external/ibm-public/postfix/dist/proto/ADDRESS_CLASS_README.html

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  16 <h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Postfix Address Classes </h1>
  17
  18 <hr>
  19
  20 <h2>Introduction</h2>
  21
  22 <p> Postfix version 2.0 introduces the concept of address classes.
  23 This is a way of grouping recipient addresses by their delivery
  24 method.  The idea comes from discussions with Victor Duchovni.
  25 Although address classes introduced a few incompatibilities they
  26 also made it possible to improve the handling of hosted domains
  27 and of unknown recipients. </p>
  28
  29 <p> This document provides information on the following topics: </p>
  30
  31 <ul>
  32
  33 <li><a href="#wtf">What are address classes good for?</a>
  34
  35 <li><a href="#classes">What address classes does Postfix implement?</a>
  36
  37 <li><a href="#improvements">Improvements compared to Postfix 1.1</a>
  38
  39 <li><a href="#incompatibility">Incompatibilities with Postfix 1.1</a>
  40
  41 </ul>
  42
  43 <h2><a name="wtf">What are address classes good for?</a></h2>
  44
  45 <p> Why should you care about address classes? This is how Postfix
  46 decides what mail to accept, and how to deliver it.  In other words,
  47 address classes are very important for the operation of Postfix. </p>
  48
  49 <p> An address class is defined by three items. </p>
  50
  51 <ul>
  52
  53 <li> <p> The list of domains that are a member of the class: for
  54 example, all local domains, or all relay domains. </p>
  55
  56 <li> <p> The default delivery transport. For example, the local,
  57 virtual or relay delivery transport (delivery transports are defined
  58 in master.cf). This helps to keep Postfix configurations simple,
  59 by avoiding the need for explicit routing information in transport
  60 maps. </p>
  61
  62 <li> <p> The list of valid recipient addresses for that address
  63 class. The Postfix SMTP server rejects invalid recipients with
  64 "User unknown in &lt;name of address class here&gt; table".  This
  65 helps to keep the Postfix queue free of undeliverable MAILER-DAEMON
  66 messages. </p>
  67
  68 </ul>
  69
  70 <h2><a name="classes">What address classes does Postfix implement?</a></h2>
  71
  72 <p> Initially the list of address classes is hard coded, but this
  73 is meant to become extensible. The summary below describes the main
  74 purpose of each class, and what the relevant configuration parameters
  75 are. </p>
  76
  77 <p> The <a name="local_domain_class">local </a> domain class. </p>
  78
  79 <ul>
  80
  81 <li> <p> Purpose: final delivery for traditional UNIX system accounts
  82 and traditional Sendmail-style aliases. This is typically used for
  83 the canonical domains of the machine.  For a discussion of the
  84 difference between canonical domains, hosted domains and other
  85 domains, see the VIRTUAL_README file. </p>
  86
  87 <li> <p> Domain names are listed with the mydestination parameter.
  88 This domain class also includes mail for <i>user@[ipaddress]</i>
  89 when the IP address is listed with the inet_interfaces or
  90 proxy_interfaces parameters. </p>
  91
  92 <li> <p> Valid recipient addresses are listed with the local_recipient_maps
  93 parameter, as described in LOCAL_RECIPIENT_README. The Postfix SMTP
  94 server rejects invalid recipients with "User unknown in local
  95 recipient table". If the local_recipient_maps parameter value is
  96 empty, then the Postfix SMTP server accepts any address in the
  97 local domain class. </p>
  98
  99 <li> <p> The mail delivery transport is specified with the
 100 local_transport parameter. The default value is <b>local:$myhostname</b>
 101 for delivery with the local(8) delivery agent. </p>
 102
 103 </ul>
 104
 105 <p> The <a name="virtual_alias_class">virtual alias </a> domain
 106 class. </p>
 107
 108 <ul>
 109
 110 <li> <p> Purpose: hosted domains where each recipient address is
 111 aliased to a local UNIX system account or to a remote address.  A
 112 virtual alias example is given in the VIRTUAL_README file. </p>
 113
 114 <li> <p> Domain names are listed in virtual_alias_domains. The
 115 default value is $virtual_alias_maps for Postfix 1.1 compatibility.
 116 </p>
 117
 118 <li> <p> Valid recipient addresses are listed with the virtual_alias_maps
 119 parameter. The Postfix SMTP server rejects invalid recipients with
 120 "User unknown in virtual alias table".  The default value is
 121 $virtual_maps for Postfix 1.1 compatibility. </p>
 122
 123 <li> <p> There is no mail delivery transport parameter. Every
 124 address must be aliased to some other address. </p>
 125
 126 </ul>
 127
 128 <p> The <a name="virtual_mailbox_class">virtual mailbox </a> domain
 129 class. </p>
 130
 131 <ul>
 132
 133 <li> <p> Purpose: final delivery for hosted domains where each
 134 recipient address can have its own mailbox, and where users do not
 135 need to have a UNIX system account.  A virtual mailbox example is
 136 given in the VIRTUAL_README file. </p>
 137
 138 <li> <p> Domain names are listed with the virtual_mailbox_domains
 139 parameter. The default value is $virtual_mailbox_maps for Postfix
 140 1.1 compatibility. </p>
 141
 142 <li> <p> Valid recipient addresses are listed with the virtual_mailbox_maps
 143 parameter. The Postfix SMTP server rejects invalid recipients with
 144 "User unknown in virtual mailbox table". If this parameter value
 145 is empty, the Postfix SMTP server accepts all recipients for domains
 146 listed in $virtual_mailbox_domains.  </p>
 147
 148 <li> <p> The mail delivery transport is specified with the
 149 virtual_transport parameter. The default value is <b>virtual</b>
 150 for delivery with the virtual(8) delivery agent. </p>
 151
 152 </ul>
 153
 154 <p> The <a name="relay_domain_class">relay </a> domain class. </p>
 155
 156 <ul>
 157
 158 <li> <p> Purpose: mail forwarding to remote destinations that list
 159 your system as primary or backup MX host. For a discussion of the
 160 basic configuration details, see the BASIC_CONFIGURATION_README
 161 document.  For a discussion of the difference between canonical
 162 domains, hosted domains and other domains, see the VIRTUAL_README
 163 file. </p>
 164
 165 <li> <p> Domain names are listed with the relay_domains parameter.
 166 </p>
 167
 168 <li> <p> Valid recipient addresses are listed with the relay_recipient_maps
 169 parameter. The Postfix SMTP server rejects invalid recipients with
 170 "User unknown in relay recipient table". If this parameter value
 171 is empty, the Postfix SMTP server accepts all recipients for domains
 172 listed with the relay_domains parameter. </p>
 173
 174 <li> <p> The mail delivery transport is specified with the
 175 relay_transport parameter. The default value is <b>relay</b> which
 176 is a clone of the smtp(8) delivery agent. </p>
 177
 178 </ul>
 179
 180 <p> The <a name="default_domain_class">default </a> domain class.
 181 </p>
 182
 183 <ul>
 184
 185 <li> <p> Purpose: mail forwarding to the Internet on behalf of
 186 authorized clients. For a discussion of the basic configuration
 187 details, see the BASIC_CONFIGURATION_README file. For a discussion
 188 of the difference between canonical domains, hosted domains and
 189 other domains, see the VIRTUAL_README file. </p>
 190
 191 <li> <p> This class has no destination domain table. </p>
 192
 193 <li> <p> This class has no valid recipient address table. </p>
 194
 195 <li> <p> The mail delivery transport is specified with the
 196 default_transport parameter. The default value is <b>smtp</b> for
 197 delivery with the smtp(8) delivery agent. </p>
 198
 199 </ul>
 200
 201 <h2><a name="improvements">Improvements compared to Postfix
 202 1.1</a></h2>
 203
 204 <p> Postfix 2.0 address classes made the following improvements
 205 possible over earlier Postfix versions: </p>
 206
 207 <ul>
 208
 209 <li> <p> You no longer need to specify all the virtual(8) mailbox
 210 domains in the Postfix transport map. The virtual(8) delivery agent
 211 has become a first-class citizen just like local(8) or smtp(8).
 212 </p>
 213
 214 <li> <p> On mail gateway systems, address classes provide separation
 215 of inbound mail relay traffic ($relay_transport) from outbound
 216 traffic ($default_transport). This eliminates a problem where
 217 inbound mail deliveries could become resource starved in the presence
 218 of a high volume of outbound mail. </p>
 219
 220 <li> <p> The SMTP server rejects unknown recipients in a more
 221 consistent manner than was possible with Postfix version 1. This
 222 is needed to keep undeliverable mail (and bounced undeliverable
 223 mail) out of the mail queue. This is controlled by the
 224 smtpd_reject_unlisted_recipient configuration parameter. </p>
 225
 226 <li> <p> As of Postfix version 2.1, the SMTP server also rejects
 227 unknown sender addresses (i.e. addresses that it would reject as
 228 unknown recipient addresses).  Sender "egress filtering" can help
 229 to slow down an email worm explosion.  This is controlled by the
 230 smtpd_reject_unlisted_sender configuration parameter. </p>
 231
 232 </ul>
 233
 234 <h2><a name="incompatibility">Incompatibilities with Postfix 1.1</a></h2>
 235
 236 <p> Postfix 2.0 address classes introduce a few incompatible changes
 237 in documented behavior. In order to ease the transitions, new
 238 parameters have default values that are backwards compatible. </p>
 239
 240 <ul>
 241
 242 <li> <p> The virtual_maps parameter is replaced by virtual_alias_maps
 243 (for address lookups) and by virtual_alias_domains (for the names
 244 of what were formerly called "Postfix-style virtual domains"). </p>
 245
 246 <p> For backwards compatibility with Postfix version 1.1, the new
 247 virtual_alias_maps parameter defaults to $virtual_maps, and the
 248 new virtual_alias_domains parameter defaults to $virtual_alias_maps.
 249 </p>
 250
 251 <li> <p> The virtual_mailbox_maps parameter now has a companion
 252 parameter called virtual_mailbox_domains (for the names of domains
 253 served by the virtual delivery agent). The virtual_mailbox_maps
 254 parameter is now used for address lookups only. </p>
 255
 256 <p> For backwards compatibility with Postfix version 1.1, the new
 257 virtual_mailbox_domains parameter defaults to $virtual_mailbox_maps.
 258 </p>
 259
 260 <li> <p> Introduction of the relay_recipient_maps parameter.  The
 261 Postfix SMTP server can use this to block mail for relay recipients
 262 that don't exist. This list is empty by default, which means accept
 263 any recipient. </p>
 264
 265 <li> <p> The local_recipient_maps feature is now turned on by
 266 default.  The Postfix SMTP server uses this to reject mail for
 267 unknown local recipients. See the LOCAL_RECIPIENT_README file hints
 268 and tips. </p>
 269
 270 <li> <p> Introduction of the relay delivery transport in master.cf.
 271 This helps to avoid mail delivery scheduling problems on inbound
 272 mail relays when there is a lot of outbound mail, but may require
 273 that you update your "defer_transports" setting. </p>
 274
 275 </ul>
 276
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