278 lines
9.8 KiB
HTML
278 lines
9.8 KiB
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<!doctype html public "-//W3C//DTD HTML 4.01 Transitional//EN"
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"http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<head>
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<title>Postfix Address Classes </title>
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<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
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</head>
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<body>
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<h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Postfix Address Classes </h1>
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<hr>
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<h2>Introduction</h2>
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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 hosted domains
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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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<ul>
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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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</ul>
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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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<ul>
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<li> <p> The list of domains that are a member of the class: for
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example, all local domains, or all relay domains. </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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simple. </p>
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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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messages. </p>
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</ul>
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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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are. </p>
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<p> The <a name="local_domain_class">local </a> domain class. </p>
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<ul>
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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 canonical domains of the machine. For a discussion of the
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difference between canonical domains, hosted domains and other
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domains, see the VIRTUAL_README file. </p>
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<li> <p> Domain names are listed with the mydestination 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 inet_interfaces or
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proxy_interfaces parameters. </p>
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<li> <p> Valid recipient addresses are listed with the local_recipient_maps
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parameter, as described in LOCAL_RECIPIENT_README. The Postfix SMTP
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server rejects invalid recipients with "User unknown in local
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recipient table". If the local_recipient_maps parameter value is
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empty, then the Postfix SMTP server accepts any address in the
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local domain class. </p>
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<li> <p> The mail delivery transport is specified with the
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local_transport parameter. The default value is <b>local:$myhostname</b>
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for delivery with the local(8) delivery agent. </p>
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</ul>
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<p> The <a name="virtual_alias_class">virtual alias </a> domain
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class. </p>
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<ul>
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<li> <p> Purpose: hosted domains 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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virtual alias example is given in the VIRTUAL_README file. </p>
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<li> <p> Domain names are listed in virtual_alias_domains. The
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default value is $virtual_alias_maps for Postfix 1.1 compatibility.
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</p>
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<li> <p> Valid recipient addresses are listed with the virtual_alias_maps
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parameter. The Postfix SMTP server rejects invalid recipients with
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"User unknown in virtual alias table". The default value is
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$virtual_maps 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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</ul>
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<p> The <a name="virtual_mailbox_class">virtual mailbox </a> domain
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class. </p>
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<ul>
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<li> <p> Purpose: final delivery for hosted domains 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 virtual mailbox example is
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given in the VIRTUAL_README file. </p>
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<li> <p> Domain names are listed with the virtual_mailbox_domains
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parameter. The default value is $virtual_mailbox_maps for Postfix
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1.1 compatibility. </p>
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<li> <p> Valid recipient addresses are listed with the virtual_mailbox_maps
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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 $virtual_mailbox_domains. </p>
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<li> <p> The mail delivery transport is specified with the
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virtual_transport parameter. The default value is <b>virtual</b>
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for delivery with the virtual(8) delivery agent. </p>
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</ul>
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<p> The <a name="relay_domain_class">relay </a> domain class. </p>
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<ul>
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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 BASIC_CONFIGURATION_README
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document. For a discussion of the difference between canonical
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domains, hosted domains and other domains, see the VIRTUAL_README
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file. </p>
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<li> <p> Domain names are listed with the relay_domains parameter.
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</p>
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<li> <p> Valid recipient addresses are listed with the relay_recipient_maps
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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 relay_domains parameter. </p>
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<li> <p> The mail delivery transport is specified with the
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relay_transport parameter. The default value is <b>relay</b> which
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is a clone of the smtp(8) delivery agent. </p>
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</ul>
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<p> The <a name="default_domain_class">default </a> domain class.
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</p>
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<ul>
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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 BASIC_CONFIGURATION_README file. For a discussion
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of the difference between canonical domains, hosted domains and
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other domains, see the VIRTUAL_README 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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default_transport parameter. The default value is <b>smtp</b> for
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delivery with the smtp(8) delivery agent. </p>
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</ul>
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<h2><a name="improvements">Improvements compared to Postfix
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1.1</a></h2>
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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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<ul>
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<li> <p> You no longer need to specify all the virtual(8) mailbox
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domains in the Postfix transport map. The virtual(8) delivery agent
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has become a first-class citizen just like local(8) or smtp(8).
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</p>
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<li> <p> On mail gateway systems, address classes provide separation
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of inbound mail relay traffic ($relay_transport) from outbound
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traffic ($default_transport). 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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smtpd_reject_unlisted_recipient 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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smtpd_reject_unlisted_sender configuration parameter. </p>
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</ul>
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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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<ul>
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<li> <p> The virtual_maps parameter is replaced by virtual_alias_maps
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(for address lookups) and by virtual_alias_domains (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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virtual_alias_maps parameter defaults to $virtual_maps, and the
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new virtual_alias_domains parameter defaults to $virtual_alias_maps.
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</p>
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<li> <p> The virtual_mailbox_maps parameter now has a companion
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parameter called virtual_mailbox_domains (for the names of domains
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served by the virtual delivery agent). The virtual_mailbox_maps
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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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virtual_mailbox_domains parameter defaults to $virtual_mailbox_maps.
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</p>
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<li> <p> Introduction of the relay_recipient_maps 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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any recipient. </p>
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<li> <p> The local_recipient_maps 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 LOCAL_RECIPIENT_README file hints
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and tips. </p>
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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 "defer_transports" setting. </p>
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</ul>
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</body>
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</html>
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