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