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
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_mail-
box_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
The mailbox pathname is constructed as follows:
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(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 recip-
ient 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 deliv-
ered in qmail maildir format. This format stores one mes-
sage 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 applica-
tion-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 vir-
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.
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 search-
ing by the mail system.
The search order is as follows. The search stops upon the
first successful lookup.
o When the recipient has an optional address exten-
sion the [email protected] address is
looked up first.
With Postfix versions before 2.1, the optional
address extension is always ignored.
o The [email protected] address, without address exten-
sion, is looked up next.
o 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
Alternatively, a table can be provided as a regular-
expression map where patterns are given as regular expres-
sions. 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). Cor-
rupted 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 trou-
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
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 vir-
tual(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.
MAILBOX DELIVERY CONTROLS
A prefix that the virtual(8) delivery agent
prepends to all pathname results from $vir-
tual_mailbox_maps table lookups.
Optional lookup tables with all valid addresses in
the domains that match $virtual_mailbox_domains.
The minimum user ID value that the virtual(8)
delivery agent accepts as a result from $vir-
tual_uid_maps table lookup.
Lookup tables with the per-recipient user ID that
the virtual(8) delivery agent uses while writing to
the recipient's mailbox.
Lookup tables with the per-recipient group ID for
virtual(8) mailbox delivery.
Available in Postfix version 2.0 and later:
Postfix is final destination for the specified list
of domains; mail is delivered via the $vir-
tual_transport mail delivery transport.
The default mail delivery transport and next-hop
destination for final delivery to domains listed
virtual_mailbox_lock (see 'postconf -d' output)
How to lock a UNIX-style virtual(8) mailbox before
The maximal number of attempts to acquire an exclu-
sive lock on a mailbox file or bounce(8) logfile.
The time between attempts to acquire an exclusive
lock on a mailbox file or bounce(8) logfile.
The time after which a stale exclusive mailbox
lockfile is removed.
RESOURCE AND RATE CONTROLS
The maximal number of parallel deliveries to the
same destination via the virtual message delivery
The maximal number of recipients per delivery via
the virtual message delivery transport.
The maximal size in bytes of an individual mailbox
or maildir file, or zero (no limit).
config_directory (see 'postconf -d' output)
The default location of the Postfix main.cf and
master.cf configuration files.
How much time a Postfix daemon process may take to
handle a request before it is terminated by a
built-in watchdog timer.
The maximal number of digits after the decimal
point when logging sub-second delay values.
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 the next service request
The maximal number of connection requests before a
Postfix daemon process terminates.
The process ID of a Postfix command or daemon
The process name of a Postfix command or daemon
queue_directory (see 'postconf -d' output)
The location of the Postfix top-level queue direc-
The syslog facility of Postfix logging.
The mail system name that is prepended to the
process name in syslog records, so that "smtpd"
becomes, for example, "postfix/smtpd".
qmgr(8), queue manager
bounce(8), delivery status reports
postconf(5), configuration parameters
syslogd(8), system logging
VIRTUAL_README, domain hosting howto
The Secure Mailer license must be distributed with this
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 sys-
tem by Daniel Bernstein.
The maildir structure appears in the qmail system by
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
connect.com.au Pty. Ltd.
Level 3, 213 Miller St
North Sydney 2060, NSW, Australia