    TCP_TABLE(5)                                                      TCP_TABLE(5)

    NAME
           tcp_table - Postfix client/server table lookup protocol

    SYNOPSIS
           postmap -q "string" tcp:host:port

           postmap -q - tcp:host:port <inputfile

    DESCRIPTION
           The  Postfix  mail system uses optional tables for address rewriting or
           mail routing. These tables are usually in dbm or  db  format.  Alterna-
           tively, table lookups can be directed to a TCP server.

           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.

    PROTOCOL DESCRIPTION
           The TCP map class implements a very simple protocol: the client sends a
           request, and the server sends one reply. Requests and replies are  sent
           as  one  line of ASCII text, terminated by the ASCII newline character.
           Request and reply parameters (see below) are separated by whitespace.

           Send and receive operations must complete in 100 seconds.

    REQUEST FORMAT
           Each request specifies a command, a lookup key, and possibly  a  lookup
           result.

           get SPACE key NEWLINE
                  Look up data under the specified key.

           put SPACE key SPACE value NEWLINE
                  This request is currently not implemented.

    REPLY FORMAT
           Each  reply specifies a status code and text. Replies must be no longer
           than 4096 characters including the newline terminator.

           500 SPACE text NEWLINE
                  In case of a lookup request, the requested data does not  exist.
                  In  case  of  an  update request, the request was rejected.  The
                  text describes the nature of the problem.

           400 SPACE text NEWLINE
                  This indicates an error condition. The text describes the nature
                  of the problem. The client should retry the request later.

           200 SPACE text NEWLINE
                  The request was successful. In the case of a lookup request, the
                  text contains an encoded version of the requested data.

    ENCODING
           In request and reply parameters, the  character  %,  each  non-printing
           character, and each whitespace character must be replaced by %XX, where
           XX is the corresponding ASCII hexadecimal character value. The hexadec-
           imal codes can be specified in any case (upper, lower, mixed).

           The  Postfix  client always encodes a request.  The server may omit the
           encoding as long as the reply is guaranteed to not  contain  the  %  or
           NEWLINE character.

    SECURITY
           Do  not  use  TCP  lookup  tables  for security critical purposes.  The
           client-server connection is not protected and the server is not authen-
           ticated.

    BUGS
           Only the lookup method is currently implemented.

           The  client  does  not  hang  up when the connection is idle for a long
           time.

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

    README FILES
           DATABASE_README, Postfix lookup table overview

    LICENSE
           The Secure Mailer license must be distributed with this software.

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

                                                                      TCP_TABLE(5)