Postfix manual - regexp_table(5)

    REGEXP_TABLE(5)                                   REGEXP_TABLE(5)

    NAME
           regexp_table - format of Postfix regular expression tables

    SYNOPSIS
           postmap -fq "string" regexp:/etc/postfix/filename

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

    DESCRIPTION
           The Postfix mail system uses optional tables  for  address
           rewriting or mail routing. These tables are usually in dbm
           or db format.

           Alternatively, lookup tables can  be  specified  in  POSIX
           regular  expression form. In this case, each input is com-
           pared against a list of patterns,  and  when  a  match  is
           found the corresponding result is returned.

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

           To test lookup tables, use  the  postmap  -fq  command  as
           described in the SYNOPSIS above.

    TABLE FORMAT
           The general form of a Postfix regular expression table is:

           /pattern/flags result
                  When pattern matches the input string, use the cor-
                  responding result value.

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

           if /pattern/flags

           endif  Match the input string against the patterns between
                  if and endif, if and only if that same input string
                  also matches pattern. The if..endif can nest.

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

           if !/pattern/flags

           endif  Match the input string against the patterns between
                  if and endif, if and only if that same input string
                  does not match pattern. The if..endif can nest.

           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  logi-
                  cal line.

           Each  pattern  is a POSIX regular expression enclosed by a
           pair of delimiters. The regular expression syntax is docu-
           mented  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 character, except
           whitespace or characters that have special meaning (tradi-
           tionally  the  forward slash is used). The regular expres-
           sion can contain whitespace.

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

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

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

           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.

    TABLE SEARCH ORDER
           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.

    TEXT SUBSTITUTION
           Substitution of substrings  from  the  matched  expression
           into the result string is possible using $1, $2, etc.. 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.

    EXAMPLE SMTPD ACCESS MAP
           # 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
           endif

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

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

           # Put your own body patterns here.

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

    README FILES
           DATABASE_README, Postfix lookup table overview

    AUTHOR(S)
           The regexp table lookup code was originally written by:
           LaMont Jones
           lamont@hp.com

           That code was based on the PCRE dictionary contributed by:
           Andrew McNamara
           andrewm@connect.com.au
           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

                                                      REGEXP_TABLE(5)