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TCP_TABLE(5) File Formats Manual TCP_TABLE(5)

tcp_table - Postfix client/server table lookup protocol

postmap -q "string" tcp:host:port
postmap -q - tcp:host:port <inputfile

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

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.

The tcp_table protocol supports only the lookup request. The request has the
  following form:
Look up data under the specified key.

Postfix will not generate partial search keys such as domain names without one or more subdomains, network addresses without one or more least-significant octets, or email addresses without the localpart, address extension or domain portion. This behavior is also found with cidr:, pcre:, and regexp: tables.

Each reply specifies a status code and text. Replies must be no longer than 4096
  characters including the newline terminator.
In case of a lookup request, the requested data does not exist. The text describes the nature of the problem.
This indicates an error condition. The text describes the nature of the problem. The client should retry the request later.
The request was successful. In the case of a lookup request, the text contains an encoded version of the requested data.

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 hexadecimal 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.

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

Only the lookup method is currently implemented.

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

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

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

The Secure Mailer license must be distributed with this software.

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