthop
+domain prior to the MX lookup, not the result of the MX lookup. For
+LMTP delivery via UNIX\-domain sockets, the verified next\-hop name is
+$myhostname.  This strategy is suitable for use with the "secure"
+policy. Case is ignored.
+.br
+.IP "dot\-nexthop"
+As above, but match server certificate names that are subdomains
+of the next\-hop domain. Case is ignored.
+.br
+.IP "hostname"
+Match against the hostname of the server, often
+obtained via an unauthenticated DNS MX lookup. For LMTP delivery via
+UNIX\-domain sockets, the verified name is $myhostname. This matches
+the verification strategy of the "MUST" keyword in the obsolete
+smtp_tls_per_site table, and is suitable for use with the "verify"
+security level. When the next\-hop name is enclosed in square brackets
+to suppress MX lookups, the "hostname" strategy is the same as the
+"nexthop" strategy. Case is ignored.
+.br
+.br
+.PP
+Sample main.cf setting:
+.PP
+.nf
+.na
+.ft C
+smtp_tls_verify_cert_match = hostname, nexthop, dot\-nexthop
+.fi
+.ad
+.ft R
+.PP
+Sample policy table override:
+.PP
+.nf
+.na
+.ft C
+example.com     verify  match=hostname:nexthop
+\&.example.com    verify  match=example.com:.example.com:hostname
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtp_tls_wrappermode (default: no)
+Request that the Postfix SMTP client connects using the
+SUBMISSIONS/SMTPS protocol instead of using the STARTTLS command.
+.PP
+This mode requires "smtp_tls_security_level = encrypt" or
+stronger.
+.PP
+Example: deliver all remote mail via a provider's server
+"mail.example.com".
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    # Client\-side SMTPS requires "encrypt" or stronger.
+    smtp_tls_security_level = encrypt
+    smtp_tls_wrappermode = yes
+    # The [] suppress MX lookups.
+    relayhost = [mail.example.com]:465
+.fi
+.ad
+.ft R
+.PP
+More examples are in TLS_README, including examples for older
+Postfix versions.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH smtp_use_tls (default: no)
+Opportunistic mode: use TLS when a remote SMTP server announces
+STARTTLS support, otherwise send the mail in the clear. Beware:
+some SMTP servers offer STARTTLS even if it is not configured.  With
+Postfix < 2.3, if the TLS handshake fails, and no other server is
+available, delivery is deferred and mail stays in the queue. If this
+is a concern for you, use the smtp_tls_per_site feature instead.
+.PP
+This feature is available in Postfix 2.2 and later. With
+Postfix 2.3 and later use smtp_tls_security_level instead.
+.SH smtp_xforward_timeout (default: 300s)
+The Postfix SMTP client time limit for sending the XFORWARD command,
+and for receiving the remote SMTP server response.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH smtpd_authorized_verp_clients (default: $authorized_verp_clients)
+What remote SMTP clients are allowed to specify the XVERP command.
+This command requests that mail be delivered one recipient at a
+time with a per recipient return address.
+.PP
+By default, no clients are allowed to specify XVERP.
+.PP
+This parameter was renamed with Postfix version 2.1. The default value
+is backwards compatible with Postfix version 2.0.
+.PP
+Specify a list of network/netmask patterns, separated by commas
+and/or whitespace. The mask specifies the number of bits in the
+network part of a host address. You can also specify hostnames or
+\&.domain names (the initial dot causes the domain to match any name
+below it),  "/file/name" or "type:table" patterns.  A "/file/name"
+pattern is replaced by its contents; a "type:table" lookup table
+is matched when a table entry matches a lookup string (the lookup
+result is ignored).  Continue long lines by starting the next line
+with whitespace. Specify "!pattern" to exclude an address or network
+block from the list. The form "!/file/name" is supported only in
+Postfix version 2.4 and later.
+.PP
+Note: IP version 6 address information must be specified inside
+[] in the smtpd_authorized_verp_clients value, and in
+files specified with "/file/name".  IP version 6 addresses contain
+the ":" character, and would otherwise be confused with a "type:table"
+pattern.
+.SH smtpd_authorized_xclient_hosts (default: empty)
+What remote SMTP clients are allowed to use the XCLIENT feature.  This
+command overrides remote SMTP client information that is used for access
+control. Typical use is for SMTP\-based content filters, fetchmail\-like
+programs, or SMTP server access rule testing. See the XCLIENT_README
+document for details.
+.PP
+This feature is available in Postfix 2.1 and later.
+.PP
+By default, no clients are allowed to specify XCLIENT.
+.PP
+Specify a list of network/netmask patterns, separated by commas
+and/or whitespace. The mask specifies the number of bits in the
+network part of a host address. You can also specify hostnames or
+\&.domain names (the initial dot causes the domain to match any name
+below it),  "/file/name" or "type:table" patterns.  A "/file/name"
+pattern is replaced by its contents; a "type:table" lookup table
+is matched when a table entry matches a lookup string (the lookup
+result is ignored).  Continue long lines by starting the next line
+with whitespace. Specify "!pattern" to exclude an address or network
+block from the list. The form "!/file/name" is supported only in
+Postfix version 2.4 and later.
+.PP
+Note: IP version 6 address information must be specified inside
+[] in the smtpd_authorized_xclient_hosts value, and in
+files specified with "/file/name".  IP version 6 addresses contain
+the ":" character, and would otherwise be confused with a "type:table"
+pattern.
+.SH smtpd_authorized_xforward_hosts (default: empty)
+What remote SMTP clients are allowed to use the XFORWARD feature.  This
+command forwards information that is used to improve logging after
+SMTP\-based content filters. See the XFORWARD_README document for
+details.
+.PP
+This feature is available in Postfix 2.1 and later.
+.PP
+By default, no clients are allowed to specify XFORWARD.
+.PP
+Specify a list of network/netmask patterns, separated by commas
+and/or whitespace. The mask specifies the number of bits in the
+network part of a host address. You can also specify hostnames or
+\&.domain names (the initial dot causes the domain to match any name
+below it),  "/file/name" or "type:table" patterns.  A "/file/name"
+pattern is replaced by its contents; a "type:table" lookup table
+is matched when a table entry matches a lookup string (the lookup
+result is ignored).  Continue long lines by starting the next line
+with whitespace. Specify "!pattern" to exclude an address or network
+block from the list. The form "!/file/name" is supported only in
+Postfix version 2.4 and later.
+.PP
+Note: IP version 6 address information must be specified inside
+[] in the smtpd_authorized_xforward_hosts value, and in
+files specified with "/file/name".  IP version 6 addresses contain
+the ":" character, and would otherwise be confused with a "type:table"
+pattern.
+.SH smtpd_banner (default: $myhostname ESMTP $mail_name)
+The text that follows the 220 status code in the SMTP greeting
+banner. Some people like to see the mail version advertised. By
+default, Postfix shows no version.
+.PP
+You MUST specify $myhostname at the start of the text. This is
+required by the SMTP protocol.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_banner = $myhostname ESMTP $mail_name ($mail_version)
+.fi
+.ad
+.ft R
+.SH smtpd_client_auth_rate_limit (default: 0)
+The maximal number of AUTH commands that any client is allowed to
+send to this service per time unit, regardless of whether or not
+Postfix actually accepts those commands.  The time unit is specified
+with the anvil_rate_time_unit configuration parameter.
+.PP
+By default, there is no limit on the number of AUTH commands that a
+client may send.
+.PP
+To disable this feature, specify a limit of 0.
+.PP
+WARNING: The purpose of this feature is to limit abuse. It must
+not be used to regulate legitimate mail traffic.
+.PP
+This feature is available in Postfix 3.1 and later.
+.SH smtpd_client_connection_count_limit (default: 50)
+How many simultaneous connections any client is allowed to
+make to this service.  By default, the limit is set to half
+the default process limit value.
+.PP
+To disable this feature, specify a limit of 0.
+.PP
+WARNING: The purpose of this feature is to limit abuse. It must
+not be used to regulate legitimate mail traffic.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_client_connection_rate_limit (default: 0)
+The maximal number of connection attempts any client is allowed to
+make to this service per time unit.  The time unit is specified
+with the anvil_rate_time_unit configuration parameter.
+.PP
+By default, a client can make as many connections per time unit as
+Postfix can accept.
+.PP
+To disable this feature, specify a limit of 0.
+.PP
+WARNING: The purpose of this feature is to limit abuse. It must
+not be used to regulate legitimate mail traffic.
+.PP
+This feature is available in Postfix 2.2 and later.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_client_connection_rate_limit = 1000
+.fi
+.ad
+.ft R
+.SH smtpd_client_event_limit_exceptions (default: $mynetworks)
+Clients that are excluded from smtpd_client_*_count/rate_limit
+restrictions. See the mynetworks parameter
+description for the parameter value syntax.
+.PP
+By default, clients in trusted networks are excluded. Specify a
+list of network blocks, hostnames or .domain names (the initial
+dot causes the domain to match any name below it).
+.PP
+Note: IP version 6 address information must be specified inside
+[] in the smtpd_client_event_limit_exceptions value, and
+in files specified with "/file/name".  IP version 6 addresses
+contain the ":" character, and would otherwise be confused with a
+"type:table" pattern.
+.PP
+Pattern matching of domain names is controlled by the presence
+or absence of "smtpd_client_event_limit_exceptions" in the
+parent_domain_matches_subdomains parameter value (Postfix 3.0 and
+later).
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_client_ipv4_prefix_length (default: 32)
+Aggregate smtpd_client_*_count and smtpd_client_*_rate statistics
+by IPv4 network blocks with the specified network prefix. Aggregation
+uses fewer \fBanvil\fR(8) resources to maintain counters. By default,
+aggregation is disabled for IPv4.
+.PP
+This feature is available in Postfix 3.8 and later.
+.SH smtpd_client_ipv6_prefix_length (default: 84)
+Aggregate smtpd_client_*_count and smtpd_client_*_rate statistics
+by IPv6 network blocks with the specified network prefix. Aggregation
+uses fewer the \fBanvil\fR(8) resources to maintain counters. By default,
+aggregation is enabled for IPv6.
+.PP
+This feature is available in Postfix 3.8 and later.
+.SH smtpd_client_message_rate_limit (default: 0)
+The maximal number of message delivery requests that any client is
+allowed to make to this service per time unit, regardless of whether
+or not Postfix actually accepts those messages.  The time unit is
+specified with the anvil_rate_time_unit configuration parameter.
+.PP
+By default, a client can send as many message delivery requests
+per time unit as Postfix can accept.
+.PP
+To disable this feature, specify a limit of 0.
+.PP
+WARNING: The purpose of this feature is to limit abuse. It must
+not be used to regulate legitimate mail traffic.
+.PP
+This feature is available in Postfix 2.2 and later.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_client_message_rate_limit = 1000
+.fi
+.ad
+.ft R
+.SH smtpd_client_new_tls_session_rate_limit (default: 0)
+The maximal number of new (i.e., uncached) TLS sessions that a
+remote SMTP client is allowed to negotiate with this service per
+time unit.  The time unit is specified with the anvil_rate_time_unit
+configuration parameter.
+.PP
+By default, a remote SMTP client can negotiate as many new TLS
+sessions per time unit as Postfix can accept.
+.PP
+To disable this feature, specify a limit of 0. Otherwise, specify
+a limit that is at least the per\-client concurrent session limit,
+or else legitimate client sessions may be rejected.
+.PP
+WARNING: The purpose of this feature is to limit abuse. It must
+not be used to regulate legitimate mail traffic.
+.PP
+This feature is available in Postfix 2.3 and later.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_client_new_tls_session_rate_limit = 100
+.fi
+.ad
+.ft R
+.SH smtpd_client_port_logging (default: no)
+Enable logging of the remote SMTP client port in addition to
+the hostname and IP address. The logging format is "host[address]:port".
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH smtpd_client_recipient_rate_limit (default: 0)
+The maximal number of recipient addresses that any client is allowed
+to send to this service per time unit, regardless of whether or not
+Postfix actually accepts those recipients.  The time unit is specified
+with the anvil_rate_time_unit configuration parameter.
+.PP
+By default, a client can send as many recipient addresses per time
+unit as Postfix can accept.
+.PP
+To disable this feature, specify a limit of 0.
+.PP
+WARNING: The purpose of this feature is to limit abuse. It must
+not be used to regulate legitimate mail traffic.
+.PP
+This feature is available in Postfix 2.2 and later.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_client_recipient_rate_limit = 1000
+.fi
+.ad
+.ft R
+.SH smtpd_client_restrictions (default: empty)
+Optional restrictions that the Postfix SMTP server applies in the
+context of a client connection request.
+See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access
+restriction lists" for a discussion of evaluation context and time.
+.PP
+The default is to allow all connection requests.
+.PP
+Specify a list of restrictions, separated by commas and/or whitespace.
+Continue long lines by starting the next line with whitespace.
+Restrictions are applied in the order as specified; the first
+restriction that matches wins.
+.PP
+The following restrictions are specific to client hostname or
+client network address information.
+.IP "\fBcheck_ccert_access \fItype:table\fR\fR"
+By default use the remote SMTP client certificate fingerprint
+or the public key
+fingerprint (Postfix 2.9 and later) as the lookup key for the specified
+\fBaccess\fR(5) database; with Postfix version 2.2, also require that the
+remote SMTP client certificate is verified successfully.
+The fingerprint digest algorithm is configurable via the
+smtpd_tls_fingerprint_digest parameter (hard\-coded as md5 prior to
+Postfix version 2.5).  This feature requires "smtpd_tls_ask_ccert
+= yes" and is available with Postfix version
+2.2 and later.
+.br
+The default algorithm is \fBsha256\fR with Postfix >= 3.6
+and the \fBcompatibility_level\fR set to 3.6 or higher. With Postfix
+<= 3.5, the default algorithm is \fBmd5\fR.  The best\-practice
+algorithm is now \fBsha256\fR. Recent advances in hash function
+cryptanalysis have led to md5 and sha1 being deprecated in favor of
+sha256.  However, as long as there are no known "second pre\-image"
+attacks against the older algorithms, their use in this context, though
+not recommended, is still likely safe.
+.br
+Alternatively, check_ccert_access accepts an explicit search
+order (Postfix 3.5 and later). The default search order as described
+above corresponds with:
+.br
+check_ccert_access { type:table, { search_order = cert_fingerprint,
+pubkey_fingerprint } }
+.br
+The commas are optional.
+.br
+.IP "\fBcheck_client_access \fItype:table\fR\fR"
+Search the specified access database for the client hostname,
+parent domains, client IP address, or networks obtained by stripping
+least significant octets. See the \fBaccess\fR(5) manual page for details.
+.br
+.IP "\fBcheck_client_a_access \fItype:table\fR\fR"
+Search the specified \fBaccess\fR(5) database for the IP addresses for the
+client hostname, and execute the corresponding action.  Note: a result
+of "OK" is not allowed for safety reasons. Instead, use DUNNO in order
+to exclude specific hosts from denylists.  This feature is available
+in Postfix 3.0 and later.
+.br
+.IP "\fBcheck_client_mx_access \fItype:table\fR\fR"
+Search the specified \fBaccess\fR(5) database for the MX hosts for the
+client hostname, and execute the corresponding action.  If no MX
+record is found, look up A or AAAA records, just like the Postfix
+SMTP client would. Note: a result
+of "OK" is not allowed for safety reasons. Instead, use DUNNO in order
+to exclude specific hosts from denylists.  This feature is available
+in Postfix 2.7 and later.
+.br
+.IP "\fBcheck_client_ns_access \fItype:table\fR\fR"
+Search the specified \fBaccess\fR(5) database for the DNS servers for
+the client hostname, and execute the corresponding action.  Note: a
+result of "OK" is not allowed for safety reasons. Instead, use DUNNO
+in order to exclude specific hosts from denylists.  This feature is
+available in Postfix 2.7 and later.
+.br
+.IP "\fBcheck_reverse_client_hostname_access \fItype:table\fR\fR"
+Search the specified access database for the unverified reverse
+client hostname, parent domains, client IP address, or networks
+obtained by stripping least significant octets. See the \fBaccess\fR(5)
+manual page for details.  Note: a result of "OK" is not allowed for
+safety reasons.  Instead, use DUNNO in order to exclude specific
+hosts from denylists.  This feature is available in Postfix 2.6
+and later.
+.br
+.IP "\fBcheck_reverse_client_hostname_a_access \fItype:table\fR\fR"
+Search the specified \fBaccess\fR(5) database for the IP addresses for the
+unverified reverse client hostname, and execute the corresponding
+action.  Note: a result of "OK" is not allowed for safety reasons.
+Instead, use DUNNO in order to exclude specific hosts from denylists.
+This feature is available in Postfix 3.0 and later.
+.br
+.IP "\fBcheck_reverse_client_hostname_mx_access \fItype:table\fR\fR"
+Search the specified \fBaccess\fR(5) database for the MX hosts for the
+unverified reverse client hostname, and execute the corresponding
+action.  If no MX record is found, look up A or AAAA records, just
+like the Postfix SMTP client would.
+Note: a result of "OK" is not allowed for safety reasons.
+Instead, use DUNNO in order to exclude specific hosts from denylists.
+This feature is available in Postfix 2.7 and later.
+.br
+.IP "\fBcheck_reverse_client_hostname_ns_access \fItype:table\fR\fR"
+Search the specified \fBaccess\fR(5) database for the DNS servers for
+the unverified reverse client hostname, and execute the corresponding
+action.  Note: a result of "OK" is not allowed for safety reasons.
+Instead, use DUNNO in order to exclude specific hosts from denylists.
+This feature is available in Postfix 2.7 and later.
+.br
+.IP "\fBcheck_sasl_access \fItype:table\fR\fR"
+Use the remote SMTP client SASL user name as the lookup key for
+the specified \fBaccess\fR(5) database. The lookup key has the form
+"username@domainname" when the smtpd_sasl_local_domain parameter
+value is non\-empty.  Unlike the check_client_access feature,
+check_sasl_access does not perform matches of parent domains or IP
+subnet ranges.  This feature is available with Postfix version 2.11
+and later.
+.br
+.IP "\fBpermit_inet_interfaces\fR"
+Permit the request when the client IP address matches
+$inet_interfaces.
+.br
+.IP "\fBpermit_mynetworks\fR"
+Permit the request when the client IP address matches any
+network or network address listed in  $mynetworks.
+.br
+.IP "\fBpermit_sasl_authenticated\fR"
+Permit the request when the client is successfully
+authenticated via the RFC 4954 (AUTH) protocol.
+.br
+.IP "\fBpermit_tls_all_clientcerts\fR"
+Permit the request when the remote SMTP client certificate is
+verified successfully.  This option must be used only if a special
+CA issues the certificates and only this CA is listed as a trusted
+CA. Otherwise, clients with a third\-party certificate would also
+be allowed to relay.  Specify "tls_append_default_CA = no" when the
+trusted CA is specified with smtpd_tls_CAfile or smtpd_tls_CApath,
+to prevent Postfix from appending the system\-supplied default CAs.
+This feature requires "smtpd_tls_ask_ccert = yes" and is available
+with Postfix version 2.2 and later.
+.br
+.IP "\fBpermit_tls_clientcerts\fR"
+Permit the request when the remote SMTP client certificate
+fingerprint or public key fingerprint (Postfix 2.9 and later) is
+listed in $relay_clientcerts.
+The fingerprint digest algorithm is configurable via the
+smtpd_tls_fingerprint_digest parameter (hard\-coded as md5 prior to
+Postfix version 2.5).  This feature requires "smtpd_tls_ask_ccert
+= yes" and is available with Postfix version 2.2 and later.
+.br
+The default algorithm is \fBsha256\fR with Postfix >= 3.6
+and the \fBcompatibility_level\fR set to 3.6 or higher. With Postfix
+<= 3.5, the default algorithm is \fBmd5\fR.  The best\-practice
+algorithm is now \fBsha256\fR. Recent advances in hash function
+cryptanalysis have led to md5 and sha1 being deprecated in favor of
+sha256.  However, as long as there are no known "second pre\-image"
+attacks against the older algorithms, their use in this context, though
+not recommended, is still likely safe.
+.br
+.IP "\fBreject_rbl_client \fIrbl_domain=d.d.d.d\fR\fR"
+Reject the request when the reversed client network address is
+listed with the A record "\fId.d.d.d\fR" under \fIrbl_domain\fR
+(Postfix version 2.1 and later only).  Each "\fId\fR" is a number,
+or a pattern inside "[]" that contains one or more ";"\-separated
+numbers or number..number ranges (Postfix version 2.8 and later).
+If no "\fI=d.d.d.d\fR" is specified, reject the request when the
+reversed client network address is listed with any A record under
+\fIrbl_domain\fR.
+.br
+The maps_rbl_reject_code parameter specifies the response code for
+rejected requests (default:  554), the default_rbl_reply  parameter
+specifies the default server reply, and the rbl_reply_maps  parameter
+specifies tables with server replies indexed by \fIrbl_domain\fR.
+This feature is available in Postfix 2.0 and later.
+.br
+.IP "\fBpermit_dnswl_client \fIdnswl_domain=d.d.d.d\fR\fR"
+Accept the request when the reversed client network address is
+listed with the A record "\fId.d.d.d\fR" under \fIdnswl_domain\fR.
+Each "\fId\fR" is a number, or a pattern inside "[]" that contains
+one or more ";"\-separated numbers or number..number ranges.
+If no "\fI=d.d.d.d\fR" is specified, accept the request when the
+reversed client network address is listed with any A record under
+\fIdnswl_domain\fR.
+.br
+For safety, permit_dnswl_client is silently
+ignored when it would override reject_unauth_destination.  The
+result is DEFER_IF_REJECT when allowlist lookup fails.  This feature
+is available in Postfix 2.8 and later.
+.br
+.IP "\fBreject_rhsbl_client \fIrbl_domain=d.d.d.d\fR\fR"
+Reject the request when the client hostname is listed with the
+A record "\fId.d.d.d\fR" under \fIrbl_domain\fR (Postfix version
+2.1 and later only).  Each "\fId\fR" is a number, or a pattern
+inside "[]" that contains one or more ";"\-separated numbers or
+number..number ranges (Postfix version 2.8 and later).  If no
+"\fI=d.d.d.d\fR" is specified, reject the request when the client
+hostname is listed with
+any A record under \fIrbl_domain\fR. See the reject_rbl_client
+description above for additional RBL related configuration parameters.
+This feature is available in Postfix 2.0 and later; with Postfix
+version 2.8 and later, reject_rhsbl_reverse_client will usually
+produce better results.
+.br
+.IP "\fBpermit_rhswl_client \fIrhswl_domain=d.d.d.d\fR\fR"
+Accept the request when the client hostname is listed with the
+A record "\fId.d.d.d\fR" under \fIrhswl_domain\fR.  Each "\fId\fR"
+is a number, or a pattern inside "[]" that contains one or more
+";"\-separated numbers or number..number ranges. If no
+"\fI=d.d.d.d\fR" is specified, accept the request when the client
+hostname is listed with any A record under \fIrhswl_domain\fR.
+.br
+Caution: client name allowlisting is fragile, since the client
+name lookup can fail due to temporary outages.  Client name
+allowlisting should be used only to reduce false positives in e.g.
+DNS\-based blocklists, and not for making access rule exceptions.
+.br
+For safety, permit_rhswl_client is silently ignored when it
+would override reject_unauth_destination.  The result is DEFER_IF_REJECT
+when allowlist lookup fails.  This feature is available in Postfix
+2.8 and later.
+.br
+.IP "\fBreject_rhsbl_reverse_client \fIrbl_domain=d.d.d.d\fR\fR"
+Reject the request when the unverified reverse client hostname
+is listed with the A record "\fId.d.d.d\fR" under \fIrbl_domain\fR.
+Each "\fId\fR" is a number, or a pattern inside "[]" that contains
+one or more ";"\-separated numbers or number..number ranges.
+If no "\fI=d.d.d.d\fR" is specified, reject the request when the
+unverified reverse client hostname is listed with any A record under
+\fIrbl_domain\fR. See the reject_rbl_client description above for
+additional RBL related configuration parameters.  This feature is
+available in Postfix 2.8 and later.
+.br
+.IP "\fBreject_unknown_client_hostname\fR (with Postfix < 2.3: reject_unknown_client)"
+Reject the request when 1) the client IP address\->name mapping
+fails, or 2) the name\->address mapping fails, or 3) the name\->address
+mapping does not match the client IP address.
+.br
+This is a
+stronger restriction than the reject_unknown_reverse_client_hostname
+feature, which triggers only under condition 1) above.
+.br
+The
+unknown_client_reject_code parameter specifies the response code
+for rejected requests (default: 450). The reply is always 450 in
+case the address\->name or name\->address lookup failed due to
+a temporary problem.
+.br
+.IP "\fBreject_unknown_reverse_client_hostname\fR"
+Reject the request when the client IP address has no address\->name
+mapping.
+.br
+This is a weaker restriction than the
+reject_unknown_client_hostname feature, which requires not only
+that the address\->name and name\->address mappings exist, but
+also that the two mappings reproduce the client IP address.
+.br
+The unknown_client_reject_code parameter specifies the response
+code for rejected requests (default: 450).  The reply is always 450
+in case the address\->name lookup failed due to a temporary
+problem.
+.br
+This feature is available in Postfix 2.3 and
+later.
+.br
+.br
+.PP
+In addition, you can use any of the following
+generic restrictions.  These restrictions are applicable in
+any SMTP command context.
+.IP "\fBcheck_policy_service \fIservername\fR\fR"
+Query the specified policy server. See the SMTPD_POLICY_README
+document for details. This feature is available in Postfix 2.1
+and later.
+.br
+.IP "\fBdefer\fR"
+Defer the request. The client is told to try again later. This
+restriction is useful at the end of a restriction list, to make
+the default policy explicit.
+.br
+The defer_code parameter specifies
+the SMTP server reply code (default: 450).
+.br
+.IP "\fBdefer_if_permit\fR"
+Defer the request if some later restriction would result in an
+explicit or implicit PERMIT action.  This is useful when a denylisting
+feature fails due to a temporary problem.  This feature is available
+in Postfix version 2.1 and later.
+.br
+.IP "\fBdefer_if_reject\fR"
+Defer the request if some later restriction would result in a
+REJECT action.  This is useful when an allowlisting feature fails
+due to a temporary problem.  This feature is available in Postfix
+version 2.1 and later.
+.br
+.IP "\fBpermit\fR"
+Permit the request. This restriction is useful at the end of
+a restriction list, to make the default policy explicit.
+.br
+.IP "\fBreject_multi_recipient_bounce\fR"
+Reject the request when the envelope sender is the null address,
+and the message has multiple envelope recipients. This usage has
+rare but legitimate applications: under certain conditions,
+multi\-recipient mail that was posted with the DSN option NOTIFY=NEVER
+may be forwarded with the null sender address.
+.br
+Note: this restriction can only work reliably
+when used in smtpd_data_restrictions or
+smtpd_end_of_data_restrictions, because the total number of
+recipients is not known at an earlier stage of the SMTP conversation.
+Use at the RCPT stage will only reject the second etc.  recipient.
+.br
+The multi_recipient_bounce_reject_code parameter specifies the
+response code for rejected requests (default:  550).  This feature
+is available in Postfix 2.1 and later.
+.br
+.IP "\fBreject_plaintext_session\fR"
+Reject the request when the connection is not encrypted. This
+restriction should not be used before the client has had a chance
+to negotiate encryption with the AUTH or STARTTLS commands.
+.br
+The plaintext_reject_code parameter specifies the response
+code for rejected requests (default:  450).  This feature is available
+in Postfix 2.3 and later.
+.br
+.IP "\fBreject_unauth_pipelining\fR"
+Reject the request when the client sends SMTP commands ahead
+of time where it is not allowed, or when the client sends SMTP
+commands ahead of time without knowing that Postfix actually supports
+ESMTP command pipelining. This stops mail from bulk mail software
+that improperly uses ESMTP command pipelining in order to speed up
+deliveries.
+.br
+With Postfix 2.6 and later, the SMTP server sets a per\-session
+flag whenever it detects illegal pipelining, including pipelined
+HELO or EHLO commands. The reject_unauth_pipelining feature simply
+tests whether the flag was set at any point in time during the
+session.
+.br
+With older Postfix versions, reject_unauth_pipelining checks
+the current status of the input read queue, and its usage is not
+recommended in contexts other than smtpd_data_restrictions.
+.br
+.IP "\fBreject\fR"
+Reject the request. This restriction is useful at the end of
+a restriction list, to make the default policy explicit.  The
+reject_code configuration parameter specifies the response code for
+rejected requests (default: 554).
+.br
+.IP "\fBsleep \fIseconds\fR\fR"
+Pause for the specified number of seconds and proceed with
+the next restriction in the list, if any. This may stop zombie
+mail when used as:
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    smtpd_client_restrictions =
+        sleep 1, reject_unauth_pipelining
+    smtpd_delay_reject = no
+.fi
+.ad
+.ft R
+This feature is available in Postfix 2.3.
+.br
+.IP "\fBwarn_if_reject\fR"
+A safety net for testing. When "warn_if_reject" is placed
+before a reject\-type restriction, access table query, or
+check_policy_service query, this logs a "reject_warning" message
+instead of rejecting a request (when a reject\-type restriction fails
+due to a temporary error, this logs a "reject_warning" message for
+any implicit "defer_if_permit" actions that would normally prevent
+mail from being accepted by some later access restriction). This
+feature has no effect on defer_if_reject restrictions.
+.br
+.br
+.PP
+Other restrictions that are valid in this context:
+.IP \(bu
+SMTP command specific restrictions that are described under
+the smtpd_helo_restrictions, smtpd_sender_restrictions or
+smtpd_recipient_restrictions parameters. When helo, sender or
+recipient restrictions are listed under smtpd_client_restrictions,
+they have effect only with "smtpd_delay_reject = yes", so that
+$smtpd_client_restrictions is evaluated at the time of the RCPT TO
+command.
+.br
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_client_restrictions = permit_mynetworks, reject_unknown_client_hostname
+.fi
+.ad
+.ft R
+.SH smtpd_command_filter (default: empty)
+A mechanism to transform commands from remote SMTP clients.
+This is a last\-resort tool to work around client commands that break
+interoperability with the Postfix SMTP server.  Other uses involve
+fault injection to test Postfix's handling of invalid commands.
+.PP
+Specify the name of a "type:table" lookup table. The search
+string is the SMTP command as received from the remote SMTP client,
+except that initial whitespace and the trailing <CR><LF>
+are removed.  The result value is executed by the Postfix SMTP
+server.
+.PP
+There is no need to use smtpd_command_filter for the following
+cases:
+.IP \(bu
+Use "resolve_numeric_domain = yes" to accept
+"\fIuser@ipaddress\fR".
+.IP \(bu
+Postfix already accepts the correct form
+"\fIuser@[ipaddress]\fR". Use virtual_alias_maps or canonical_maps
+to translate these into domain names if necessary.
+.IP \(bu
+Use "strict_rfc821_envelopes = no" to accept "RCPT TO:<\fIUser
+Name <user@example.com>>\fR". Postfix will ignore the "\fIUser
+Name\fR" part and deliver to the \fI<user@example.com>\fR address.
+.br
+.PP
+Examples of problems that can be solved with the smtpd_command_filter
+feature:
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    smtpd_command_filter = pcre:/etc/postfix/command_filter
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/command_filter:
+    # Work around clients that send malformed HELO commands.
+    /^HELO\es*$/ HELO domain.invalid
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+    # Work around clients that send empty lines.
+    /^\es*$/     NOOP
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+    # Work around clients that send RCPT TO:<'user@domain'>.
+    # WARNING: do not lose the parameters that follow the address.
+    /^(RCPT\es+TO:\es*<)'([^[:space:]]+)'(>.*)/     $1$2$3
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+    # Append XVERP to MAIL FROM commands to request VERP\-style delivery.
+    # See VERP_README for more information on how to use Postfix VERP.
+    /^(MAIL\es+FROM:\es*<listname@example\e.com>.*)/   $1 XVERP
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+    # Bounce\-never mail sink. Use notify_classes=bounce,resource,software
+    # to send bounced mail to the postmaster (with message body removed).
+    /^(RCPT\es+TO:\es*<.*>.*)\es+NOTIFY=\eS+(.*)/     $1 NOTIFY=NEVER$2
+    /^(RCPT\es+TO:.*)/                             $1 NOTIFY=NEVER
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.7.
+.SH smtpd_data_restrictions (default: empty)
+Optional access restrictions that the Postfix SMTP server applies
+in the context of the SMTP DATA command.
+See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access
+restriction lists" for a discussion of evaluation context and time.
+.PP
+This feature is available in Postfix 2.0 and later.
+.PP
+Specify a list of restrictions, separated by commas and/or whitespace.
+Continue long lines by starting the next line with whitespace.
+Restrictions are applied in the order as specified; the first
+restriction that matches wins.
+.PP
+The following restrictions are valid in this context:
+.IP \(bu
+Generic restrictions that can be used
+in any SMTP command context, described under smtpd_client_restrictions.
+.IP \(bu
+SMTP command specific restrictions described under
+smtpd_client_restrictions, smtpd_helo_restrictions,
+smtpd_sender_restrictions or smtpd_recipient_restrictions.
+.IP \(bu
+However, no recipient information is available in the case of
+multi\-recipient mail. Acting on only one recipient would be misleading,
+because any decision will affect all recipients equally. Acting on
+all recipients would require a possibly very large amount of memory,
+and would also be misleading for the reasons mentioned before.
+.br
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+smtpd_data_restrictions = reject_unauth_pipelining
+smtpd_data_restrictions = reject_multi_recipient_bounce
+.fi
+.ad
+.ft R
+.SH smtpd_delay_open_until_valid_rcpt (default: yes)
+Postpone the start of an SMTP mail transaction until a valid
+RCPT TO command is received. Specify "no" to create a mail transaction
+as soon as the Postfix SMTP server receives a valid MAIL FROM
+command.
+.PP
+With sites that reject lots of mail, the default setting reduces
+the use of
+disk, CPU and memory resources. The downside is that rejected
+recipients are logged with NOQUEUE instead of a mail transaction
+ID. This complicates the logfile analysis of multi\-recipient mail.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtpd_delay_reject (default: yes)
+Wait until the RCPT TO command before evaluating
+$smtpd_client_restrictions, $smtpd_helo_restrictions and
+$smtpd_sender_restrictions, or wait until the ETRN command before
+evaluating $smtpd_client_restrictions and $smtpd_helo_restrictions.
+.PP
+This feature is turned on by default because some clients apparently
+mis\-behave when the Postfix SMTP server rejects commands before
+RCPT TO.
+.PP
+The default setting has one major benefit: it allows Postfix to log
+recipient address information when rejecting a client name/address
+or sender address, so that it is possible to find out whose mail
+is being rejected.
+.SH smtpd_discard_ehlo_keyword_address_maps (default: empty)
+Lookup tables, indexed by the remote SMTP client address, with
+case insensitive lists of EHLO keywords (pipelining, starttls, auth,
+etc.) that the Postfix SMTP server will not send in the EHLO response
+to a
+remote SMTP client. See smtpd_discard_ehlo_keywords for details.
+The tables are not searched by hostname for robustness reasons.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_discard_ehlo_keywords (default: empty)
+A case insensitive list of EHLO keywords (pipelining, starttls,
+auth, etc.) that the Postfix SMTP server will not send in the EHLO
+response
+to a remote SMTP client.
+.PP
+This feature is available in Postfix 2.2 and later.
+.PP
+Notes:
+.IP \(bu
+Specify the \fBsilent\-discard\fR pseudo keyword to prevent
+this action from being logged.
+.IP \(bu
+Use the smtpd_discard_ehlo_keyword_address_maps feature
+to discard EHLO keywords selectively.
+.br
+.SH smtpd_dns_reply_filter (default: empty)
+Optional filter for Postfix SMTP server DNS lookup results.
+See smtp_dns_reply_filter for details including an example.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH smtpd_end_of_data_restrictions (default: empty)
+Optional access restrictions that the Postfix SMTP server
+applies in the context of the SMTP END\-OF\-DATA command.
+See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access
+restriction lists" for a discussion of evaluation context and time.
+.PP
+This feature is available in Postfix 2.2 and later.
+.PP
+See smtpd_data_restrictions for details and limitations.
+.SH smtpd_enforce_tls (default: no)
+Mandatory TLS: announce STARTTLS support to remote SMTP clients,
+and require that clients use TLS encryption.  According to RFC 2487
+this MUST NOT be applied in case of a publicly\-referenced SMTP
+server.  This option is therefore off by default.
+.PP
+Note 1: "smtpd_enforce_tls = yes" implies "smtpd_tls_auth_only = yes".
+.PP
+Note 2: when invoked via "\fBsendmail \-bs\fR", Postfix will never offer
+STARTTLS due to insufficient privileges to access the server private
+key. This is intended behavior.
+.PP
+This feature is available in Postfix 2.2 and later. With
+Postfix 2.3 and later use smtpd_tls_security_level instead.
+.SH smtpd_error_sleep_time (default: 1s)
+With Postfix version 2.1 and later: the SMTP server response delay after
+a client has made more than $smtpd_soft_error_limit errors, and
+fewer than $smtpd_hard_error_limit errors, without delivering mail.
+.PP
+With Postfix version 2.0 and earlier: the SMTP server delay
+before sending a reject (4xx or 5xx) response, when the client has
+made fewer than $smtpd_soft_error_limit errors without delivering
+mail. When the client has made $smtpd_soft_error_limit or more errors,
+delay all responses with the larger of (number of errors) seconds
+or $smtpd_error_sleep_time.
+.PP
+Specify a non\-negative time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH smtpd_etrn_restrictions (default: empty)
+Optional restrictions that the Postfix SMTP server applies in the
+context of a client ETRN command.
+See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access
+restriction lists" for a discussion of evaluation context and time.
+.PP
+The Postfix ETRN implementation accepts only destinations that are
+eligible for the Postfix "fast flush" service. See the ETRN_README
+file for details.
+.PP
+Specify a list of restrictions, separated by commas and/or whitespace.
+Continue long lines by starting the next line with whitespace.
+Restrictions are applied in the order as specified; the first
+restriction that matches wins.
+.PP
+The following restrictions are specific to the domain name information
+received with the ETRN command.
+.IP "\fBcheck_etrn_access \fItype:table\fR\fR"
+Search the specified access database for the ETRN domain name
+or its parent domains. See the \fBaccess\fR(5) manual page for details.
+.br
+.br
+.PP
+Other restrictions that are valid in this context:
+.IP \(bu
+Generic restrictions that can be used
+in any SMTP command context, described under smtpd_client_restrictions.
+.IP \(bu
+SMTP command specific restrictions described under
+smtpd_client_restrictions and smtpd_helo_restrictions.
+.br
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_etrn_restrictions = permit_mynetworks, reject
+.fi
+.ad
+.ft R
+.SH smtpd_expansion_filter (default: see "postconf \-d" output)
+What characters are allowed in $name expansions of RBL reply
+templates. Characters not in the allowed set are replaced by "_".
+Use C like escapes to specify special characters such as whitespace.
+.PP
+The smtpd_expansion_filter value is not subject to Postfix configuration
+parameter $name expansion.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH smtpd_forbid_bare_newline (default: Postfix < 3.9: no)
+Reject or restrict input lines from an SMTP client that end in
+<LF> instead of the standard <CR><LF>. Such line
+endings are commonly allowed with UNIX\-based SMTP servers, but they
+violate RFC 5321, and allowing such line endings can make a server
+vulnerable to
+SMTP smuggling.
+.PP
+Specify one of the following values (case does not matter):
+.IP "\fBnormalize\fR"
+Require the standard
+End\-of\-DATA sequence <CR><LF>.<CR><LF>.
+Otherwise, allow command or message content lines ending in the
+non\-standard <LF>, and process them as if the client sent the
+standard <CR><LF>.
+.br
+.br
+This maintains compatibility
+with many legitimate SMTP client applications that send a mix of
+standard and non\-standard line endings, but will fail to receive
+email from client implementations that do not terminate DATA content
+with the standard End\-of\-DATA sequence
+<CR><LF>.<CR><LF>.
+.br
+.br
+Such clients
+can be excluded with smtpd_forbid_bare_newline_exclusions.
+.br
+.IP "\fByes\fR"
+Compatibility alias for \fBnormalize\fR.
+.br
+.IP "\fBreject\fR"
+Require the standard End\-of\-DATA
+sequence <CR><LF>.<CR><LF>. Reject a command
+or message content when a line contains bare <LF>, log a "bare
+<LF> received" error, and reply with the SMTP status code in
+$smtpd_forbid_bare_newline_reject_code.
+.br
+.br
+This will reject
+email from SMTP clients that send any non\-standard line endings
+such as web applications, netcat, or load balancer health checks.
+.br
+.br
+This will also reject email from services that use BDAT
+to send MIME text containing a bare newline (RFC 3030 Section 3
+requires canonical MIME format for text message types, defined in
+RFC 2045 Sections 2.7 and 2.8).
+.br
+.br
+Such clients can be
+excluded with smtpd_forbid_bare_newline_exclusions (or, in the case
+of BDAT violations, BDAT can be selectively disabled with
+smtpd_discard_ehlo_keyword_address_maps, or globally disabled with
+smtpd_discard_ehlo_keywords).
+.br
+.IP "\fBno\fR (default)"
+Do not require the standard
+End\-of\-DATA
+sequence <CR><LF>.<CR><LF>. Always process
+a bare <LF> as if the client sent <CR><LF>. This
+option is fully backwards compatible, but is not recommended for
+an Internet\-facing SMTP server, because it is vulnerable to  SMTP smuggling.
+.br
+.br
+.PP
+Recommended settings:
+.sp
+.in +4
+.nf
+.na
+.ft C
+# Require the standard End\-of\-DATA sequence <CR><LF>.<CR><LF>.
+# Otherwise, allow bare <LF> and process it as if the client sent
+# <CR><LF>.
+#
+# This maintains compatibility with many legitimate SMTP client
+# applications that send a mix of standard and non\-standard line
+# endings, but will fail to receive email from client implementations
+# that do not terminate DATA content with the standard End\-of\-DATA
+# sequence <CR><LF>.<CR><LF>.
+#
+# Such clients can be allowlisted with smtpd_forbid_bare_newline_exclusions.
+# The example below allowlists SMTP clients in trusted networks.
+#
+smtpd_forbid_bare_newline = normalize
+smtpd_forbid_bare_newline_exclusions = $mynetworks
+.fi
+.ad
+.ft R
+.in -4
+.PP
+Alternative:
+.sp
+.in +4
+.nf
+.na
+.ft C
+# Reject input lines that contain <LF> and log a "bare <LF> received"
+# error. Require that input lines end in <CR><LF>, and require the
+# standard End\-of\-DATA sequence <CR><LF>.<CR><LF>.
+#
+# This will reject email from SMTP clients that send any non\-standard
+# line endings such as web applications, netcat, or load balancer
+# health checks.
+#
+# This will also reject email from services that use BDAT to send
+# MIME text containing a bare newline (RFC 3030 Section 3 requires
+# canonical MIME format for text message types, defined in RFC 2045
+# Sections 2.7 and 2.8).
+#
+# Such clients can be allowlisted with smtpd_forbid_bare_newline_exclusions.
+# The example below allowlists SMTP clients in trusted networks.
+#
+smtpd_forbid_bare_newline = reject
+smtpd_forbid_bare_newline_exclusions = $mynetworks
+#
+# Alternatively, in the case of BDAT violations, BDAT can be selectively
+# disabled with smtpd_discard_ehlo_keyword_address_maps, or globally
+# disabled with smtpd_discard_ehlo_keywords.
+#
+# smtpd_discard_ehlo_keyword_address_maps = cidr:/path/to/file
+# /path/to/file:
+#     10.0.0.0/24 chunking, silent\-discard
+# smtpd_discard_ehlo_keywords = chunking, silent\-discard
+.fi
+.ad
+.ft R
+.in -4
+.PP
+This feature with settings \fByes\fR and \fBno\fR is available
+in Postfix 3.8.4, 3.7.9, 3.6.13, and 3.5.23. Additionally, the
+settings \fBreject\fR, and \fBnormalize\fR are available with
+Postfix >= 3.9, 3.8.5, 3.7.10, 3.6.14, and 3.5.24.
+.SH smtpd_forbid_bare_newline_exclusions (default: $mynetworks)
+Exclude the specified clients from smtpd_forbid_bare_newline
+enforcement. This setting uses the same syntax and parent\-domain
+matching behavior as mynetworks.
+.PP
+This feature is available in Postfix >= 3.9, 3.8.4, 3.7.9,
+3.6.13, and 3.5.23.
+.SH smtpd_forbid_bare_newline_reject_code (default: 550)
+The numerical Postfix SMTP server response code when rejecting a
+request with "smtpd_forbid_bare_newline = reject".
+Specify a 5XX status code (521 to disconnect).
+.PP
+This feature is available in Postfix >= 3.9, 3.8.5, 3.7.10,
+3.6.14, and 3.5.24.
+.SH smtpd_forbid_unauth_pipelining (default: Postfix >= 3.9: yes)
+Disconnect remote SMTP clients that violate RFC 2920 (or 5321)
+command pipelining constraints. The server replies with "554 5.5.0
+Error: SMTP protocol synchronization" and logs the unexpected remote
+SMTP client input. Specify "smtpd_forbid_unauth_pipelining = yes"
+to enable. This feature is enabled by default with Postfix >=
+3.9.
+.PP
+This feature is available in Postfix >= 3.9, 3.8.1, 3.7.6,
+3.6.10, and 3.5.20.
+.SH smtpd_forbidden_commands (default: CONNECT GET POST regexp:{{/^[^A\-Z]/ Bogus}})
+List of commands that cause the Postfix SMTP server to immediately
+terminate the session with a 221 code. This can be used to disconnect
+clients that obviously attempt to abuse the system. In addition to the
+commands listed in this parameter, commands that follow the "Label:"
+format of message headers will also cause a disconnect. With Postfix
+versions 3.6 and earlier, the default value is "CONNECT GET POST".
+.PP
+This feature is available in Postfix 2.2 and later.
+.PP
+Support for inline regular expressions was added in Postfix version
+3.7. See \fBregexp_table\fR(5) for a description of the syntax and features.
+.SH smtpd_hard_error_limit (default: normal: 20, overload: 1)
+The maximal number of errors a remote SMTP client is allowed to
+make without delivering mail. The Postfix SMTP server disconnects
+when the limit is reached. Normally the default limit is 20, but
+it changes under overload to just 1. With Postfix 2.5 and earlier,
+the SMTP server always allows up to 20 errors by default.
+Valid values are greater than zero.
+.SH smtpd_helo_required (default: no)
+Require that a remote SMTP client introduces itself with the HELO
+or EHLO command before sending the MAIL command or other commands
+that require EHLO negotiation.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_helo_required = yes
+.fi
+.ad
+.ft R
+.SH smtpd_helo_restrictions (default: empty)
+Optional restrictions that the Postfix SMTP server applies in the
+context of a client HELO command.
+See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access
+restriction lists" for a discussion of evaluation context and time.
+.PP
+The default is to permit everything.
+.PP
+Note: specify "smtpd_helo_required = yes" to fully enforce this
+restriction (without "smtpd_helo_required = yes", a client can
+simply skip smtpd_helo_restrictions by not sending HELO or EHLO).
+.PP
+Specify a list of restrictions, separated by commas and/or whitespace.
+Continue long lines by starting the next line with whitespace.
+Restrictions are applied in the order as specified; the first
+restriction that matches wins.
+.PP
+The following restrictions are specific to the hostname information
+received with the HELO or EHLO command.
+.IP "\fBcheck_helo_access \fItype:table\fR\fR"
+Search the specified \fBaccess\fR(5) database for the HELO or EHLO
+hostname or parent domains, and execute the corresponding action.
+Note: specify "smtpd_helo_required = yes" to fully enforce this
+restriction (without "smtpd_helo_required = yes", a client can
+simply skip check_helo_access by not sending HELO or EHLO).
+.br
+.IP "\fBcheck_helo_a_access \fItype:table\fR\fR"
+Search the specified \fBaccess\fR(5) database for the IP addresses for
+the HELO or EHLO hostname, and execute the corresponding action.
+Note 1: a result of "OK" is not allowed for safety reasons. Instead,
+use DUNNO in order to exclude specific hosts from denylists.  Note
+2: specify "smtpd_helo_required = yes" to fully enforce this
+restriction (without "smtpd_helo_required = yes", a client can
+simply skip check_helo_a_access by not sending HELO or EHLO).  This
+feature is available in Postfix 3.0 and later.
+.br
+.IP "\fBcheck_helo_mx_access \fItype:table\fR\fR"
+Search the specified \fBaccess\fR(5) database for the MX hosts for
+the HELO or EHLO hostname, and execute the corresponding action.
+If no MX record is found, look up A or AAAA records, just like the
+Postfix SMTP client would.
+Note 1: a result of "OK" is not allowed for safety reasons. Instead,
+use DUNNO in order to exclude specific hosts from denylists.  Note
+2: specify "smtpd_helo_required = yes" to fully enforce this
+restriction (without "smtpd_helo_required = yes", a client can
+simply skip check_helo_mx_access by not sending HELO or EHLO).  This
+feature is available in Postfix 2.1 and later.
+.br
+.IP "\fBcheck_helo_ns_access \fItype:table\fR\fR"
+Search the specified \fBaccess\fR(5) database for the DNS servers
+for the HELO or EHLO hostname, and execute the corresponding action.
+Note 1: a result of "OK" is not allowed for safety reasons. Instead,
+use DUNNO in order to exclude specific hosts from denylists.  Note
+2: specify "smtpd_helo_required = yes" to fully enforce this
+restriction (without "smtpd_helo_required = yes", a client can
+simply skip check_helo_ns_access by not sending HELO or EHLO). This
+feature is available in Postfix 2.1 and later.
+.br
+.IP "\fBreject_invalid_helo_hostname\fR (with Postfix < 2.3: reject_invalid_hostname)"
+Reject the request when the HELO or EHLO hostname is malformed.
+Note: specify "smtpd_helo_required = yes" to fully enforce
+this restriction (without "smtpd_helo_required = yes", a client can simply
+skip reject_invalid_helo_hostname by not sending HELO or EHLO).
+.br
+The invalid_hostname_reject_code specifies the response code
+for rejected requests (default: 501).
+.br
+.IP "\fBreject_non_fqdn_helo_hostname\fR (with Postfix < 2.3: reject_non_fqdn_hostname)"
+Reject the request when the HELO or EHLO hostname is not in
+fully\-qualified domain or address literal form, as required by the
+RFC. Note: specify
+"smtpd_helo_required = yes" to fully enforce this restriction
+(without "smtpd_helo_required = yes", a client can simply skip
+reject_non_fqdn_helo_hostname by not sending HELO or EHLO).
+.br
+The non_fqdn_reject_code parameter specifies the response code for
+rejected requests (default: 504).
+.br
+.IP "\fBreject_rhsbl_helo \fIrbl_domain=d.d.d.d\fR\fR"
+Reject the request when the HELO or EHLO hostname is
+listed with the A record "\fId.d.d.d\fR" under \fIrbl_domain\fR
+(Postfix version 2.1 and later only).  Each "\fId\fR" is a number,
+or a pattern inside "[]" that contains one or more ";"\-separated
+numbers or number..number ranges (Postfix version 2.8 and later).
+If no "\fI=d.d.d.d\fR" is
+specified, reject the request when the HELO or EHLO hostname is
+listed with any A record under \fIrbl_domain\fR. See the
+reject_rbl_client description for additional RBL related configuration
+parameters.  Note: specify "smtpd_helo_required = yes" to fully
+enforce this restriction (without "smtpd_helo_required = yes", a
+client can simply skip reject_rhsbl_helo by not sending HELO or
+EHLO). This feature is available in Postfix 2.0
+and later.
+.br
+.IP "\fBreject_unknown_helo_hostname\fR (with Postfix < 2.3: reject_unknown_hostname)"
+Reject the request when the HELO or EHLO hostname has no DNS A
+or MX record.
+.br
+The reply is specified with the
+unknown_hostname_reject_code parameter (default: 450) or
+unknown_helo_hostname_tempfail_action (default: defer_if_permit).
+See the respective parameter descriptions for details.
+.br
+Note: specify "smtpd_helo_required = yes" to fully
+enforce this restriction (without "smtpd_helo_required = yes", a
+client can simply skip reject_unknown_helo_hostname by not sending
+HELO or EHLO).
+.br
+.br
+.PP
+Other restrictions that are valid in this context:
+.IP \(bu
+Generic restrictions that can be used
+in any SMTP command context, described under smtpd_client_restrictions.
+.IP \(bu
+Client hostname or network address specific restrictions
+described under smtpd_client_restrictions.
+.IP \(bu
+SMTP command specific restrictions described under
+smtpd_sender_restrictions or smtpd_recipient_restrictions.  When
+sender or recipient restrictions are listed under smtpd_helo_restrictions,
+they have effect only with "smtpd_delay_reject = yes", so that
+$smtpd_helo_restrictions is evaluated at the time of the RCPT TO
+command.
+.br
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+smtpd_helo_restrictions = permit_mynetworks, reject_invalid_helo_hostname
+smtpd_helo_restrictions = permit_mynetworks, reject_unknown_helo_hostname
+.fi
+.ad
+.ft R
+.SH smtpd_history_flush_threshold (default: 100)
+The maximal number of lines in the Postfix SMTP server command history
+before it is flushed upon receipt of EHLO, RSET, or end of DATA.
+.SH smtpd_junk_command_limit (default: normal: 100, overload: 1)
+The number of junk commands (NOOP, VRFY, ETRN or RSET) that a remote
+SMTP client can send before the Postfix SMTP server starts to
+increment the error counter with each junk command.  The junk
+command count is reset after mail is delivered.  See also the
+smtpd_error_sleep_time and smtpd_soft_error_limit configuration
+parameters.  Normally the default limit is 100, but it changes under
+overload to just 1. With Postfix 2.5 and earlier, the SMTP server
+always allows up to 100 junk commands by default.
+.SH smtpd_log_access_permit_actions (default: empty)
+Enable logging of the named "permit" actions in SMTP server
+access lists (by default, the SMTP server logs "reject" actions but
+not "permit" actions).  This feature does not affect conditional
+actions such as "defer_if_permit".
+.PP
+Specify a list of "permit" action names, "/file/name" or
+"type:table" patterns, separated by commas and/or whitespace. The
+list is matched left to right, and the search stops on the first
+match. A "/file/name" pattern is replaced by its contents; a
+"type:table" lookup table is matched when a name matches a lookup
+key (the lookup result is ignored).  Continue long lines by starting
+the next line with whitespace. Specify "!pattern" to exclude a name
+from the list.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    # Log all "permit" actions.
+    smtpd_log_access_permit_actions = static:all
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    # Log "permit_dnswl_client" only.
+    smtpd_log_access_permit_actions = permit_dnswl_client
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.10 and later.
+.SH smtpd_milter_maps (default: empty)
+Lookup tables with Milter settings per remote SMTP client IP
+address.  The lookup result overrides the smtpd_milters setting,
+and has the same syntax.
+.PP
+Note: lookup tables cannot return empty responses. Specify a
+lookup result of DISABLE (case does not matter) to indicate that
+Milter support should be disabled.
+.PP
+Example to disable Milters for local clients:
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    smtpd_milter_maps = cidr:/etc/postfix/smtpd_milter_map
+    smtpd_milters = inet:host:port, { inet:host:port, ... }, ...
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/smtpd_milter_map:
+    # Disable Milters for local clients.
+    127.0.0.0/8    DISABLE
+    192.168.0.0/16 DISABLE
+    ::/64          DISABLE
+    2001:db8::/32  DISABLE
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 3.2 and later.
+.SH smtpd_milters (default: empty)
+A list of Milter (mail filter) applications for new mail that
+arrives via the Postfix \fBsmtpd\fR(8) server. Specify space or comma as
+separator. See the MILTER_README document for details.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtpd_min_data_rate (default: 500)
+The minimum plaintext data transfer rate in bytes/second for
+DATA and BDAT requests, when deadlines are enabled with
+smtpd_per_request_deadline. After a read operation transfers N
+plaintext message bytes (possibly after TLS decryption), and after
+the DATA or BDAT request deadline is decremented by the elapsed
+time of that read operation, the DATA or BDAT request deadline is
+incremented by N/smtpd_min_data_rate seconds. However, the deadline
+will never be incremented beyond the time limit specified with
+smtpd_timeout.
+.PP
+This feature is available in Postfix 3.7 and later.
+.SH smtpd_noop_commands (default: empty)
+List of commands that the Postfix SMTP server replies to with "250
+Ok", without doing any syntax checks and without changing state.
+This list overrides any commands built into the Postfix SMTP server.
+.SH smtpd_null_access_lookup_key (default: <>)
+The lookup key to be used in SMTP \fBaccess\fR(5) tables instead of the
+null sender address.
+.SH smtpd_peername_lookup (default: yes)
+Attempt to look up the remote SMTP client hostname, and verify that
+the name matches the client IP address. A client name is set to
+"unknown" when it cannot be looked up or verified, or when name
+lookup is disabled.  Turning off name lookup reduces delays due to
+DNS lookup and increases the maximal inbound delivery rate.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtpd_per_record_deadline (default: normal: no, overload: yes)
+Change the behavior of the smtpd_timeout and smtpd_starttls_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).  This
+limits the impact from hostile peers that trickle data one byte at
+a time.
+.PP
+Note: when per\-record deadlines are enabled, a short timeout
+may cause problems with TLS over very slow network connections.
+The reasons are that a TLS protocol message can be up to 16 kbytes
+long (with TLSv1), and that an entire TLS protocol message must be
+sent or received within the per\-record deadline.
+.PP
+This feature is available in Postfix 2.9\-3.6. With older
+Postfix releases, the behavior is as if this parameter is set to
+"no". Postfix 3.7 and later use smtpd_per_request_deadline.
+.SH smtpd_per_request_deadline (default: normal: no, overload: yes)
+Change the behavior of the smtpd_timeout and smtpd_starttls_timeout
+time limits, from a time limit per plaintext or TLS read or write
+call, to a combined time limit for receiving a complete SMTP request
+and for sending a complete SMTP response. The deadline limits only
+the time spent waiting for plaintext or TLS read or write calls,
+not time spent elsewhere. The per\-request deadline limits the impact
+from hostile peers that trickle data one byte at a time.
+.PP
+See smtpd_min_data_rate for how the per\-request deadline is
+managed during the DATA and BDAT phase.
+.PP
+Note: when per\-request deadlines are enabled, a short time limit
+may cause problems with TLS over very slow network connections. The
+reason is that a TLS protocol message can be up to 16 kbytes long
+(with TLSv1), and that an entire TLS protocol message must be
+transferred within the per\-request deadline.
+.PP
+This feature is available in Postfix 3.7 and later. A weaker
+feature, called smtpd_per_record_deadline, is available with Postfix
+2.9\-3.6. With older Postfix releases, the behavior is as if this
+parameter is set to "no".
+.PP
+This feature is available in Postfix 3.7 and later.
+.SH smtpd_policy_service_default_action (default: 451 4.3.5 Server configuration problem)
+The default action when an SMTPD policy service request fails.
+Specify "DUNNO" to behave as if the failed  SMTPD policy service
+request was not sent, and to continue processing other access
+restrictions, if any.
+.PP
+Limitations:
+.IP \(bu
+This parameter may specify any value that would be a valid
+SMTPD policy server response (or \fBaccess\fR(5) map lookup result).  An
+\fBaccess\fR(5) map or policy server in this parameter value may need to
+be declared in advance with a restriction_class setting.
+.IP \(bu
+If the specified action invokes another check_policy_service
+request, that request will have the built\-in default action.
+.br
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH smtpd_policy_service_max_idle (default: 300s)
+The time after which an idle SMTPD policy service connection is
+closed.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH smtpd_policy_service_max_ttl (default: 1000s)
+The time after which an active SMTPD policy service connection is
+closed.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH smtpd_policy_service_policy_context (default: empty)
+Optional information that the Postfix SMTP server specifies in
+the "policy_context" attribute of a policy service request (originally,
+to share the same service endpoint among multiple check_policy_service
+clients).
+.PP
+This feature is available in Postfix 3.1 and later.
+.SH smtpd_policy_service_request_limit (default: 0)
+The maximal number of requests per SMTPD policy service connection,
+or zero (no limit). Once a connection reaches this limit, the
+connection is closed and the next request will be sent over a new
+connection. This is a workaround to avoid error\-recovery delays
+with policy servers that cannot maintain a persistent connection.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH smtpd_policy_service_retry_delay (default: 1s)
+The delay between attempts to resend a failed SMTPD policy
+service request. Specify a value greater than zero.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH smtpd_policy_service_timeout (default: 100s)
+The time limit for connecting to, writing to, or receiving from a
+delegated SMTPD policy server.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH smtpd_policy_service_try_limit (default: 2)
+The maximal number of attempts to send an SMTPD policy service
+request before giving up. Specify a value greater than zero.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH smtpd_proxy_ehlo (default: $myhostname)
+How the Postfix SMTP server announces itself to the proxy filter.
+By default, the Postfix hostname is used.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH smtpd_proxy_filter (default: empty)
+The hostname and TCP port of the mail filtering proxy server.
+The proxy receives all mail from the Postfix SMTP server, and is
+supposed to give the result to another Postfix SMTP server process.
+.PP
+Specify "host:port" or "inet:host:port" for a TCP endpoint, or
+"unix:pathname" for a UNIX\-domain endpoint. The host can be specified
+as an IP address or as a symbolic name; no MX lookups are done.
+When no "host" or "host:" is specified, the local machine is
+assumed.  Pathname interpretation is relative to the Postfix queue
+directory.
+.PP
+This feature is available in Postfix 2.1 and later.
+.PP
+The "inet:" and "unix:" prefixes are available in Postfix 2.3
+and later.
+.SH smtpd_proxy_options (default: empty)
+List of options that control how the Postfix SMTP server
+communicates with a before\-queue content filter. Specify zero or
+more of the following, separated by comma or whitespace.
+.IP "\fBspeed_adjust\fR"
+Do not connect to a before\-queue content filter until an entire
+message has been received. This reduces the number of simultaneous
+before\-queue content filter processes.
+.PP
+NOTE 1: A filter must not \fIselectively\fR reject recipients
+of a multi\-recipient message.  Rejecting all recipients is OK, as
+is accepting all recipients.
+.PP
+NOTE 2: This feature increases the minimum amount of free queue
+space by $message_size_limit. The extra space is needed to save the
+message to a temporary file.
+.br
+.br
+.PP
+This feature is available in Postfix 2.7 and later.
+.SH smtpd_proxy_timeout (default: 100s)
+The time limit for connecting to a proxy filter and for sending or
+receiving information.  When a connection fails the client gets a
+generic error message while more detailed information is logged to
+the maillog file.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH smtpd_recipient_limit (default: 1000)
+The maximal number of recipients that the Postfix SMTP server
+accepts per message delivery request.
+.SH smtpd_recipient_overshoot_limit (default: 1000)
+The number of recipients that a remote SMTP client can send in
+excess of the limit specified with $smtpd_recipient_limit, before
+the Postfix SMTP server increments the per\-session error count
+for each excess recipient.
+.SH smtpd_recipient_restrictions (default: see "postconf \-d" output)
+Optional restrictions that the Postfix SMTP server applies in the
+context of a client RCPT TO command, after smtpd_relay_restrictions.
+See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access
+restriction lists" for a discussion of evaluation context and time.
+.PP
+With Postfix versions before 2.10, the rules for relay permission
+and spam blocking were combined under smtpd_recipient_restrictions,
+resulting in error\-prone configuration.  As of Postfix 2.10, relay
+permission rules are preferably implemented with smtpd_relay_restrictions,
+so that a permissive spam blocking policy under
+smtpd_recipient_restrictions will no longer result in a permissive
+mail relay policy.
+.PP
+For backwards compatibility, sites that migrate from Postfix
+versions before 2.10 can set smtpd_relay_restrictions to the empty
+value, and use smtpd_recipient_restrictions exactly as before.
+.PP
+IMPORTANT: Either the smtpd_relay_restrictions or the
+smtpd_recipient_restrictions parameter must specify
+at least one of the following restrictions. Otherwise Postfix will
+refuse to receive mail:
+.sp
+.in +4
+.nf
+.na
+.ft C
+reject, reject_unauth_destination
+.fi
+.ad
+.ft R
+.in -4
+.sp
+.in +4
+.nf
+.na
+.ft C
+defer, defer_if_permit, defer_unauth_destination
+.fi
+.ad
+.ft R
+.in -4
+.PP
+Specify a list of restrictions, separated by commas and/or whitespace.
+Continue long lines by starting the next line with whitespace.
+Restrictions are applied in the order as specified; the first
+restriction that matches wins.
+.PP
+The following restrictions are specific to the recipient address
+that is received with the RCPT TO command.
+.IP "\fBcheck_recipient_access \fItype:table\fR\fR"
+Search the specified \fBaccess\fR(5) database for the resolved RCPT
+TO address, domain, parent domains, or localpart@, and execute the
+corresponding action.
+.br
+.IP "\fBcheck_recipient_a_access \fItype:table\fR\fR"
+Search the specified \fBaccess\fR(5) database for the IP addresses for
+the RCPT TO domain, and execute the corresponding action.  Note:
+a result of "OK" is not allowed for safety reasons. Instead, use
+DUNNO in order to exclude specific hosts from denylists.  This
+feature is available in Postfix 3.0 and later.
+.br
+.IP "\fBcheck_recipient_mx_access \fItype:table\fR\fR"
+Search the specified \fBaccess\fR(5) database for the MX hosts for
+the RCPT TO domain, and execute the corresponding action.  If no
+MX record is found, look up A or AAAA records, just like the Postfix
+SMTP client would. Note:
+a result of "OK" is not allowed for safety reasons. Instead, use
+DUNNO in order to exclude specific hosts from denylists.  This
+feature is available in Postfix 2.1 and later.
+.br
+.IP "\fBcheck_recipient_ns_access \fItype:table\fR\fR"
+Search the specified \fBaccess\fR(5) database for the DNS servers
+for the RCPT TO domain, and execute the corresponding action.
+Note: a result of "OK" is not allowed for safety reasons. Instead,
+use DUNNO in order to exclude specific hosts from denylists.  This
+feature is available in Postfix 2.1 and later.
+.br
+.IP "\fBpermit_auth_destination\fR"
+Permit the request when one of the following is true:
+.IP \(bu
+Postfix is a mail forwarder: the resolved RCPT TO domain matches
+$relay_domains or a subdomain thereof, and the address contains no
+sender\-specified routing (user@elsewhere@domain),
+.IP \(bu
+Postfix is the final destination: the resolved RCPT TO domain
+matches $mydestination, $inet_interfaces, $proxy_interfaces,
+$virtual_alias_domains, or $virtual_mailbox_domains, and the address
+contains no sender\-specified routing (user@elsewhere@domain).
+.br
+.br
+.IP "\fBpermit_mx_backup\fR"
+Permit the request when the local mail system is a backup MX for
+the RCPT TO domain, or when the domain is an authorized destination
+(see permit_auth_destination for definition).
+.IP \(bu
+Safety: permit_mx_backup does not accept addresses that have
+sender\-specified routing information (example: user@elsewhere@domain).
+.IP \(bu
+Safety: permit_mx_backup can be vulnerable to mis\-use when
+access is not restricted with permit_mx_backup_networks.
+.IP \(bu
+Safety: as of Postfix version 2.3, permit_mx_backup no longer
+accepts the address when the local mail system is a primary MX for
+the recipient domain.  Exception: permit_mx_backup accepts the address
+when it specifies an authorized destination (see permit_auth_destination
+for definition).
+.IP \(bu
+Limitation: mail may be rejected in case of a temporary DNS
+lookup problem with Postfix prior to version 2.0.
+.br
+.br
+.IP "\fBreject_non_fqdn_recipient\fR"
+Reject the request when the RCPT TO address specifies a
+domain that is not in
+fully\-qualified domain form, as required by the RFC.
+.br
+The
+non_fqdn_reject_code parameter specifies the response code for
+rejected requests (default: 504).
+.br
+.IP "\fBreject_rhsbl_recipient \fIrbl_domain=d.d.d.d\fR\fR"
+Reject the request when the RCPT TO domain is listed with the
+A record "\fId.d.d.d\fR" under \fIrbl_domain\fR (Postfix version
+2.1 and later only).  Each "\fId\fR" is a number, or a pattern
+inside "[]" that contains one or more ";"\-separated numbers or
+number..number ranges (Postfix version 2.8 and later). If no
+"\fI=d.d.d.d\fR" is specified, reject
+the request when the RCPT TO domain is listed with
+any A record under \fIrbl_domain\fR.
+.br
+The maps_rbl_reject_code
+parameter specifies the response code for rejected requests (default:
+554); the default_rbl_reply parameter specifies the default server
+reply; and the rbl_reply_maps parameter specifies tables with server
+replies indexed by \fIrbl_domain\fR.  This feature is available
+in Postfix version 2.0 and later.
+.br
+.IP "\fBreject_unauth_destination\fR"
+Reject the request unless one of the following is true:
+.IP \(bu
+Postfix is a mail forwarder: the resolved RCPT TO domain matches
+$relay_domains or a subdomain thereof, and contains no sender\-specified
+routing (user@elsewhere@domain),
+.IP \(bu
+Postfix is the final destination: the resolved RCPT TO domain
+matches $mydestination, $inet_interfaces, $proxy_interfaces,
+$virtual_alias_domains, or $virtual_mailbox_domains, and contains
+no sender\-specified routing (user@elsewhere@domain).
+.br
+The relay_domains_reject_code parameter specifies the response
+code for rejected requests (default: 554).
+.br
+.IP "\fBdefer_unauth_destination\fR"
+Reject the same requests as reject_unauth_destination, with a
+non\-permanent error code.  This feature is available in Postfix
+2.10 and later.
+.br
+.IP "\fBreject_unknown_recipient_domain\fR"
+Reject the request when Postfix is not final destination for
+the recipient domain, and the RCPT TO domain has 1) no DNS MX and
+no DNS A
+record or 2) a malformed MX record such as a record with
+a zero\-length MX hostname (Postfix version 2.3 and later).
+.br
+The
+reply is specified with the unknown_address_reject_code parameter
+(default: 450), unknown_address_tempfail_action (default:
+defer_if_permit), or 556 (nullmx, Postfix 3.0 and
+later). See the respective parameter descriptions for details.
+.br
+.IP "\fBreject_unlisted_recipient\fR (with Postfix version 2.0: check_recipient_maps)"
+Reject the request when the RCPT TO address is not listed in
+the list of valid recipients for its domain class. See the
+smtpd_reject_unlisted_recipient parameter description for details.
+This feature is available in Postfix 2.1 and later.
+.br
+.IP "\fBreject_unverified_recipient\fR"
+Reject the request when mail to the RCPT TO address is known
+to bounce, or when the recipient address destination is not reachable.
+Address verification information is managed by the \fBverify\fR(8) server;
+see the ADDRESS_VERIFICATION_README file for details.
+.br
+The
+unverified_recipient_reject_code parameter specifies the numerical
+response code when an address is known to bounce (default: 450,
+change it to 550 when you are confident that it is safe to do so).
+.br
+The unverified_recipient_defer_code parameter specifies the
+numerical response code when an address probe failed due to a
+temporary problem (default: 450).
+.br
+The
+unverified_recipient_tempfail_action parameter specifies the action
+after address probe failure due to a temporary problem (default:
+defer_if_permit).
+.br
+This feature breaks for aliased addresses
+with "enable_original_recipient = no" (Postfix <= 3.2).
+.br
+This feature is available in Postfix 2.1 and later.
+.br
+.br
+.PP
+Other restrictions that are valid in this context:
+.IP \(bu
+Generic restrictions that can be used
+in any SMTP command context, described under smtpd_client_restrictions.
+.IP \(bu
+SMTP command specific restrictions described under
+smtpd_client_restrictions, smtpd_helo_restrictions and
+smtpd_sender_restrictions.
+.br
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+# The Postfix before 2.10 default mail relay policy. Later Postfix
+# versions implement this preferably with smtpd_relay_restrictions.
+smtpd_recipient_restrictions = permit_mynetworks, reject_unauth_destination
+.fi
+.ad
+.ft R
+.SH smtpd_reject_footer (default: empty)
+Optional information that is appended after each Postfix SMTP
+server
+4XX or 5XX response.
+.PP
+The following example uses "\ec" at the start of the template
+(supported in Postfix 2.10 and later) to suppress the line break
+between the reply text and the footer text. With earlier Postfix
+versions, the footer text always begins on a new line, and the "\ec"
+is output literally.
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    smtpd_reject_footer = \ec. For assistance, call 800\-555\-0101.
+     Please provide the following information in your problem report:
+     time ($localtime), client ($client_address) and server
+     ($server_name).
+.fi
+.ad
+.ft R
+.PP
+Server response:
+.PP
+.nf
+.na
+.ft C
+    550\-5.5.1 <user@example> Recipient address rejected: User
+    unknown. For assistance, call 800\-555\-0101. Please provide the
+    following information in your problem report: time (Jan 4 15:42:00),
+    client (192.168.1.248) and server (mail1.example.com).
+.fi
+.ad
+.ft R
+.PP
+Note: the above text is meant to make it easier to find the
+Postfix logfile records for a failed SMTP session. The text itself
+is not logged to the Postfix SMTP server's maillog file.
+.PP
+Be sure to keep the text as short as possible. Long text may
+be truncated before it is logged to the remote SMTP client's maillog
+file, or before it is returned to the sender in a delivery status
+notification.
+.PP
+The template text is not subject to Postfix configuration
+parameter $name expansion. Instead, this feature supports a limited
+number of $name attributes in the footer text. These attributes are
+replaced with their current value for the SMTP session.
+.PP
+Note: specify $$name in footer text that is looked up from
+regexp: or pcre:\-based smtpd_reject_footer_maps, otherwise the
+Postfix server will not use the footer text and will log a warning
+instead.
+.IP "\fBclient_address\fR"
+The Client IP address that
+is logged in the maillog file.
+.br
+.IP "\fBclient_port\fR"
+The client TCP port that is
+logged in the maillog file.
+.br
+.IP "\fBlocaltime\fR"
+The server local time (Mmm dd
+hh:mm:ss) that is logged in the maillog file.
+.br
+.IP "\fBserver_name\fR"
+The server's myhostname value.
+This attribute is made available for sites with multiple MTAs
+(perhaps behind a load\-balancer), where the server name can help
+the server support team to quickly find the right log files.
+.br
+.br
+.PP
+Notes:
+.IP \(bu
+NOT SUPPORTED are other attributes such as sender, recipient,
+or main.cf parameters.
+.IP \(bu
+For safety reasons, text that does not match
+$smtpd_expansion_filter is censored.
+.br
+.PP
+This feature supports the two\-character sequence \en as a request
+for a line break in the footer text. Postfix automatically inserts
+after each line break the three\-digit SMTP reply code (and optional
+enhanced status code) from the original Postfix reject message.
+.PP
+To work around mail software that mis\-handles multi\-line replies,
+specify the two\-character sequence \ec at the start of the template.
+This suppresses the line break between the reply text and the footer
+text (Postfix 2.10 and later).
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH smtpd_reject_footer_maps (default: empty)
+Lookup tables, indexed by the complete Postfix SMTP server 4xx or
+5xx response, with reject footer templates. See smtpd_reject_footer
+for details.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH smtpd_reject_unlisted_recipient (default: yes)
+Request that the Postfix SMTP server rejects mail for unknown
+recipient addresses, even when no explicit reject_unlisted_recipient
+access restriction is specified. This prevents the Postfix queue
+from filling up with undeliverable MAILER\-DAEMON messages.
+.PP
+An address is considered "unknown" when 1) it does not match a
+\fBvirtual\fR(5) alias or \fBcanonical\fR(5) mapping, and 2) the address is not
+valid for its address class. For a definition of class\-based address
+validation, see
+ADDRESS_CLASS_README.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH smtpd_reject_unlisted_sender (default: no)
+Request that the Postfix SMTP server rejects mail from unknown
+sender addresses, even when no explicit reject_unlisted_sender
+access restriction is specified. This can slow down an explosion
+of forged mail from worms or viruses.
+.PP
+An address is considered "unknown" when 1) it does not match a
+\fBvirtual\fR(5) alias or \fBcanonical\fR(5) mapping, and 2) the address is not
+valid for its address class. For a definition of class\-based address
+validation, see
+ADDRESS_CLASS_README.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH smtpd_relay_before_recipient_restrictions (default: see "postconf \-d" output)
+Evaluate smtpd_relay_restrictions before smtpd_recipient_restrictions.
+Historically, smtpd_relay_restrictions was evaluated after
+smtpd_recipient_restrictions, contradicting documented behavior.
+.PP
+Background: the smtpd_relay_restrictions feature is primarily
+designed to enforce a mail relaying policy, while
+smtpd_recipient_restrictions is primarily designed to enforce spam
+blocking policy. Both are evaluated while replying to the RCPT TO
+command, and both support the same features.
+.PP
+This feature is available in Postfix 3.6 and later.
+.SH smtpd_relay_restrictions (default: permit_mynetworks, permit_sasl_authenticated, defer_unauth_destination)
+Access restrictions for mail relay control that the Postfix
+SMTP server applies in the context of the RCPT TO command, before
+smtpd_recipient_restrictions.
+See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access
+restriction lists" for a discussion of evaluation context and time.
+.PP
+With Postfix versions before 2.10, the rules for relay permission
+and spam blocking were combined under smtpd_recipient_restrictions,
+resulting in error\-prone configuration.  As of Postfix 2.10, relay
+permission rules are preferably implemented with smtpd_relay_restrictions,
+so that a permissive spam blocking policy under
+smtpd_recipient_restrictions will no longer result in a permissive
+mail relay policy.
+.PP
+For backwards compatibility, sites that migrate from Postfix
+versions before 2.10 can set smtpd_relay_restrictions to the empty
+value, and use smtpd_recipient_restrictions exactly as before.
+.PP
+By default, the Postfix SMTP server accepts:
+.IP \(bu
+Mail from clients whose IP address matches $mynetworks, or:
+.IP \(bu
+Mail from clients who are SASL authenticated, or:
+.IP \(bu
+Mail to remote destinations that match $relay_domains, except
+for addresses that contain sender\-specified routing
+(user@elsewhere@domain), or:
+.IP \(bu
+Mail to local destinations that match $inet_interfaces
+or $proxy_interfaces, $mydestination, $virtual_alias_domains, or
+$virtual_mailbox_domains.
+.br
+.PP
+IMPORTANT: Either the smtpd_relay_restrictions or the
+smtpd_recipient_restrictions parameter must specify
+at least one of the following restrictions. Otherwise Postfix will
+refuse to receive mail:
+.sp
+.in +4
+.nf
+.na
+.ft C
+reject, reject_unauth_destination
+.fi
+.ad
+.ft R
+.in -4
+.sp
+.in +4
+.nf
+.na
+.ft C
+defer, defer_if_permit, defer_unauth_destination
+.fi
+.ad
+.ft R
+.in -4
+.PP
+Specify a list of restrictions, separated by commas and/or whitespace.
+Continue long lines by starting the next line with whitespace.
+The same restrictions are available as documented under
+smtpd_recipient_restrictions.
+.PP
+This feature is available in Postix 2.10 and later.
+.SH smtpd_restriction_classes (default: empty)
+User\-defined aliases for groups of access restrictions. The aliases
+can be specified in smtpd_recipient_restrictions etc., and on the
+right\-hand side of a Postfix \fBaccess\fR(5) table.
+.PP
+One major application is for implementing per\-recipient UCE control.
+See the RESTRICTION_CLASS_README document for other examples.
+.SH smtpd_sasl_application_name (default: smtpd)
+The application name that the Postfix SMTP server uses for SASL
+server initialization. This
+controls the name of the SASL configuration file. The default value
+is \fBsmtpd\fR, corresponding to a SASL configuration file named
+\fBsmtpd.conf\fR.
+.PP
+This feature is available in Postfix 2.1 and 2.2. With Postfix 2.3
+it was renamed to smtpd_sasl_path.
+.SH smtpd_sasl_auth_enable (default: no)
+Enable SASL authentication in the Postfix SMTP server. By default,
+the Postfix SMTP server does not use authentication.
+.PP
+If a remote SMTP client is authenticated, the permit_sasl_authenticated
+access restriction can be used to permit relay access, like this:
+.sp
+.in +4
+.nf
+.na
+.ft C
+# With Postfix 2.10 and later, the mail relay policy is
+# preferably specified under smtpd_relay_restrictions.
+smtpd_relay_restrictions =
+    permit_mynetworks, permit_sasl_authenticated, ...
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+# With Postfix before 2.10, the relay policy can be
+# specified only under smtpd_recipient_restrictions.
+smtpd_recipient_restrictions =
+    permit_mynetworks, permit_sasl_authenticated, ...
+.fi
+.ad
+.ft R
+.in -4
+.PP
+To reject all SMTP connections from unauthenticated clients,
+specify "smtpd_delay_reject = yes" (which is the default) and use:
+.sp
+.in +4
+.nf
+.na
+.ft C
+smtpd_client_restrictions = permit_sasl_authenticated, reject
+.fi
+.ad
+.ft R
+.in -4
+.PP
+See the SASL_README file for SASL configuration and operation details.
+.SH smtpd_sasl_authenticated_header (default: no)
+Report the SASL authenticated user name in the \fBsmtpd\fR(8) Received
+message header.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtpd_sasl_exceptions_networks (default: empty)
+What remote SMTP clients the Postfix SMTP server will not offer
+AUTH support to.
+.PP
+Some clients (Netscape 4 at least) have a bug that causes them to
+require a login and password whenever AUTH is offered, whether it's
+necessary or not. To work around this, specify, for example,
+$mynetworks to prevent Postfix from offering AUTH to local clients.
+.PP
+Specify a list of network/netmask patterns, separated by commas
+and/or whitespace. The mask specifies the number of bits in the
+network part of a host address. You can also specify "/file/name" or
+"type:table" patterns.  A "/file/name" pattern is replaced by its
+contents; a "type:table" lookup table is matched when a table entry
+matches a lookup string (the lookup result is ignored).  Continue
+long lines by starting the next line with whitespace. Specify
+"!pattern" to exclude an address or network block from the list.
+The form "!/file/name" is supported only in Postfix version 2.4 and
+later.
+.PP
+Note: IP version 6 address information must be specified inside
+[] in the smtpd_sasl_exceptions_networks value, and in
+files specified with "/file/name".  IP version 6 addresses contain
+the ":" character, and would otherwise be confused with a "type:table"
+pattern.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_sasl_exceptions_networks = $mynetworks
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH smtpd_sasl_local_domain (default: empty)
+The name of the Postfix SMTP server's local SASL authentication
+realm.
+.PP
+By default, the local authentication realm name is the null string.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+smtpd_sasl_local_domain = $mydomain
+smtpd_sasl_local_domain = $myhostname
+.fi
+.ad
+.ft R
+.SH smtpd_sasl_mechanism_filter (default: !external, static:rest)
+If non\-empty, a filter for the SASL mechanism names that the
+Postfix SMTP server will announce in the EHLO response. By default,
+the Postfix SMTP server will not announce the EXTERNAL mechanism,
+because Postfix support for that is not implemented.
+.PP
+Specify mechanism names, "/file/name" patterns, or "type:table"
+lookup tables, separated by comma or whitespace. The right\-hand
+side result from "type:table" lookups is ignored. Specify "!pattern"
+to exclude a mechanism name from the list.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+smtpd_sasl_mechanism_filter = !external, !gssapi, static:rest
+smtpd_sasl_mechanism_filter = login, plain
+smtpd_sasl_mechanism_filter = /etc/postfix/smtpd_mechs
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 3.6 and later.
+.SH smtpd_sasl_path (default: smtpd)
+Implementation\-specific information that the Postfix SMTP server
+passes through to
+the SASL plug\-in implementation that is selected with
+\fBsmtpd_sasl_type\fR.  Typically this specifies the name of a
+configuration file or rendezvous point.
+.PP
+This feature is available in Postfix 2.3 and later. In earlier
+releases it was called \fBsmtpd_sasl_application_name\fR.
+.SH smtpd_sasl_response_limit (default: 12288)
+The maximum length of a SASL client's response to a server challenge.
+When the client's "initial response" is longer than the normal limit for
+SMTP commands, the client must omit its initial response, and wait for an
+empty server challenge; it can then send what would have been its "initial
+response" as a response to the empty server challenge.  RFC4954 requires the
+server to accept client responses up to at least 12288 octets of
+base64\-encoded text.  The default value is therefore also the minimum value
+accepted for this parameter.
+.PP
+This feature is available in Postfix 3.4 and later. Prior versions use
+"line_length_limit", which may need to be raised to accommodate larger client
+responses, as may be needed with GSSAPI authentication of Windows AD users
+who are members of many groups.
+.SH smtpd_sasl_security_options (default: noanonymous)
+Postfix SMTP server SASL security options; as of Postfix 2.3
+the list of available
+features depends on the SASL server implementation that is selected
+with \fBsmtpd_sasl_type\fR.
+.PP
+The following security features are defined for the \fBcyrus\fR
+server SASL implementation:
+.PP
+Restrict what authentication mechanisms the Postfix SMTP server
+will offer to the client.  The list of available authentication
+mechanisms is system dependent.
+.PP
+Specify zero or more of the following:
+.IP "\fBnoplaintext\fR"
+Disallow methods that use plaintext passwords.
+.br
+.IP "\fBnoactive\fR"
+Disallow methods subject to active (non\-dictionary) attack.
+.br
+.IP "\fBnodictionary\fR"
+Disallow methods subject to passive (dictionary) attack.
+.br
+.IP "\fBnoanonymous\fR"
+Disallow methods that allow anonymous authentication.
+.br
+.IP "\fBforward_secrecy\fR"
+Only allow methods that support forward secrecy (Dovecot only).
+.br
+.IP "\fBmutual_auth\fR"
+Only allow methods that provide mutual authentication (not available
+with Cyrus SASL version 1).
+.br
+.br
+.PP
+By default, the Postfix SMTP server accepts plaintext passwords but
+not anonymous logins.
+.PP
+Warning: it appears that clients try authentication methods in the
+order as advertised by the server (e.g., PLAIN ANONYMOUS CRAM\-MD5)
+which means that if you disable plaintext passwords, clients will
+log in anonymously, even when they should be able to use CRAM\-MD5.
+So, if you disable plaintext logins, disable anonymous logins too.
+Postfix treats anonymous login as no authentication.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_sasl_security_options = noanonymous, noplaintext
+.fi
+.ad
+.ft R
+.SH smtpd_sasl_service (default: smtp)
+The service name that is passed to the SASL plug\-in that is
+selected with \fBsmtpd_sasl_type\fR and \fBsmtpd_sasl_path\fR.
+.PP
+This feature is available in Postfix 2.11 and later. Prior
+versions behave as if "\fBsmtp\fR" is specified.
+.SH smtpd_sasl_tls_security_options (default: $smtpd_sasl_security_options)
+The SASL authentication security options that the Postfix SMTP
+server uses for TLS encrypted SMTP sessions.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_sasl_type (default: cyrus)
+The SASL plug\-in type that the Postfix SMTP server should use
+for authentication. The available types are listed with the
+"\fBpostconf \-a\fR" command.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtpd_sender_login_maps (default: empty)
+Optional lookup table with the SASL login names that own the sender
+(MAIL FROM) addresses.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.  With lookups from
+indexed files such as DB or DBM, or from networked tables such as
+NIS, LDAP or SQL, the following search operations are done with a
+sender address of \fIuser@domain\fR:
+.IP "1) \fIuser@domain\fR"
+This table lookup is always done and has the highest precedence.
+.br
+.IP "2) \fIuser\fR"
+This table lookup is done only when the \fIdomain\fR part of the
+sender address matches $myorigin, $mydestination, $inet_interfaces
+or $proxy_interfaces.
+.br
+.IP "3) \fI@domain\fR"
+This table lookup is done last and has the lowest precedence.
+.br
+.br
+.PP
+In all cases the result of table lookup must be either "not found"
+or a list of SASL login names separated by comma and/or whitespace.
+.SH smtpd_sender_restrictions (default: empty)
+Optional restrictions that the Postfix SMTP server applies in the
+context of a client MAIL FROM command.
+See SMTPD_ACCESS_README, section "Delayed evaluation of SMTP access
+restriction lists" for a discussion of evaluation context and time.
+.PP
+The default is to permit everything.
+.PP
+Specify a list of restrictions, separated by commas and/or whitespace.
+Continue long lines by starting the next line with whitespace.
+Restrictions are applied in the order as specified; the first
+restriction that matches wins.
+.PP
+The following restrictions are specific to the sender address
+received with the MAIL FROM command.
+.IP "\fBcheck_sender_access \fItype:table\fR\fR"
+Search the specified \fBaccess\fR(5) database for the MAIL FROM
+address, domain, parent domains, or localpart@, and execute the
+corresponding action.
+.br
+.IP "\fBcheck_sender_a_access \fItype:table\fR\fR"
+Search the specified \fBaccess\fR(5) database for the IP addresses for
+the MAIL FROM domain, and execute the corresponding action.  Note:
+a result of "OK" is not allowed for safety reasons. Instead, use
+DUNNO in order to exclude specific hosts from denylists.  This
+feature is available in Postfix 3.0 and later.
+.br
+.IP "\fBcheck_sender_mx_access \fItype:table\fR\fR"
+Search the specified \fBaccess\fR(5) database for the MX hosts for
+the MAIL FROM domain, and execute the corresponding action.  If no
+MX record is found, look up A or AAAA records, just like the Postfix
+SMTP client would. Note:
+a result of "OK" is not allowed for safety reasons. Instead, use
+DUNNO in order to exclude specific hosts from denylists.  This
+feature is available in Postfix 2.1 and later.
+.br
+.IP "\fBcheck_sender_ns_access \fItype:table\fR\fR"
+Search the specified \fBaccess\fR(5) database for the DNS servers
+for the MAIL FROM domain, and execute the corresponding action.
+Note: a result of "OK" is not allowed for safety reasons. Instead,
+use DUNNO in order to exclude specific hosts from denylists.  This
+feature is available in Postfix 2.1 and later.
+.br
+.IP "\fBreject_authenticated_sender_login_mismatch\fR"
+Reject the request when the client is authenticated with SASL,
+but either the MAIL FROM address is not listed in $smtpd_sender_login_maps,
+or the SASL login name is not an owner for that address.
+.br
+This prevents an authenticated client from using a MAIL FROM address
+that they do not explicitly own.
+.br
+This feature is available in Postfix version 2.1 and later.
+.br
+.IP "\fBreject_known_sender_login_mismatch\fR"
+When the client is authenticated with SASL, reject the request
+when the MAIL FROM address is listed in $smtpd_sender_login_maps,
+but the SASL login name is not an owner for that address.
+.br
+When the client is not authenticated with SASL, reject the request
+when SASL is enabled, and the MAIL FROM address is listed in
+$smtpd_sender_login_maps.
+.br
+This protects any MAIL FROM address that is listed in
+$smtpd_sender_login_maps, while still allowing a client to use any
+unlisted MAIL FROM address.
+.br
+This feature is available in Postfix version 2.11 and later.
+.br
+.IP "\fBreject_non_fqdn_sender\fR"
+Reject the request when the MAIL FROM address specifies a
+domain that is not in
+fully\-qualified domain form as required by the RFC.
+.br
+The
+non_fqdn_reject_code parameter specifies the response code for
+rejected requests (default: 504).
+.br
+.IP "\fBreject_rhsbl_sender \fIrbl_domain=d.d.d.d\fR\fR"
+Reject the request when the MAIL FROM domain is listed with
+the A record "\fId.d.d.d\fR" under \fIrbl_domain\fR (Postfix
+version 2.1 and later only).  Each "\fId\fR" is a number, or a
+pattern inside "[]" that contains one or more ";"\-separated numbers
+or number..number ranges (Postfix version 2.8 and later). If no
+"\fI=d.d.d.d\fR" is specified,
+reject the request when the MAIL FROM domain is
+listed with any A record under \fIrbl_domain\fR.
+.br
+The
+maps_rbl_reject_code parameter specifies the response code for
+rejected requests (default:  554); the default_rbl_reply parameter
+specifies the default server reply; and the rbl_reply_maps parameter
+specifies tables with server replies indexed by \fIrbl_domain\fR.
+This feature is available in Postfix 2.0 and later.
+.br
+.IP "\fBreject_sender_login_mismatch\fR"
+As of Postfix 2.1, this is an alias for
+"reject_authenticated_sender_login_mismatch,
+reject_unauthenticated_sender_login_mismatch".
+.br
+.IP "\fBreject_unauthenticated_sender_login_mismatch\fR"
+Reject the request when SASL is enabled, the MAIL FROM address
+is listed in $smtpd_sender_login_maps, but the client is not
+authenticated with SASL.
+.br
+With SASL enabled, this prevents an unauthenticated client from
+using any MAIL FROM address that is listed in $smtpd_sender_login_maps.
+.br
+This feature is available in Postfix version 2.1 and later.
+.br
+.IP "\fBreject_unknown_sender_domain\fR"
+Reject the request when Postfix is not the final destination for
+the sender address, and the MAIL FROM domain has 1) no DNS MX and
+no DNS A
+record, or 2) a malformed MX record such as a record with
+a zero\-length MX hostname (Postfix version 2.3 and later).
+.br
+The
+reply is specified with the unknown_address_reject_code parameter
+(default: 450), unknown_address_tempfail_action (default:
+defer_if_permit), or 550 (nullmx, Postfix 3.0 and
+later). See the respective parameter descriptions for details.
+.br
+.IP "\fBreject_unlisted_sender\fR"
+Reject the request when the MAIL FROM address is not listed in
+the list of valid recipients for its domain class. See the
+smtpd_reject_unlisted_sender parameter description for details.
+This feature is available in Postfix 2.1 and later.
+.br
+.IP "\fBreject_unverified_sender\fR"
+Reject the request when mail to the MAIL FROM address is known to
+bounce, or when the sender address destination is not reachable.
+Address verification information is managed by the \fBverify\fR(8) server;
+see the ADDRESS_VERIFICATION_README file for details.
+.br
+The
+unverified_sender_reject_code parameter specifies the numerical
+response code when an address is known to bounce (default: 450,
+change into 550 when you are confident that it is safe to do so).
+.br
+The unverified_sender_defer_code specifies the numerical response
+code when an address probe failed due to a temporary problem
+(default: 450).
+.br
+The unverified_sender_tempfail_action parameter
+specifies the action after address probe failure due to a temporary
+problem (default: defer_if_permit).
+.br
+This feature breaks for
+aliased addresses with "enable_original_recipient = no" (Postfix
+<= 3.2).
+.br
+This feature is available in Postfix 2.1 and later.
+.br
+.br
+.PP
+Other restrictions that are valid in this context:
+.IP \(bu
+Generic restrictions that can be used
+in any SMTP command context, described under smtpd_client_restrictions.
+.IP \(bu
+SMTP command specific restrictions described under
+smtpd_client_restrictions and smtpd_helo_restrictions.
+.IP \(bu
+SMTP command specific restrictions described under
+smtpd_recipient_restrictions. When recipient restrictions are listed
+under smtpd_sender_restrictions, they have effect only with
+"smtpd_delay_reject = yes", so that $smtpd_sender_restrictions is
+evaluated at the time of the RCPT TO command.
+.br
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+smtpd_sender_restrictions = reject_unknown_sender_domain
+smtpd_sender_restrictions = reject_unknown_sender_domain,
+    check_sender_access hash:/etc/postfix/access
+.fi
+.ad
+.ft R
+.SH smtpd_service_name (default: smtpd)
+The internal service that \fBpostscreen\fR(8) hands off allowed
+connections to. In a future version there may be different
+classes of SMTP service.
+.PP
+This feature is available in Postfix 2.8.
+.SH smtpd_soft_error_limit (default: 10)
+The number of errors a remote SMTP client is allowed to make without
+delivering mail before the Postfix SMTP server slows down all its
+responses.
+.IP \(bu
+With Postfix version 2.1 and later, when the error count
+is > $smtpd_soft_error_limit, the Postfix SMTP server
+delays all responses by $smtpd_error_sleep_time.
+.IP \(bu
+With Postfix versions 2.0 and earlier, when the error count
+is > $smtpd_soft_error_limit, the Postfix SMTP server delays all
+responses by the larger of (number of errors) seconds or
+$smtpd_error_sleep_time.
+.IP \(bu
+With Postfix versions 2.0 and earlier, when the error count
+is <= $smtpd_soft_error_limit, the Postfix SMTP server delays 4XX
+and 5XX responses by $smtpd_error_sleep_time.
+.br
+.SH smtpd_starttls_timeout (default: see "postconf \-d" output)
+The time limit for Postfix SMTP server write and read operations
+during TLS startup and shutdown handshake procedures. The current
+default value is stress\-dependent. Before Postfix version 2.8, it
+was fixed at 300s.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_timeout (default: normal: 300s, overload: 10s)
+When the Postfix SMTP server wants to send an SMTP server
+response, how long the Postfix SMTP server will wait for an underlying
+network write operation to complete; and when the Postfix SMTP
+server Postfix wants to receive an SMTP client request, how long
+the Postfix SMTP server will wait for an underlying network read
+operation to complete. See the smtpd_per_request_deadline for how
+this time limit may be enforced (with Postfix 2.9\-3.6 see
+smtpd_per_record_deadline).
+.PP
+Normally the default limit
+is 300s, but it changes under overload to just 10s. With Postfix
+2.5 and earlier, the SMTP server always uses a time limit of 300s
+by default.
+.PP
+Note: if you set SMTP time limits to very large values you may have
+to update the global ipc_timeout parameter.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH smtpd_tls_CAfile (default: empty)
+A file containing (PEM format) CA certificates of root CAs trusted
+to sign either remote SMTP client certificates or intermediate CA
+certificates.  These are loaded into memory before the \fBsmtpd\fR(8) server
+enters the chroot jail. If the number of trusted roots is large, consider
+using smtpd_tls_CApath instead, but note that the latter directory must
+be present in the chroot jail if the \fBsmtpd\fR(8) server is chrooted. This
+file may also be used to augment the server certificate trust chain,
+but it is best to include all the required certificates directly in the
+server certificate file.
+.PP
+Specify "smtpd_tls_CAfile = /path/to/system_CA_file" to use ONLY
+the system\-supplied default Certification Authority certificates.
+.PP
+Specify "tls_append_default_CA = no" to prevent Postfix from
+appending the system\-supplied default CAs and trusting third\-party
+certificates.
+.PP
+By default (see smtpd_tls_ask_ccert), client certificates are not
+requested, and smtpd_tls_CAfile should remain empty. If you do make use
+of client certificates, the distinguished names (DNs) of the Certification
+Authorities listed in smtpd_tls_CAfile are sent to the remote SMTP client
+in the client certificate request message. MUAs with multiple client
+certificates may use the list of preferred Certification Authorities
+to select the correct client certificate.  You may want to put your
+"preferred" CA or CAs in this file, and install other trusted CAs in
+$smtpd_tls_CApath.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_tls_CAfile = /etc/postfix/CAcert.pem
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_tls_CApath (default: empty)
+A directory containing (PEM format) CA certificates of root CAs
+trusted to sign either remote SMTP client certificates or intermediate CA
+certificates. Do not forget to create the necessary "hash" links with,
+for example, "$OPENSSL_HOME/bin/c_rehash /etc/postfix/certs". To use
+smtpd_tls_CApath in chroot mode, this directory (or a copy) must be
+inside the chroot jail.
+.PP
+Specify "smtpd_tls_CApath = /path/to/system_CA_directory" to
+use ONLY the system\-supplied default Certification Authority certificates.
+.PP
+Specify "tls_append_default_CA = no" to prevent Postfix from
+appending the system\-supplied default CAs and trusting third\-party
+certificates.
+.PP
+By default (see smtpd_tls_ask_ccert), client certificates are
+not requested, and smtpd_tls_CApath should remain empty. In contrast
+to smtpd_tls_CAfile, DNs of Certification Authorities installed
+in $smtpd_tls_CApath are not included in the client certificate
+request message. MUAs with multiple client certificates may use the
+list of preferred Certification Authorities to select the correct
+client certificate.  You may want to put your "preferred" CA or
+CAs in $smtpd_tls_CAfile, and install the remaining trusted CAs in
+$smtpd_tls_CApath.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_tls_CApath = /etc/postfix/certs
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_tls_always_issue_session_ids (default: yes)
+Force the Postfix SMTP server to issue a TLS session id, even
+when TLS session caching is turned off (smtpd_tls_session_cache_database
+is empty). This behavior is compatible with Postfix < 2.3.
+.PP
+With Postfix 2.3 and later the Postfix SMTP server can disable
+session id generation when TLS session caching is turned off. This
+keeps remote SMTP clients from caching sessions that almost certainly cannot
+be re\-used.
+.PP
+By default, the Postfix SMTP server always generates TLS session
+ids. This works around a known defect in mail client applications
+such as MS Outlook, and may also prevent interoperability issues
+with other MTAs.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_tls_always_issue_session_ids = no
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtpd_tls_ask_ccert (default: no)
+Ask a remote SMTP client for a client certificate. This
+information is needed for certificate based mail relaying with,
+for example, the permit_tls_clientcerts feature.
+.PP
+Some clients such as Netscape will either complain if no
+certificate is available (for the list of CAs in $smtpd_tls_CAfile)
+or will offer multiple client certificates to choose from. This
+may be annoying, so this option is "off" by default.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_tls_auth_only (default: no)
+When TLS encryption is optional in the Postfix SMTP server, do
+not announce or accept SASL authentication over unencrypted
+connections.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_tls_ccert_verifydepth (default: 9)
+The verification depth for remote SMTP client certificates. A
+depth of 1 is sufficient if the issuing CA is listed in a local CA
+file.
+.PP
+The default verification depth is 9 (the OpenSSL default) for
+compatibility with earlier Postfix behavior. Prior to Postfix 2.5,
+the default value was 5, but the limit was not actually enforced. If
+you have set this to a lower non\-default value, certificates with longer
+trust chains may now fail to verify. Certificate chains with 1 or 2
+CAs are common, deeper chains are more rare and any number between 5
+and 9 should suffice in practice. You can choose a lower number if,
+for example, you trust certificates directly signed by an issuing CA
+but not any CAs it delegates to.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_tls_cert_file (default: empty)
+File with the Postfix SMTP server RSA certificate in PEM format.
+This file may also contain the Postfix SMTP server private RSA key.
+With Postfix >= 3.4 the preferred way to configure server keys and
+certificates is via the "smtpd_tls_chain_files" parameter.
+.PP
+Public Internet MX hosts without certificates signed by a "reputable"
+CA must generate, and be prepared to present to most clients, a
+self\-signed or private\-CA signed certificate. The client will not be
+able to authenticate the server, but unless it is running Postfix 2.3 or
+similar software, it will still insist on a server certificate.
+.PP
+For servers that are \fBnot\fR public Internet MX hosts, Postfix
+supports configurations with no certificates. This entails the use of
+just the anonymous TLS ciphers, which are not supported by typical SMTP
+clients. Since some clients may not fall back to plain text after a TLS
+handshake failure, a certificate\-less Postfix SMTP server will be unable
+to receive email from some TLS\-enabled clients. To avoid accidental
+configurations with no certificates, Postfix enables certificate\-less
+operation only when the administrator explicitly sets
+"smtpd_tls_cert_file = none". This ensures that new Postfix SMTP server
+configurations will not accidentally enable TLS without certificates.
+.PP
+Note that server certificates are not optional in TLS 1.3. To run
+without certificates you'd have to disable the TLS 1.3 protocol by
+including '!TLSv1.3' in "smtpd_tls_protocols" and perhaps also
+"smtpd_tls_mandatory_protocols".  It is simpler instead to just
+configure a certificate chain.  Certificate\-less operation is not
+recommended.
+.PP
+Both RSA and DSA certificates are supported.  When both types
+are present, the cipher used determines which certificate will be
+presented to the client.  For Netscape and OpenSSL clients without
+special cipher choices the RSA certificate is preferred.
+.PP
+To enable a remote SMTP client to verify the Postfix SMTP server
+certificate, the issuing CA certificates must be made available to the
+client. You should include the required certificates in the server
+certificate file, the server certificate first, then the issuing
+CA(s) (bottom\-up order).
+.PP
+Example: the certificate for "server.example.com" was issued by
+"intermediate CA" which itself has a certificate of "root CA".
+Create the server.pem file with "cat server_cert.pem intermediate_CA.pem
+root_CA.pem > server.pem".
+.PP
+If you also want to verify client certificates issued by these
+CAs, you can add the CA certificates to the smtpd_tls_CAfile, in which
+case it is not necessary to have them in the smtpd_tls_cert_file,
+smtpd_tls_dcert_file (obsolete) or smtpd_tls_eccert_file.
+.PP
+A certificate supplied here must be usable as an SSL server certificate
+and hence pass the "openssl verify \-purpose sslserver ..." test.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_tls_cert_file = /etc/postfix/server.pem
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_tls_chain_files (default: empty)
+List of one or more PEM files, each holding one or more private keys
+directly followed by a corresponding certificate chain.  The file names
+are separated by commas and/or whitespace.  This parameter obsoletes the
+legacy algorithm\-specific key and certificate file settings.  When this
+parameter is non\-empty, the legacy parameters are ignored, and a warning
+is logged if any are also non\-empty.
+.PP
+With the proliferation of multiple private key algorithms-which,
+as of OpenSSL 1.1.1, include DSA (obsolete), RSA, ECDSA, Ed25519
+and Ed448-it is increasingly impractical to use separate
+parameters to configure the key and certificate chain for each
+algorithm.  Therefore, Postfix now supports storing multiple keys and
+corresponding certificate chains in a single file or in a set of files.
+.PP
+Each key must appear \fBimmediately before\fR the corresponding
+certificate, optionally followed by additional issuer certificates that
+complete the certificate chain for that key.  When multiple files are
+specified, they are equivalent to a single file that is concatenated
+from those files in the given order.  Thus, while a key must always
+precede its certificate and issuer chain, it can be in a separate file,
+so long as that file is listed immediately before the file that holds
+the corresponding certificate chain.  Once all the files are
+concatenated, the sequence of PEM objects must be: \fIkey1, cert1,
+[chain1], key2, cert2, [chain2], ..., keyN, certN, [chainN].\fR
+.PP
+Storing the private key in the same file as the corresponding
+certificate is more reliable.  With the key and certificate in separate
+files, there is a chance that during key rollover a Postfix process
+might load a private key and certificate from separate files that don't
+match.  Various operational errors may even result in a persistent
+broken configuration in which the certificate does not match the private
+key.
+.PP
+The file or files must contain at most one key of each type.  If,
+for example, two or more RSA keys and corresponding chains are listed,
+depending on the version of OpenSSL either only the last one will be
+used or a configuration error may be detected.  Note that while
+"Ed25519" and "Ed448" are considered separate algorithms, the various
+ECDSA curves (typically one of prime256v1, secp384r1 or secp521r1) are
+considered as different parameters of a single "ECDSA" algorithm, so it
+is not presently possible to configure keys for more than one ECDSA
+curve.
+.PP
+RSA is still the most widely supported algorithm.  Presently (late
+2018), ECDSA support is common, but not yet universal, and Ed25519 and
+Ed448 support is mostly absent.  Therefore, an RSA key should generally
+be configured, along with any additional keys for the other algorithms
+when desired.
+.PP
+Example (separate files for each key and corresponding certificate chain):
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    smtpd_tls_chain_files =
+        ${config_directory}/ed25519.pem,
+        ${config_directory}/ed448.pem,
+        ${config_directory}/rsa.pem
+.fi
+.ad
+.ft R
+.in -4
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/ed25519.pem:
+    \-\-\-\-\-BEGIN PRIVATE KEY\-\-\-\-\-
+    MC4CAQAwBQYDK2VwBCIEIEJfbbO4BgBQGBg9NAbIJaDBqZb4bC4cOkjtAH+Efbz3
+    \-\-\-\-\-END PRIVATE KEY\-\-\-\-\-
+    \-\-\-\-\-BEGIN CERTIFICATE\-\-\-\-\-
+    MIIBKzCB3qADAgECAhQaw+rflRreYuUZBp0HuNn/e5rMZDAFBgMrZXAwFDESMBAG
+    ...
+    nC0egv51YPDWxEHom4QA
+    \-\-\-\-\-END CERTIFICATE\-\-\-\-\-
+.fi
+.ad
+.ft R
+.in -4
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/ed448.pem:
+    \-\-\-\-\-BEGIN PRIVATE KEY\-\-\-\-\-
+    MEcCAQAwBQYDK2VxBDsEOQf+m0P+G0qi+NZ0RolyeiE5zdlPQR8h8y4jByBifpIe
+    LNler7nzHQJ1SLcOiXFHXlxp/84VZuh32A==
+    \-\-\-\-\-END PRIVATE KEY\-\-\-\-\-
+    \-\-\-\-\-BEGIN CERTIFICATE\-\-\-\-\-
+    MIIBdjCB96ADAgECAhQSv4oP972KypOZPNPF4fmsiQoRHzAFBgMrZXEwFDESMBAG
+    ...
+    pQcWsx+4J29e6YWH3Cy/CdUaexKP4RPCZDrPX7bk5C2BQ+eeYOxyThMA
+    \-\-\-\-\-END CERTIFICATE\-\-\-\-\-
+.fi
+.ad
+.ft R
+.in -4
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/rsa.pem:
+    \-\-\-\-\-BEGIN PRIVATE KEY\-\-\-\-\-
+    MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQDc4QusgkahH9rL
+    ...
+    ahQkZ3+krcaJvDSMgvu0tDc=
+    \-\-\-\-\-END PRIVATE KEY\-\-\-\-\-
+    \-\-\-\-\-BEGIN CERTIFICATE\-\-\-\-\-
+    MIIC+DCCAeCgAwIBAgIUIUkrbk1GAemPCT8i9wKsTGDH7HswDQYJKoZIhvcNAQEL
+    ...
+    Rirz15HGVNTK8wzFd+nulPzwUo6dH2IU8KazmyRi7OGvpyrMlm15TRE2oyE=
+    \-\-\-\-\-END CERTIFICATE\-\-\-\-\-
+.fi
+.ad
+.ft R
+.in -4
+.PP
+Example (all keys and certificates in a single file):
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    smtpd_tls_chain_files = ${config_directory}/chains.pem
+.fi
+.ad
+.ft R
+.in -4
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/chains.pem:
+    \-\-\-\-\-BEGIN PRIVATE KEY\-\-\-\-\-
+    MC4CAQAwBQYDK2VwBCIEIEJfbbO4BgBQGBg9NAbIJaDBqZb4bC4cOkjtAH+Efbz3
+    \-\-\-\-\-END PRIVATE KEY\-\-\-\-\-
+    \-\-\-\-\-BEGIN CERTIFICATE\-\-\-\-\-
+    MIIBKzCB3qADAgECAhQaw+rflRreYuUZBp0HuNn/e5rMZDAFBgMrZXAwFDESMBAG
+    ...
+    nC0egv51YPDWxEHom4QA
+    \-\-\-\-\-END CERTIFICATE\-\-\-\-\-
+    \-\-\-\-\-BEGIN PRIVATE KEY\-\-\-\-\-
+    MEcCAQAwBQYDK2VxBDsEOQf+m0P+G0qi+NZ0RolyeiE5zdlPQR8h8y4jByBifpIe
+    LNler7nzHQJ1SLcOiXFHXlxp/84VZuh32A==
+    \-\-\-\-\-END PRIVATE KEY\-\-\-\-\-
+    \-\-\-\-\-BEGIN CERTIFICATE\-\-\-\-\-
+    MIIBdjCB96ADAgECAhQSv4oP972KypOZPNPF4fmsiQoRHzAFBgMrZXEwFDESMBAG
+    ...
+    pQcWsx+4J29e6YWH3Cy/CdUaexKP4RPCZDrPX7bk5C2BQ+eeYOxyThMA
+    \-\-\-\-\-END CERTIFICATE\-\-\-\-\-
+    \-\-\-\-\-BEGIN PRIVATE KEY\-\-\-\-\-
+    MIIEvQIBADANBgkqhkiG9w0BAQEFAASCBKcwggSjAgEAAoIBAQDc4QusgkahH9rL
+    ...
+    ahQkZ3+krcaJvDSMgvu0tDc=
+    \-\-\-\-\-END PRIVATE KEY\-\-\-\-\-
+    \-\-\-\-\-BEGIN CERTIFICATE\-\-\-\-\-
+    MIIC+DCCAeCgAwIBAgIUIUkrbk1GAemPCT8i9wKsTGDH7HswDQYJKoZIhvcNAQEL
+    ...
+    Rirz15HGVNTK8wzFd+nulPzwUo6dH2IU8KazmyRi7OGvpyrMlm15TRE2oyE=
+    \-\-\-\-\-END CERTIFICATE\-\-\-\-\-
+.fi
+.ad
+.ft R
+.in -4
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH smtpd_tls_cipherlist (default: empty)
+Obsolete Postfix < 2.3 control for the Postfix SMTP server TLS
+cipher list. It is easy to create interoperability problems by choosing
+a non\-default cipher list. Do not use a non\-default TLS cipherlist for
+MX hosts on the public Internet. Clients that begin the TLS handshake,
+but are unable to agree on a common cipher, may not be able to send any
+email to the SMTP server. Using a restricted cipher list may be more
+appropriate for a dedicated MSA or an internal mailhub, where one can
+exert some control over the TLS software and settings of the connecting
+clients.
+.PP
+\fBNote:\fR do not use "" quotes around the parameter value.
+.PP
+This feature is available with Postfix version 2.2. It is not used with
+Postfix 2.3 and later; use smtpd_tls_mandatory_ciphers instead.
+.SH smtpd_tls_ciphers (default: medium)
+The minimum TLS cipher grade that the Postfix SMTP server
+will use with opportunistic TLS encryption. Cipher types listed in
+smtpd_tls_exclude_ciphers are excluded from the base definition of
+the selected cipher grade.  The default value is "medium" for Postfix
+releases after the middle of 2015, "export" for older releases.
+.PP
+When TLS is mandatory the cipher grade is chosen via the
+smtpd_tls_mandatory_ciphers configuration parameter, see there for syntax
+details.
+.PP
+This feature is available in Postfix 2.6 and later. With earlier Postfix
+releases only the smtpd_tls_mandatory_ciphers parameter is implemented,
+and opportunistic TLS always uses "export" or better (i.e. all) ciphers.
+.SH smtpd_tls_dcert_file (default: empty)
+File with the Postfix SMTP server DSA certificate in PEM format.
+This file may also contain the Postfix SMTP server private DSA key.
+The DSA algorithm is obsolete and should not be used.
+.PP
+See the discussion under smtpd_tls_cert_file for more details.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_tls_dcert_file = /etc/postfix/server\-dsa.pem
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_tls_dh1024_param_file (default: empty)
+File with DH parameters that the Postfix SMTP server should
+use with non\-export EDH ciphers.
+.PP
+With Postfix >= 3.7, built with OpenSSL version is 3.0.0 or later, if the
+parameter value is either empty or "\fBauto\fR", then the DH parameter
+selection is delegated to the OpenSSL library, which selects appropriate
+parameters based on the TLS handshake.  This choice is likely to be the most
+interoperable with SMTP clients using various TLS libraries, and custom local
+parameters are no longer recommended when using Postfix >= 3.7 built against
+OpenSSL 3.0.0.
+.PP
+The best\-practice choice of parameters uses a 2048\-bit prime.  This is fine,
+despite the historical "1024" in the parameter name.  Do not be tempted to use
+much larger values, performance degrades quickly, and you may also cease to
+interoperate with some mainstream SMTP clients.  As of Postfix 3.1, the
+compiled\-in default prime is 2048\-bits, and it is not strictly necessary,
+though perhaps somewhat beneficial to generate custom DH parameters.
+.PP
+Instead of using the exact same parameter sets as distributed
+with other TLS packages, it is more secure to generate your own
+set of parameters with something like the following commands:
+.sp
+.in +4
+.nf
+.na
+.ft C
+openssl dhparam \-out /etc/postfix/dh2048.pem 2048
+openssl dhparam \-out /etc/postfix/dh1024.pem 1024
+# As of Postfix 3.6, export\-grade 512\-bit DH parameters are no longer
+# supported or needed.
+openssl dhparam \-out /etc/postfix/dh512.pem 512
+.fi
+.ad
+.ft R
+.in -4
+.PP
+It is safe to share the same DH parameters between multiple
+Postfix instances.  If you prefer, you can generate separate
+parameters for each instance.
+.PP
+If you want to take maximal advantage of ciphers that offer forward secrecy see
+the Getting
+started section of FORWARD_SECRECY_README.  The
+full document conveniently presents all information about Postfix
+"perfect" forward secrecy support in one place: what forward secrecy
+is, how to tweak settings, and what you can expect to see when
+Postfix uses ciphers with forward secrecy.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_tls_dh1024_param_file = /etc/postfix/dh2048.pem
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_tls_dh512_param_file (default: empty)
+File with DH parameters that the Postfix SMTP server should
+use with export\-grade EDH ciphers.  The default SMTP server cipher
+grade is "medium" with Postfix releases after the middle of 2015,
+and as a result export\-grade cipher suites are by default not used.
+.PP
+With Postfix >= 3.6 export\-grade Diffie\-Hellman key exchange
+is no longer supported, and this parameter is silently ignored.
+.PP
+See also the discussion under the smtpd_tls_dh1024_param_file
+configuration parameter.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_tls_dh512_param_file = /etc/postfix/dh_512.pem
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.2 and later,
+but is ignored in Postfix 3.6 and later.
+.SH smtpd_tls_dkey_file (default: $smtpd_tls_dcert_file)
+File with the Postfix SMTP server DSA private key in PEM format.
+This file may be combined with the Postfix SMTP server DSA certificate
+file specified with $smtpd_tls_dcert_file. The DSA algorithm is obsolete
+and should not be used.
+.PP
+The private key must be accessible without a pass\-phrase, i.e. it
+must not be encrypted. File permissions should grant read\-only
+access to the system superuser account ("root"), and no access
+to anyone else.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_tls_eccert_file (default: empty)
+File with the Postfix SMTP server ECDSA certificate in PEM format.
+This file may also contain the Postfix SMTP server private ECDSA key.
+With Postfix >= 3.4 the preferred way to configure server keys and
+certificates is via the "smtpd_tls_chain_files" parameter.
+.PP
+See the discussion under smtpd_tls_cert_file for more details.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_tls_eccert_file = /etc/postfix/ecdsa\-scert.pem
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.6 and later, when Postfix is
+compiled and linked with OpenSSL 1.0.0 or later.
+.SH smtpd_tls_eckey_file (default: $smtpd_tls_eccert_file)
+File with the Postfix SMTP server ECDSA private key in PEM format.
+This file may be combined with the Postfix SMTP server ECDSA certificate
+file specified with $smtpd_tls_eccert_file.  With Postfix >= 3.4 the
+preferred way to configure server keys and certificates is via the
+"smtpd_tls_chain_files" parameter.
+.PP
+The private key must be accessible without a pass\-phrase, i.e. it
+must not be encrypted. File permissions should grant read\-only
+access to the system superuser account ("root"), and no access
+to anyone else.
+.PP
+This feature is available in Postfix 2.6 and later, when Postfix is
+compiled and linked with OpenSSL 1.0.0 or later.
+.SH smtpd_tls_eecdh_grade (default: see "postconf \-d" output)
+The Postfix SMTP server security grade for ephemeral elliptic\-curve
+Diffie\-Hellman (EECDH) key exchange.   As of Postfix 3.6, the value of
+this parameter is always ignored, and Postfix behaves as though the
+\fBauto\fR value (described below) was chosen.
+.PP
+The available choices are:
+.IP "\fBauto\fR"
+Use the most preferred curve that is
+supported by both the client and the server.  This setting requires
+Postfix >= 3.2 compiled and linked with OpenSSL >= 1.0.2.  This
+is the default setting under the above conditions (and the only
+setting used with Postfix >= 3.6).
+.br
+.IP "\fBnone\fR"
+Don't use EECDH. Ciphers based on EECDH key
+exchange will be disabled. This is the default in Postfix versions
+2.6 and 2.7.
+.br
+.IP "\fBstrong\fR"
+Use EECDH with approximately 128 bits of
+security at a reasonable computational cost. This is the default in
+Postfix versions 2.8-3.5.
+.br
+.IP "\fBultra\fR"
+Use EECDH with approximately 192 bits of
+security at computational cost that is approximately twice as high
+as 128 bit strength ECC.
+.br
+.br
+.PP
+If you want to take maximal advantage of ciphers that offer forward secrecy see
+the Getting
+started section of FORWARD_SECRECY_README.  The
+full document conveniently presents all information about Postfix
+"perfect" forward secrecy support in one place: what forward secrecy
+is, how to tweak settings, and what you can expect to see when
+Postfix uses ciphers with forward secrecy.
+.PP
+This feature is available in Postfix 2.6 and later, when it is
+compiled and linked with OpenSSL 1.0.0 or later on platforms
+where EC algorithms have not been disabled by the vendor.
+.SH smtpd_tls_exclude_ciphers (default: empty)
+List of ciphers or cipher types to exclude from the SMTP server
+cipher list at all TLS security levels. Excluding valid ciphers
+can create interoperability problems. DO NOT exclude ciphers unless it
+is essential to do so. This is not an OpenSSL cipherlist; it is a simple
+list separated by whitespace and/or commas. The elements are a single
+cipher, or one or more "+" separated cipher properties, in which case
+only ciphers matching \fBall\fR the properties are excluded.
+.PP
+Examples (some of these will cause problems):
+.sp
+.in +4
+.nf
+.na
+.ft C
+smtpd_tls_exclude_ciphers = aNULL
+smtpd_tls_exclude_ciphers = MD5, DES
+smtpd_tls_exclude_ciphers = DES+MD5
+smtpd_tls_exclude_ciphers = AES256\-SHA, DES\-CBC3\-MD5
+smtpd_tls_exclude_ciphers = kEDH+aRSA
+.fi
+.ad
+.ft R
+.in -4
+.PP
+The first setting disables anonymous ciphers. The next setting
+disables ciphers that use the MD5 digest algorithm or the (single) DES
+encryption algorithm. The next setting disables ciphers that use MD5 and
+DES together.  The next setting disables the two ciphers "AES256\-SHA"
+and "DES\-CBC3\-MD5". The last setting disables ciphers that use "EDH"
+key exchange with RSA authentication.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtpd_tls_fingerprint_digest (default: see "postconf \-d" output)
+The message digest algorithm to construct remote SMTP client\-certificate
+fingerprints or public key fingerprints (Postfix 2.9 and later) for
+\fBcheck_ccert_access\fR and \fBpermit_tls_clientcerts\fR.
+.PP
+The default algorithm is \fBsha256\fR with Postfix >= 3.6
+and the \fBcompatibility_level\fR set to 3.6 or higher. With Postfix
+<= 3.5, the default algorithm is \fBmd5\fR.
+.PP
+The best\-practice algorithm is now \fBsha256\fR. Recent advances in hash
+function cryptanalysis have led to md5 and sha1 being deprecated in favor of
+sha256.  However, as long as there are no known "second pre\-image" attacks
+against the older algorithms, their use in this context, though not
+recommended, is still likely safe.
+.PP
+While additional digest algorithms are often available with OpenSSL's
+libcrypto, only those used by libssl in SSL cipher suites are available to
+Postfix.  You'll likely find support for md5, sha1, sha256 and sha512.
+.PP
+To find the fingerprint of a specific certificate file, with a
+specific digest algorithm, run:
+.sp
+.in +4
+.nf
+.na
+.ft C
+$ openssl x509 \-noout \-fingerprint \-\fIdigest\fR \-in \fIcertfile\fR.pem
+.fi
+.ad
+.ft R
+.in -4
+.PP
+The text to the right of "=" sign is the desired fingerprint.
+For example:
+.sp
+.in +4
+.nf
+.na
+.ft C
+$ openssl x509 \-noout \-fingerprint \-sha256 \-in cert.pem
+SHA256 Fingerprint=D4:6A:AB:19:24:...:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A
+.fi
+.ad
+.ft R
+.in -4
+.PP
+To extract the public key fingerprint from an X.509 certificate,
+you need to extract the public key from the certificate and compute
+the appropriate digest of its DER (ASN.1) encoding. With OpenSSL
+the "\-pubkey" option of the "x509" command extracts the public
+key always in "PEM" format. We pipe the result to another OpenSSL
+command that converts the key to DER and then to the "dgst" command
+to compute the fingerprint.
+.PP
+Example:
+.sp
+.in +4
+.nf
+.na
+.ft C
+$ openssl x509 \-in cert.pem \-noout \-pubkey |
+    openssl pkey \-pubin \-outform DER |
+    openssl dgst \-sha256 \-c
+(stdin)= 64:3f:1f:f6:e5:1e:d4:2a:56:8b:fc:09:1a:61:98:b5:bc:7c:60:58
+.fi
+.ad
+.ft R
+.in -4
+.PP
+The Postfix SMTP server and client log the peer (leaf) certificate
+fingerprint and public key fingerprint when the TLS loglevel is 2 or
+higher.
+.PP
+Example: client\-certificate access table, with sha256 fingerprints:
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    smtpd_tls_fingerprint_digest = sha256
+    smtpd_client_restrictions =
+        check_ccert_access hash:/etc/postfix/access,
+        reject
+.fi
+.ad
+.ft R
+.nf
+.na
+.ft C
+/etc/postfix/access:
+    # Action folded to next line...
+    AF:88:7C:AD:51:95:6F:36:96:...:01:FB:2E:48:CD:AB:49:25:A2:3B
+        OK
+    85:16:78:FD:73:6E:CE:70:E0:...:5F:0D:3C:C8:6D:C4:2C:24:59:E1
+        permit_auth_destination
+.fi
+.ad
+.ft R
+.in -4
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH smtpd_tls_key_file (default: $smtpd_tls_cert_file)
+File with the Postfix SMTP server RSA private key in PEM format.
+This file may be combined with the Postfix SMTP server RSA certificate
+file specified with $smtpd_tls_cert_file.  With Postfix >= 3.4 the
+preferred way to configure server keys and certificates is via the
+"smtpd_tls_chain_files" parameter.
+.PP
+The private key must be accessible without a pass\-phrase, i.e. it
+must not be encrypted. File permissions should grant read\-only
+access to the system superuser account ("root"), and no access
+to anyone else.
+.SH smtpd_tls_loglevel (default: 0)
+Enable additional Postfix SMTP server logging of TLS activity.
+Each logging level also includes the information that is logged at
+a lower logging level.
+.IP ""
+0 Disable logging of TLS activity.
+.br
+.IP ""
+1 Log only a summary message on TLS handshake completion
+- no logging of client certificate trust\-chain verification errors
+if client certificate verification is not required.  With Postfix 2.8 and
+earlier, log the summary message, peer certificate summary information
+and unconditionally log trust\-chain verification errors.
+.br
+.IP ""
+2 Also log levels during TLS negotiation.
+.br
+.IP ""
+3 Also log hexadecimal and ASCII dump of TLS negotiation
+process.
+.br
+.IP ""
+4 Also log hexadecimal and ASCII dump of complete
+transmission after STARTTLS.
+.br
+.br
+.PP
+Do not use "smtpd_tls_loglevel = 2" or higher except in case
+of problems. Use of loglevel 4 is strongly discouraged.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_tls_mandatory_ciphers (default: medium)
+The minimum TLS cipher grade that the Postfix SMTP server will
+use with mandatory TLS encryption. The default grade ("medium") is
+sufficiently strong that any benefit from globally restricting TLS
+sessions to a more stringent grade is likely negligible, especially
+given the fact that many implementations still do not offer any stronger
+("high" grade) ciphers, while those that do, will always use "high"
+grade ciphers. So insisting on "high" grade ciphers is generally
+counter\-productive. Allowing "export" or "low" ciphers is typically
+not a good idea, as systems limited to just these are limited to
+obsolete browsers. No known SMTP clients fail to support at least
+one "medium" or "high" grade cipher.
+.PP
+The following cipher grades are supported:
+.IP "\fBhigh\fR"
+Enable only "HIGH" grade OpenSSL ciphers. The
+underlying cipherlist is specified via the tls_high_cipherlist
+configuration parameter, which you are strongly encouraged to
+not change.
+.br
+.IP "\fBmedium\fR"
+Enable "MEDIUM" grade or stronger OpenSSL ciphers. These use 128\-bit
+or longer symmetric bulk\-encryption keys. This is the default minimum
+strength for mandatory TLS encryption. The underlying cipherlist is
+specified via the tls_medium_cipherlist configuration parameter, which
+you are strongly encouraged not to change.
+.br
+.IP "\fBnull\fR"
+Enable only the "NULL" OpenSSL ciphers, these provide authentication
+without encryption.  This setting is only appropriate in the rare
+case that all clients are prepared to use NULL ciphers (not normally
+enabled in TLS clients). The underlying cipherlist is specified via the
+tls_null_cipherlist configuration parameter, which you are strongly
+encouraged not to change.
+.br
+.IP "\fBlow\fR"
+Enable "LOW" grade or stronger OpenSSL ciphers.  In Postfix
+>= 3.8 this cipher grade is always identical to "medium".  Recent
+versions of OpenSSL do not support any "LOW" grade ciphers.  In
+earlier Postfix releases the underlying cipherlist was specified
+via the tls_low_cipherlist configuration parameter, which you are
+strongly encouraged not to change.  This obsolete cipher grade
+SHOULD NOT be used.
+.br
+.IP "\fBexport\fR"
+Enable "EXPORT" grade or stronger OpenSSL ciphers.  In Postfix
+>= 3.8 this cipher grade is always identical to "medium".  Recent
+versions of OpenSSL do not support any "EXPORT" grade ciphers.  In
+earlier Postfix releases the underlying cipherlist was specified
+via the tls_export_cipherlist configuration parameter, which you are
+strongly encouraged not to change.  This obsolete cipher grade
+SHOULD NOT be used.
+.br
+.br
+.PP
+Cipher types listed in
+smtpd_tls_mandatory_exclude_ciphers or smtpd_tls_exclude_ciphers are
+excluded from the base definition of the selected cipher grade. See
+smtpd_tls_ciphers for cipher controls that apply to opportunistic
+TLS.
+.PP
+The underlying cipherlists for grades other than "null" include
+anonymous ciphers, but these are automatically filtered out if the
+server is configured to ask for remote SMTP client certificates.  You are very
+unlikely to need to take any steps to exclude anonymous ciphers, they
+are excluded automatically as required.  If you must exclude anonymous
+ciphers even when Postfix does not need or use peer certificates, set
+"smtpd_tls_exclude_ciphers = aNULL". To exclude anonymous ciphers only
+when TLS is enforced, set "smtpd_tls_mandatory_exclude_ciphers = aNULL".
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtpd_tls_mandatory_exclude_ciphers (default: empty)
+Additional list of ciphers or cipher types to exclude from the
+Postfix SMTP server cipher list at mandatory TLS security levels.
+This list
+works in addition to the exclusions listed with smtpd_tls_exclude_ciphers
+(see there for syntax details).
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtpd_tls_mandatory_protocols (default: see "postconf \-d" output)
+TLS protocols accepted by the Postfix SMTP server with mandatory TLS
+encryption.  If the list is empty, the server supports all available TLS
+protocol versions.  A non\-empty value is a list of protocol names to
+include or exclude, separated by whitespace, commas or colons.
+.PP
+The valid protocol names (see \fBSSL_get_version\fR(3)) are "SSLv2",
+"SSLv3", "TLSv1", "TLSv1.1", "TLSv1.2" and "TLSv1.3".  Starting with
+Postfix 3.6, the default value is ">=TLSv1", which sets TLS 1.0 as
+the lowest supported TLS protocol version (see below).  Older releases
+use the "!" exclusion syntax, also described below.
+.PP
+As of Postfix 3.6, the preferred way to limit the range of
+acceptable protocols is to set the lowest acceptable TLS protocol
+version and/or the highest acceptable TLS protocol version.  To set the
+lower bound include an element of the form: ">=\fIversion\fR" where
+\fIversion\fR is a either one of the TLS protocol names listed above,
+or a hexadecimal number corresponding to the desired TLS protocol
+version (0301 for TLS 1.0, 0302 for TLS 1.1, etc.).  For the upper
+bound, use "<=\fIversion\fR".  There must be no whitespace between
+the ">=" or "<=" symbols and the protocol name or number.
+.PP
+Hexadecimal protocol numbers make it possible to specify protocol
+bounds for TLS versions that are known to OpenSSL, but might not be
+known to Postfix.  They cannot be used with the legacy exclusion syntax.
+Leading "0" or "0x" prefixes are supported, but not required.
+Therefore, "301", "0301", "0x301" and "0x0301" are all equivalent to
+"TLSv1".  Hexadecimal versions unknown to OpenSSL will fail to set the
+upper or lower bound, and a warning will be logged.  Hexadecimal
+versions should only be used when Postfix is linked with some future
+version of OpenSSL that supports TLS 1.4 or later, but Postfix does not
+yet support a symbolic name for that protocol version.
+.PP
+Hexadecimal example (Postfix >= 3.6):
+.sp
+.in +4
+.nf
+.na
+.ft C
+# Allow only TLS 1.2 through (hypothetical) TLS 1.4, once supported
+# in some future version of OpenSSL (presently a warning is logged).
+smtpd_tls_mandatory_protocols = >=TLSv1.2, <=0305
+# Allow only TLS 1.2 and up:
+smtpd_tls_mandatory_protocols = >=0x0303
+.fi
+.ad
+.ft R
+.in -4
+.PP
+With Postfix < 3.6 there is no support for a minimum or maximum
+version, and the protocol range is configured via protocol exclusions.
+To require at least TLS 1.0, set "smtpd_tls_mandatory_protocols =
+!SSLv2, !SSLv3".  Listing the protocols to include, rather than
+protocols to exclude, is supported, but not recommended.  The exclusion
+form more accurately matches the underlying OpenSSL interface.
+.PP
+Support for "TLSv1.3" was introduced in OpenSSL 1.1.1.  Disabling
+this protocol via "!TLSv1.3" is supported since Postfix 3.4 (or patch
+releases >= 3.0.14, 3.1.10, 3.2.7 and 3.3.2).
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+# Preferred syntax with Postfix >= 3.6:
+smtpd_tls_mandatory_protocols = >=TLSv1.2, <=TLSv1.3
+# Legacy syntax:
+smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3, !TLSv1, !TLSv1.1
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtpd_tls_protocols (default: see postconf \-d output)
+TLS protocols accepted by the Postfix SMTP server with opportunistic
+TLS encryption. If the list is empty, the server supports all available
+TLS protocol versions.  A non\-empty value is a list of protocol names to
+include or exclude, separated by whitespace, commas or colons.
+.PP
+The valid protocol names (see \fBSSL_get_version\fR(3)) are "SSLv2",
+"SSLv3", "TLSv1", "TLSv1.1", "TLSv1.2" and "TLSv1.3".  Starting with
+Postfix 3.6, the default value is ">=TLSv1", which sets TLS 1.0 as
+the lowest supported TLS protocol version (see below).  Older releases
+use the "!" exclusion syntax, also described below.
+.PP
+As of Postfix 3.6, the preferred way to limit the range of
+acceptable protocols is to set the lowest acceptable TLS protocol
+version and/or the highest acceptable TLS protocol version.  To set the
+lower bound include an element of the form: ">=\fIversion\fR" where
+\fIversion\fR is a either one of the TLS protocol names listed above,
+or a hexadecimal number corresponding to the desired TLS protocol
+version (0301 for TLS 1.0, 0302 for TLS 1.1, etc.).  For the upper
+bound, use "<=\fIversion\fR".  There must be no whitespace between
+the ">=" or "<=" symbols and the protocol name or number.
+.PP
+Hexadecimal protocol numbers make it possible to specify protocol
+bounds for TLS versions that are known to OpenSSL, but might not be
+known to Postfix.  They cannot be used with the legacy exclusion syntax.
+Leading "0" or "0x" prefixes are supported, but not required.
+Therefore, "301", "0301", "0x301" and "0x0301" are all equivalent to
+"TLSv1".  Hexadecimal versions unknown to OpenSSL will fail to set the
+upper or lower bound, and a warning will be logged.  Hexadecimal
+versions should only be used when Postfix is linked with some future
+version of OpenSSL that supports TLS 1.4 or later, but Postfix does not
+yet support a symbolic name for that protocol version.
+.PP
+Hexadecimal example (Postfix >= 3.6):
+.sp
+.in +4
+.nf
+.na
+.ft C
+# Allow only TLS 1.0 through (hypothetical) TLS 1.4, once supported
+# in some future version of OpenSSL (presently a warning is logged).
+smtpd_tls_protocols = >=TLSv1, <=0305
+# Allow only TLS 1.0 and up:
+smtpd_tls_protocols = >=0x0301
+.fi
+.ad
+.ft R
+.in -4
+.PP
+With Postfix < 3.6 there is no support for a minimum or maximum
+version, and the protocol range is configured via protocol exclusions.
+To require at least TLS 1.0, set "smtpd_tls_protocols = !SSLv2, !SSLv3".
+Listing the protocols to include, rather than protocols to exclude, is
+supported, but not recommended.  The exclusion form more accurately
+matches the underlying OpenSSL interface.
+.PP
+Support for "TLSv1.3" was introduced in OpenSSL 1.1.1.  Disabling
+this protocol via "!TLSv1.3" is supported since Postfix 3.4 (or patch
+releases >= 3.0.14, 3.1.10, 3.2.7 and 3.3.2).
+.PP
+Example:
+.nf
+.na
+.ft C
+# Preferred syntax with Postfix >= 3.6:
+smtpd_tls_protocols = >=TLSv1, <=TLSv1.3
+# Legacy syntax:
+smtpd_tls_protocols = !SSLv2, !SSLv3
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH smtpd_tls_received_header (default: no)
+Request that the Postfix SMTP server produces Received:  message
+headers that include information about the protocol and cipher used,
+as well as the remote SMTP client CommonName and client certificate issuer
+CommonName.  This is disabled by default, as the information may
+be modified in transit through other mail servers.  Only information
+that was recorded by the final destination can be trusted.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_tls_req_ccert (default: no)
+With mandatory TLS encryption, require a trusted remote SMTP client
+certificate in order to allow TLS connections to proceed.  This
+option implies "smtpd_tls_ask_ccert = yes".
+.PP
+When TLS encryption is optional, this setting is ignored with
+a warning written to the mail log.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_tls_security_level (default: empty)
+The SMTP TLS security level for the Postfix SMTP server; when
+a non\-empty value is specified, this overrides the obsolete parameters
+smtpd_use_tls and smtpd_enforce_tls. This parameter is ignored with
+"smtpd_tls_wrappermode = yes".
+.PP
+Specify one of the following security levels:
+.IP "\fBnone\fR"
+TLS will not be used.
+.br
+.IP "\fBmay\fR"
+Opportunistic TLS: announce STARTTLS support
+to remote SMTP clients, but do not require that clients use TLS encryption.
+.br
+.IP "\fBencrypt\fR"
+Mandatory TLS encryption: announce
+STARTTLS support to remote SMTP clients, and require that clients use TLS
+encryption. According to RFC 2487 this MUST NOT be applied in case
+of a publicly\-referenced SMTP server. Instead, this option should
+be used only on dedicated servers.
+.br
+.br
+.PP
+Note 1: the "fingerprint", "verify" and "secure" levels are not
+supported here.
+The Postfix SMTP server logs a warning and uses "encrypt" instead.
+To verify remote SMTP client certificates, see TLS_README for a discussion
+of the smtpd_tls_ask_ccert, smtpd_tls_req_ccert, and permit_tls_clientcerts
+features.
+.PP
+Note 2: The parameter setting "smtpd_tls_security_level =
+encrypt" implies "smtpd_tls_auth_only = yes".
+.PP
+Note 3: when invoked via "sendmail \-bs", Postfix will never
+offer STARTTLS due to insufficient privileges to access the server
+private key. This is intended behavior.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH smtpd_tls_session_cache_database (default: empty)
+Name of the file containing the optional Postfix SMTP server
+TLS session cache. Specify a database type that supports enumeration,
+such as \fBbtree\fR or \fBsdbm\fR; there is no need to support
+concurrent access.  The file is created if it does not exist. The \fBsmtpd\fR(8)
+daemon does not use this parameter directly, rather the cache is
+implemented indirectly in the \fBtlsmgr\fR(8) daemon. This means that
+per\-smtpd\-instance master.cf overrides of this parameter are not
+effective. Note that each of the cache databases supported by \fBtlsmgr\fR(8)
+daemon: $smtpd_tls_session_cache_database, $smtp_tls_session_cache_database
+(and with Postfix 2.3 and later $lmtp_tls_session_cache_database), needs to be
+stored separately. It is not at this time possible to store multiple
+caches in a single database.
+.PP
+Note: \fBdbm\fR databases are not suitable. TLS
+session objects are too large.
+.PP
+As of version 2.5, Postfix no longer uses root privileges when
+opening this file. The file should now be stored under the Postfix\-owned
+data_directory. As a migration aid, an attempt to open the file
+under a non\-Postfix directory is redirected to the Postfix\-owned
+data_directory, and a warning is logged.
+.PP
+As of Postfix 2.11 the preferred mechanism for session resumption
+is RFC 5077 TLS session tickets, which don't require server\-side
+storage.  Consequently, for Postfix >= 2.11 this parameter should
+generally be left empty.  TLS session tickets require an OpenSSL
+library (at least version 0.9.8h) that provides full support for
+this TLS extension.  See also smtpd_tls_session_cache_timeout.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+smtpd_tls_session_cache_database = btree:/var/lib/postfix/smtpd_scache
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_tls_session_cache_timeout (default: 3600s)
+The expiration time of Postfix SMTP server TLS session cache
+information. A cache cleanup is performed periodically
+every $smtpd_tls_session_cache_timeout seconds. As with
+$smtpd_tls_session_cache_database, this parameter is implemented in the
+\fBtlsmgr\fR(8) daemon and therefore per\-smtpd\-instance master.cf overrides
+are not possible.
+.PP
+As of Postfix 2.11 this setting cannot exceed 100 days.  If set
+<= 0, session caching is disabled, not just via the database, but
+also via RFC 5077 TLS session tickets, which don't require server\-side
+storage.  If set to a positive value less than 2 minutes, the minimum
+value of 2 minutes is used instead.  TLS session tickets require
+an OpenSSL library (at least version 0.9.8h) that provides full
+support for this TLS extension.
+.PP
+Specify a non\-negative time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.2 and later, and updated
+for TLS session ticket support in Postfix 2.11.
+.SH smtpd_tls_wrappermode (default: no)
+Run the Postfix SMTP server in TLS "wrapper" mode,
+instead of using the STARTTLS command.
+.PP
+If you want to support this service, enable a special port in
+master.cf, and specify "\-o smtpd_tls_wrappermode=yes" on the SMTP
+server's command line. Port 465 (submissions/smtps) is reserved for
+this purpose.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH smtpd_upstream_proxy_protocol (default: empty)
+The name of the proxy protocol used by an optional before\-smtpd
+proxy agent. When a proxy agent is used, this protocol conveys local
+and remote address and port information.  Specify
+"smtpd_upstream_proxy_protocol = haproxy" to enable the haproxy
+protocol; version 2 is supported with Postfix 3.5 and later.
+.PP
+NOTE: To use the nginx proxy with \fBsmtpd\fR(8), enable the XCLIENT
+protocol with smtpd_authorized_xclient_hosts. This supports SASL
+authentication in the proxy agent (Postfix 2.9 and later).
+.PP
+This feature is available in Postfix 2.10 and later.
+.SH smtpd_upstream_proxy_timeout (default: 5s)
+The time limit for the proxy protocol specified with the
+smtpd_upstream_proxy_protocol parameter.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.10 and later.
+.SH smtpd_use_tls (default: no)
+Opportunistic TLS: announce STARTTLS support to remote SMTP clients,
+but do not require that clients use TLS encryption.
+.PP
+Note: when invoked via "\fBsendmail \-bs\fR", Postfix will never offer
+STARTTLS due to insufficient privileges to access the server private
+key. This is intended behavior.
+.PP
+This feature is available in Postfix 2.2 and later. With
+Postfix 2.3 and later use smtpd_tls_security_level instead.
+.SH smtputf8_autodetect_classes (default: sendmail, verify)
+Detect that a message requires SMTPUTF8 support for the specified
+mail origin classes.  This is a workaround to avoid chicken\-and\-egg
+problems during the initial SMTPUTF8 roll\-out in environments with
+pre\-existing mail flows that contain UTF8. Those mail flows should
+not break because Postfix suddenly refuses to deliver such mail
+to down\-stream MTAs that don't announce SMTPUTF8 support.
+.PP
+The problem is that Postfix cannot rely solely on the sender's
+declaration that a message requires SMTPUTF8 support, because UTF8
+may be introduced during local processing (for example, the client
+hostname in Postfix's Received: header, adding @$myorigin or
+\&.$mydomain to an incomplete address, address rewriting, alias
+expansion, automatic BCC recipients, local forwarding, and changes
+made by header checks or Milter applications).
+.PP
+For now, the default is to enable "SMTPUTF8 required" autodetection
+only for Postfix sendmail command\-line submissions and address
+verification probes.  This may change once SMTPUTF8 support achieves
+world domination.  However, sites that add UTF8 content via local
+processing (see above) should autodetect the need for SMTPUTF8
+support for all email.
+.PP
+Specify one or more of the following:
+.IP "\fB sendmail \fR"
+Submission with the Postfix
+\fBsendmail\fR(1) command.
+.br
+.IP "\fB smtpd \fR"
+Mail received with the \fBsmtpd\fR(8)
+daemon.
+.br
+.IP "\fB qmqpd \fR"
+Mail received with the \fBqmqpd\fR(8)
+daemon.
+.br
+.IP "\fB forward \fR"
+Local forwarding or aliasing.  When
+a message is received with "SMTPUTF8 required", then the forwarded
+(aliased) message always has "SMTPUTF8 required".
+.br
+.IP "\fB bounce \fR"
+Submission by the \fBbounce\fR(8) daemon.
+When a message is received with "SMTPUTF8 required", then the
+delivery status notification always has "SMTPUTF8 required".
+.br
+.IP "\fB notify \fR"
+Postmaster notification from the
+\fBsmtp\fR(8) or \fBsmtpd\fR(8) daemon.
+.br
+.IP "\fB verify \fR"
+Address verification probe from the
+\fBverify\fR(8) daemon.
+.br
+.IP "\fB all \fR"
+Enable SMTPUTF8 autodetection for all
+mail.
+.br
+.br
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH smtputf8_enable (default: yes)
+Enable preliminary SMTPUTF8 support for the protocols described
+in RFC 6531, RFC 6532, and RFC 6533. This requires that Postfix is
+built to support these protocols.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH soft_bounce (default: no)
+Safety net to keep mail queued that would otherwise be returned to
+the sender.  This parameter disables locally\-generated bounces,
+changes the handling of negative responses from remote servers,
+content filters or plugins,
+and prevents the Postfix SMTP server from rejecting mail permanently
+by changing 5xx reply codes into 4xx.  However, soft_bounce is no
+cure for address rewriting mistakes or mail routing mistakes.
+.PP
+Note: "soft_bounce = yes" is in some cases implemented by modifying
+server responses. Therefore, the response that Postfix logs may
+differ from the response that Postfix actually sends or receives.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+soft_bounce = yes
+.fi
+.ad
+.ft R
+.SH stale_lock_time (default: 500s)
+The time after which a stale exclusive mailbox lockfile is removed.
+This is used for delivery to file or mailbox.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH stress (default: empty)
+This feature is documented in the STRESS_README document.
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH strict_7bit_headers (default: no)
+Reject mail with 8\-bit text in message headers. This blocks mail
+from poorly written applications.
+.PP
+This feature should not be enabled on a general purpose mail server,
+because it is likely to reject legitimate email.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH strict_8bitmime (default: no)
+Enable both strict_7bit_headers and strict_8bitmime_body.
+.PP
+This feature should not be enabled on a general purpose mail server,
+because it is likely to reject legitimate email.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH strict_8bitmime_body (default: no)
+Reject 8\-bit message body text without 8\-bit MIME content encoding
+information.  This blocks mail from poorly written applications.
+.PP
+Unfortunately, this also rejects majordomo approval requests when
+the included request contains valid 8\-bit MIME mail, and it rejects
+bounces from mailers that do not MIME encapsulate 8\-bit content
+(for example, bounces from qmail or from old versions of Postfix).
+.PP
+This feature should not be enabled on a general purpose mail server,
+because it is likely to reject legitimate email.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH strict_mailbox_ownership (default: yes)
+Defer delivery when a mailbox file is not owned by its recipient.
+The default setting is not backwards compatible.
+.PP
+This feature is available in Postfix 2.5.3 and later.
+.SH strict_mime_encoding_domain (default: no)
+Reject mail with invalid Content\-Transfer\-Encoding: information
+for the message/* or multipart/* MIME content types.  This blocks
+mail from poorly written software.
+.PP
+This feature should not be enabled on a general purpose mail server,
+because it will reject mail after a single violation.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH strict_rfc821_envelopes (default: no)
+Require that addresses received in SMTP MAIL FROM and RCPT TO
+commands are enclosed with <>, and that those addresses do
+not contain RFC 822 style comments or phrases.  This stops mail
+from poorly written software.
+.PP
+By default, the Postfix SMTP server accepts RFC 822 syntax in MAIL
+FROM and RCPT TO addresses.
+.SH strict_smtputf8 (default: no)
+Enable stricter enforcement of the SMTPUTF8 protocol. The Postfix
+SMTP server accepts UTF8 sender or recipient addresses only when
+the client requests an SMTPUTF8 mail transaction.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH sun_mailtool_compatibility (default: no)
+Obsolete SUN mailtool compatibility feature. Instead, use
+"mailbox_delivery_lock = dotlock".
+.SH swap_bangpath (default: yes)
+Enable the rewriting of "site!user" into "user@site".  This is
+necessary if your machine is connected to UUCP networks.  It is
+enabled by default.
+.PP
+Note: with Postfix version 2.2, message header address rewriting
+happens only when one of the following conditions is true:
+.IP \(bu
+The message is received with the Postfix \fBsendmail\fR(1) command,
+.IP \(bu
+The message is received from a network client that matches
+$local_header_rewrite_clients,
+.IP \(bu
+The message is received from the network, and the
+remote_header_rewrite_domain parameter specifies a non\-empty value.
+.br
+.PP
+To get the behavior before Postfix version 2.2, specify
+"local_header_rewrite_clients = static:all".
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+swap_bangpath = no
+.fi
+.ad
+.ft R
+.SH syslog_facility (default: mail)
+The syslog facility of Postfix logging. Specify a facility as
+defined in syslog.\fBconf\fR(5). The default facility is "mail".
+.PP
+Warning: a non\-default syslog_facility setting takes effect only
+after a Postfix process has completed initialization.  Errors during
+process initialization will be logged with the default facility.
+Examples are errors while parsing the command line arguments, and
+errors while accessing the Postfix main.cf configuration file.
+.SH syslog_name (default: see "postconf \-d" output)
+A prefix that is prepended to the process name in syslog
+records, so that, for example, "smtpd" becomes "prefix/smtpd".
+.PP
+Warning: a non\-default syslog_name setting takes effect only after
+a Postfix process has completed initialization. Errors during
+process initialization will be logged with the default name. Examples
+are errors while parsing the command line arguments, and errors
+while accessing the Postfix main.cf configuration file.
+.SH tcp_windowsize (default: 0)
+An optional workaround for routers that break TCP window scaling.
+Specify a value > 0 and < 65536 to enable this feature.  With
+Postfix TCP servers (\fBsmtpd\fR(8), \fBqmqpd\fR(8)), this feature is implemented
+by the Postfix \fBmaster\fR(8) daemon.
+.PP
+To change this parameter without stopping Postfix, you need to
+first terminate all Postfix TCP servers:
+.sp
+.in +4
+.nf
+.na
+.ft C
+# postconf \-e master_service_disable=inet
+# postfix reload
+.fi
+.ad
+.ft R
+.in -4
+.PP
+This immediately terminates all processes that accept network
+connections.  Next, you enable Postfix TCP servers with the updated
+tcp_windowsize setting:
+.sp
+.in +4
+.nf
+.na
+.ft C
+# postconf \-e tcp_windowsize=65535 master_service_disable=
+# postfix reload
+.fi
+.ad
+.ft R
+.in -4
+.PP
+If you skip these steps with a running Postfix system, then the
+tcp_windowsize change will work only for Postfix TCP clients (\fBsmtp\fR(8),
+\fBlmtp\fR(8)).
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH tls_append_default_CA (default: no)
+Append the system\-supplied default Certification Authority
+certificates to the ones specified with *_tls_CApath or *_tls_CAfile.
+The default is "no"; this prevents Postfix from trusting third\-party
+certificates and giving them relay permission with
+permit_tls_all_clientcerts.
+.PP
+This feature is available in Postfix 2.4.15, 2.5.11, 2.6.8,
+2.7.2 and later versions. Specify "tls_append_default_CA = yes" for
+backwards compatibility, to avoid breaking certificate verification
+with sites that don't use permit_tls_all_clientcerts.
+.SH tls_config_file (default: default)
+Optional configuration file with baseline OpenSSL settings.
+OpenSSL loads any SSL settings found in the configuration file for
+the selected application name (see tls_config_name) or else the
+built\-in application name "openssl_conf" when no application name is
+specified, or no corresponding configuration section is present.
+.PP
+With OpenSSL releases 1.1.1 and 1.1.1a, applications (including
+Postfix) can neither specify an alternative configuration file, nor
+avoid loading the default configuration file.
+.PP
+With OpenSSL 1.1.1b or later, this parameter may be set to one of:
+.IP "\fBdefault\fR (default)"
+Load the system\-wide
+"openssl.cnf" configuration file.
+.br
+.IP "\fBnone\fR (recommended, OpenSSL 1.1.1b or later only)"
+This setting disables loading of  the system\-wide "openssl.cnf"
+file.
+.br
+.IP "\fB\fI/absolute\-path\fR\fR (OpenSSL 1.1.1b or later only)"
+Load the configuration file specified by \fI/absolute\-path\fR.
+With this setting it is an error for the file to not contain any
+settings for the selected tls_config_name.  There is no fallback to
+the default "openssl_conf" name.
+.br
+.br
+.PP
+Failures in processing of the built\-in default configuration file,
+are silently ignored.  Any errors in loading a non\-default configuration
+file are detected by Postfix, and cause TLS support to be disabled.
+.PP
+The OpenSSL configuration file format is not documented here,
+beyond giving two examples.
+.PP
+Example: Default settings for all applications.
+.sp
+.in +4
+.nf
+.na
+.ft C
+# The name 'openssl_conf' is the default application name
+# The section name to the right of the '=' sign is arbitrary,
+# any name will do, so long as it refers to the desired section.
+#
+# The name 'system_default' selects the settings applied internally
+# by the SSL library as part of SSL object creation.  Applications
+# can then apply any additional settings of their choice.
+#
+# In this example, TLS versions prior to 1.2 are disabled by default.
+#
+openssl_conf = system_wide_settings
+[system_wide_settings]
+ssl_conf = ssl_library_settings
+[ssl_library_settings]
+system_default = initial_ssl_settings
+[initial_ssl_settings]
+MinProtocol = TLSv1.2
+.fi
+.ad
+.ft R
+.in -4
+.PP
+Example: Custom settings for an application named "postfix".
+.sp
+.in +4
+.nf
+.na
+.ft C
+# The mapping from an application name to the corresponding configuration
+# section must appear near the top of the file, (in what is sometimes called
+# the "default section") prior to the start of any explicitly named
+# "[sections]".  The named sections can appear in any order and don't nest.
+#
+postfix = postfix_settings
+[postfix_settings]
+ssl_conf = postfix_ssl_settings
+[postfix_ssl_settings]
+system_default = baseline_postfix_settings
+[baseline_postfix_settings]
+MinProtocol = TLSv1
+.fi
+.ad
+.ft R
+.in -4
+.PP
+This feature is available in Postfix >= 3.9, 3.8.1, 3.7.6,
+3.6.10, and 3.5.20.
+.SH tls_config_name (default: empty)
+The application name passed by Postfix to OpenSSL library
+initialization functions.  This name is used to select the desired
+configuration "section" in the OpenSSL configuration file specified
+via the tls_config_file parameter.  When empty, or when the
+selected name is not present in the configuration file, the default
+application name ("openssl_conf") is used as a fallback.
+.PP
+This feature is available in Postfix >= 3.9, 3.8.1, 3.7.6,
+3.6.10, and 3.5.20.
+.SH tls_daemon_random_bytes (default: 32)
+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).  The default of 32
+bytes (equivalent to 256 bits) is sufficient to generate a 128bit
+(or 168bit) session key.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH tls_dane_digest_agility (default: on)
+Configure RFC7671 DANE TLSA digest algorithm agility.
+Do not change this setting from its default value.
+.PP
+See Section 8 of RFC7671 for correct key rotation procedures.
+.PP
+This feature is available in Postfix 2.11 through 3.1.  Postfix
+3.2 and later ignore this configuration parameter and behave as
+though it were set to "on".
+.SH tls_dane_digests (default: sha512 sha256)
+DANE TLSA (RFC 6698, RFC 7671, RFC 7672) resource\-record "matching
+type" digest algorithms in descending preference order.  All the
+specified algorithms must be supported by the underlying OpenSSL
+library, otherwise the Postfix SMTP client will not support DANE
+TLSA security.
+.PP
+Specify a list of digest names separated by commas and/or
+whitespace.  Each digest name may be followed by an optional
+"=<number>" suffix.  For example, "sha512" may instead be specified
+as "sha512=2" and "sha256" may instead be specified as "sha256=1".
+The optional number must match the <a
+href="https://www.iana.org/assignments/dane\-parameters/dane\-parameters.xhtml#matching\-types"
+>IANA assigned TLSA matching type number the algorithm in question.
+Postfix will check this constraint for the algorithms it knows about.
+Additional matching type algorithms registered with IANA can be added
+with explicit numbers provided they are supported by OpenSSL.
+.PP
+Invalid list elements are logged with a warning and disable DANE
+support.  TLSA RRs that specify digests not included in the list are
+ignored with a warning.
+.PP
+Note: It is unwise to omit sha256 from the digest list.  This
+digest algorithm is the only mandatory to implement digest algorithm
+in RFC 6698, and many servers are expected to publish TLSA records
+with just sha256 digests.  Unless one of the standard digests is
+seriously compromised and servers have had ample time to update their
+TLSA records you should not omit any standard digests, just arrange
+them in order from strongest to weakest.
+.PP
+This feature is available in Postfix 2.11 and later.
+.SH tls_dane_trust_anchor_digest_enable (default: yes)
+Enable support for RFC 6698 (DANE TLSA) DNS records that contain
+digests of trust\-anchors with certificate usage "2".  Do not change
+this setting from its default value.
+.PP
+This feature is available in Postfix 2.11 through 3.1.  It has
+been withdrawn in Postfix 3.2, as trust\-anchor TLSA records are now
+widely used and have proved sufficiently reliable.  Postfix 3.2 and
+later ignore this configuration parameter and behaves as though it
+were set to "yes".
+.SH tls_disable_workarounds (default: see "postconf \-d" output)
+List or bit\-mask of OpenSSL bug work\-arounds to disable.
+.PP
+The OpenSSL toolkit includes a set of work\-arounds for buggy SSL/TLS
+implementations. Applications, such as Postfix, that want to maximize
+interoperability ask the OpenSSL library to enable the full set of
+recommended work\-arounds.
+.PP
+From time to time, it is discovered that a work\-around creates a
+security issue, and should no longer be used. If upgrading OpenSSL
+to a fixed version is not an option or an upgrade is not available
+in a timely manner, or in closed environments where no buggy clients
+or servers exist, it may be appropriate to disable some or all of the
+OpenSSL interoperability work\-arounds. This parameter specifies which
+bug work\-arounds to disable.
+.PP
+If the value of the parameter is a hexadecimal long integer starting
+with "0x", the bug work\-arounds corresponding to the bits specified in
+its value are removed from the \fBSSL_OP_ALL\fR work\-around bit\-mask
+(see openssl/ssl.h and \fBSSL_CTX_set_options\fR(3)). You can specify more
+bits than are present in SSL_OP_ALL, excess bits are ignored. Specifying
+0xFFFFFFFF disables all bug\-workarounds on a 32\-bit system. This should
+also be sufficient on 64\-bit systems, until OpenSSL abandons support
+for 32\-bit systems and starts using the high 32 bits of a 64\-bit
+bug\-workaround mask.
+.PP
+Otherwise, the parameter is a white\-space or comma separated list
+of specific named bug work\-arounds chosen from the list below. It
+is possible that your OpenSSL version includes new bug work\-arounds
+added after your Postfix source code was last updated, in that case
+you can only disable one of these via the hexadecimal syntax above.
+.IP "\fBCRYPTOPRO_TLSEXT_BUG\fR"
+New with GOST support in
+OpenSSL 1.0.0.
+.br
+.IP "\fBDONT_INSERT_EMPTY_FRAGMENTS\fR"
+See
+\fBSSL_CTX_set_options\fR(3)
+.br
+.IP "\fBLEGACY_SERVER_CONNECT\fR"
+See \fBSSL_CTX_set_options\fR(3)
+.br
+.IP "\fBMICROSOFT_BIG_SSLV3_BUFFER\fR"
+See
+\fBSSL_CTX_set_options\fR(3)
+.br
+.IP "\fBMICROSOFT_SESS_ID_BUG\fR"
+See \fBSSL_CTX_set_options\fR(3)
+.br
+.IP "\fBMSIE_SSLV2_RSA_PADDING\fR"
+also aliased as
+\fBCVE\-2005\-2969\fR. Postfix 2.8 disables this work\-around by
+default with OpenSSL versions that may predate the fix. Fixed in
+OpenSSL 0.9.7h and OpenSSL 0.9.8a.
+.br
+.IP "\fBNETSCAPE_CHALLENGE_BUG\fR"
+See \fBSSL_CTX_set_options\fR(3)
+.br
+.IP "\fBNETSCAPE_REUSE_CIPHER_CHANGE_BUG\fR"
+also aliased
+as \fBCVE\-2010\-4180\fR. Postfix 2.8 disables this work\-around by
+default with OpenSSL versions that may predate the fix. Fixed in
+OpenSSL 0.9.8q and OpenSSL 1.0.0c.
+.br
+.IP "\fBSSLEAY_080_CLIENT_DH_BUG\fR"
+See
+\fBSSL_CTX_set_options\fR(3)
+.br
+.IP "\fBSSLREF2_REUSE_CERT_TYPE_BUG\fR"
+See
+\fBSSL_CTX_set_options\fR(3)
+.br
+.IP "\fBTLS_BLOCK_PADDING_BUG\fR"
+See \fBSSL_CTX_set_options\fR(3)
+.br
+.IP "\fBTLS_D5_BUG\fR"
+See \fBSSL_CTX_set_options\fR(3)
+.br
+.IP "\fBTLS_ROLLBACK_BUG\fR"
+See \fBSSL_CTX_set_options\fR(3).
+This is disabled in OpenSSL 0.9.7 and later. Nobody should still
+be using 0.9.6!
+.br
+.IP "\fBTLSEXT_PADDING\fR"
+Postfix >= 3.4. See \fBSSL_CTX_set_options\fR(3).
+.br
+.br
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tls_eecdh_auto_curves (default: see "postconf \-d" output)
+The prioritized list of elliptic curves supported by the Postfix
+SMTP client and server.  These curves are used by the Postfix SMTP
+server when "smtpd_tls_eecdh_grade = auto".  The selected curves must be
+implemented by OpenSSL and be standardized for use in TLS (RFC 8422).
+It is unwise to list only "bleeding\-edge" curves supported by a small
+subset of clients.  The default list is suitable for most users.
+.PP
+Postfix skips curve names that are unknown to OpenSSL, or that
+are known but not yet implemented.  This makes it possible to
+"anticipate" support for curves that should be used once they become
+available.  In particular, in some OpenSSL versions, the new RFC
+8031 curves "X25519" and "X448" may be known by name, but ECDH
+support for either or both may be missing.  These curves may appear
+in the default value of this parameter, even though they'll only
+be usable with later versions of OpenSSL.
+.PP
+See also the "tls_ffdhe_auto_groups" parameter, which supports
+customizing the list of FFDHE groups enabled with TLS 1.3.  That setting
+is introduced with Postfix 3.8, when built against OpenSSL 3.0 or later.
+.PP
+This feature is available in Postfix 3.2 and later, when it is
+compiled and linked with OpenSSL 1.0.2 or later on platforms where
+EC algorithms have not been disabled by the vendor.
+.SH tls_eecdh_strong_curve (default: prime256v1)
+The elliptic curve used by the Postfix SMTP server for sensibly
+strong
+ephemeral ECDH key exchange. This curve is used by the Postfix SMTP
+server when "smtpd_tls_eecdh_grade = strong". The phrase "sensibly
+strong" means approximately 128\-bit security based on best known
+attacks. The selected curve must be implemented by OpenSSL (as
+reported by \fBecparam\fR(1) with the "\-list_curves" option) and be one
+of the curves listed in Section 5.1.1 of RFC 8422. You should not
+generally change this setting.  Remote SMTP client implementations
+must support this curve for EECDH key exchange to take place.  It
+is unwise to choose only "bleeding\-edge" curves supported by only a
+small subset of clients.
+.PP
+The default "strong" curve is rated in NSA Suite
+B for information classified up to SECRET.
+.PP
+Note: elliptic curve names are poorly standardized; different
+standards groups are assigning different names to the same underlying
+curves.  The curve with the X9.62 name "prime256v1" is also known
+under the SECG name "secp256r1", but OpenSSL does not recognize the
+latter name.
+.PP
+If you want to take maximal advantage of ciphers that offer forward secrecy see
+the Getting
+started section of FORWARD_SECRECY_README.  The
+full document conveniently presents all information about Postfix
+"perfect" forward secrecy support in one place: what forward secrecy
+is, how to tweak settings, and what you can expect to see when
+Postfix uses ciphers with forward secrecy.
+.PP
+This feature is available in Postfix 2.6 and later, when it is
+compiled and linked with OpenSSL 1.0.0 or later on platforms where
+EC algorithms have not been disabled by the vendor.
+.SH tls_eecdh_ultra_curve (default: secp384r1)
+The elliptic curve used by the Postfix SMTP server for maximally
+strong
+ephemeral ECDH key exchange. This curve is used by the Postfix SMTP
+server when "smtpd_tls_eecdh_grade = ultra". The phrase "maximally
+strong" means approximately 192\-bit security based on best known attacks.
+This additional strength comes at a significant computational cost, most
+users should instead set "smtpd_tls_eecdh_grade = strong".  The selected
+curve must be implemented by OpenSSL (as reported by \fBecparam\fR(1) with the
+"\-list_curves" option) and be one of the curves listed in Section 5.1.1
+of RFC 8422. You should not generally change this setting.  Remote SMTP
+client implementations must support this curve for EECDH key exchange
+to take place.  It is unwise to choose only "bleeding\-edge" curves
+supported by only a small subset of clients.
+.PP
+This default "ultra" curve is rated in NSA Suite
+B for information classified up to TOP SECRET.
+.PP
+If you want to take maximal advantage of ciphers that offer forward secrecy see
+the Getting
+started section of FORWARD_SECRECY_README.  The
+full document conveniently presents all information about Postfix
+"perfect" forward secrecy support in one place: what forward secrecy
+is, how to tweak settings, and what you can expect to see when
+Postfix uses ciphers with forward secrecy.
+.PP
+This feature is available in Postfix 2.6 and later, when it is
+compiled and linked with OpenSSL 1.0.0 or later on platforms where
+EC algorithms have not been disabled by the vendor.
+.SH tls_export_cipherlist (default: see "postconf \-d" output)
+The OpenSSL cipherlist for "export" or higher grade ciphers.
+Ignored as of Postfix 3.8.  In earlier Postfix releases this
+defined the meaning of the "export" setting in smtpd_tls_ciphers,
+smtpd_tls_mandatory_ciphers, smtp_tls_ciphers,
+smtp_tls_mandatory_ciphers, lmtp_tls_ciphers, and
+lmtp_tls_mandatory_ciphers.  You are strongly encouraged not to
+change this setting.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH tls_fast_shutdown_enable (default: yes)
+A workaround for implementations that hang Postfix while shutting
+down a TLS session, until Postfix times out. With this enabled,
+Postfix will not wait for the remote TLS peer to respond to a TLS
+\&'close' notification. This behavior is recommended for TLSv1.0 and
+later.
+.SH tls_ffdhe_auto_groups (default: see "postconf \-d" output)
+The prioritized list of finite\-field Diffie\-Hellman ephemeral
+(FFDHE) key exchange groups supported by the Postfix SMTP client and
+server.  OpenSSL 3.0 adds support for FFDHE key agreement in TLS 1.3.
+In OpenSSL 1.1.1, TLS 1.3 was only supported with elliptic\-curve based
+key agreement.  The "tls_ffdhe_auto_groups" parameter makes it possible
+to configure the list of FFDHE groups that the Postfix client or server
+will enable in OpenSSL 3.0 and up.  This parameter has no effect when
+Postfix is built against earlier OpenSSL versions.
+.PP
+The default list of FFDHE groups that Postfix enables in OpenSSL 3.0
+and up includes just the 2048 and 3072\-bit groups.  Stronger FFDHE
+groups perform poorly and EC groups are a much better choice for the
+same security level.  Postfix ignores group names that are unknown to
+OpenSSL, or that are known but not yet implemented.  The FFDHE groups
+are largely a backup, in case some peer does not support EC key
+exchange, or EC key exchange needs to be disabled for some pressing
+reason.
+.PP
+Setting this parameter empty disables FFDHE support in TLS 1.3.
+Whether FFDHE key agreement is enabled in TLS 1.2 and earlier depends
+on whether any of the "kDHE" ciphers are included in the cipherlist.
+.PP
+Conversely, setting "tls_eecdh_auto_curves" empty disables TLS 1.3
+EC key agreement in OpenSSL 3.0 and later.  Note that at least one of
+"tls_eecdh_auto_curves" and "tls_ffdhe_auto_groups" must be non\-empty,
+this is required by OpenSSL 3.0.  If both are inadvertently set empty,
+Postfix will fall back to the compiled\-in defaults.
+.PP
+All the default groups and EC curves should sufficiently strong
+to make "pruning" the defaults unwise.  At a minimum, "X25519" and
+"P\-256" (a.k.a. "prime256v1") should be among the enabled EC curves,
+while "dhe2048" and "dhe3072" should be among the FFDHE groups.
+.PP
+This feature is available in Postfix 3.8 and later, when it is
+compiled and linked with OpenSSL 3.0 or later.
+.SH tls_high_cipherlist (default: see "postconf \-d" output)
+The OpenSSL cipherlist for "high" grade ciphers. This defines
+the meaning of the "high" setting in smtpd_tls_ciphers,
+smtpd_tls_mandatory_ciphers, smtp_tls_ciphers, smtp_tls_mandatory_ciphers,
+lmtp_tls_ciphers, and lmtp_tls_mandatory_ciphers. You are strongly
+encouraged not to change this setting.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH tls_legacy_public_key_fingerprints (default: no)
+A temporary migration aid for sites that use certificate
+\fIpublic\-key\fR fingerprints with Postfix 2.9.0..2.9.5, which use
+an incorrect algorithm. This parameter has no effect on the certificate
+fingerprint support that is available since Postfix 2.2.
+.PP
+Specify "tls_legacy_public_key_fingerprints = yes" temporarily,
+pending a migration from configuration files with incorrect Postfix
+2.9.0..2.9.5 certificate public\-key finger prints, to the correct
+fingerprints used by Postfix 2.9.6 and later.  To compute the correct
+certificate public\-key fingerprints, see TLS_README.
+.PP
+This feature is available in Postfix 2.9.6 and later.
+.SH tls_low_cipherlist (default: see "postconf \-d" output)
+The OpenSSL cipherlist for "low" or higher grade ciphers.
+Ignored as of Postfix 3.8.  In earlier Postfix releases this
+defined the meaning of the "low" setting in smtpd_tls_ciphers,
+smtpd_tls_mandatory_ciphers, smtp_tls_ciphers,
+smtp_tls_mandatory_ciphers, lmtp_tls_ciphers, and
+lmtp_tls_mandatory_ciphers. You are strongly encouraged not to
+change this setting.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH tls_medium_cipherlist (default: see "postconf \-d" output)
+The OpenSSL cipherlist for "medium" or higher grade ciphers. This
+defines the meaning of the "medium" setting in smtpd_tls_ciphers,
+smtpd_tls_mandatory_ciphers, smtp_tls_ciphers, smtp_tls_mandatory_ciphers,
+lmtp_tls_ciphers, and lmtp_tls_mandatory_ciphers.  This is the
+default cipherlist for mandatory TLS encryption in the TLS client
+(with anonymous ciphers disabled when verifying server certificates).
+This is the default cipherlist for opportunistic TLS with Postfix
+releases after the middle of 2015.  You are strongly encouraged not
+to change this setting.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH tls_null_cipherlist (default: eNULL:!aNULL)
+The OpenSSL cipherlist for "NULL" grade ciphers that provide
+authentication without encryption. This defines the meaning of the "null"
+setting in smtpd_tls_mandatory_ciphers, smtp_tls_mandatory_ciphers and
+lmtp_tls_mandatory_ciphers.  You are strongly encouraged not to
+change this setting.
+.PP
+This feature is available in Postfix 2.3 and later.
+.SH tls_preempt_cipherlist (default: no)
+With SSLv3 and later, use the Postfix SMTP server's cipher
+preference order instead of the remote client's cipher preference
+order.
+.PP
+By default, the OpenSSL server selects the client's most preferred
+cipher that the server supports. With SSLv3 and later, the server may
+choose its own most preferred cipher that is supported (offered) by
+the client. Setting "tls_preempt_cipherlist = yes" enables server cipher
+preferences.
+.PP
+While server cipher selection may in some cases lead to a more secure
+or performant cipher choice, there is some risk of interoperability
+issues. In the past, some SSL clients have listed lower priority ciphers
+that they did not implement correctly. If the server chooses a cipher
+that the client prefers less, it may select a cipher whose client
+implementation is flawed. Most notably Windows 2003 Microsoft
+Exchange servers have flawed implementations of DES\-CBC3\-SHA, which
+OpenSSL considers stronger than RC4\-SHA.  Enabling server cipher\-suite
+selection may create interoperability issues with Windows 2003
+Microsoft Exchange clients.
+.PP
+This feature is available in Postfix 2.8 and later, in combination
+with OpenSSL 0.9.7 and later.
+.SH tls_random_bytes (default: 32)
+The number of bytes that \fBtlsmgr\fR(8) reads from $tls_random_source
+when (re)seeding the in\-memory pseudo random number generator (PRNG)
+pool. The default of 32 bytes (256 bits) is good enough for 128bit
+symmetric keys.  If using EGD or a device file, a maximum of 255
+bytes is read.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH tls_random_exchange_name (default: see "postconf \-d" output)
+Name of the pseudo random number generator (PRNG) state file
+that is maintained by \fBtlsmgr\fR(8). The file is created when it does
+not exist, and its length is fixed at 1024 bytes.
+.PP
+As of version 2.5, Postfix no longer uses root privileges when
+opening this file, and the default file location was changed from
+${config_directory}/prng_exch to ${data_directory}/prng_exch.  As
+a migration aid, an attempt to open the file under a non\-Postfix
+directory is redirected to the Postfix\-owned data_directory, and a
+warning is logged.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH tls_random_prng_update_period (default: 3600s)
+The time between attempts by \fBtlsmgr\fR(8) to save the state of
+the pseudo random number generator (PRNG) to the file specified
+with $tls_random_exchange_name.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH tls_random_reseed_period (default: 3600s)
+The maximal time between attempts by \fBtlsmgr\fR(8) to re\-seed the
+in\-memory pseudo random number generator (PRNG) pool from external
+sources.  The actual time between re\-seeding attempts is calculated
+using the PRNG, and is between 0 and the time specified.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH tls_random_source (default: see "postconf \-d" output)
+The external entropy source for the in\-memory \fBtlsmgr\fR(8) pseudo
+random number generator (PRNG) pool. Be sure to specify a non\-blocking
+source.  If this source is not a regular file, the entropy source
+type must be prepended:  egd:/path/to/egd_socket for a source with
+EGD compatible socket interface, or dev:/path/to/device for a
+device file.
+.PP
+Note: on OpenBSD systems specify dev:/dev/arandom when dev:/dev/urandom
+gives timeout errors.
+.PP
+This feature is available in Postfix 2.2 and later.
+.SH tls_server_sni_maps (default: empty)
+Optional lookup tables that map names received from remote SMTP
+clients via the TLS Server Name Indication (SNI) extension to the
+appropriate keys and certificate chains.  This parameter is implemented
+in the Postfix TLS library, and applies to both \fBsmtpd\fR(8) and the SMTP
+server mode of \fBtlsproxy\fR(8).
+.PP
+When this parameter is non\-empty, the Postfix SMTP server enables
+SNI extension processing, and logs SNI values that are invalid or
+don't match an entry in the specified tables.  When an entry
+does match, the SNI name is logged as part of the connection summary
+at log levels 1 and higher.
+.PP
+The lookup key is either the verbatim SNI domain name or an
+ancestor domain prefixed with a leading dot.  For internationalized
+domains, the lookup key must be in IDNA 2008 A\-label form (as
+required in the TLS SNI extension).
+.PP
+The syntax of the lookup value is the same as with the
+smtp_tls_chain_files parameter (see there for additional details),
+but here scoped to just TLS connections in which the client sends
+a matching SNI domain name.
+.PP
+Example:
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    #
+    # The indexed SNI table must be created with "postmap \-F"
+    #
+    indexed = ${default_database_type}:${config_directory}/
+    tls_server_sni_maps = ${indexed}sni
+.fi
+.ad
+.ft R
+.in -4
+.sp
+.in +4
+.nf
+.na
+.ft C
+/etc/postfix/sni:
+    #
+    # The example.com domain has both an RSA and ECDSA certificate
+    # chain.  The chain files MUST start with the private key,
+    # with the certificate chain next, starting with the leaf
+    # (server) certificate, and then the issuer certificates.
+    #
+    example.com /etc/postfix/sni\-chains/rsa2048.example.com.pem,
+                /etc/postfix/sni\-chains/ecdsa\-p256.example.com.pem
+    #
+    # The example.net domain has a wildcard certificate, and two
+    # additional DNS names.  So its certificate chain is also used
+    # with any subdomain, plus the additional names.
+    #
+    example.net /etc/postfix/sni\-chains/example.net.pem
+    .example.net /etc/postfix/sni\-chains/example.net.pem
+    example.info /etc/postfix/sni\-chains/example.net.pem
+    example.org /etc/postfix/sni\-chains/example.net.pem
+.fi
+.ad
+.ft R
+.in -4
+.PP
+Note that the SNI lookup tables should also have entries for
+the domains that correspond to the Postfix SMTP server's default
+certificate(s). This ensures that the remote SMTP client's TLS SNI
+extension gets a positive response when it specifies one of the
+Postfix SMTP server's default domains, and ensures that the Postfix
+SMTP server will not log an SNI name mismatch for such a domain.
+The Postfix SMTP server's default certificates are then only used
+when the client sends no SNI or when it sends SNI with a domain
+that the server knows no certificate(s) for.
+.PP
+The mapping from an SNI domain name to a certificate chain is indirect.  In
+the input source files for "cdb", "hash", "btree" or other tables that are
+converted to on\-disk indexed files via \fBpostmap\fR(1), the value specified for each
+key is a list of filenames.  When \fBpostmap\fR(1) is used with the \fB\-F\fR option,
+the generated table stores for each lookup key the base64\-encoded contents of
+the associated files.  When querying tables via \fBpostmap \-Fq\fR, the table
+value is decoded from base64, yielding the original file content, plus a new
+line.
+.PP
+With "regexp", "pcre", "inline", "texthash", "static" and similar
+tables that are interpreted at run\-time, and don't have a separate
+source format, the table value is again a list files, that are loaded
+into memory when the table is opened.
+.PP
+With tables whose content is managed outside of Postfix, such
+as LDAP, MySQL, PostgreSQL, socketmap and tcp, the value must be a
+concatenation of the desired PEM keys and certificate chains, that
+is then further encoded to yield a single\-line base64 string.
+Creation of such tables and secure storage (the value includes
+private key material) are outside the responsibility of Postfix.
+.PP
+With "socketmap" and "tcp" the data will be transmitted in the clear, and
+there is no query access control, so these are generally unsuitable for storing
+SNI chains.  With LDAP and SQL, you should restrict read access and use TLS to
+protect the sensitive data in transit.
+.PP
+Typically there is only one private key and its chain of certificates
+starting with the "leaf" certificate corresponding to that key, and
+continuing with the appropriate intermediate issuer CA certificates,
+with each certificate ideally followed by its issuer.  Servers
+that have keys and certificates for more than one algorithm (e.g.
+both an RSA key and an ECDSA key, or even RSA, ECDSA and Ed25519)
+can use multiple chains concatenated together, with the key always
+listed before the corresponding certificates.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH tls_session_ticket_cipher (default: Postfix >= 3.0: aes\-256\-cbc, Postfix < 3.0: aes\-128\-cbc)
+Algorithm used to encrypt RFC5077 TLS session tickets.  This
+algorithm must use CBC mode, have a 128\-bit block size, and must
+have a key length between 128 and 256 bits.  The default is
+aes\-256\-cbc.  Overriding the default to choose a different algorithm
+is discouraged.
+.PP
+Setting this parameter empty disables session ticket support
+in the Postfix SMTP server.  Another way to disable session ticket
+support is via the tls_ssl_options parameter.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH tls_ssl_options (default: empty)
+List or bit\-mask of OpenSSL options to enable.
+.PP
+The OpenSSL toolkit provides a set of options that applications
+can enable to tune the OpenSSL behavior.  Some of these work around
+bugs in other implementations and are on by default.  You can use
+the tls_disable_workarounds parameter to selectively disable some
+or all of the bug work\-arounds, making OpenSSL more strict at the
+cost of non\-interoperability with SSL clients or servers that exhibit
+the bugs.
+.PP
+Other options are off by default, and typically enable or disable
+features rather than bug work\-arounds.  These may be turned on (with
+care) via the tls_ssl_options parameter.  The value is a white\-space
+or comma separated list of named options chosen from the list below.
+The names are not case\-sensitive, you can use lower\-case if you
+prefer.  The upper case values below match the corresponding macro
+name in the ssl.h header file with the SSL_OP_ prefix removed.  It
+is possible that your OpenSSL version includes new options added
+after your Postfix source code was last updated, in that case you
+can only enable one of these via the hexadecimal syntax below.
+.PP
+You should only enable features via the hexadecimal mask when
+the need to control the feature is critical (to deal with a new
+vulnerability or a serious interoperability problem).  Postfix DOES
+NOT promise backwards compatible behavior with respect to the mask
+bits.  A feature enabled via the mask in one release may be enabled
+by other means in a later release, and the mask bit will then be
+ignored.  Therefore, use of the hexadecimal mask is only a temporary
+measure until a new Postfix or OpenSSL release provides a better
+solution.
+.PP
+If the value of the parameter is a hexadecimal long integer
+starting with "0x", the options corresponding to the bits specified
+in its value are enabled (see openssl/ssl.h and \fBSSL_CTX_set_options\fR(3)).
+You can only enable options not already controlled by other Postfix
+settings.  For example, you cannot disable protocols or enable
+server cipher preference.  Do not attempt to enable all features by
+specifying 0xFFFFFFFF, this is unlikely to be a good idea.  Some
+bug work\-arounds are also valid here, allowing them to be re\-enabled
+if/when they're no longer enabled by default.  The supported values
+include:
+.IP "\fBENABLE_MIDDLEBOX_COMPAT\fR"
+Postfix >= 3.4. See
+\fBSSL_CTX_set_options\fR(3).
+.br
+.IP "\fBLEGACY_SERVER_CONNECT\fR"
+See \fBSSL_CTX_set_options\fR(3).
+.br
+.IP "\fBNO_TICKET\fR"
+Enabled by default when needed in
+fully\-patched Postfix >= 2.7.  Not needed at all for Postfix >=
+2.11, unless for some reason you do not want to support TLS session
+resumption.  Best not set explicitly.  See \fBSSL_CTX_set_options\fR(3).
+.br
+.IP "\fBNO_COMPRESSION\fR"
+Disable SSL compression even if
+supported by the OpenSSL library.  Compression is CPU\-intensive,
+and compression before encryption does not always improve security.
+.br
+.IP "\fBNO_RENEGOTIATION\fR"
+Postfix >= 3.4.  This can
+reduce opportunities for a potential CPU exhaustion attack.  See
+\fBSSL_CTX_set_options\fR(3).
+.br
+.IP "\fBNO_SESSION_RESUMPTION_ON_RENEGOTIATION\fR"
+Postfix
+>= 3.4. See \fBSSL_CTX_set_options\fR(3).
+.br
+.IP "\fBPRIORITIZE_CHACHA\fR"
+Postfix >= 3.4. See \fBSSL_CTX_set_options\fR(3).
+.br
+.br
+.PP
+This feature is available in Postfix 2.11 and later.
+.SH tls_wildcard_matches_multiple_labels (default: yes)
+Match multiple DNS labels with "*" in wildcard certificates.
+.PP
+Some mail service providers prepend the customer domain name
+to a base domain for which they have a wildcard TLS certificate.
+For example, the MX records for example.com hosted by example.net
+may be:
+.sp
+.in +4
+.nf
+.na
+.ft C
+example.com. IN MX 0 example.com.mx1.example.net.
+example.com. IN MX 0 example.com.mx2.example.net.
+.fi
+.ad
+.ft R
+.in -4
+.PP
+and the TLS certificate may be for "*.example.net". The "*"
+then corresponds with multiple labels in the mail server domain
+name.  While multi\-label wildcards are not widely supported, and
+are not blessed by any standard, there is little to be gained by
+disallowing their use in this context.
+.PP
+Notes:
+.IP \(bu
+In a certificate name, the "*" is special only when it is
+used as the first label.
+.IP \(bu
+While Postfix (2.11 or later) can match "*" with multiple
+domain name labels, other implementations likely will not.
+.IP \(bu
+Earlier Postfix implementations behave as if
+"tls_wildcard_matches_multiple_labels = no".
+.br
+.PP
+This feature is available in Postfix 2.11 and later.
+.SH tlsmgr_service_name (default: tlsmgr)
+The name of the \fBtlsmgr\fR(8) service entry in master.cf. This
+service maintains TLS session caches and other information in support
+of TLS.
+.PP
+This feature is available in Postfix 2.11 and later.
+.SH tlsproxy_client_CAfile (default: $smtp_tls_CAfile)
+A file containing CA certificates of root CAs trusted to sign
+either remote TLS server certificates or intermediate CA certificates.
+See smtp_tls_CAfile for further details.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH tlsproxy_client_CApath (default: $smtp_tls_CApath)
+Directory with PEM format Certification Authority certificates
+that the Postfix \fBtlsproxy\fR(8) client uses to verify a remote TLS
+server certificate. See smtp_tls_CApath for further details.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH tlsproxy_client_cert_file (default: $smtp_tls_cert_file)
+File with the Postfix \fBtlsproxy\fR(8) client RSA certificate in PEM
+format. See smtp_tls_cert_file for further details.  The preferred way
+to configure tlsproxy client keys and certificates is via the
+"tlsproxy_client_chain_files" parameter.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH tlsproxy_client_chain_files (default: $smtp_tls_chain_files)
+Files with the Postfix \fBtlsproxy\fR(8) client keys and certificate
+chains in PEM format. See smtp_tls_chain_files for further details.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH tlsproxy_client_dcert_file (default: $smtp_tls_dcert_file)
+File with the Postfix \fBtlsproxy\fR(8) client DSA certificate in PEM
+format. See smtp_tls_dcert_file for further details. DSA is obsolete and
+should not be used.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH tlsproxy_client_dkey_file (default: $smtp_tls_dkey_file)
+File with the Postfix \fBtlsproxy\fR(8) client DSA private key in PEM
+format. See smtp_tls_dkey_file for further details. DSA is obsolete and
+should not be used.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH tlsproxy_client_eccert_file (default: $smtp_tls_eccert_file)
+File with the Postfix \fBtlsproxy\fR(8) client ECDSA certificate in PEM
+format. See smtp_tls_eccert_file for further details. The preferred way
+to configure tlsproxy client keys and certificates is via the
+"tlsproxy_client_chain_files" parameter.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH tlsproxy_client_eckey_file (default: $smtp_tls_eckey_file)
+File with the Postfix \fBtlsproxy\fR(8) client ECDSA private key in PEM
+format. See smtp_tls_eckey_file for further details.  The preferred way
+to configure tlsproxy client keys and certificates is via the
+"tlsproxy_client_chain_files" parameter.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH tlsproxy_client_enforce_tls (default: $smtp_enforce_tls)
+Enforcement mode: require that SMTP servers use TLS encryption.
+See smtp_enforce_tls for further details. Use
+tlsproxy_client_security_level instead.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH tlsproxy_client_fingerprint_digest (default: $smtp_tls_fingerprint_digest)
+The message digest algorithm used to construct remote TLS server
+certificate fingerprints. See smtp_tls_fingerprint_digest for
+further details.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH tlsproxy_client_key_file (default: $smtp_tls_key_file)
+File with the Postfix \fBtlsproxy\fR(8) client RSA private key in PEM
+format. See smtp_tls_key_file for further details. The preferred way to
+configure tlsproxy client keys and certificates is via the
+"tlsproxy_client_chain_files" parameter.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH tlsproxy_client_level (default: $smtp_tls_security_level)
+The default TLS security level for the Postfix \fBtlsproxy\fR(8)
+client. See smtp_tls_security_level for further details.
+.PP
+This feature is available in Postfix 3.4 \- 3.6. It was
+renamed to tlsproxy_client_security_level in Postfix 3.7.
+.SH tlsproxy_client_loglevel (default: $smtp_tls_loglevel)
+Enable additional Postfix \fBtlsproxy\fR(8) client logging of TLS
+activity. See smtp_tls_loglevel for further details.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH tlsproxy_client_loglevel_parameter (default: smtp_tls_loglevel)
+The name of the parameter that provides the tlsproxy_client_loglevel
+value.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH tlsproxy_client_per_site (default: $smtp_tls_per_site)
+Optional lookup tables with the Postfix \fBtlsproxy\fR(8) client TLS
+usage policy by next\-hop destination and by remote TLS server
+hostname.  See smtp_tls_per_site for further details.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH tlsproxy_client_policy (default: $smtp_tls_policy_maps)
+Optional lookup tables with the Postfix \fBtlsproxy\fR(8) client TLS
+security policy by next\-hop destination. See smtp_tls_policy_maps
+for further details.
+.PP
+This feature is available in Postfix 3.4 \- 3.6. It was
+renamed to tlsproxy_client_policy_maps in Postfix 3.7.
+.SH tlsproxy_client_policy_maps (default: $smtp_tls_policy_maps)
+Optional lookup tables with the Postfix \fBtlsproxy\fR(8) client TLS
+security policy by next\-hop destination. See smtp_tls_policy_maps
+for further details.
+.PP
+This feature is available in Postfix 3.7 and later. It
+was previously called tlsproxy_client_policy.
+.SH tlsproxy_client_scert_verifydepth (default: $smtp_tls_scert_verifydepth)
+The verification depth for remote TLS server certificates.
+See smtp_tls_scert_verifydepth for further details.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH tlsproxy_client_security_level (default: $smtp_tls_security_level)
+The default TLS security level for the Postfix \fBtlsproxy\fR(8)
+client. See smtp_tls_security_level for further details.
+.PP
+This feature is available in Postfix 3.7 and later. It
+was previously called tlsproxy_client_level.
+.SH tlsproxy_client_use_tls (default: $smtp_use_tls)
+Opportunistic mode: use TLS when a remote server announces TLS
+support. See smtp_use_tls for further details. Use
+tlsproxy_client_security_level instead.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH tlsproxy_enforce_tls (default: $smtpd_enforce_tls)
+Mandatory TLS: announce STARTTLS support to remote SMTP clients, and
+require that clients use TLS encryption. See smtpd_enforce_tls for
+further details. Use tlsproxy_tls_security_level instead.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_service_name (default: tlsproxy)
+The name of the \fBtlsproxy\fR(8) service entry in master.cf. This
+service performs plaintext <=> TLS ciphertext conversion.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_CAfile (default: $smtpd_tls_CAfile)
+A file containing (PEM format) CA certificates of root CAs
+trusted to sign either remote SMTP client certificates or intermediate
+CA certificates.  See smtpd_tls_CAfile for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_CApath (default: $smtpd_tls_CApath)
+A directory containing (PEM format) CA certificates of root CAs
+trusted to sign either remote SMTP client certificates or intermediate
+CA certificates. See smtpd_tls_CApath for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_always_issue_session_ids (default: $smtpd_tls_always_issue_session_ids)
+Force the Postfix \fBtlsproxy\fR(8) server to issue a TLS session id,
+even when TLS session caching is turned off. See
+smtpd_tls_always_issue_session_ids for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_ask_ccert (default: $smtpd_tls_ask_ccert)
+Ask a remote SMTP client for a client certificate. See
+smtpd_tls_ask_ccert for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_ccert_verifydepth (default: $smtpd_tls_ccert_verifydepth)
+The verification depth for remote SMTP client certificates. A
+depth of 1 is sufficient if the issuing CA is listed in a local CA
+file. See smtpd_tls_ccert_verifydepth for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_cert_file (default: $smtpd_tls_cert_file)
+File with the Postfix \fBtlsproxy\fR(8) server RSA certificate in PEM
+format.  This file may also contain the Postfix \fBtlsproxy\fR(8) server
+private RSA key.  See smtpd_tls_cert_file for further details.  With
+Postfix >= 3.4 the preferred way to configure tlsproxy server keys and
+certificates is via the "tlsproxy_tls_chain_files" parameter.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_chain_files (default: $smtpd_tls_chain_files)
+Files with the Postfix \fBtlsproxy\fR(8) server keys and certificate
+chains in PEM format. See smtpd_tls_chain_files for further details.
+.PP
+This feature is available in Postfix 3.4 and later.
+.SH tlsproxy_tls_ciphers (default: $smtpd_tls_ciphers)
+The minimum TLS cipher grade that the Postfix \fBtlsproxy\fR(8) server
+will use with opportunistic TLS encryption. See smtpd_tls_ciphers
+for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_dcert_file (default: $smtpd_tls_dcert_file)
+File with the Postfix \fBtlsproxy\fR(8) server DSA certificate in PEM
+format.  This file may also contain the Postfix \fBtlsproxy\fR(8) server
+private DSA key.  DSA is obsolete and should not be used.  See
+smtpd_tls_dcert_file for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_dh1024_param_file (default: $smtpd_tls_dh1024_param_file)
+File with DH parameters that the Postfix \fBtlsproxy\fR(8) server
+should use with non\-export EDH ciphers. See smtpd_tls_dh1024_param_file
+for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_dh512_param_file (default: $smtpd_tls_dh512_param_file)
+File with DH parameters that the Postfix \fBtlsproxy\fR(8) server
+should use with export\-grade EDH ciphers. See smtpd_tls_dh512_param_file
+for further details.  The default SMTP server cipher grade is
+"medium" with Postfix releases after the middle of 2015, and as a
+result export\-grade cipher suites are by default not used.
+.PP
+With Postfix >= 3.6 export\-grade Diffie\-Hellman key exchange
+is no longer supported, and this parameter is silently ignored.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_dkey_file (default: $smtpd_tls_dkey_file)
+File with the Postfix \fBtlsproxy\fR(8) server DSA private key in PEM
+format.  This file may be combined with the Postfix \fBtlsproxy\fR(8) server
+DSA certificate file specified with $smtpd_tls_dcert_file.  DSA is
+obsolete and should not be used.  See smtpd_tls_dkey_file for further
+details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_eccert_file (default: $smtpd_tls_eccert_file)
+File with the Postfix \fBtlsproxy\fR(8) server ECDSA certificate in PEM
+format.  This file may also contain the Postfix \fBtlsproxy\fR(8) server
+private ECDSA key.  See smtpd_tls_eccert_file for further details.  With
+Postfix >= 3.4 the preferred way to configure tlsproxy server keys and
+certificates is via the "tlsproxy_tls_chain_files" parameter.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_eckey_file (default: $smtpd_tls_eckey_file)
+File with the Postfix \fBtlsproxy\fR(8) server ECDSA private key in PEM
+format.  This file may be combined with the Postfix \fBtlsproxy\fR(8) server
+ECDSA certificate file specified with $smtpd_tls_eccert_file.  See
+smtpd_tls_eckey_file for further details.  With Postfix >= 3.4 the
+preferred way to configure tlsproxy server keys and certificates is via
+the "tlsproxy_tls_chain_files" parameter.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_eecdh_grade (default: $smtpd_tls_eecdh_grade)
+The Postfix \fBtlsproxy\fR(8) server security grade for ephemeral
+elliptic\-curve Diffie\-Hellman (EECDH) key exchange. See
+smtpd_tls_eecdh_grade for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_exclude_ciphers (default: $smtpd_tls_exclude_ciphers)
+List of ciphers or cipher types to exclude from the \fBtlsproxy\fR(8)
+server cipher list at all TLS security levels. See
+smtpd_tls_exclude_ciphers for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_fingerprint_digest (default: $smtpd_tls_fingerprint_digest)
+The message digest algorithm to construct remote SMTP
+client\-certificate
+fingerprints. See smtpd_tls_fingerprint_digest for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_key_file (default: $smtpd_tls_key_file)
+File with the Postfix \fBtlsproxy\fR(8) server RSA private key in PEM
+format.  This file may be combined with the Postfix \fBtlsproxy\fR(8) server
+RSA certificate file specified with $smtpd_tls_cert_file.  See
+smtpd_tls_key_file for further details.  With Postfix >= 3.4 the
+preferred way to configure tlsproxy server keys and certificates is via
+the "tlsproxy_tls_chain_files" parameter.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_loglevel (default: $smtpd_tls_loglevel)
+Enable additional Postfix \fBtlsproxy\fR(8) server logging of TLS
+activity.  Each logging level also includes the information that
+is logged at a lower logging level. See smtpd_tls_loglevel for
+further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_mandatory_ciphers (default: $smtpd_tls_mandatory_ciphers)
+The minimum TLS cipher grade that the Postfix \fBtlsproxy\fR(8) server
+will use with mandatory TLS encryption. See smtpd_tls_mandatory_ciphers
+for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_mandatory_exclude_ciphers (default: $smtpd_tls_mandatory_exclude_ciphers)
+Additional list of ciphers or cipher types to exclude from the
+\fBtlsproxy\fR(8) server cipher list at mandatory TLS security levels.
+See smtpd_tls_mandatory_exclude_ciphers for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_mandatory_protocols (default: $smtpd_tls_mandatory_protocols)
+The SSL/TLS protocols accepted by the Postfix \fBtlsproxy\fR(8) server
+with mandatory TLS encryption. If the list is empty, the server
+supports all available SSL/TLS protocol versions.  See
+smtpd_tls_mandatory_protocols for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_protocols (default: $smtpd_tls_protocols)
+List of TLS protocols that the Postfix \fBtlsproxy\fR(8) server will
+exclude or include with opportunistic TLS encryption. See
+smtpd_tls_protocols for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_req_ccert (default: $smtpd_tls_req_ccert)
+With mandatory TLS encryption, require a trusted remote SMTP
+client certificate in order to allow TLS connections to proceed.
+See smtpd_tls_req_ccert for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_security_level (default: $smtpd_tls_security_level)
+The SMTP TLS security level for the Postfix \fBtlsproxy\fR(8) server;
+when a non\-empty value is specified, this overrides the obsolete
+parameters smtpd_use_tls and smtpd_enforce_tls. See
+smtpd_tls_security_level for further details.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_tls_session_cache_timeout (default: $smtpd_tls_session_cache_timeout)
+Obsolete expiration time of Postfix \fBtlsproxy\fR(8) server TLS session
+cache information. Since the cache is shared with \fBsmtpd\fR(8) and managed
+by \fBtlsmgr\fR(8), there is only one expiration time for the SMTP server cache
+shared by all three services, namely smtpd_tls_session_cache_timeout.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_use_tls (default: $smtpd_use_tls)
+Opportunistic TLS: announce STARTTLS support to remote SMTP clients,
+but do not require that clients use TLS encryption. See smtpd_use_tls
+for further details. Use tlsproxy_tls_security_level instead.
+.PP
+This feature is available in Postfix 2.8 and later.
+.SH tlsproxy_watchdog_timeout (default: 10s)
+How much time a \fBtlsproxy\fR(8) process may take to process local
+or remote I/O before it is terminated by a built\-in watchdog timer.
+This is a safety mechanism that prevents \fBtlsproxy\fR(8) from becoming
+non\-responsive due to a bug in Postfix itself or in system software.
+To avoid false alarms and unnecessary cache corruption this limit
+cannot be set under 10s.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+This feature is available in Postfix 2.8 and later
+.SH trace_service_name (default: trace)
+The name of the trace service. This service is implemented by the
+\fBbounce\fR(8) daemon and maintains a record
+of mail deliveries and produces a mail delivery report when verbose
+delivery is requested with "\fBsendmail \-v\fR".
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH transport_delivery_slot_cost (default: $default_delivery_slot_cost)
+A transport\-specific override for the default_delivery_slot_cost
+parameter value, where \fItransport\fR is the master.cf name of
+the message delivery transport.
+.PP
+Note: \fItransport\fR_delivery_slot_cost parameters will not
+show up in "postconf" command output before Postfix version 2.9.
+This limitation applies to many parameters whose name is a combination
+of a master.cf service name and a built\-in suffix (in this case:
+"_delivery_slot_cost").
+.SH transport_delivery_slot_discount (default: $default_delivery_slot_discount)
+A transport\-specific override for the default_delivery_slot_discount
+parameter value, where \fItransport\fR is the master.cf name of
+the message delivery transport.
+.PP
+Note: \fItransport\fR_delivery_slot_discount parameters will
+not show up in "postconf" command output before Postfix version
+2.9.  This limitation applies to many parameters whose name is a
+combination of a master.cf service name and a built\-in suffix (in
+this case: "_delivery_slot_discount").
+.SH transport_delivery_slot_loan (default: $default_delivery_slot_loan)
+A transport\-specific override for the default_delivery_slot_loan
+parameter value, where \fItransport\fR is the master.cf name of
+the message delivery transport.
+.PP
+Note: \fItransport\fR_delivery_slot_loan parameters will not
+show up in "postconf" command output before Postfix version 2.9.
+This limitation applies to many parameters whose name is a combination
+of a master.cf service name and a built\-in suffix (in this case:
+"_delivery_slot_loan").
+.SH transport_destination_concurrency_failed_cohort_limit (default: $default_destination_concurrency_failed_cohort_limit)
+A transport\-specific override for the
+default_destination_concurrency_failed_cohort_limit parameter value,
+where \fItransport\fR is the master.cf name of the message delivery
+transport.
+.PP
+Note: some \fItransport\fR_destination_concurrency_failed_cohort_limit
+parameters will not show up in "postconf" command output before
+Postfix version 2.9.  This limitation applies to many parameters
+whose name is a combination of a master.cf service name and a
+built\-in suffix (in this case:
+"_destination_concurrency_failed_cohort_limit").
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH transport_destination_concurrency_limit (default: $default_destination_concurrency_limit)
+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.
+.PP
+Note: some \fItransport\fR_destination_concurrency_limit
+parameters will not show up in "postconf" command output before
+Postfix version 2.9.  This limitation applies to many parameters
+whose name is a combination of a master.cf service name and a
+built\-in suffix (in this case: "_destination_concurrency_limit").
+.SH transport_destination_concurrency_negative_feedback (default: $default_destination_concurrency_negative_feedback)
+A transport\-specific override for the
+default_destination_concurrency_negative_feedback parameter value,
+where \fItransport\fR is the master.cf name of the message delivery
+transport.
+.PP
+Note: some \fItransport\fR_destination_concurrency_negative_feedback
+parameters will not show up in "postconf" command output before
+Postfix version 2.9.  This limitation applies to many parameters
+whose name is a combination of a master.cf service name and a
+built\-in suffix (in this case:
+"_destination_concurrency_negative_feedback").
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH transport_destination_concurrency_positive_feedback (default: $default_destination_concurrency_positive_feedback)
+A transport\-specific override for the
+default_destination_concurrency_positive_feedback parameter value,
+where \fItransport\fR is the master.cf name of the message delivery
+transport.
+.PP
+Note: some \fItransport\fR_destination_concurrency_positive_feedback
+parameters will not show up in "postconf" command output before
+Postfix version 2.9.  This limitation applies to many parameters
+whose name is a combination of a master.cf service name and a
+built\-in suffix (in this case:
+"_destination_concurrency_positive_feedback").
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH transport_destination_rate_delay (default: $default_destination_rate_delay)
+A transport\-specific override for the default_destination_rate_delay
+parameter value, where \fItransport\fR is the master.cf name of
+the message delivery transport.
+.PP
+Note: some \fItransport\fR_destination_rate_delay parameters
+will not show up in "postconf" command output before Postfix version
+2.9.  This limitation applies to many parameters whose name is a
+combination of a master.cf service name and a built\-in suffix (in
+this case: "_destination_rate_delay").
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH transport_destination_recipient_limit (default: $default_destination_recipient_limit)
+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.
+.PP
+Note: some \fItransport\fR_destination_recipient_limit parameters
+will not show up in "postconf" command output before Postfix version
+2.9.  This limitation applies to many parameters whose name is a
+combination of a master.cf service name and a built\-in suffix (in
+this case: "_destination_recipient_limit").
+.SH transport_extra_recipient_limit (default: $default_extra_recipient_limit)
+A transport\-specific override for the default_extra_recipient_limit
+parameter value, where \fItransport\fR is the master.cf name of
+the message delivery transport.
+.PP
+Note: \fItransport\fR_extra_recipient_limit parameters will
+not show up in "postconf" command output before Postfix version
+2.9.  This limitation applies to many parameters whose name is a
+combination of a master.cf service name and a built\-in suffix (in
+this case: "_extra_recipient_limit").
+.SH transport_initial_destination_concurrency (default: $initial_destination_concurrency)
+A transport\-specific override for the initial_destination_concurrency
+parameter value, where \fItransport\fR is the master.cf name of
+the message delivery transport.
+.PP
+Note: some \fItransport\fR_initial_destination_concurrency
+parameters will not show up in "postconf" command output before
+Postfix version 2.9.  This limitation applies to many parameters
+whose name is a combination of a master.cf service name and a
+built\-in suffix (in this case: "_initial_destination_concurrency").
+.PP
+This feature is available in Postfix 2.5 and later.
+.SH transport_maps (default: empty)
+Optional lookup tables with mappings from recipient address to
+(message delivery transport, next\-hop destination).  See \fBtransport\fR(5)
+for details.
+.PP
+Specify zero or more "type:table" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.  If you use this
+feature with local files, run "\fBpostmap /etc/postfix/transport\fR"
+after making a change.
+.PP
+Pattern matching of domain names is controlled by the presence
+or absence of "transport_maps" in the parent_domain_matches_subdomains
+parameter value.
+.PP
+For safety reasons, as of Postfix 2.3 this feature does not
+allow $number substitutions in regular expression maps.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+transport_maps = dbm:/etc/postfix/transport
+transport_maps = hash:/etc/postfix/transport
+.fi
+.ad
+.ft R
+.SH transport_minimum_delivery_slots (default: $default_minimum_delivery_slots)
+A transport\-specific override for the default_minimum_delivery_slots
+parameter value, where \fItransport\fR is the master.cf name of
+the message delivery transport.
+.PP
+Note: \fItransport\fR_minimum_delivery_slots parameters will
+not show up in "postconf" command output before Postfix version
+2.9.  This limitation applies to many parameters whose name is a
+combination of a master.cf service name and a built\-in suffix (in
+this case: "_minimum_delivery_slots").
+.SH transport_recipient_limit (default: $default_recipient_limit)
+A transport\-specific override for the default_recipient_limit
+parameter value, where \fItransport\fR is the master.cf name of
+the message delivery transport.
+.PP
+Note: some \fItransport\fR_recipient_limit parameters will not
+show up in "postconf" command output before Postfix version 2.9.
+This limitation applies to many parameters whose name is a combination
+of a master.cf service name and a built\-in suffix (in this case:
+"_recipient_limit").
+.SH transport_recipient_refill_delay (default: $default_recipient_refill_delay)
+A transport\-specific override for the default_recipient_refill_delay
+parameter value, where \fItransport\fR is the master.cf name of
+the message delivery transport.
+.PP
+Note: \fItransport\fR_recipient_refill_delay parameters will
+not show up in "postconf" command output before Postfix version
+2.9.  This limitation applies to many parameters whose name is a
+combination of a master.cf service name and a built\-in suffix (in
+this case: "_recipient_refill_delay").
+.PP
+This feature is available in Postfix 2.4 and later.
+.SH transport_recipient_refill_limit (default: $default_recipient_refill_limit)
+A transport\-specific override for the default_recipient_refill_limit
+parameter value, where \fItransport\fR is the master.cf name of
+the message delivery transport.
+.PP
+Note: \fItransport\fR_recipient_refill_limit parameters will
+not show up in "postconf" command output before Postfix version
+2.9.  This limitation applies to many parameters whose name is a
+combination of a master.cf service name and a built\-in suffix (in
+this case: "_recipient_refill_limit").
+.PP
+This feature is available in Postfix 2.4 and later.
+.SH transport_retry_time (default: 60s)
+The time between attempts by the Postfix queue manager to contact
+a malfunctioning message delivery transport.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH transport_time_limit (default: $command_time_limit)
+A transport\-specific override for the command_time_limit parameter
+value, where \fItransport\fR is the master.cf name of the message
+delivery transport.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+Note: \fItransport\fR_time_limit parameters will not show up
+in "postconf" command output before Postfix version 2.9.  This
+limitation applies to many parameters whose name is a combination
+of a master.cf service name and a built\-in suffix (in this case:
+"_time_limit").
+.SH transport_transport_rate_delay (default: $default_transport_rate_delay)
+A transport\-specific override for the default_transport_rate_delay
+parameter value, where the initial \fItransport\fR in the parameter
+name is the master.cf name of the message delivery transport.
+.PP
+Specify a non\-negative time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.PP
+Note: \fItransport\fR_transport_rate_delay parameters will
+not show up in "postconf" command output before Postfix version
+2.9.  This limitation applies to many parameters whose name is a
+combination of a master.cf service name and a built\-in suffix (in
+this case: "_transport_rate_delay").
+.SH trigger_timeout (default: 10s)
+The time limit for sending a trigger to a Postfix daemon (for
+example, the \fBpickup\fR(8) or \fBqmgr\fR(8) daemon). This time limit prevents
+programs from getting stuck when the mail system is under heavy
+load.
+.PP
+Specify a non\-zero time value (an integral value plus an optional
+one\-letter suffix that specifies the time unit).  Time units: s
+(seconds), m (minutes), h (hours), d (days), w (weeks).
+The default time unit is s (seconds).
+.SH undisclosed_recipients_header (default: see "postconf \-d" output)
+Message header that the Postfix \fBcleanup\fR(8) server inserts when a
+message contains no To: or Cc: message header. With Postfix 2.8
+and later, the default value is empty. With Postfix 2.4\-2.7,
+specify an empty value to disable this feature.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+# Default value before Postfix 2.8.
+# Note: the ":" and ";" are both required.
+undisclosed_recipients_header = To: undisclosed\-recipients:;
+.fi
+.ad
+.ft R
+.SH unknown_address_reject_code (default: 450)
+The numerical response code when the Postfix SMTP server rejects a
+sender or recipient address because its domain is unknown.  This
+is one of the possible replies from the restrictions
+reject_unknown_sender_domain and reject_unknown_recipient_domain.
+.PP
+Do not change this unless you have a complete understanding of RFC 5321.
+.SH unknown_address_tempfail_action (default: $reject_tempfail_action)
+The Postfix SMTP server's action when reject_unknown_sender_domain
+or reject_unknown_recipient_domain fail due to a temporary error
+condition. Specify "defer" to defer the remote SMTP client request
+immediately. With the default "defer_if_permit" action, the Postfix
+SMTP server continues to look for opportunities to reject mail, and
+defers the client request only if it would otherwise be accepted.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH unknown_client_reject_code (default: 450)
+The numerical Postfix SMTP server response code when a client
+without valid address <=> name mapping is rejected by the
+reject_unknown_client_hostname restriction. The SMTP server always replies
+with 450 when the mapping failed due to a temporary error condition.
+.PP
+Do not change this unless you have a complete understanding of RFC 5321.
+.SH unknown_helo_hostname_tempfail_action (default: $reject_tempfail_action)
+The Postfix SMTP server's action when reject_unknown_helo_hostname
+fails due to a temporary error condition. Specify "defer" to defer
+the remote SMTP client request immediately. With the default
+"defer_if_permit" action, the Postfix SMTP server continues to look
+for opportunities to reject mail, and defers the client request
+only if it would otherwise be accepted.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH unknown_hostname_reject_code (default: 450)
+The numerical Postfix SMTP server response code when the hostname
+specified with the HELO or EHLO command is rejected by the
+reject_unknown_helo_hostname restriction.
+.PP
+Do not change this unless you have a complete understanding of RFC 5321.
+.SH unknown_local_recipient_reject_code (default: 550)
+The numerical Postfix SMTP server response code when a recipient
+address is local, and $local_recipient_maps specifies a list of
+lookup tables that does not match the recipient.  A recipient
+address is local when its domain matches $mydestination,
+$proxy_interfaces or $inet_interfaces.
+.PP
+The default setting is 550 (reject mail) but it is safer to initially
+use 450 (try again later) so you have time to find out if your
+local_recipient_maps settings are OK.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+unknown_local_recipient_reject_code = 450
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH unknown_relay_recipient_reject_code (default: 550)
+The numerical Postfix SMTP server reply code when a recipient
+address matches $relay_domains, and relay_recipient_maps specifies
+a list of lookup tables that does not match the recipient address.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH unknown_virtual_alias_reject_code (default: 550)
+The Postfix SMTP server reply code when a recipient address matches
+$virtual_alias_domains, and $virtual_alias_maps specifies a list
+of lookup tables that does not match the recipient address.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH unknown_virtual_mailbox_reject_code (default: 550)
+The Postfix SMTP server reply code when a recipient address matches
+$virtual_mailbox_domains, and $virtual_mailbox_maps specifies a list
+of lookup tables that does not match the recipient address.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH unverified_recipient_defer_code (default: 450)
+The numerical Postfix SMTP server response when a recipient address
+probe fails due to a temporary error condition.
+.PP
+Unlike elsewhere in Postfix, you can specify 250 in order to
+accept the address anyway.
+.PP
+Do not change this unless you have a complete understanding of RFC 5321.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH unverified_recipient_reject_code (default: 450)
+The numerical Postfix SMTP server response when a recipient address
+is rejected by the reject_unverified_recipient restriction.
+.PP
+Unlike elsewhere in Postfix, you can specify 250 in order to
+accept the address anyway.
+.PP
+Do not change this unless you have a complete understanding of RFC 5321.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH unverified_recipient_reject_reason (default: empty)
+The Postfix SMTP server's reply when rejecting mail with
+reject_unverified_recipient. Do not include the numeric SMTP reply
+code or the enhanced status code. By default, the response includes
+actual address verification details.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+unverified_recipient_reject_reason = Recipient address lookup failed
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH unverified_recipient_tempfail_action (default: $reject_tempfail_action)
+The Postfix SMTP server's action when reject_unverified_recipient
+fails due to a temporary error condition. Specify "defer" to defer
+the remote SMTP client request immediately. With the default
+"defer_if_permit" action, the Postfix SMTP server continues to look
+for opportunities to reject mail, and defers the client request
+only if it would otherwise be accepted.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH unverified_sender_defer_code (default: 450)
+The numerical Postfix SMTP server response code when a sender address
+probe fails due to a temporary error condition.
+.PP
+Unlike elsewhere in Postfix, you can specify 250 in order to
+accept the address anyway.
+.PP
+Do not change this unless you have a complete understanding of RFC 5321.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH unverified_sender_reject_code (default: 450)
+The numerical Postfix SMTP server response code when a recipient
+address is rejected by the reject_unverified_sender restriction.
+.PP
+Unlike elsewhere in Postfix, you can specify 250 in order to
+accept the address anyway.
+.PP
+Do not change this unless you have a complete understanding of RFC 5321.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH unverified_sender_reject_reason (default: empty)
+The Postfix SMTP server's reply when rejecting mail with
+reject_unverified_sender. Do not include the numeric SMTP reply
+code or the enhanced status code. By default, the response includes
+actual address verification details.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+unverified_sender_reject_reason = Sender address lookup failed
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH unverified_sender_tempfail_action (default: $reject_tempfail_action)
+The Postfix SMTP server's action when reject_unverified_sender
+fails due to a temporary error condition. Specify "defer" to defer
+the remote SMTP client request immediately. With the default
+"defer_if_permit" action, the Postfix SMTP server continues to look
+for opportunities to reject mail, and defers the client request
+only if it would otherwise be accepted.
+.PP
+This feature is available in Postfix 2.6 and later.
+.SH use_srv_lookup (default: empty)
+Enables discovery for the specified service(s) using DNS SRV
+records. For example, with "use_srv_lookup = submission" and
+"relayhost = example.com:submission", the Postfix SMTP client will
+look up DNS SRV records for _submission._tcp.example.com, and will
+relay email through the hosts and ports that are specified with
+those records. See RFC 2782 for details of the host selection
+process.
+.PP
+Specify zero or more service names separated by comma and/or
+whitespace. Any name in the \fBservices\fR(5) database may be specified,
+though in practice only submission, submissions, and smtp make
+sense.
+.PP
+When SRV record lookup is enabled with use_srv_lookup, you can
+enclose a domain name in "[]" to force IP address lookup instead
+of SRV record lookup.
+.PP
+Example 1: MUA\-to\-MTA submission using SRV record lookup for
+the "submission" service for domain "example.com". This uses the
+default SMTP delivery agent with STARTTLS, and looks up SRV records
+for "_submission._tcp.example.com".
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    use_srv_lookup = submission
+    relayhost = example.com:submission
+    smtp_tls_security_level = may
+    ...see SASL_README for sasl configuration...
+.fi
+.ad
+.ft R
+.PP
+Example 2: MUA\-to\-MTA submission using SRV record lookup for
+the "submissions" service for domain "example.org". This uses a
+dedicated SMTP delivery agent (smtp\-wraptls) with tls_wrappermode
+turned on, and looks up SRV records for "_submissions._tcp.example.org".
+.PP
+Note: specify the older name "smtps" instead of "submissions"
+when a provider has DNS SRV records like "_smtps._tcp.example.org"
+instead of "_submissions._tcp.example.org".
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    use_srv_lookup = submissions
+    default_transport = smtp\-wraptls:example.org:submissions
+    ...see SASL_README for sasl configuration...
+.fi
+.ad
+.ft R
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/master.cf:
+    smtp\-wraptls   unix   ...   ...   ...   ...   ...   smtp
+        \-o { smtp_tls_wrappermode = yes }
+        \-o { smtp_tls_security_level = encrypt }
+.fi
+.ad
+.ft R
+.PP
+Example 3: Sender\-dependent selection for a combination of
+MUA\-to\-MTA submission services. This combines examples 1 and 2 with
+examples of how to disable SRV and look up IP address records for
+"smtp\-relay.example.net" and "smtp\-relay.other.example".  Again,
+specify the older name "smtps" instead of "submissions" when a
+provider has DNS SRV records like "_smtps._tcp.example.org" instead
+of "_submissions._tcp.example.org".
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    use_srv_lookup = submission, submissions
+    sender_dependent_default_transport_maps = inline:{
+        # Destinations that support SRV record lookup.
+        { user1@example.com = smtp:example.com:submission }
+        { user2@example.org = smtp\-wraptls:example.org:submissions }
+        # Use [destination] to force IP address lookups.
+        { user3@example.net = smtp:[smtp\-relay.example.net]:submission }
+        { user4@other.example =
+              smtp\-wraptls:[smtp\-relay.other.example]:submissions } }
+    ...see SASL_README for sasl configuration...
+.fi
+.ad
+.ft R
+.PP
+Example 4: MTA\-to\-MTA traffic, using SRV record lookup for the
+SMTP service. This is useful for Postfix tests, and may be useful
+in environments where ports are dynamically assigned to servers.
+.PP
+.nf
+.na
+.ft C
+/etc/postfix/main.cf:
+    use_srv_lookup = smtp
+    # Fall back to MX record lookup when SRV records are unavailable.
+    #allow_srv_lookup_fallback = yes
+    #ignore_srv_lookup_error = yes
+.fi
+.ad
+.ft R
+.PP
+This feature is available in Postfix 3.8 and later.
+.SH verp_delimiter_filter (default: \-=+)
+The characters Postfix accepts as VERP delimiter characters on the
+Postfix \fBsendmail\fR(1) command line and in SMTP commands.
+.PP
+This feature is available in Postfix 1.1 and later.
+.SH virtual_alias_address_length_limit (default: 1000)
+The maximal length of an email address after virtual alias expansion.
+This stops virtual aliasing loops that increase the address length
+exponentially.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH virtual_alias_domains (default: $virtual_alias_maps)
+Postfix is the final destination for the specified list of virtual
+alias domains, that is, domains for which all addresses are aliased
+to addresses in other local or remote domains. The SMTP server
+validates recipient addresses with $virtual_alias_maps and rejects
+non\-existent recipients. See also the virtual alias domain class
+in the ADDRESS_CLASS_README file
+.PP
+This feature is available in Postfix 2.0 and later. The default
+value is backwards compatible with Postfix version 1.1.
+.PP
+The default value is $virtual_alias_maps so that you can keep all
+information about virtual alias domains in one place.  If you have
+many users, it is better to separate information that changes more
+frequently (virtual address \-> local or remote address mapping)
+from information that changes less frequently (the list of virtual
+domain names).
+.PP
+Specify a list of host or domain names, "/file/name" or
+"type:table" patterns, separated by commas and/or whitespace. A
+"/file/name" pattern is replaced by its contents; a "type:table"
+lookup table is matched when a table entry matches a host or domain name
+(the lookup result is ignored).  Continue long lines by starting
+the next line with whitespace. Specify "!pattern" to exclude a host
+or domain name from the list. The form "!/file/name" is supported
+only in Postfix version 2.4 and later.
+.PP
+See also the VIRTUAL_README and ADDRESS_CLASS_README documents
+for further information.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+virtual_alias_domains = virtual1.tld virtual2.tld
+.fi
+.ad
+.ft R
+.SH virtual_alias_expansion_limit (default: 1000)
+The maximal number of addresses that virtual alias expansion produces
+from each original recipient.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH virtual_alias_maps (default: $virtual_maps)
+Optional lookup tables that alias specific mail addresses or domains
+to other local or remote addresses.  The table format and lookups
+are documented in \fBvirtual\fR(5). For an overview of Postfix address
+manipulations see the ADDRESS_REWRITING_README document.
+.PP
+This feature is available in Postfix 2.0 and later. The default
+value is backwards compatible with Postfix version 1.1.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+Note: these lookups are recursive.
+.PP
+If you use this feature with indexed files, run "\fBpostmap
+/etc/postfix/virtual\fR" after changing the file.
+.PP
+Examples:
+.PP
+.nf
+.na
+.ft C
+virtual_alias_maps = dbm:/etc/postfix/virtual
+virtual_alias_maps = hash:/etc/postfix/virtual
+.fi
+.ad
+.ft R
+.SH virtual_alias_recursion_limit (default: 1000)
+The maximal nesting depth of virtual alias expansion.  Currently
+the recursion limit is applied only to the left branch of the
+expansion graph, so the depth of the tree can in the worst case
+reach the sum of the expansion and recursion limits.  This may
+change in the future.
+.PP
+This feature is available in Postfix 2.1 and later.
+.SH virtual_delivery_status_filter (default: $default_delivery_status_filter)
+Optional filter for the \fBvirtual\fR(8) delivery agent to change the
+delivery status code or explanatory text of successful or unsuccessful
+deliveries.  See default_delivery_status_filter for details.
+.PP
+This feature is available in Postfix 3.0 and later.
+.SH virtual_destination_concurrency_limit (default: $default_destination_concurrency_limit)
+The maximal number of parallel deliveries to the same destination
+via the virtual message delivery transport. This limit is enforced
+by the queue manager. The message delivery transport name is the
+first field in the entry in the master.cf file.
+.SH virtual_destination_recipient_limit (default: $default_destination_recipient_limit)
+The maximal number of recipients per message for the virtual
+message delivery transport. This limit is enforced by the queue
+manager. The message delivery transport name is the first field in
+the entry in the master.cf file.
+.PP
+Setting this parameter to a value of 1 changes the meaning of
+virtual_destination_concurrency_limit from concurrency per domain
+into concurrency per recipient.
+.SH virtual_gid_maps (default: empty)
+Lookup tables with the per\-recipient group ID for \fBvirtual\fR(8) mailbox
+delivery.
+.PP
+This parameter is specific to the \fBvirtual\fR(8) delivery agent.
+It does not apply when mail is delivered with a different mail
+delivery program.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.PP
+In a lookup table, specify a left\-hand side of "@domain.tld" to
+match any user in the specified domain that does not have a specific
+"user@domain.tld" entry.
+.PP
+When a recipient address has an optional address extension
+(user+foo@domain.tld), the \fBvirtual\fR(8) delivery agent looks up
+the full address first, and when the lookup fails, it looks up the
+unextended address (user@domain.tld).
+.PP
+Note 1: for security reasons, the \fBvirtual\fR(8) delivery agent disallows
+regular expression substitution of $1 etc. in regular expression
+lookup tables, because that would open a security hole.
+.PP
+Note 2: for security reasons, the \fBvirtual\fR(8) delivery agent will
+silently ignore requests to use the \fBproxymap\fR(8) server. Instead
+it will open the table directly. Before Postfix version 2.2, the
+\fBvirtual\fR(8) delivery agent will terminate with a fatal error.
+.SH virtual_mailbox_base (default: empty)
+A prefix that the \fBvirtual\fR(8) delivery agent prepends to all pathname
+results from $virtual_mailbox_maps table lookups.  This is a safety
+measure to ensure that an out of control map doesn't litter the
+file system with mailboxes.  While virtual_mailbox_base could be
+set to "/", this setting isn't recommended.
+.PP
+This parameter is specific to the \fBvirtual\fR(8) delivery agent.
+It does not apply when mail is delivered with a different mail
+delivery program.
+.PP
+Example:
+.PP
+.nf
+.na
+.ft C
+virtual_mailbox_base = /var/mail
+.fi
+.ad
+.ft R
+.SH virtual_mailbox_domains (default: $virtual_mailbox_maps)
+Postfix is the final destination for the specified list of domains;
+mail is delivered via the $virtual_transport mail delivery transport.
+By default this is the Postfix \fBvirtual\fR(8) delivery agent.  The SMTP
+server validates recipient addresses with $virtual_mailbox_maps
+and rejects mail for non\-existent recipients.  See also the virtual
+mailbox domain class in the ADDRESS_CLASS_README file.
+.PP
+This parameter expects the same syntax as the mydestination
+configuration parameter.
+.PP
+This feature is available in Postfix 2.0 and later. The default
+value is backwards compatible with Postfix version 1.1.
+.SH virtual_mailbox_limit (default: 51200000)
+The maximal size in bytes of an individual \fBvirtual\fR(8) mailbox or
+maildir file, or zero (no limit).
+.PP
+This parameter is specific to the \fBvirtual\fR(8) delivery agent.
+It does not apply when mail is delivered with a different mail
+delivery program.
+.SH virtual_mailbox_lock (default: see "postconf \-d" output)
+How to lock a UNIX\-style \fBvirtual\fR(8) mailbox before attempting
+delivery.  For a list of available file locking methods, use the
+"\fBpostconf \-l\fR" command.
+.PP
+This parameter is specific to the \fBvirtual\fR(8) delivery agent.
+It does not apply when mail is delivered with a different mail
+delivery program.
+.PP
+This setting is ignored with \fBmaildir\fR style delivery, because
+such deliveries are safe without application\-level locks.
+.PP
+Note 1: the \fBdotlock\fR method requires that the recipient UID
+or GID has write access to the parent directory of the recipient's
+mailbox file.
+.PP
+Note 2: the default setting of this parameter is system dependent.
+.SH virtual_mailbox_maps (default: empty)
+Optional lookup tables with all valid addresses in the domains that
+match $virtual_mailbox_domains.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.PP
+In a lookup table, specify a left\-hand side of "@domain.tld" to
+match any user in the specified domain that does not have a specific
+"user@domain.tld" entry.
+.PP
+With the default "virtual_mailbox_domains = $virtual_mailbox_maps",
+lookup tables also need entries with a left\-hand side of "domain.tld"
+to satisfy virtual_mailbox_domain lookups (the right\-hand side is
+required but will not be used).
+.PP
+The remainder of this text is specific to the \fBvirtual\fR(8) delivery
+agent.  It does not apply when mail is delivered with a different
+mail delivery program.
+.PP
+The \fBvirtual\fR(8) delivery agent uses this table to look up the
+per\-recipient mailbox or maildir pathname.  If the lookup result
+ends in a slash ("/"), maildir\-style delivery is carried out,
+otherwise the path is assumed to specify a UNIX\-style mailbox file.
+Note that $virtual_mailbox_base is unconditionally prepended to
+this path.
+.PP
+When a recipient address has an optional address extension
+(user+foo@domain.tld), the \fBvirtual\fR(8) delivery agent looks up
+the full address first, and when the lookup fails, it looks up the
+unextended address (user@domain.tld).
+.PP
+Note 1: for security reasons, the \fBvirtual\fR(8) delivery agent disallows
+regular expression substitution of $1 etc. in regular expression
+lookup tables, because that would open a security hole.
+.PP
+Note 2: for security reasons, the \fBvirtual\fR(8) delivery agent will
+silently ignore requests to use the \fBproxymap\fR(8) server. Instead
+it will open the table directly. Before Postfix version 2.2, the
+\fBvirtual\fR(8) delivery agent will terminate with a fatal error.
+.SH virtual_maps (default: empty)
+Optional lookup tables with a) names of domains for which all
+addresses are aliased to addresses in other local or remote domains,
+and b) addresses that are aliased to addresses in other local or
+remote domains.  Available before Postfix version 2.0. With Postfix
+version 2.0 and later, this is replaced by separate controls: virtual_alias_domains
+and virtual_alias_maps.
+.SH virtual_minimum_uid (default: 100)
+The minimum user ID value that the \fBvirtual\fR(8) delivery agent accepts
+as a result from $virtual_uid_maps table lookup.  Returned
+values less than this will be rejected, and the message will be
+deferred.
+.PP
+This parameter is specific to the \fBvirtual\fR(8) delivery agent.
+It does not apply when mail is delivered with a different mail
+delivery program.
+.SH virtual_transport (default: virtual)
+The default mail delivery transport and next\-hop destination for
+final delivery to domains listed with $virtual_mailbox_domains.
+This information can be overruled with the \fBtransport\fR(5) table.
+.PP
+Specify a string of the form \fItransport:nexthop\fR, where \fItransport\fR
+is the name of a mail delivery transport defined in master.cf.
+The \fI:nexthop\fR destination is optional; its syntax is documented
+in the manual page of the corresponding delivery agent.
+.PP
+This feature is available in Postfix 2.0 and later.
+.SH virtual_uid_maps (default: empty)
+Lookup tables with the per\-recipient user ID that the \fBvirtual\fR(8)
+delivery agent uses while writing to the recipient's mailbox.
+.PP
+This parameter is specific to the \fBvirtual\fR(8) delivery agent.
+It does not apply when mail is delivered with a different mail
+delivery program.
+.PP
+Specify zero or more "type:name" lookup tables, separated by
+whitespace or comma. Tables will be searched in the specified order
+until a match is found.
+.PP
+In a lookup table, specify a left\-hand side of "@domain.tld"
+to match any user in the specified domain that does not have a
+specific "user@domain.tld" entry.
+.PP
+When a recipient address has an optional address extension
+(user+foo@domain.tld), the \fBvirtual\fR(8) delivery agent looks up
+the full address first, and when the lookup fails, it looks up the
+unextended address (user@domain.tld).
+.PP
+Note 1: for security reasons, the \fBvirtual\fR(8) delivery agent disallows
+regular expression substitution of $1 etc. in regular expression
+lookup tables, because that would open a security hole.
+.PP
+Note 2: for security reasons, the \fBvirtual\fR(8) delivery agent will
+silently ignore requests to use the \fBproxymap\fR(8) server. Instead
+it will open the table directly. Before Postfix version 2.2, the
+\fBvirtual\fR(8) delivery agent will terminate with a fatal error.
+.SH SEE ALSO
+.na
+.nf
+postconf(1), Postfix configuration parameter maintenance
+master(5), Postfix daemon configuration maintenance
+.SH LICENSE
+.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
+.sp
+Wietse Venema
+Google, Inc.
+111 8th Avenue
+New York, NY 10011, USA
+.sp
+Viktor Dukhovni