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<title> Postfix manual - master(5) </title>
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master - Postfix master process configuration file format
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The Postfix mail system is implemented by small number of
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(mostly) client commands that are invoked by users, and by
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a larger number of services that run in the background.
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Postfix services are implemented by daemon processes.
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These run in the background under control of the <a href="master.8.html"><b>master</b>(8)</a>
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process. The master.cf configuration file defines how a
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client program connects to a service, and what daemon pro-
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gram runs when a service is requested. Most daemon pro-
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cesses are short-lived and terminate after serving <b><a href="postconf.5.html#max_use">max_use</a></b>
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clients, or after inactivity for <b><a href="postconf.5.html#max_idle">max_idle</a></b> or more units of
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All daemons specified here must speak a Postfix-internal
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protocol. In order to execute non-Postfix software use the
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<a href="local.8.html"><b>local</b>(8)</a>, <a href="pipe.8.html"><b>pipe</b>(8)</a> or <a href="spawn.8.html"><b>spawn</b>(8)</a> services, or run the server
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under control by <b>inetd</b>(8) or equivalent.
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After changing master.cf you must execute "<b>postfix reload</b>"
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to reload the configuration.
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The general format of the master.cf file is as follows:
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<b>o</b> Each logical line defines a single Postfix service.
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Each service is identified by its name and type as
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described below. When multiple lines specify the
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same service name and type, only the last one is
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remembered. Otherwise, the order of master.cf ser-
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vice definitions does not matter.
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<b>o</b> Empty lines and whitespace-only lines are ignored,
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as are lines whose first non-whitespace character
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<b>o</b> A logical line starts with non-whitespace text. A
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line that starts with whitespace continues a logi-
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Each logical line consists of eight fields separated by
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whitespace. These are described below in the order as
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they appear in the master.cf file.
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Where applicable a field of "-" requests that the built-in
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default value be used. For boolean fields specify "y" or
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"n" to override the default value.
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The service name syntax depends on the service type
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Specify one of the following service types:
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<b>inet</b> The service listens on a TCP/IP socket and
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is accessible via the network.
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The service name is specified as <i>host:port</i>,
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denoting the host and port on which new con-
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nections should be accepted. The host part
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(and colon) may be omitted. Either host or
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port may be given in symbolic form (host or
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service name) or in numeric form (IP address
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or port number). Host information may be
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enclosed inside "[]", but this form is not
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Examples: a service named <b>127.0.0.1:smtp</b> or
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<b>::1:smtp</b> receives mail via the loopback
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interface only; and a service named <b>10025</b>
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accepts connections on TCP port 10025 via
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all interfaces configured with the
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<b><a href="postconf.5.html#inet_interfaces">inet_interfaces</a></b> parameter.
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Note: with Postfix version 2.2 and later
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specify "<b><a href="postconf.5.html#inet_interfaces">inet_interfaces</a> = loopback-only</b>" in
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main.cf, instead of hard-coding loopback IP
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address information in master.cf or in
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<b>unix</b> The service listens on a UNIX-domain socket
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and is accessible for local clients only.
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The service name is a pathname relative to
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the Postfix queue directory (pathname con-
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trolled with the <b><a href="postconf.5.html#queue_directory">queue_directory</a></b> configura-
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tion parameter in main.cf).
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On Solaris systems the <b>unix</b> type is imple-
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mented with streams sockets.
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<b>fifo</b> The service listens on a FIFO (named pipe)
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and is accessible for local clients only.
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The service name is a pathname relative to
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the Postfix queue directory (pathname con-
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trolled with the <b><a href="postconf.5.html#queue_directory">queue_directory</a></b> configura-
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tion parameter in main.cf).
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<b>Private (default: y)</b>
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Whether or not access is restricted to the mail
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system. Internet (type <b>inet</b>) services can't be
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<b>Unprivileged (default: y)</b>
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Whether the service runs with root privileges or as
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the owner of the Postfix system (the owner name is
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controlled by the <b><a href="postconf.5.html#mail_owner">mail_owner</a></b> configuration variable
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in the main.cf file).
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The <a href="local.8.html"><b>local</b>(8)</a>, <a href="pipe.8.html"><b>pipe</b>(8)</a>, <a href="spawn.8.html"><b>spawn</b>(8)</a>, and <a href="virtual.8.html"><b>virtual</b>(8)</a>
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daemons require privileges.
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<b>Chroot (default: y)</b>
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Whether or not the service runs chrooted to the
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mail queue directory (pathname is controlled by the
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<b><a href="postconf.5.html#queue_directory">queue_directory</a></b> configuration variable in the
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Chroot should not be used with the <a href="local.8.html"><b>local</b>(8)</a>,
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<a href="pipe.8.html"><b>pipe</b>(8)</a>, <a href="spawn.8.html"><b>spawn</b>(8)</a>, and <a href="virtual.8.html"><b>virtual</b>(8)</a> daemons.
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Although the <a href="proxymap.8.html"><b>proxymap</b>(8)</a> server can run chrooted,
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doing so defeats most of the purpose of having that
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service in the first place.
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The files in the examples/chroot-setup subdirectory
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of the Postfix source archive describe how to set
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up a Postfix chroot environment for your type of
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machine, and <a href="BASIC_CONFIGURATION_README.html">BASIC_CONFIGURATION_README</a> discusses
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issues related to running daemons chrooted.
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<b>Wake up time (default: 0)</b>
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Automatically wake up the named service after the
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specified number of seconds. The wake up is imple-
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mented by connecting to the service and sending a
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wake up request. A ? at the end of the wake-up
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time field requests that wake up events be sent
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only to services that are actually being used.
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Specify 0 for no automatic wake up.
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The <a href="pickup.8.html"><b>pickup</b>(8)</a>, <a href="qmgr.8.html"><b>qmgr</b>(8)</a> and <a href="flush.8.html"><b>flush</b>(8)</a> daemons require
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<b>Process limit (default: $<a href="postconf.5.html#default_process_limit">default_process_limit</a>)</b>
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The maximum number of processes that may execute
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this service simultaneously. Specify 0 for no
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NOTE: Some Postfix services must be configured as a
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single-process service (for example, <a href="qmgr.8.html"><b>qmgr</b>(8)</a>) and
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some services must be configured with no process
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limit (for example, <a href="cleanup.8.html"><b>cleanup</b>(8)</a>). These limits must
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<b>Command name + arguments</b>
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The command to be executed. Characters that are
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special to the shell such as ">" or "|" have no
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special meaning here, and quotes cannot be used to
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protect arguments containing whitespace.
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The command name is relative to the Postfix daemon
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directory (pathname is controlled by the <b><a href="postconf.5.html#daemon_directory">dae</a>-</b>
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<b><a href="postconf.5.html#daemon_directory">mon_directory</a></b> configuration variable).
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The command argument syntax for specific commands
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is specified in the respective daemon manual page.
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The following command-line options have the same
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effect for all daemon programs:
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<b>-D</b> Run the daemon under control by the command
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specified with the <b><a href="postconf.5.html#debugger_command">debugger_command</a></b> variable
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in the main.cf configuration file. See
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<a href="DEBUG_README.html">DEBUG_README</a> for hints and tips.
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<b>-o</b> <i>name</i>=<i>value</i>
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Override the named main.cf configuration
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parameter. The parameter value can refer to
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other parameters as <i>$name</i> etc., just like in
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main.cf. See <a href="postconf.5.html"><b>postconf</b>(5)</a> for syntax.
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NOTE 1: do not specify whitespace around the
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"=". In parameter values, either avoid
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whitespace altogether, use commas instead of
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spaces, or consider overrides like "-o
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name=$override_parameter" with $over-
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ride_parameter set in main.cf.
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NOTE 2: Over-zealous use of parameter over-
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rides makes the Postfix configuration hard
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to understand and maintain. At a certain
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point, it might be easier to configure mul-
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tiple instances of Postfix, instead of con-
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figuring multiple personalities via mas-
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<b>-v</b> Increase the verbose logging level. Specify
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multiple <b>-v</b> options to make a Postfix daemon
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process increasingly verbose.
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<a href="master.8.html">master(8)</a>, process manager
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<a href="postconf.5.html">postconf(5)</a>, configuration parameters
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<a href="BASIC_CONFIGURATION_README.html">BASIC_CONFIGURATION_README</a>, basic configuration
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<a href="DEBUG_README.html">DEBUG_README</a>, Postfix debugging
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The Secure Mailer license must be distributed with this
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Lund Institute of Technology
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IBM T.J. Watson Research
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Yorktown Heights, NY 10598, USA
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