VIRTUAL(8) System Manager's Manual VIRTUAL(8)
NAME
virtual - Postfix virtual domain mail delivery agent
SYNOPSIS
virtual [generic Postfix daemon options]
DESCRIPTION
The virtual(8) delivery agent is designed for virtual mail hosting ser-
vices. Originally based on the Postfix local(8) delivery agent, this
agent looks up recipients with map lookups of their full recipient ad-
dress, instead of using hard-coded unix password file lookups of the ad-
dress 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 vir-
tual_mailbox_maps configuration parameters (see below). The vir-
tual_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(8) delivery agent prepends a "From sender time_stamp" enve-
lope 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 mail-
box 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(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
Mailbox ownership is controlled by the virtual_uid_maps and vir-
tual_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.
CASE FOLDING
All delivery decisions are made using the full recipient address, folded
to lower case. See also the next section for a few exceptions with op-
tional address extensions.
TABLE SEARCH ORDER
Normally, a lookup table is specified as a text file that serves as in-
put 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 success-
ful lookup.
• When the recipient has an optional address extension the user+ex-
tension@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.
SECURITY
The virtual(8) delivery agent is not security sensitive, provided that
the lookup tables with recipient user/group ID information are ade-
quately 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.
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 problem cases, mail for an existing recip-
ient is deferred and a warning is logged.
Problems and transactions are logged to syslogd(8) or postlogd(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 trouble.
BUGS
This delivery agent supports address extensions in email addresses and
in lookup table keys, but does not propagate address extension informa-
tion to the result of table lookup.
Postfix should have lookup tables that can return multiple result at-
tributes. In order to avoid the inconvenience of maintaining three ta-
bles, use an LDAP or MYSQL database.
CONFIGURATION PARAMETERS
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.
MAILBOX DELIVERY CONTROLS
virtual_mailbox_base (empty)
A prefix that the virtual(8) delivery agent prepends to all path-
name 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 ac-
cepts 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 the final destination for the specified list of do-
mains; mail is delivered via the $virtual_transport mail delivery
transport.
virtual_transport (virtual)
The default mail delivery transport and next-hop destination for
final delivery to domains listed with $virtual_mailbox_domains.
Available in Postfix version 2.5.3 and later:
strict_mailbox_ownership (yes)
Defer delivery when a mailbox file is not owned by its recipient.
LOCKING CONTROLS
virtual_mailbox_lock (see 'postconf -d' output)
How to lock a UNIX-style virtual(8) mailbox before attempting de-
livery.
deliver_lock_attempts (20)
The maximal number of attempts to acquire an exclusive lock on a
mailbox file or bounce(8) logfile.
deliver_lock_delay (1s)
The time between attempts to acquire an exclusive lock on a mail-
box file or bounce(8) logfile.
stale_lock_time (500s)
The time after which a stale exclusive mailbox lockfile is re-
moved.
RESOURCE AND RATE CONTROLS
virtual_mailbox_limit (51200000)
The maximal size in bytes of an individual virtual(8) mailbox or
maildir file, or zero (no limit).
Implemented in the qmgr(8) daemon:
virtual_destination_concurrency_limit ($default_destination_concur-
rency_limit)
The maximal number of parallel deliveries to the same destination
via the virtual message delivery transport.
virtual_destination_recipient_limit ($default_destination_recipi-
ent_limit)
The maximal number of recipients per message for the virtual mes-
sage delivery transport.
MISCELLANEOUS CONTROLS
config_directory (see 'postconf -d' output)
The default location of the Postfix main.cf and master.cf config-
uration files.
daemon_timeout (18000s)
How much time a Postfix daemon process may take to handle a re-
quest before it is terminated by a built-in watchdog timer.
delay_logging_resolution_limit (2)
The maximal number of digits after the decimal point when logging
sub-second delay values.
ipc_timeout (3600s)
The time limit for sending or receiving information over an in-
ternal communication channel.
max_idle (100s)
The maximum amount of time that an idle Postfix daemon process
waits for an incoming connection before terminating voluntarily.
max_use (100)
The maximal number of incoming connections that a Postfix daemon
process will service before terminating voluntarily.
process_id (read-only)
The process ID of a Postfix command or daemon process.
process_name (read-only)
The process name of a Postfix command or daemon process.
queue_directory (see 'postconf -d' output)
The location of the Postfix top-level queue directory.
syslog_facility (mail)
The syslog facility of Postfix logging.
syslog_name (see 'postconf -d' output)
A prefix that is prepended to the process name in syslog records,
so that, for example, "smtpd" becomes "prefix/smtpd".
Available in Postfix version 3.0 and later:
virtual_delivery_status_filter ($default_delivery_status_filter)
Optional filter for the virtual(8) delivery agent to change the
delivery status code or explanatory text of successful or unsuc-
cessful deliveries.
Available in Postfix version 3.3 and later:
enable_original_recipient (yes)
Enable support for the original recipient address after an ad-
dress 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.).
SEE ALSO
qmgr(8), queue manager
bounce(8), delivery status reports
postconf(5), configuration parameters
postlogd(8), Postfix logging
syslogd(8), system logging
README_FILES
Use "postconf readme_directory" or
"postconf html_directory" to locate this information.
VIRTUAL_README, domain hosting howto
LICENSE
The Secure Mailer license must be distributed with this software.
HISTORY
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
Bernstein.
The maildir structure appears in the qmail system by Daniel Bernstein.
AUTHOR(S)
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
andrewm@connect.com.au
connect.com.au Pty. Ltd.
Level 3, 213 Miller St
North Sydney 2060, NSW, Australia
VIRTUAL(8)
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