Go to main content

man pages section 5: File Formats

Exit Print View

Updated: Wednesday, February 9, 2022

master (5)


master - Postfix master process configuration file format


Please see following description for synopsis


MASTER(5)                     File Formats Manual                    MASTER(5)

       master - Postfix master process configuration file format

       The  Postfix  mail  system  is  implemented by small number of (mostly)
       client commands that are invoked by users, and by a  larger  number  of
       services that run in the background.

       Postfix  services are implemented by daemon processes. These run in the
       background under control of the master(8) process.  The master.cf  con-
       figuration file defines how a client program connects to a service, and
       what daemon program runs when a service is requested.  Most daemon pro-
       cesses  are short-lived and terminate voluntarily after serving max_use
       clients, or after inactivity for max_idle or more units of time.

       All daemons specified here must speak a Postfix-internal  protocol.  In
       order  to  execute  non-Postfix  software  use the local(8), pipe(8) or
       spawn(8) services, or run the  server  under  control  by  inetd(8)  or

       After  changing  master.cf  you must execute "postfix reload" to reload
       the configuration.

       The general format of the master.cf file is as follows:

       o      Empty lines and whitespace-only lines are ignored, as are  lines
              whose first non-whitespace character is a `#'.

       o      A  logical  line  starts  with  non-whitespace text. A line that
              starts with whitespace continues a logical line.

       o      Each logical line defines a single Postfix service.   Each  ser-
              vice  is  identified  by  its  name and type as described below.
              When multiple lines specify the same service name and type, only
              the  last  one is remembered.  Otherwise, the order of master.cf
              service definitions does not matter.

       Each logical line consists of eight  fields  separated  by  whitespace.
       These  are described below in the order as they appear in the master.cf

       Where applicable a field of "-"  requests  that  the  built-in  default
       value  be  used.  For boolean fields specify "y" or "n" to override the
       default value.

       Service name
              The service name syntax depends on the service type as described

       Service type
              Specify one of the following service types:

              inet   The  service listens on a TCP/IP socket and is accessible
                     via the network.

                     The service name is specified as host:port, denoting  the
                     host   and  port  on  which  new  connections  should  be
                     accepted. The host  part  (and  colon)  may  be  omitted.
                     Either  host  or  port may be given in symbolic form (see
                     hosts(5) or services(5)) or in numeric form  (IP  address
                     or port number).  Host information may be enclosed inside
                     "[]"; this form is necessary only with IPv6 addresses.

                     Examples: a  service  named  or  ::1:smtp
                     receives mail via the loopback interface only; and a ser-
                     vice named 10025 accepts connections on  TCP  port  10025
                     via  all  interfaces  configured with the inet_interfaces

                     Note:  with  Postfix  version  2.2  and   later   specify
                     "inet_interfaces  = loopback-only" in main.cf, instead of
                     hard-coding loopback IP address information in  master.cf
                     or in main.cf.

              unix   The service listens on a UNIX-domain socket and is acces-
                     sible for local clients only.

                     The service name is a pathname relative  to  the  Postfix
                     queue    directory    (pathname   controlled   with   the
                     queue_directory configuration parameter in main.cf).

                     On Solaris 8 and earlier systems the unix type is  imple-
                     mented with streams sockets.

              fifo   The  service listens on a FIFO (named pipe) and is acces-
                     sible for local clients only.

                     The service name is a pathname relative  to  the  Postfix
                     queue    directory    (pathname   controlled   with   the
                     queue_directory configuration parameter in main.cf).

              pass   The service listens  on  a  UNIX-domain  socket,  and  is
                     accessible  to  local  clients only. It receives one open
                     connection  (file  descriptor  passing)  per   connection

                     The  service  name  is a pathname relative to the Postfix
                     queue   directory   (pathname   controlled    with    the
                     queue_directory configuration parameter in main.cf).

                     On  Solaris 8 and earlier systems the pass type is imple-
                     mented with streams sockets.

                     This feature is available as of Postfix version 2.5.

       Private (default: y)
              Whether or not access is restricted to the mail system.   Inter-
              net (type inet) services can't be private.

       Unprivileged (default: y)
              Whether the service runs with root privileges or as the owner of
              the  Postfix  system  (the  owner  name  is  controlled  by  the
              mail_owner configuration variable in the main.cf file).

              The  local(8), pipe(8), spawn(8), and virtual(8) daemons require

       Chroot (default: Postfix >= 3.0: n, Postfix <3.0: y)
              Whether or not the service  runs  chrooted  to  the  mail  queue
              directory (pathname is controlled by the queue_directory config-
              uration variable in the main.cf file).

              Chroot should not be used with the local(8), pipe(8),  spawn(8),
              and virtual(8) daemons.  Although the proxymap(8) server can run
              chrooted, doing so defeats most of the purpose  of  having  that
              service in the first place.

              The files in the examples/chroot-setup subdirectory of the Post-
              fix source archive show set up a Postfix chroot environment on a
              variety  of  systems.  See  also  BASIC_CONFIGURATION_README for
              issues related to running daemons chrooted.

       Wake up time (default: 0)
              Automatically wake up the named service after the specified num-
              ber  of seconds. The wake up is implemented by connecting to the
              service and sending a wake up request.  A ? at the  end  of  the
              wake-up  time  field  requests  that  no  wake up events be sent
              before the first time a service is used.  Specify 0 for no auto-
              matic wake up.

              The  pickup(8),  qmgr(8)  and flush(8) daemons require a wake up

       Process limit (default: $default_process_limit)
              The maximum number of processes that may  execute  this  service
              simultaneously. Specify 0 for no process count limit.

              NOTE:  Some  Postfix  services  must  be  configured  as  a sin-
              gle-process service (for example,  qmgr(8))  and  some  services
              must   be   configured  with  no  process  limit  (for  example,
              cleanup(8)).  These limits must not be changed.

       Command name + arguments
              The command to be executed.  Characters that are special to  the
              shell  such  as  ">"  or  "|"  have no special meaning here, and
              quotes cannot be used to  protect  arguments  containing  white-
              space.  To  protect  whitespace,  use  "{"  and "}" as described

              The command name is relative to  the  Postfix  daemon  directory
              (pathname  is  controlled  by the daemon_directory configuration

              The command argument syntax for specific commands  is  specified
              in the respective daemon manual page.

              The  following command-line options have the same effect for all
              daemon programs:

              -D     Run the daemon under control  by  the  command  specified
                     with the debugger_command variable in the main.cf config-
                     uration file.  See DEBUG_README for hints and tips.

              -o { name = value } (long form, Postfix >= 3.0)

              -o name=value (short form)
                     Override the named main.cf configuration  parameter.  The
                     parameter  value  can  refer to other parameters as $name
                     etc., just like in main.cf.  See postconf(5) for syntax.

                     NOTE 1: With the  "long  form"  shown  above,  whitespace
                     after  "{",  around  "=",  and before "}" is ignored, and
                     whitespace within the parameter value is preserved.

                     NOTE 2: with the "short form" shown above, do not specify
                     whitespace  around  the  "="  or  in parameter values. To
                     specify a parameter value that contains  whitespace,  use
                     the  long  form described above, or use commas instead of
                     spaces, or specify the value in main.cf. Example:

                         submission inet .... smtpd
                             -o smtpd_xxx_yyy=$submission_xxx_yyy

                         submission_xxx_yyy = text with whitespace...

                     NOTE 3: Over-zealous use of parameter overrides makes the
                     Postfix  configuration  hard  to understand and maintain.
                     At a certain point, it might be easier to configure  mul-
                     tiple instances of Postfix, instead of configuring multi-
                     ple personalities via master.cf.

              -v     Increase the verbose logging level. Specify  multiple  -v
                     options  to  make  a  Postfix daemon process increasingly

              Other command-line arguments
                     Specify "{" and "}" around command arguments that contain
                     whitespace  (Postfix 3.0 and later). Whitespace after "{"
                     and before "}" is ignored.

       See attributes(7) for descriptions of the following attributes:

       |ATTRIBUTE TYPE |       ATTRIBUTE VALUE        |
       |Availability   | service/network/smtp/postfix |
       |Stability      | Volatile                     |

       master(8), process manager
       postconf(5), configuration parameters

       Use "postconf readme_directory" or "postconf html_directory" to  locate
       this information.
       BASIC_CONFIGURATION_README, basic configuration
       DEBUG_README, Postfix debugging

       The Secure Mailer license must be distributed with this software.

       Initial version by
       Magnus Baeck
       Lund Institute of Technology

       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA

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

       Source code for open source software components in Oracle Solaris can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-

       This software was built from source available at
       https://github.com/oracle/solaris-userland.  The original community
       source was downloaded from  https://archive.mgm51.com/mirrors/postfix-

       Further information about this software can be found on the open source
       community website at http://www.postfix.org.