Updated: 2021/Apr/14

VIRTUAL(8)                  System Manager's Manual                 VIRTUAL(8)

       virtual - Postfix virtual domain mail delivery agent

       virtual [generic Postfix daemon options]

       The virtual(8) delivery agent is designed for virtual mail hosting
       services. Originally based on the Postfix local(8) delivery agent, this
       agent looks up recipients with map lookups of their full recipient
       address, instead of using hard-coded unix password file lookups of the
       address local part only.

       This delivery agent only delivers mail.  Other features such as mail
       forwarding, out-of-office notifications, etc., must be configured via
       virtual_alias maps or via similar lookup mechanisms.

       The mailbox location is controlled by the virtual_mailbox_base and
       virtual_mailbox_maps configuration parameters (see below).  The
       virtual_mailbox_maps table is indexed by the recipient address as
       described under TABLE SEARCH ORDER below.

       The mailbox pathname is constructed as follows:


       where recipient is the full recipient address.

       When the mailbox location does not end in /, the message is delivered
       in UNIX mailbox format.   This format stores multiple messages in one

       The virtual(8) delivery agent prepends a "From sender time_stamp"
       envelope header to each message, prepends a Delivered-To: message
       header with the envelope recipient address, prepends an X-Original-To:
       header with the recipient address as given to Postfix, prepends a
       Return-Path: message header with the envelope sender address, prepends
       a > character to lines beginning with "From ", and appends an empty

       The mailbox is locked for exclusive access while delivery is in
       progress. In case of problems, an attempt is made to truncate the
       mailbox to its original length.

       When the mailbox location ends in /, the message is delivered in qmail
       maildir format. This format stores one message per file.

       The virtual(8) delivery agent prepends a Delivered-To: message header
       with the final envelope recipient address, prepends an X-Original-To:
       header with the recipient address as given to Postfix, and prepends a
       Return-Path: message header with the envelope sender address.

       By definition, maildir format does not require application-level file
       locking during mail delivery or retrieval.

       Mailbox ownership is controlled by the virtual_uid_maps and
       virtual_gid_maps lookup tables, which are indexed with the full
       recipient address. Each table provides a string with the numerical user
       and group ID, respectively.

       The virtual_minimum_uid parameter imposes a lower bound on numerical
       user ID values that may be specified in any virtual_uid_maps.

       All delivery decisions are made using the full recipient address,
       folded to lower case. See also the next section for a few exceptions
       with optional address extensions.

       Normally, a lookup table is specified as a text file that serves as
       input to the postmap(1) command. The result, an indexed file in dbm or
       db format, is used for fast searching by the mail system.

       The search order is as follows. The search stops upon the first
       successful lookup.

       ⊕      When the recipient has an optional address extension the
              user+extension@domain.tld address is looked up first.

              With Postfix versions before 2.1, the optional address extension
              is always ignored.

       ⊕      The user@domain.tld address, without address extension, is
              looked up next.

       ⊕      Finally, the recipient @domain is looked up.

       When the table is provided via other means such as NIS, LDAP or SQL,
       the same lookups are done as for ordinary indexed files.

       Alternatively, a table can be provided as a regular-expression map
       where patterns are given as regular expressions. In that case, only the
       full recipient address is given to the regular-expression map.

       The virtual(8) delivery agent is not security sensitive, provided that
       the lookup tables with recipient user/group ID information are
       adequately protected. This program is not designed to run chrooted.

       The virtual(8) delivery agent disallows regular expression substitution
       of $1 etc. in regular expression lookup tables, because that would open
       a security hole.

       The virtual(8) delivery agent will silently ignore requests to use the
       proxymap(8) server. Instead it will open the table directly. Before
       Postfix version 2.2, the virtual delivery agent will terminate with a
       fatal error.

       RFC 822 (ARPA Internet Text Messages)

       Mail bounces when the recipient has no mailbox or when the recipient is
       over disk quota. In all other cases, mail for an existing recipient is
       deferred and a warning is logged.

       Problems and transactions are logged to syslogd(8) or postlogd(8).
       Corrupted message files are marked so that the queue manager can move
       them to the corrupt queue afterwards.

       Depending on the setting of the notify_classes parameter, the
       postmaster is notified of bounces and of other trouble.

       This delivery agent supports address extensions in email addresses and
       in lookup table keys, but does not propagate address extension
       information to the result of table lookup.

       Postfix should have lookup tables that can return multiple result
       attributes. In order to avoid the inconvenience of maintaining three
       tables, use an LDAP or MYSQL database.

       Changes to main.cf are picked up automatically, as virtual(8) processes
       run for only a limited amount of time. 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.


       virtual_mailbox_base (empty)
              A prefix that the virtual(8) delivery agent prepends to all
              pathname results from $virtual_mailbox_maps table lookups.

       virtual_mailbox_maps (empty)
              Optional lookup tables with all valid addresses in the domains
              that match $virtual_mailbox_domains.

       virtual_minimum_uid (100)
              The minimum user ID value that the virtual(8) delivery agent
              accepts as a result from $virtual_uid_maps table lookup.

       virtual_uid_maps (empty)
              Lookup tables with the per-recipient user ID that the virtual(8)
              delivery agent uses while writing to the recipient's mailbox.

       virtual_gid_maps (empty)
              Lookup tables with the per-recipient group ID for virtual(8)
              mailbox delivery.

       Available in Postfix version 2.0 and later:

       virtual_mailbox_domains ($virtual_mailbox_maps)
              Postfix is final destination for the specified list of domains;
              mail is delivered via the $virtual_transport mail delivery

       virtual_transport (virtual)
              The default mail delivery transport and next-hop destination for
              final delivery to domains listed with $virtual_mailbox_domains.

       Available in Postfix version 2.5.3 and later:

       strict_mailbox_ownership (yes)
              Defer delivery when a mailbox file is not owned by its


       virtual_mailbox_lock (see 'postconf -d' output)
              How to lock a UNIX-style virtual(8) mailbox before attempting

       deliver_lock_attempts (20)
              The maximal number of attempts to acquire an exclusive lock on a
              mailbox file or bounce(8) logfile.

       deliver_lock_delay (1s)
              The time between attempts to acquire an exclusive lock on a
              mailbox file or bounce(8) logfile.

       stale_lock_time (500s)
              The time after which a stale exclusive mailbox lockfile is


       virtual_mailbox_limit (51200000)
              The maximal size in bytes of an individual virtual(8) mailbox or
              maildir file, or zero (no limit).

       Implemented in the qmgr(8) daemon:

              The maximal number of parallel deliveries to the same
              destination via the virtual message delivery transport.

              The maximal number of recipients per message for the virtual
              message delivery transport.


       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.

       delay_logging_resolution_limit (2)
              The maximal number of digits after the decimal point when
              logging sub-second delay values.

       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 an incoming connection before terminating voluntarily.

       max_use (100)
              The maximal number of incoming connections that a Postfix daemon
              process will service before terminating voluntarily.

       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.

       queue_directory (see 'postconf -d' output)
              The location of the Postfix top-level queue directory.

       syslog_facility (mail)
              The syslog facility of Postfix logging.

       syslog_name (see 'postconf -d' output)
              A prefix that is prepended to the process name in syslog
              records, so that, for example, "smtpd" becomes "prefix/smtpd".

       Available in Postfix version 3.0 and later:

       virtual_delivery_status_filter ($default_delivery_status_filter)
              Optional filter for the virtual(8) delivery agent to change the
              delivery status code or explanatory text of successful or
              unsuccessful deliveries.

       Available in Postfix version 3.3 and later:

       enable_original_recipient (yes)
              Enable support for the original recipient address after an
              address is rewritten to a different address (for example with
              aliasing or with canonical mapping).

       service_name (read-only)
              The master.cf service name of a Postfix daemon process.

       Available in Postfix 3.5 and later:

       info_log_address_format (external)
              The email address form that will be used in non-debug logging
              (info, warning, etc.).

       qmgr(8), queue manager
       bounce(8), delivery status reports
       postconf(5), configuration parameters
       postlogd(8), Postfix logging
       syslogd(8), system logging

       Use "postconf readme_directory" or
       "postconf html_directory" to locate this information.
       VIRTUAL_README, domain hosting howto

       The Secure Mailer license must be distributed with this software.

       This delivery agent was originally based on the Postfix local delivery
       agent. Modifications mainly consisted of removing code that either was
       not applicable or that was not safe in this context: aliases,
       ~user/.forward files, delivery to "|command" or to /file/name.

       The Delivered-To: message header appears in the qmail system by Daniel

       The maildir structure appears in the qmail system by Daniel Bernstein.

       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

       Andrew McNamara
       connect.com.au Pty. Ltd.
       Level 3, 213 Miller St
       North Sydney 2060, NSW, Australia