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<h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Postfix Address Classes </h1>
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<h2>Introduction</h2>
<p> Postfix version 2.0 introduces the concept of address classes.
This is a way of grouping recipient addresses by their delivery
method. The idea comes from discussions with Victor Duchovni.
Although address classes introduced a few incompatibilities they
also made it possible to improve the handling of <a href="VIRTUAL_README.html#canonical">hosted domains</a>
and of unknown recipients. </p>
<p> This document provides information on the following topics: </p>
<ul>
<li><a href="#wtf">What are address classes good for?</a>
<li><a href="#classes">What address classes does Postfix implement?</a>
<li><a href="#improvements">Improvements compared to Postfix 1.1</a>
<li><a href="#incompatibility">Incompatibilities with Postfix 1.1</a>
</ul>
<h2><a name="wtf">What are address classes good for?</a></h2>
<p> Why should you care about address classes? This is how Postfix
decides what mail to accept, and how to deliver it. In other words,
address classes are very important for the operation of Postfix. </p>
<p> An address class is defined by three items. </p>
<ul>
<li> <p> The list of domains that are a member of the class: for
example, all <a href="ADDRESS_CLASS_README.html#local_domain_class">local domains</a>, or all <a href="ADDRESS_CLASS_README.html#relay_domain_class">relay domains</a>. </p>
<li> <p> The default delivery transport. For example, the local,
virtual or relay delivery transport (delivery transports are defined
in <a href="master.5.html">master.cf</a>). This helps to keep Postfix configurations simple,
by avoiding the need for explicit routing information in transport
maps. </p>
<li> <p> The list of valid recipient addresses for that address
class. The Postfix SMTP server rejects invalid recipients with
"User unknown in <name of address class here> table". This
helps to keep the Postfix queue free of undeliverable MAILER-DAEMON
messages. </p>
</ul>
<h2><a name="classes">What address classes does Postfix implement?</a></h2>
<p> Initially the list of address classes is hard coded, but this
is meant to become extensible. The summary below describes the main
purpose of each class, and what the relevant configuration parameters
are. </p>
<p> The <a name="local_domain_class">local </a> domain class. </p>
<ul>
<li> <p> Purpose: final delivery for traditional UNIX system accounts
and traditional Sendmail-style aliases. This is typically used for
the <a href="VIRTUAL_README.html#canonical">canonical domains</a> of the machine. For a discussion of the
difference between <a href="VIRTUAL_README.html#canonical">canonical domains</a>, <a href="VIRTUAL_README.html#canonical">hosted domains</a> and other
domains, see the <a href="VIRTUAL_README.html">VIRTUAL_README</a> file. </p>
<li> <p> Domain names are listed with the <a href="postconf.5.html#mydestination">mydestination</a> parameter.
This domain class also includes mail for <i>user@[ipaddress]</i>
when the IP address is listed with the <a href="postconf.5.html#inet_interfaces">inet_interfaces</a> or
<a href="postconf.5.html#proxy_interfaces">proxy_interfaces</a> parameters. </p>
<li> <p> Valid recipient addresses are listed with the <a href="postconf.5.html#local_recipient_maps">local_recipient_maps</a>
parameter, as described in <a href="LOCAL_RECIPIENT_README.html">LOCAL_RECIPIENT_README</a>. The Postfix SMTP
server rejects invalid recipients with "User unknown in local
recipient table". If the <a href="postconf.5.html#local_recipient_maps">local_recipient_maps</a> parameter value is
empty, then the Postfix SMTP server accepts any address in the
<a href="ADDRESS_CLASS_README.html#local_domain_class">local domain</a> class. </p>
<li> <p> The mail delivery transport is specified with the
<a href="postconf.5.html#local_transport">local_transport</a> parameter. The default value is <b><a href="local.8.html">local</a>:$<a href="postconf.5.html#myhostname">myhostname</a></b>
for delivery with the <a href="local.8.html">local(8)</a> delivery agent. </p>
</ul>
<p> The <a name="virtual_alias_class">virtual alias </a> domain
class. </p>
<ul>
<li> <p> Purpose: <a href="VIRTUAL_README.html#canonical">hosted domains</a> where each recipient address is
aliased to a local UNIX system account or to a remote address. A
<a href="VIRTUAL_README.html#virtual_alias">virtual alias example</a> is given in the <a href="VIRTUAL_README.html">VIRTUAL_README</a> file. </p>
<li> <p> Domain names are listed in <a href="postconf.5.html#virtual_alias_domains">virtual_alias_domains</a>. The
default value is $<a href="postconf.5.html#virtual_alias_maps">virtual_alias_maps</a> for Postfix 1.1 compatibility.
</p>
<li> <p> Valid recipient addresses are listed with the <a href="postconf.5.html#virtual_alias_maps">virtual_alias_maps</a>
parameter. The Postfix SMTP server rejects invalid recipients with
"User unknown in virtual alias table". The default value is
$<a href="postconf.5.html#virtual_maps">virtual_maps</a> for Postfix 1.1 compatibility. </p>
<li> <p> There is no mail delivery transport parameter. Every
address must be aliased to some other address. </p>
</ul>
<p> The <a name="virtual_mailbox_class">virtual mailbox </a> domain
class. </p>
<ul>
<li> <p> Purpose: final delivery for <a href="VIRTUAL_README.html#canonical">hosted domains</a> where each
recipient address can have its own mailbox, and where users do not
need to have a UNIX system account. A <a href="VIRTUAL_README.html#virtual_mailbox">virtual mailbox example</a> is
given in the <a href="VIRTUAL_README.html">VIRTUAL_README</a> file. </p>
<li> <p> Domain names are listed with the <a href="postconf.5.html#virtual_mailbox_domains">virtual_mailbox_domains</a>
parameter. The default value is $<a href="postconf.5.html#virtual_mailbox_maps">virtual_mailbox_maps</a> for Postfix
1.1 compatibility. </p>
<li> <p> Valid recipient addresses are listed with the <a href="postconf.5.html#virtual_mailbox_maps">virtual_mailbox_maps</a>
parameter. The Postfix SMTP server rejects invalid recipients with
"User unknown in virtual mailbox table". If this parameter value
is empty, the Postfix SMTP server accepts all recipients for domains
listed in $<a href="postconf.5.html#virtual_mailbox_domains">virtual_mailbox_domains</a>. </p>
<li> <p> The mail delivery transport is specified with the
<a href="postconf.5.html#virtual_transport">virtual_transport</a> parameter. The default value is <b>virtual</b>
for delivery with the <a href="virtual.8.html">virtual(8)</a> delivery agent. </p>
</ul>
<p> The <a name="relay_domain_class">relay </a> domain class. </p>
<ul>
<li> <p> Purpose: mail forwarding to remote destinations that list
your system as primary or backup MX host. For a discussion of the
basic configuration details, see the <a href="BASIC_CONFIGURATION_README.html">BASIC_CONFIGURATION_README</a>
document. For a discussion of the difference between canonical
domains, <a href="VIRTUAL_README.html#canonical">hosted domains</a> and other domains, see the <a href="VIRTUAL_README.html">VIRTUAL_README</a>
file. </p>
<li> <p> Domain names are listed with the <a href="postconf.5.html#relay_domains">relay_domains</a> parameter.
</p>
<li> <p> Valid recipient addresses are listed with the <a href="postconf.5.html#relay_recipient_maps">relay_recipient_maps</a>
parameter. The Postfix SMTP server rejects invalid recipients with
"User unknown in relay recipient table". If this parameter value
is empty, the Postfix SMTP server accepts all recipients for domains
listed with the <a href="postconf.5.html#relay_domains">relay_domains</a> parameter. </p>
<li> <p> The mail delivery transport is specified with the
<a href="postconf.5.html#relay_transport">relay_transport</a> parameter. The default value is <b>relay</b> which
is a clone of the <a href="smtp.8.html">smtp(8)</a> delivery agent. </p>
</ul>
<p> The <a name="default_domain_class">default </a> domain class.
</p>
<ul>
<li> <p> Purpose: mail forwarding to the Internet on behalf of
authorized clients. For a discussion of the basic configuration
details, see the <a href="BASIC_CONFIGURATION_README.html">BASIC_CONFIGURATION_README</a> file. For a discussion
of the difference between <a href="VIRTUAL_README.html#canonical">canonical domains</a>, <a href="VIRTUAL_README.html#canonical">hosted domains</a> and
other domains, see the <a href="VIRTUAL_README.html">VIRTUAL_README</a> file. </p>
<li> <p> This class has no destination domain table. </p>
<li> <p> This class has no valid recipient address table. </p>
<li> <p> The mail delivery transport is specified with the
<a href="postconf.5.html#default_transport">default_transport</a> parameter. The default value is <b>smtp</b> for
delivery with the <a href="smtp.8.html">smtp(8)</a> delivery agent. </p>
</ul>
<h2><a name="improvements">Improvements compared to Postfix
1.1</a></h2>
<p> Postfix 2.0 address classes made the following improvements
possible over earlier Postfix versions: </p>
<ul>
<li> <p> You no longer need to specify all the <a href="virtual.8.html">virtual(8)</a> mailbox
domains in the Postfix transport map. The <a href="virtual.8.html">virtual(8)</a> delivery agent
has become a first-class citizen just like <a href="local.8.html">local(8)</a> or <a href="smtp.8.html">smtp(8)</a>.
</p>
<li> <p> On mail gateway systems, address classes provide separation
of inbound mail relay traffic ($<a href="postconf.5.html#relay_transport">relay_transport</a>) from outbound
traffic ($<a href="postconf.5.html#default_transport">default_transport</a>). This eliminates a problem where
inbound mail deliveries could become resource starved in the presence
of a high volume of outbound mail. </p>
<li> <p> The SMTP server rejects unknown recipients in a more
consistent manner than was possible with Postfix version 1. This
is needed to keep undeliverable mail (and bounced undeliverable
mail) out of the mail queue. This is controlled by the
<a href="postconf.5.html#smtpd_reject_unlisted_recipient">smtpd_reject_unlisted_recipient</a> configuration parameter. </p>
<li> <p> As of Postfix version 2.1, the SMTP server also rejects
unknown sender addresses (i.e. addresses that it would reject as
unknown recipient addresses). Sender "egress filtering" can help
to slow down an email worm explosion. This is controlled by the
<a href="postconf.5.html#smtpd_reject_unlisted_sender">smtpd_reject_unlisted_sender</a> configuration parameter. </p>
</ul>
<h2><a name="incompatibility">Incompatibilities with Postfix 1.1</a></h2>
<p> Postfix 2.0 address classes introduce a few incompatible changes
in documented behavior. In order to ease the transitions, new
parameters have default values that are backwards compatible. </p>
<ul>
<li> <p> The <a href="postconf.5.html#virtual_maps">virtual_maps</a> parameter is replaced by <a href="postconf.5.html#virtual_alias_maps">virtual_alias_maps</a>
(for address lookups) and by <a href="postconf.5.html#virtual_alias_domains">virtual_alias_domains</a> (for the names
of what were formerly called "Postfix-style virtual domains"). </p>
<p> For backwards compatibility with Postfix version 1.1, the new
<a href="postconf.5.html#virtual_alias_maps">virtual_alias_maps</a> parameter defaults to $<a href="postconf.5.html#virtual_maps">virtual_maps</a>, and the
new <a href="postconf.5.html#virtual_alias_domains">virtual_alias_domains</a> parameter defaults to $<a href="postconf.5.html#virtual_alias_maps">virtual_alias_maps</a>.
</p>
<li> <p> The <a href="postconf.5.html#virtual_mailbox_maps">virtual_mailbox_maps</a> parameter now has a companion
parameter called <a href="postconf.5.html#virtual_mailbox_domains">virtual_mailbox_domains</a> (for the names of domains
served by the virtual delivery agent). The <a href="postconf.5.html#virtual_mailbox_maps">virtual_mailbox_maps</a>
parameter is now used for address lookups only. </p>
<p> For backwards compatibility with Postfix version 1.1, the new
<a href="postconf.5.html#virtual_mailbox_domains">virtual_mailbox_domains</a> parameter defaults to $<a href="postconf.5.html#virtual_mailbox_maps">virtual_mailbox_maps</a>.
</p>
<li> <p> Introduction of the <a href="postconf.5.html#relay_recipient_maps">relay_recipient_maps</a> parameter. The
Postfix SMTP server can use this to block mail for relay recipients
that don't exist. This list is empty by default, which means accept
any recipient. </p>
<li> <p> The <a href="postconf.5.html#local_recipient_maps">local_recipient_maps</a> feature is now turned on by
default. The Postfix SMTP server uses this to reject mail for
unknown local recipients. See the <a href="LOCAL_RECIPIENT_README.html">LOCAL_RECIPIENT_README</a> file hints
and tips. </p>
<li> <p> Introduction of the relay delivery transport in <a href="master.5.html">master.cf</a>.
This helps to avoid mail delivery scheduling problems on inbound
mail relays when there is a lot of outbound mail, but may require
that you update your "<a href="postconf.5.html#defer_transports">defer_transports</a>" setting. </p>
</ul>
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