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
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.
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(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 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(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
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.
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 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 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.
SECURITY
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.
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
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 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
transport.
- virtual_transport (virtual)
- The default mail delivery transport and next-hop
destination for final delivery to domains listed with
$virtual_mailbox_domains.
Available in Postfix version 2.5.3 and later:
- strict_mailbox_ownership (yes)
- Defer delivery when a mailbox file is not owned by its
recipient.
LOCKING CONTROLS
- virtual_mailbox_lock (see 'postconf -d' output)
- How to lock a UNIX-style virtual(8) mailbox before
attempting delivery.
- deliver_lock_attempts (20)
- The maximal number of attempts to acquire an exclusive lock
on a mailbox file or bounce(8) logfile.
- deliver_lock_delay (1s)
- The time between attempts to acquire an exclusive lock on a
mailbox file or bounce(8) logfile.
- stale_lock_time (500s)
- The time after which a stale exclusive mailbox lockfile is
removed.
RESOURCE AND RATE CONTROLS
- virtual_destination_concurrency_limit
($default_destination_concurrency_limit)
- The maximal number of parallel deliveries to the same
destination via the virtual message delivery transport.
- virtual_destination_recipient_limit
($default_destination_recipient_limit)
- The maximal number of recipients per message for the
virtual message delivery transport.
- virtual_mailbox_limit (51200000)
- The maximal size in bytes of an individual
virtual(8) mailbox or maildir file, or zero (no limit).
MISCELLANEOUS CONTROLS
- config_directory (see 'postconf -d' output)
- The default location of the Postfix main.cf and master.cf
configuration files.
- daemon_timeout (18000s)
- How much time a Postfix daemon process may take to handle a
request before it is terminated by a built-in watchdog timer.
- delay_logging_resolution_limit (2)
- The maximal number of digits after the decimal point when
logging sub-second delay values.
- ipc_timeout (3600s)
- The time limit for sending or receiving information over an
internal communication channel.
- max_idle (100s)
- The maximum amount of time that an idle Postfix daemon
process waits for an incoming connection before terminating
voluntarily.
- max_use (100)
- The maximal number of incoming connections that a Postfix
daemon process will service before terminating voluntarily.
- process_id (read-only)
- The process ID of a Postfix command or daemon process.
- process_name (read-only)
- The process name of a Postfix command or daemon
process.
- queue_directory (see 'postconf -d' output)
- The location of the Postfix top-level queue directory.
- syslog_facility (mail)
- The syslog facility of Postfix logging.
- syslog_name (see 'postconf -d' output)
- The mail system name that is prepended to the process name
in syslog records, so that "smtpd" becomes, for example,
"postfix/smtpd".
Available in Postfix version 3.0 and later:
- virtual_delivery_status_filter
($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.
SEE ALSO
qmgr(8), queue manager
bounce(8), delivery status reports
postconf(5), configuration parameters
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