  Control the SMTP client program
  Cristiano Otto Von Trompczynski


  11..  MMiisscceellllaanneeoouuss ccoonnttrroollss


     BBeesstt mmxx ttrraannssppoorrtt
        The "Best mx transport" option controls what happens when the
        local system is listed as the best MX host for a destination. By
        default, Postfix reports a "mail loops back to myself" error and
        bounces the message. Specify "local" to pass the mail to the
        local delivery agent. You can specify any transport that is
        defined in the master.cf file.  This option sets the
        "best_mx_transport" postfix variable.


     FFaallllbbaacckk rreellaayy
        The "Fallback relay" option specifies zero or more hosts or
        domains to hand off mail to if a message destination is not
        found, or if a destination is unreachable.

        By default, mail is bounced when a destination is not found, and
        delivery is deferred if a destination is unreachable.  This
        option sets the "fallback_relay" postfix variable.


     IIggnnoorree mmxx llooookkuupp eerrrroorr
        The "Ignore mx lookup error" option controls what happens when a
        name server fails to respond to an MX lookup request. By
        default, Postfix defers delivery and tries again after some
        delay. Specify "yes" to force an A record lookup instead.  This
        option sets the "ignore_mx_lookup_error" postfix variable.


     SSmmttpp sskkiipp 44xxxx ggrreeeettiinngg
        The "Smtp skip 4xx greeting" option controls what happens when
        an SMTP server greets us with a 4XX status code. By default,
        Postfix backs off. Specify "yes" to move on the next mail
        exchanger.  This option sets the "smtp_skip_4xx_greeting"
        postfix variable.


     SSmmttpp sskkiipp qquuiitt rreessppoonnssee
        The "Smtp skip quit response" option controls whether the SMTP
        client waits for the response to the QUIT command. The default
        is to not wait.  This option sets the "smtp_skip_quit_response"
        postfix variable.


  22..  RRaattee ccoonnttrroollss


     SSmmttpp ddeessttiinnaattiioonn ccoonnccuurrrreennccyy lliimmiitt
        The "Smtp destination concurrency limit" option limits the
        number of parallel deliveries to the same destination via the
        smtp delivery agent.

        The default limit is the "Default destination concurrency limit"
        option. It is probably safer to limit the concurrency to 10.
        This option sets the "smtp_destination_concurrency_limit"
        postfix variable.

     SSmmttpp ddeessttiinnaattiioonn rreecciippiieenntt lliimmiitt
        The "Smtp destination recipient limit" option limits the number
        of recipients per delivery via the smtp delivery agent.

        The default is taken from the "Default destination recipient
        limit" option. This option sets the "Smtp destination recipient
        limit" postfix variable.  This option sets the
        "smtp_destination_recipient_limit" postfix variable.


     DDeeffaauulltt ddeessttiinnaattiioonn rreecciippiieenntt lliimmiitt
        The "Default destination recipient limit" option specifies a
        default limit on the number of recipients per message delivery.
        This is the default limit for delivery via SMTP, via the local
        delivery agent and via the pipe mailer.  This option sets the
        "default_destination_recipient_limit" postfix variable.


  33..  PPaarraalllleell ddeelliivveerryy ttoo tthhee ssaammee ddeessttiinnaattiioonn


     LLooccaall ddeessttiinnaattiioonn ccoonnccuurrrreennccyy lliimmiitt
        How many parallel deliveries to the same user or domain? With
        local delivery, it does not make sense to do massively parallel
        delivery to the same user, because mailbox updates must happen
        sequentially, and expensive pipelines in .forward files can
        cause disasters when too many are run at the same time. With
        SMTP deliveries, 10 simultaneous connections to the same domain
        could be sufficient to raise eyebrows.

        Each message delivery transport has its
        XXX_destination_concurrency_limit parameter.  The default is is
        taken from the "Default destination concurrency limit" option.

        This option sets the "local_destination_concurrency_limit"
        postfix variable.


     DDeeffaauulltt ddeessttiinnaattiioonn ccoonnccuurrrreennccyy lliimmiitt
        The "Default destination concurrency limit" option specifies a
        default limit on the number of parallel deliveries to the same
        destination.  This is the default limit for delivery via SMTP,
        via the local delivery agent and via the pipe mailer.  This
        option sets the "default_destination_concurrency_limit" postfix
        variable.


  44..  TTiimmeeoouutt ccoonnttrroollss


     SSmmttpp ccoonnnneecctt ttiimmeeoouutt
        The "Smtp connect timeout" option specifies the SMTP client
        timeout in seconds for completing a TCP connection.

        When no connection can be made within the deadline, the SMTP
        client tries the next address on the mail exchanger list.
        Specify 0 to disable the timeout. This option sets the
        "smtp_connect_timeout" postfix variable.


     SSmmttpp hheelloo ttiimmeeoouutt
        The "Smtp helo timeout" option specifies the SMTP client timeout
        in seconds for receiving the SMTP greeting banner.

        When the server drops the connection without sending a greeting
        banner, or when it sends no greeting banner within the deadline,
        the SMTP client tries the next address on the mail exchanger
        list.  This option sets the "smtp_helo_timeout" postfix
        variable.


     SSmmttpp mmaaiill ttiimmeeoouutt
        The "Smtp mail timeout" option specifies the SMTP client timeout
        in seconds for sending the SMTP MAIL FROM command, and for
        receiving the server response.

        In case of problems the client does NOT try the next address on
        the mail exchanger list.  This option sets the
        "smtp_mail_timeout" postfix variable.


     SSmmttpp rrccpptt ttiimmeeoouutt
        The "Smtp rcpt timeout" option specifies the SMTP client timeout
        in seconds for sending the SMTP RCPT TO command, and for
        receiving the server response.

        In case of problems the client does NOT try the next address on
        the mail exchanger list.  This option sets the
        "smtp_rcpt_timeout" postfix variable.


     SSmmttpp ddaattaa iinniitt ttiimmeeoouutt
        The "Smtp data init timeout" option specifies the SMTP client
        timeout in seconds for sending the SMTP DATA command, and for
        receiving the server response.

        In case of problems the client does NOT try the next address on
        the mail exchanger list.  This option sets the
        "smtp_data_init_timeout" postfix variable.


     SSmmttpp ddaattaa xxffeerr ttiimmeeoouutt
        The "Smtp data xfer timeout" option specifies the SMTP client
        timeout in seconds for sending the SMTP message content. When
        the connection stalls for more than "Smtp_data_xfer_timeout"
        option them SMTP client terminates the transfer.

        In case of problems the client does NOT try the next address on
        the mail exchanger list.  This option sets the
        "smtp_data_xfer_timeout" postfix variable.


     SSmmttpp ddaattaa ddoonnee ttiimmeeoouutt
        The "Smtp data done timeout" option specifies the SMTP client
        timeout in seconds for sending the SMTP ".", and for receiving
        the server response.

        When no response is received within the deadline, a warning is
        logged that the mail may be delivered multiple times.

        In case of problems the client does NOT try the next address on
        the mail exchanger list.  This option sets the
        "smtp_data_done_timeout" postfix variable.


     SSmmttpp qquuiitt ttiimmeeoouutt
        The "Smtp quit timeout" option specifies the SMTP client timeout
        in seconds for sending the SMTP QUIT command, and for receiving
        the server response.  This option sets the "smtp_quit_timeout"
        postfix variable.


  55..  DDeelliivveerryy ttoo mmaaiillbbooxx


     HHoommee mmaaiillbbooxx
        The "Home mailbox" option specifies the optional pathname of a
        mailbox file relative to a user's home directory. The default
        mailbox file is /var/spool/mail/user or /var/mail/user.  Specify
        "Maildir/" for qmail-style delivery (the / is required). This
        option sets the "home_mailbox" postfix variable.


     MMaaiill ssppooooll ddiirreeccttoorryy
        The "Mail spool directory" option specifies the directory where
        UNIX-style mailboxes are kept. The default setting depends on
        the system type. This option sets the "mail_spool_directory"
        postfix variable.


     MMaaiillbbooxx ccoommmmaanndd
        The "Mailbox command" option specifies the optional external
        command to use instead of mailbox delivery. The command is run
        as the recipient with proper HOME, SHELL and LOGNAME environment
        settings.  Exception:  delivery for root is done as
        "$default_user".

        Other environment variables of interest: USER (recipient
        username), EXTENSION (address extension), DOMAIN (domain part of
        address), and LOCAL (the address localpart).

        Unlike other Postfix configuration parameters, the "Mailbox
        command" option is not subjected to "$parameter" substitutions.
        This is to make it easier to specify shell syntax (see example
        below).

        Avoid shell meta characters because they will force Postfix to
        run an expensive shell process. Procmail alone is expensive
        enough.

        This option sets the "mailbox_command" postfix variable.

        IF YOU USE THIS TO DELIVER MAIL SYSTEM-WIDE, YOU MUST SET UP AN
        ALIAS THAT FORWARDS MAIL FOR ROOT TO A REAL USER.

        mailbox_command = /some/where/procmail mailbox_command =
        /some/where/procmail -a "$EXTENSION"


     MMaaiillbbooxx ttrraannssppoorrtt
        The "Mailbox transport" option specifies the optional transport
        in master.cf to use after processing aliases and .forward files.
        This option has precedence over the 'Mailbox command', the
        "mailbox_transport" postfix variable.


     FFaallllbbaacckk ttrraannssppoorrtt
        The "Fallback transport" specifies the optional transport in
        master.cf to use for recipients that are not found in the UNIX
        passwd database.  This parameter has precedence over the "Luser
        relay" option. This option sets the "fallback_transport" postfix
        variable.

     LLuusseerr rreellaayy
        The "Luser relay" option specifies an optional destination
        address for unknown recipients.  By default, mail for unknown
        local recipients is bounced. This option sets the "luser_relay"
        postfix variable.

        The following expansions are done on luser_relay: $user
        (recipient username), $shell (recipient shell), $home (recipient
        home directory), $recipient (full recipient address), $extension
        (recipient address extension), $domain (recipient domain),
        $local (entire recipient localpart), $recipient_delimiter.
        Specify ${name?value} or ${name:value} to expand value only when
        $name does (does not) exist.