Manual Reference Pages  - MEMCACHE_TABLE (5)


memcache_table - Postfix memcache client configuration




postmap -q "string" memcache:/etc/postfix/filename

postmap -q - memcache:/etc/postfix/filename <inputfile


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 as memcache instances. To use memcache lookups, define a memcache source as a lookup table in, for example:

    virtual_alias_maps = memcache:/etc/postfix/

The file /etc/postfix/ has the same format as the Postfix file, and specifies the parameters described below.

The Postfix memcache client supports the lookup, update, delete and sequence (first/next) operations. The sequence operation requires a backup database that supports the operation.


memcache (default: inet:localhost:11211) The memcache server (note: singular) that Postfix will try to connect to. For a TCP server specify "inet:" followed by a hostname or address, ":", and a port name or number. Specify an IPv6 address inside "[]". For a UNIX-domain server specify "unix:" followed by the socket pathname. Examples:

    memcache =
    memcache = inet:
    memcache = inet:[fc00:8d00:189::3]:11211
    memcache = unix:/path/to/socket

NOTE: to access a UNIX-domain socket with the proxymap(8) server, the socket must be accessible by the unprivileged postfix user.

backup (default: undefined) An optional Postfix database that provides persistent backup for the memcache database. The Postfix memcache client will update the memcache database whenever it looks up or changes information in the persistent database. Specify a Postfix "type:table" database. Examples:

    # Non-shared postscreen cache.
    backup = btree:/var/lib/postfix/postscreen_cache_map

# Shared postscreen cache for processes on the same host. backup = proxy:btree:/var/lib/postfix/postscreen_cache_map

Access to remote proxymap servers is under development.

NOTE 1: When using memcache with persistent backup as postscreen(8) or verify(8) cache, disable automatic cache cleanup (*_cache_cleanup_interval = 0) in all Postfix instances except for one instance that will be responsible for cache cleanup.

NOTE 2: In the case of a proxied backup database, the full backup database name (including the "proxy:" prefix) must be specified in the proxymap server’s proxy_read_maps or proxy_write_maps setting (depending on whether the access is read-only or read-write).

flags (default: 0) Optional flags that should be stored along with a memcache update.
ttl (default: 3600) The expiration time in seconds of memcache updates.

NOTE 1: When using a memcache table as postscreen(8) or verify(8) cache without persistent backup, specify a zero *_cache_cleanup_interval value with all Postfix instances that use the memcache, and specify the largest postscreen(8) *_ttl value or verify(8) *_expire_time value as the memcache table’s ttl value.

NOTE 2: According to memcache protocol documentation, a value greater than 30 days (2592000 seconds) specifies absolute UNIX time. Smaller values are relative to the time of the update.


key_format (default: %s) Format of the lookup and update keys in memcache requests. By default, these are the same as the lookup and update keys that are given to the Postfix memcache client.

NOTE: The key_format feature is not used for backup database requests.

When the same memcache database is used to cache information from multiple tables, you can use the key_format feature to avoid name collisions by prepending a fixed string. Examples:

    key_format = aliases:%s
    key_format = access:%s

The key_format parameter supports the following ’%’ expansions:
%% This is replaced by a literal ’%’ character.
%s This is replaced by the memcache client input key.
%u When the input key is an address of the form user@domain, %u is replaced by the SQL quoted local part of the address. Otherwise, %u is replaced by the entire search string. If the localpart is empty, a lookup is silently suppressed and returns no results (an update is skipped with a warning).
%d When the input key is an address of the form user@domain, %d is replaced by the domain part of the address. Otherwise, a lookup is silently suppressed and returns no results (an update is skipped with a warning).
%[SUD] The upper-case equivalents of the above expansions behave in the key_format parameter identically to their lower-case counter-parts.
%[1-9] The patterns %1, %2, ... %9 are replaced by the corresponding most significant component of the input key’s domain. If the input key is, then %1 is com, %2 is example and %3 is mail. If the input key is unqualified or does not have enough domain components to satisfy all the specified patterns, a lookup is silently suppressed and returns no results (an update is skipped with a warning).

domain (default: no domain list) This feature can significantly reduce database server load. Specify a list of domain names, paths to files, or "type:table" databases. When specified, only fully qualified search keys with a *non-empty* localpart and a matching domain are eligible for lookup or update: bare ’user’ lookups, bare domain lookups and "@domain" lookups are silently skipped (updates are skipped with a warning). Example:

    domain =, hash:/etc/postfix/searchdomains


data_size_limit (default: 10240) The maximal memcache reply data length in bytes.
line_size_limit (default: 1024) The maximal memcache reply line length in bytes.
max_try (default: 2) The number of times to try a memcache command before giving up. The memcache client does not retry a command when the memcache server accepts no connection.
retry_pause (default: 1) The time in seconds before retrying a failed memcache command.
timeout (default: 2) The time limit for sending a memcache command and for receiving a memcache reply.


The Postfix memcache client cannot be used for security-sensitive tables such as alias_maps (these may contain "|command and "/file/name" destinations), or virtual_uid_maps, virtual_gid_maps and virtual_mailbox_maps (these specify UNIX process privileges or "/file/name" destinations). In a typical deployment a memcache database is writable by any process that can talk to the memcache server; in contrast, security-sensitive tables must never be writable by the unprivileged Postfix user.

The Postfix memcache client requires additional configuration when used as postscreen(8) or verify(8) cache. For details see the backup and ttl parameter discussions in the MEMCACHE MAIN PARAMETERS section above.


postmap(1), Postfix lookup table manager
postconf(5), configuration parameters


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


The Secure Mailer license must be distributed with this software.


Memcache support was introduced with Postfix version 2.9.


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

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