DOKK / manpages / debian 11 / postfix / proxymap.8postfix.en
PROXYMAP(8postfix) PROXYMAP(8postfix)

proxymap - Postfix lookup table proxy server

proxymap [generic Postfix daemon options]


The proxymap(8) server provides read-only or read-write table lookup service to Postfix processes. These services are implemented with distinct service names: proxymap and proxywrite, respectively. The purpose of these services 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.

  • To provide single-updater functionality for lookup tables that do not reliably support multiple writers (i.e. all file-based tables).

The proxymap(8) server implements the following requests:

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

To implement single-updater maps, specify a process limit of 1 in the master.cf file entry for the proxywrite service.

This request is supported in Postfix 2.5 and later.

Delete the data stored under the requested key. The reply is the request completion status code. The maptype:mapname and flags are the same as with the open request.

This request is supported in Postfix 2.5 and later.

Iterate over the specified database. The function is one of DICT_SEQ_FUN_FIRST or DICT_SEQ_FUN_NEXT. The reply is the request completion status code and a lookup key and result value, if found.

This request is supported in Postfix 2.9 and later.

The request completion status is one of OK, RETRY, NOKEY (lookup failed because the key was not found), BAD (malformed request) or DENY (the table is not approved for proxy read or update access).

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 or proxy_write_maps configuration
    parameters, 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 UNIX 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.


Postfix-writable data files should be stored under a dedicated
    directory that is writable only by the Postfix mail system, such as the
    Postfix-owned data_directory.


In particular, Postfix-writable files should never exist in
    root-owned directories. That would open up a particular type of security
    hole where ownership of a file or directory does not match the provider of
    its content.










Problems and transactions are logged to syslogd(8) or
    postlogd(8).










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


The proxymap(8) read-write service does not explicitly
    close lookup tables (even if it did, this could not be relied on, because
    the process may be terminated between table updates). The read-write service
    should therefore not be used with tables that leave persistent storage in an
    inconsistent state between updates (for example, CDB). Tables that support
    "sync on update" should be safe (for example, Berkeley DB) as
    should tables that are implemented by a real DBMS.










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.



  

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

  

  
The directory with Postfix-writable data files (for example: caches,
      pseudo-random numbers).

  

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

  

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

  

  
The maximum amount of time that an idle Postfix daemon process waits for
      an incoming connection before terminating voluntarily.

  

  
The maximal number of incoming connections that a Postfix daemon process
      will service before terminating voluntarily.

  

  
The process ID of a Postfix command or daemon process.

  

  
The process name of a Postfix command or daemon process.

  

  
The lookup tables that the proxymap(8) server is allowed to access
      for the read-only service.




Available in Postfix 2.5 and later:



  

  
The directory with Postfix-writable data files (for example: caches,
      pseudo-random numbers).

  

  
The lookup tables that the proxymap(8) server is allowed to access
      for the read-write service.




Available in Postfix 3.3 and later:



  

  
The master.cf service name of a Postfix daemon process.










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
Wietse Venema
Google, Inc.
111 8th Avenue
New York, NY 10011, USA