proxymap - Postfix lookup table proxy server

proxymap [generic Postfix daemon options]

The proxymap(8) server provides read-only table lookup service to Postfix processes. The purpose of the service is:

•

To overcome chroot restrictions. For example, a chrooted SMTP server needs access to the system passwd file in order to reject mail for non-existent local addresses, but it is not practical to maintain a copy of the passwd file in the chroot jail. The solution: local_recipient_maps = proxy:unix:passwd.byname $alias_maps

•

To consolidate the number of open lookup tables by sharing one open table among multiple processes. For example, making mysql connections from every Postfix daemon process results in "too many connections" errors. The solution: virtual_alias_maps = proxy:mysql:/etc/postfix/virtual_alias.cf The total number of connections is limited by the number of proxymap server processes.

The proxymap(8) server implements the following requests:

open maptype:mapname flags

Open the table with type maptype and name mapname, as controlled by flags. The reply includes the maptype dependent flags (to distinguish a fixed string table from a regular expression table).

lookup maptype:mapname flags key

Look up the data stored under the requested key. The reply is the request completion status code (below) and the lookup result value. The maptype:mapname and flags are the same as with the open request.

There is no close command, nor are tables implicitly closed when a client disconnects. The purpose is to share tables among multiple client processes.

proxymap(8) servers run under control by the Postfix master(8) server. Each server can handle multiple simultaneous connections. When all servers are busy while a client connects, the master(8) creates a new proxymap(8) server process, provided that the process limit is not exceeded. Each server terminates after serving at least $max_use clients or after $max_idle seconds of idle time.

The proxymap(8) server opens only tables that are approved via the proxy_read_maps configuration parameter, does not talk to users, and can run at fixed low privilege, chrooted or not. However, running the proxymap server chrooted severely limits usability, because it can open only chrooted tables.

The proxymap(8) server is not a trusted daemon process, and must not be used to look up sensitive information such as user or group IDs, mailbox file/directory names or external commands.

In Postfix version 2.2 and later, the proxymap client recognizes requests to access a table for security-sensitive purposes, and opens the table directly. This allows the same main.cf setting to be used by sensitive and non-sensitive processes.

Problems and transactions are logged to syslogd(8).

The proxymap(8) server provides service to multiple clients, and must therefore not be used for tables that have high-latency lookups.

On busy mail systems a long time may pass before proxymap(8) relevant changes to main.cf are picked up. Use the command "postfix reload" to speed up a change.

The text below provides only a parameter summary. See postconf(5) for more details including examples.

config_directory (see 'postconf -d' output)

The default location of the Postfix main.cf and master.cf configuration files.

daemon_timeout (18000s)

How much time a Postfix daemon process may take to handle a request before it is terminated by a built-in watchdog timer.

ipc_timeout (3600s)

The time limit for sending or receiving information over an internal communication channel.

max_idle (100s)

The maximum amount of time that an idle Postfix daemon process waits for the next service request before exiting.

max_use (100)

The maximal number of connection requests before a Postfix daemon process terminates.

process_id (read-only)

The process ID of a Postfix command or daemon process.

process_name (read-only)

The process name of a Postfix command or daemon process.

proxy_read_maps (see 'postconf -d' output)

The lookup tables that the proxymap(8) server is allowed to access.

postconf(5), configuration parameters
master(5), generic daemon options

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.

The proxymap service was introduced with Postfix 2.0.

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