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<html>
<head>
<title> Postfix Configuration - Address Manipulation</title>
</head>
<body>
<h1><a href="big-picture.html"><img src="small-picture.gif" width="115" height="45"></a> Postfix Configuration - Address Manipulation</h1>
<hr>
<a href="index.html">Up one level</a> |
<a href="basic.html"> Basic Configuration</a> | <a href="uce.html">UCE
Controls</a> | <a href="rate.html"> Rate Controls</a> | <a
href="resource.html"> Resource Controls</a> | Address Manipulation
<h2> Introduction</h2>
Although the initial Postfix release has no address rewriting
language, it can do quite a bit of address manipulation via table
lookup. While a message flows through the Postfix system, its
addresses are mangled in the order described in this document.
<p>
Unless indicated otherwise, all parameters described here are in
the <b>main.cf</b> file. If you change parameters of a running
Postfix system, don't forget to issue a <b>postfix reload</b>
command.
<p>
All mail:
<p>
<ul>
<li> <a href="#standard"> Rewrite addresses to standard form</a>
<p>
<li> <a href="#canonical"> Canonical address mapping</a>
<p>
<li> <a href="#masquerade"> Address masquerading</a>
<p>
<li> <a href="#virtual"> Virtual address mapping</a>
<p>
<li> <a href="#relocated"> Relocated users table</a>
<p>
<li> <a href="#transport"> Mail transport switch</a>
</ul>
<p>
Local delivery:
<p>
<ul>
<li> <a href="#aliases"> Alias database</a>
<p>
<li> <a href="#forward"> Per-user .forward files</a>
<p>
<li> <a href="#luser_relay"> Non-existent users</a>
</ul>
<a name="standard"> <h2> Rewrite addresses to standard form</h2>
Before the <a href="cleanup.8.html">cleanup</a> daemon runs an
address through any lookup table, it first rewrites the address to
the standard <i>user@fully.qualified.domain</i> form, by sending
the address to the <a href="trivial-rewrite.8.html">trivial-rewrite</a>
daemon. The purpose of rewriting to standard form is to reduce the
number of entries needed in lookup tables. The Postfix <a
href="trivial-rewrite.8.html">trivial-rewrite </a> program implements
the following hard-coded address manipulations:
<dl>
<dt>Rewrite <i>@hosta,@hostb:user@site</i> to <i>user@site</i>
<dd>The source route feature has been deprecated. Postfix has no
ability to handle such addresses, other than to strip off the source
route.
<p>
<a name="swap_bangpath">
<dt>Rewrite <i>site!user</i> to <i>user@site</i>
<dd> This feature is controlled by the boolean <b>swap_bangpath</b>
parameter (default: <b>yes</b>). The purpose is to rewrite
<b>UUCP</b>-style addresses to domain style. This is useful only when you
receive mail via <b>UUCP</b>, but it probably does not hurt otherwise.
<p>
<a name="percent_hack">
<dt>Rewrite <i>user%domain</i> to <i>user@domain</i>
<dd> This feature is controlled by the boolean <b>allow_percent_hack</b>
parameter (default: <b>yes</b>). Typically, this is used in order
to deal with monstrosities such as <i>user%domain@otherdomain</i>.
<p>
<a name="append_at_myorigin">
<dt>Rewrite <i>user</i> to <i>user@<a
href="basic.html#myorigin">$myorigin</a></i>
<dd> This feature is controlled by the boolean <b>append_at_myorigin</b>
parameter (default: <b>yes</b>). The purpose is to get consistent
treatment of <i>user</i> on every machine in <b>$myorigin</b>.
<p>
You probably should never turn off this feature, because a lot of
Postfix components expect that all addresses have the form
<i>user@domain</i>.
<p>
If your machine is not the main machine for <b>$myorigin</b> and
you wish to have some users delivered locally without going via
that main machine, make an entry in the <a href="#virtual">virtual</a>
table that redirects <i>user@$myorigin</i> to <i>user@$myhostname</i>.
<p>
<a name="append_dot_mydomain">
<dt>Rewrite <i>user@host</i> to <i>user@host.<a
href="basic.html#mydomain">$mydomain</a></i>
<dd> This feature is controlled by the boolean <b>append_dot_mydomain</b>
parameter (default: <b>yes</b>). The purpose is to get consistent
treatment of different forms of the same hostname.
<p>
Some will argue that rewriting <i>host</i> to <i>host.$mydomain</i>
is bad. That is why it can be turned off. Others like the convenience of having
the local domain appended automatically.
<p>
<a name="strip_trailing_dot">
<dt>Rewrite <i>user@site.</i> to <i>user@site</i> (without the
trailing dot).
</dl>
<a name="canonical"> <h2> Canonical address mapping</h2>
Before the <a href="cleanup.8.html">cleanup</a> daemon stores
inbound mail into the <b>incoming</b> queue, it uses the <a
href="canonical.5.html">canonical</a> table to rewrite all addresses
in message envelopes and in message headers, local or remote. The
mapping is useful to replace login names by <i>Firstname.Lastname</i>
style addresses, or to clean up invalid domains in mail addresses
produced by legacy mail systems.
<p>
Canonical mapping is disabled by default. To enable, edit the <b>
canonical_maps</b> parameter in the <b>main.cf</b> file and
specify one or more lookup tables, separated by whitespace or commas.
For example:
<dl>
<dd><b>canonical_maps = hash:/etc/postfix/canonical</b>
</dl>
<p>
In addition to the canonical maps which are applied to both sender
and recipient addresses, you can specify canonical maps that are
applied only to sender addresses or to recipient addresses. For
example:
<dl>
<dd><b>sender_canonical_maps = hash:/etc/postfix/sender_canonical</b>
<p>
<dd><b>recipient_canonical_maps = hash:/etc/postfix/recipient_canonical</b>
</dl>
<p>
The sender and recipient canonical maps are applied before
the common canonical maps.
<p>
Sender-specific rewriting is useful when you want to rewrite ugly
sender addresses to pretty ones, and still want to be able to
send mail to the those ugly address without creating a mailer loop.
<a name="masquerade"> <h2> Address masquerading</h2>
Address masquerading is a method to hide all hosts below a domain
behind their mail gateway, and to make it appear as if the mail
comes from the gateway itself, instead of from individual machines.
<p>
Address masquerading is disabled by default. To enable, edit the
<b>masquerade_domains</b> parameter in the <b>main.cf</b>
file and specify one or more domain names separated by whitespace
or commas. For example:
<dl>
<dd><b>masquerade_domains = $mydomain</b>
</dl>
<p>
In this example, addresses of the form <i>user@host.$mydomain</i>
would be rewritten to <i>user@$mydomain</i>.
<p>
The <b>masquerade_exceptions</b> configuration parameter specifies
what user names should not be subjected to address masquerading.
Specify one or more user names separated by whitespace or commas.
For example,
<dl>
<dd><b>masquerade_exceptions = root</b>
</dl>
<p>
By default, Postfix makes no exceptions.
<p>
Subtle point: address masquerading is applied only to message
headers and envelope sender addresses, not to envelope recipients.
<a name="virtual"> <h2> Virtual address mapping</h2>
After applying the canonical and masquerade mappings, the <a
href="cleanup.8.html">cleanup</a> daemon uses the <a
href="virtual.5.html">virtual</a> table to redirect mail for all
recipients, local or remote. The mapping affects only envelope
recipients; it has no effect on message headers or envelope senders.
Virtual lookups are useful to redirect mail for virtual domains to
real user mailboxes, and to redirect mail for domains that no longer
exist. Virtual lookups can also be used to transform <i>
Firstname.Lastname </i> back into UNIX login names, although it
seems that local <a href="#aliases">aliases</a> are a more appropriate
vehicle.
<p>
Virtual mapping is disabled by default. To enable, edit the <b>
virtual_maps</b> parameter in the <b>main.cf</b> file and
specify one or more lookup tables, separated by whitespace or
commas. For example:
<dl>
<dd><b>virtual_maps = hash:/etc/postfix/virtual</b>
</dl>
<p>
Addresses found in virtual maps are subjected to another iteration
of virtual mapping, but are not subjected to canonical mapping, in
order to avoid loops.
<a name="relocated"> <h2> Relocated users table</h2>
Next, the queue manager runs each recipient name through the
<a href="relocated.5.html">relocated</a> database. This table
provides information on how to reach users that no longer have an
account, or what to do with mail for entire domains that no longer
exist. When mail is sent to an address that is listed in this
table, the message is bounced with an informative message.
<p>
Lookups of relocated users are disabled by default. To enable, edit
the <b>relocated_maps</b> parameter in the <b>main.cf</b>
file and specify one or more lookup tables, separated by whitespace
or commas. For example:
<dl>
<dd><b>relocated_maps = hash:/etc/postfix/relocated</b>
</dl>
<a name="transport"> <h2> Mail transport switch</h2>
Once the queue manager has established the destination of a message,
the optional <a href="transport.5.html">transport</a> table controls
how the message will be delivered (this table is used by the address
rewriting and resolving daemon). By default, everything is sent
via the <a href="smtp.8.html">smtp</a> transport. The transport
table can be used to send mail to specific sites via <b>UUCP</b>,
or to send mail to a really broken mail system that can handle only
one SMTP connection at a time (yes, such systems exist and people
used to pay real money for them).
<p>
Transport table lookups are disabled by default. To enable, edit
the <b>transport_maps</b> parameter in the <b>main.cf</b> file and
specify one or more lookup tables, separated by whitespace or
commas. For example:
<dl>
<dd><b>transport_maps = hash:/etc/postfix/transport</b>
</dl>
<a name="aliases"> <h2> Alias database</h2>
When mail is to be delivered locally, the <a href="local.8.html">local</a>
delivery agent runs each local recipient name through the <a
href="aliases.5.html"> aliases</a> database. The mapping does not
affect addresses in message headers. Local aliases are typically
used to implement distribution lists, or to direct mail for standard
aliases such as <b>postmaster</b> to real people. The table can
also be used to map <i>Firstname.Lastname</i> addresses to login
names.
<p>
Alias lookups are enabled by default. The default configuration
depends on the system environment, but it is typically one of the
following:
<p>
<dl>
<dd> <b>alias_maps = hash:/etc/aliases</b>
<dd> <b>alias_maps = dbm:/etc/aliases, nis:mail.aliases</b>
</dl>
<p>
The path to the alias database file is controlled via the
<b>alias_database</b> configuration parameter. The value is system
dependent. Usually it is one of the following:
<dl>
<dd> <b>alias_database = hash:/etc/aliases</b> (4.4BSD, LINUX)
<dd> <b>alias_database = dbm:/etc/aliases</b> (4.3BSD, SYSV<4)
<dd> <b>alias_database = dbm:/etc/mail/aliases</b> (SYSV4)
</dl>
<p>
For security reasons, deliveries to command and file destinations
are performed with the rights of the alias database owner. A
default userid, <b>default_privs</b>, is used for deliveries to
commands/files in <i>root</i>-owned aliases.
<a name="forward"> <h2> Per-user .forward files</h2>
Users can control their own mail delivery by specifying destinations
in a file called <b>.forward</b> in their home directories. The
syntax of these files is the same as with system aliases, except
that the lookup key and colon are not present.
<a name="luser_relay"> <h2> Non-existent users</h2>
When the local delivery agent finds that a message recipient does
not exist, the message is normally bounced to the sender ("user
unknown"). Sometimes it is desirable to forward mail for non-existing
recipients to another machine. For this purpose you can specify
an alternative destination with the <b>luser_relay</b> configuration
parameter.
<p>
Alternatively, mail for non-existent recipients can be delegated
to an entirely different message transport, as specified with the
<b>fallback_transport</b> configuration parameter. For details,
see the <a href="local.8.html"> local</a> delivery agent.
<p>
<b>luser_relay</b> can specify one address. It is subjected to
<i>$name</i> expansions. The most useful examples are:
<p>
<dl>
<dt><b>$user@other.host</b>
<dd>The bare username, without address extension, is prepended to
<i>@other.host</i>. For example, mail for <i>username+foo</i> is
sent to <i>username@other.host</i>.
<p>
<dt><b>$mailbox@other.host</b>
<dd>The entire original recipient localpart, including address
extension, is prepended to <i>@other.host</i>. For example, mail
for <i>username+foo</i> is sent to <i>username+foo@other.host</i>.
<p>
<dt><b>sysadmin+$user</b>
<dd>The bare username, without address extension, is appended to
<i>sysadmin</i>. For example, mail for <i>username+foo</i> is sent
to <i>sysadmin+username</i>.
<dt><b>sysadmin+$mailbox</b>
<dd>The entire original recipient localpart, including address
extension, is appended to <i>sysadmin</i>. For example, mail for
<i>username+foo</i> is sent to <i>sysadmin+username+foo</i>.
</dl>
<hr>
<a href="index.html">Up one level</a> |
<a href="basic.html"> Basic Configuration</a> | <a href="uce.html">UCE
Controls</a> | <a href="rate.html"> Rate Controls</a> | <a
href="resource.html"> Resource Controls</a> | Address Manipulation
</body>
</html>
|
