VIRTUAL(8)

NAME
virtual - Postfix virtual domain mail delivery agent

SYNOPSIS
virtual [generic Postfix daemon options]

DESCRIPTION
The virtual delivery agent is designed for virtual mail hosting services. Originally based on the Postfix local 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.

MAILBOX LOCATION
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:
$virtual_mailbox_base/$virtual_mailbox_maps(recipient) where recipient is the full recipient address.

UNIX MAILBOX FORMAT
When the mailbox location does not end in /, the message is delivered in UNIX mailbox format. This format stores multiple messages in one textfile. The virtual 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 line. 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.

QMAIL MAILDIR FORMAT
When the mailbox location ends in /, the message is delivered in qmail maildir format. This format stores one message per file. The virtual delivery agent daemon 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
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.

TABLE SEARCH ORDER
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 canonical 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.

•   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.

SECURITY
The virtual 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.

STANDARDS
RFC 822 (ARPA Internet Text Messages)

DIAGNOSTICS
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). 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.

BUGS
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.

CONFIGURATION PARAMETERS
The following main.cf parameters are especially relevant to this program. See the Postfix main.cf file for syntax details and for default values. Use the postfix reload command after a configuration change.

Mailbox delivery

virtual_mailbox_base
    Specifies a path that is prepended to all mailbox or maildir paths. This is a safety measure to ensure that an out of control map in virtual_mailbox_maps doesn't litter the filesystem with mailboxes. While it could be set to "/", this setting isn't recommended.

virtual_mailbox_maps
    Recipients are looked up in these maps to determine the path to their mailbox or maildir. If the returned path ends in a slash ("/"), maildir-style delivery is carried out, otherwise the path is assumed to specify a UNIX-style mailbox file. While searching a lookup table, an address extension (user+foo@domain.tld) is ignored. In a lookup table, specify a left-hand side of @domain.tld to match any user in the specified domain that does not have a specific user@domain.tld entry. Note that virtual_mailbox_base is unconditionally prepended to this path. For security reasons, regular expression maps are allowed but regular expression substitution of $1 etc. is disallowed, because that would open a security hole. For security reasons, proxied table lookup is not allowed, because that would open a security hole.

virtual_mailbox_domains
    The list of domains that should be delivered via the Postfix virtual delivery agent. This uses the same syntax as the mydestination configuration parameter.

virtual_minimum_uid
    Specifies a minimum uid that will be accepted as a return from a virtual_uid_maps lookup. Returned values less than this will be rejected, and the message will be deferred.

virtual_uid_maps
    Recipients are looked up in these maps to determine the user ID to be used when writing to the target mailbox. While searching a lookup table, an address extension (user+foo@domain.tld) is ignored. In a lookup table, specify a left-hand side of @domain.tld to match any user in the specified domain that does not have a specific user@domain.tld entry. For security reasons, regular expression maps are allowed but regular expression substitution of $1 etc. is disallowed, because that would open a security hole. For security reasons, proxied table lookup is not allowed, because that would open a security hole.

virtual_gid_maps
    Recipients are looked up in these maps to determine the group ID to be used when writing to the target mailbox. While searching a lookup table, an address extension (user+foo@domain.tld) is ignored. In a lookup table, specify a left-hand side of @domain.tld to match any user in the specified domain that does not have a specific user@domain.tld entry. For security reasons, regular expression maps are allowed but regular expression substitution of $1 etc. is disallowed, because that would open a security hole. For security reasons, proxied table lookup is not allowed, because that would open a security hole.

Locking controls

virtual_mailbox_lock
    How to lock UNIX-style mailboxes: one or more of flock, fcntl or dotlock. The dotlock method requires that the recipient UID or GID has write access to the parent directory of the mailbox file. This setting is ignored with maildir style delivery, because such deliveries are safe without explicit locks. Use the command postconf -l to find out what locking methods are available on your system.

deliver_lock_attempts
    Limit the number of attempts to acquire an exclusive lock on a UNIX-style mailbox file.

deliver_lock_delay
    Time (default: seconds) between successive attempts to acquire an exclusive lock on a UNIX-style mailbox file. The actual delay is slightly randomized.

stale_lock_time
    Limit the time after which a stale lockfile is removed (applicable to UNIX-style mailboxes only).

Resource controls

virtual_destination_concurrency_limit
    Limit the number of parallel deliveries to the same domain via the virtual delivery agent. The default limit is taken from the default_destination_concurrency_limit parameter. The limit is enforced by the Postfix queue manager.

virtual_destination_recipient_limit
    Limit the number of recipients per message delivery via the virtual delivery agent. The default limit is taken from the default_destination_recipient_limit parameter. The limit is enforced by the Postfix queue manager.

virtual_mailbox_limit
    The maximal size in bytes of a mailbox or maildir file. Set to zero to disable the limit.

HISTORY
This 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: header appears in the qmail system by Daniel Bernstein. The maildir structure appears in the qmail system by Daniel Bernstein.

SEE ALSO
regexp_table(5) POSIX regular expression table format
pcre_table(5) Perl Compatible Regular Expression table format
bounce(8) non-delivery status reports
syslogd(8) system logging
qmgr(8) queue manager

LICENSE
The Secure Mailer license must be distributed with this software.

AUTHOR(S)
Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
Andrew McNamara
andrewm@connect.com.au
connect.com.au Pty. Ltd.
Level 3, 213 Miller St
North Sydney 2060, NSW, Australia