---
name: "socketmap_table"
section: "5"
platform: "linux"
package: "postfix"
version: "3.11.7-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "macos"]
url: "https://new.carta.tech/socketmap_table"
---

# socketmap\_table(5)

Postfix socketmap table lookup client

## NAME

socketmap\_table - Postfix socketmap table lookup client

## SYNOPSIS

```
postmap -q "string" socketmap:inet:host:port:name
postmap -q "string" socketmap:unix:pathname:name
postmap -q - socketmap:inet:host:port:name <inputfile
postmap -q - socketmap:unix:pathname:name <inputfile
```

## DESCRIPTION

The Postfix mail system uses optional tables for address rewriting or mail routing. These tables are usually in **lmdb:**, **cdb:**, **hash:**, or **dbm:** format.

The Postfix socketmap client expects TCP endpoint names of the form **inet:***host***:***port***:***name*, or UNIX-domain endpoints of the form **unix:***pathname***:***name*. In both cases, *name* specifies the name field in a socketmap client request (see "REQUEST FORMAT" below).

## PROTOCOL

```

```

Socketmaps use a simple protocol: the client sends one request, and the server sends one reply.  Each request and each reply are sent as one netstring object.

## REQUEST FORMAT

```

```

The socketmap protocol supports only the lookup request. The request has the following form:

- *name* **\<space\>** *key*

  Search the named socketmap for 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.

## REPLY FORMAT

```

```

Replies must have the following form:

- **OK \<space\>** *data*

  The requested data was found.

- **NOTFOUND \<space\>**

  The requested data was not found.

- **TEMP \<space\>** *reason*

  - **TIMEOUT \<space\>** *reason*

  - **PERM \<space\>** *reason*

  The request failed. The reason, if non-empty, is descriptive text.

## PROTOCOL LIMITS

```

```

The Postfix socketmap client requires that replies are no longer than 100000 bytes (not including the netstring encapsulation). This limit can be changed with the socketmap\_max\_reply\_size configuration parameter (Postfix 3.10 and later).

The Postfix socketmap client enforces a 100s time limit to connect to a socketmap server, to send a request, and to receive a reply. It closes an idle connection after 10s, and closes an active connection after 100s. These limits are not (yet) configurable.

## SECURITY

```

```

This map cannot be used for security-sensitive information, because neither the connection nor the server are authenticated.

## CONFIGURATION PARAMETERS

```

```

- **socketmap\_max\_reply\_size (100000)**

  The maximum allowed reply size from a socketmap server, not including the netstring encapsulation.

## SEE ALSO

```
https://cr.yp.to/proto/netstrings.txt, netstring definition
postconf(1), Postfix supported lookup tables
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

```

```

Use "**postconf readme\_directory**" or "**postconf html\_directory**" to locate this information.

```
DATABASE_README, Postfix lookup table overview
```

## BUGS

The protocol time limits are not yet configurable.

## LICENSE

```

```

The Secure Mailer license must be distributed with this software.

## HISTORY

Socketmap support was introduced with Postfix version 2.10.

The socketmap protocol was published with Sendmail v8.13.

## AUTHOR(S)

```
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
Wietse Venema
porcupine.org
```