Updated: 2022/Sep/29

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REGEXP_TABLE(5)               File Formats Manual              REGEXP_TABLE(5)

       regexp_table - format of Postfix regular expression tables

       postmap -q "string" regexp:/etc/postfix/filename

       postmap -q - regexp:/etc/postfix/filename <inputfile

       The Postfix mail system uses optional tables for address rewriting,
       mail routing, or access control. These tables are usually in dbm or db

       Alternatively, lookup tables can be specified in POSIX regular
       expression form. In this case, each input is compared against a list of
       patterns. When a match is found, the corresponding result is returned
       and the search is terminated.

       To find out what types of lookup tables your Postfix system supports
       use the "postconf -m" command.

       To test lookup tables, use the "postmap -q" command as described in the
       SYNOPSIS above. Use "postmap -hmq - <file" for header_checks(5)
       patterns, and "postmap -bmq - <file" for body_checks(5) (Postfix 2.6
       and later).

       With Postfix version 2.2 and earlier specify "postmap -fq" to query a
       table that contains case sensitive patterns. Patterns are case
       insensitive by default.

       The general form of a Postfix regular expression table is:

       /pattern/flags result
              When pattern matches the input string, use the corresponding
              result value.

       !/pattern/flags result
              When pattern does not match the input string, use the
              corresponding result value.

       if /pattern/flags

       endif  If the input string matches /pattern/, then match that input
              string against the patterns between if and endif.  The if..endif
              can nest.

              Note: do not prepend whitespace to patterns inside if..endif.

              This feature is available in Postfix 2.1 and later.

       if !/pattern/flags

       endif  If the input string does not match /pattern/, then match that
              input string against the patterns between if and endif. The
              if..endif can nest.

              Note: do not prepend whitespace to patterns inside if..endif.

              This feature is available in Postfix 2.1 and later.

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

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

       Each pattern is a POSIX regular expression enclosed by a pair of
       delimiters. The regular expression syntax is documented in re_format(7)
       with 4.4BSD, in regex(5) with Solaris, and in regex(7) with Linux.
       Other systems may use other document names.

       The expression delimiter can be any non-alphanumerical character,
       except whitespace or characters that have special meaning
       (traditionally the forward slash is used). The regular expression can
       contain whitespace.

       By default, matching is case-insensitive, and newlines are not treated
       as special characters. The behavior is controlled by flags, which are
       toggled by appending one or more of the following characters after the

       i (default: on)
              Toggles the case sensitivity flag. By default, matching is case

       m (default: off)
              Toggle the multi-line mode flag. When this flag is on, the ^ and
              $ metacharacters match immediately after and immediately before
              a newline character, respectively, in addition to matching at
              the start and end of the input string.

       x (default: on)
              Toggles the extended expression syntax flag. By default, support
              for extended expression syntax is enabled.

       Patterns are applied in the order as specified in the table, until a
       pattern is found that matches the input string.

       Each pattern is applied to the entire input string.  Depending on the
       application, that string is an entire client hostname, an entire client
       IP address, or an entire mail address.  Thus, no parent domain or
       parent network search is done, and user@domain mail addresses are not
       broken up into their user and domain constituent parts, nor is user+foo
       broken up into user and foo.

       Substitution of substrings (text that matches patterns inside "()")
       from the matched expression into the result string is requested with
       $1, $2, etc.; specify $$ to produce a $ character as output.  The
       macros in the result string may need to be written as ${n} or $(n) if
       they aren't followed by whitespace.

       Note: since negated patterns (those preceded by !) return a result when
       the expression does not match, substitutions are not available for
       negated patterns.

       # Disallow sender-specified routing. This is a must if you relay mail
       # for other domains.
       /[%!@].*[%!@]/       550 Sender-specified routing rejected

       # Postmaster is OK, that way they can talk to us about how to fix
       # their problem.
       /^postmaster@/       OK

       # Protect your outgoing majordomo exploders
       if !/^owner-/
       /^(.*)-outgoing@(.*)$/  550 Use ${1}@${2} instead

       # These were once common in junk mail.
       /^Subject: make money fast/     REJECT
       /^To: friend@public\.com/       REJECT

       # First skip over base 64 encoded text to save CPU cycles.
       ~^[[:alnum:]+/]{60,}$~          OK

       # Put your own body patterns here.

       postmap(1), Postfix lookup table manager
       pcre_table(5), format of PCRE tables
       cidr_table(5), format of CIDR tables

       Use "postconf readme_directory" or "postconf html_directory" to locate
       this information.
       DATABASE_README, Postfix lookup table overview

       The regexp table lookup code was originally written by:
       LaMont Jones

       That code was based on the PCRE dictionary contributed by:
       Andrew McNamara
       connect.com.au Pty. Ltd.
       Level 3, 213 Miller St
       North Sydney, NSW, Australia

       Adopted and adapted by:
       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