postfix-master/STANDARD_CONFIGURATION_README.html

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  16 <h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Postfix Standard Configuration Examples</h1>
  17
  18 <hr>
  19
  20 <h2>Purpose of this document</h2>
  21
  22 <p> This document presents a number of typical Postfix configurations.
  23 This document should be reviewed after you have followed the basic
  24 configuration steps as described in the <a href="BASIC_CONFIGURATION_README.html">BASIC_CONFIGURATION_README</a>
  25 document. In particular, do not proceed here if you don't already
  26 have Postfix working for local mail submission and for local mail
  27 delivery. </p>
  28
  29 <p> The first part of this document presents standard configurations
  30 that each solve one specific problem. </p>
  31
  32 <ul>
  33
  34 <li><a href="#stand_alone">Postfix on a stand-alone Internet host</a>
  35
  36 <li><a href="#null_client">Postfix on a null client</a>
  37
  38 <li><a href="#local_network">Postfix on a local network</a>
  39
  40 <li><a href="#firewall">Postfix email firewall/gateway</a>
  41
  42 </ul>
  43
  44 <p> The second part of this document presents additional configurations
  45 for hosts in specific environments. </p>
  46
  47 <ul>
  48
  49 <li><a href="#some_local">Delivering some but not all accounts locally</a>
  50
  51 <li><a href="#intranet">Running Postfix behind a firewall</a>
  52
  53 <li><a href="#backup">Configuring Postfix as primary or backup MX host for a remote
  54 site</a>
  55
  56 <li><a href="#dialup">Postfix on a dialup machine</a>
  57
  58 <li><a href="#fantasy">Postfix on hosts without a real
  59 Internet hostname</a>
  60
  61 </ul>
  62
  63 <h2><a name="stand_alone">Postfix on a stand-alone Internet host</a></h2>
  64
  65 <p> Postfix should work out of the box without change on a stand-alone
  66 machine that has direct Internet access.  At least, that is how
  67 Postfix installs when you download the Postfix source code via
  68 <a href="http://www.postfix.org/">http://www.postfix.org/</a>. </p>
  69
  70 <p> You can use the command "<b>postconf -n</b>" to find out what
  71 settings are overruled by your <a href="postconf.5.html">main.cf</a>. Besides a few pathname
  72 settings, few parameters should be set on a stand-alone box, beyond
  73 what is covered in the <a href="BASIC_CONFIGURATION_README.html">BASIC_CONFIGURATION_README</a> document: </p>
  74
  75 <blockquote>
  76 <pre>
  77 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
  78     # Optional: send mail as user@domainname instead of user@hostname.
  79     #<a href="postconf.5.html#myorigin">myorigin</a> = $<a href="postconf.5.html#mydomain">mydomain</a>
  80
  81     # Optional: specify NAT/proxy external address.
  82     #<a href="postconf.5.html#proxy_interfaces">proxy_interfaces</a> = 1.2.3.4
  83
  84     # Alternative 1: don't relay mail from other hosts.
  85     <a href="postconf.5.html#mynetworks_style">mynetworks_style</a> = host
  86     <a href="postconf.5.html#relay_domains">relay_domains</a> =
  87
  88     # Alternative 2: relay mail from local clients only.
  89     # <a href="postconf.5.html#mynetworks">mynetworks</a> = 192.168.1.0/28
  90     # <a href="postconf.5.html#relay_domains">relay_domains</a> =
  91 </pre>
  92 </blockquote>
  93
  94 <p> See also the section "<a href="#fantasy">Postfix on hosts without
  95 a real Internet hostname</a>" if this is applicable to your configuration.
  96 </p>
  97
  98 <h2><a name="null_client">Postfix on a null client</a></h2>
  99
 100 <p> A null client is a machine that can only send mail. It receives no
 101 mail from the network, and it does not deliver any mail locally. A
 102 null client typically uses POP, IMAP or NFS for mailbox access. </p>
 103
 104 <p> In this example we assume that the Internet domain name is
 105 "example.com" and that the machine is named "nullclient.example.com".
 106 As usual, the examples show only parameters that are not left at
 107 their default settings. </p>
 108
 109 <blockquote>
 110 <pre>
 111 1 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 112 2     <a href="postconf.5.html#myorigin">myorigin</a> = $<a href="postconf.5.html#mydomain">mydomain</a>
 113 3     <a href="postconf.5.html#relayhost">relayhost</a> = $<a href="postconf.5.html#mydomain">mydomain</a>
 114 4     <a href="postconf.5.html#inet_interfaces">inet_interfaces</a> = loopback-only
 115 5     <a href="postconf.5.html#local_transport">local_transport</a> = <a href="error.8.html">error</a>:local delivery is disabled
 116 6
 117 7 /etc/postfix/<a href="master.5.html">master.cf</a>:
 118 8     Comment out the local delivery agent entry
 119 </pre>
 120 </blockquote>
 121
 122 <p> Translation: </p>
 123
 124 <ul>
 125
 126 <li> <p> Line 2: Send mail as "user@example.com" (instead of
 127 "user@nullclient.example.com"), so that nothing ever has a reason
 128 to send mail to "user@nullclient.example.com". </p>
 129
 130 <li> <p> Line 3: Forward all mail to the mail server that is
 131 responsible for the "example.com" domain. This prevents mail from
 132 getting stuck on the null client if it is turned off while some
 133 remote destination is unreachable. </p>
 134
 135 <li> <p> Line 4: Do not accept mail from the network. </p>
 136
 137 <li> <p> Lines 5-8: Disable local mail delivery. All mail goes to
 138 the mail server as specified in line 3.  </p>
 139
 140 </ul>
 141
 142 <h2><a name="local_network">Postfix on a local network</a></h2>
 143
 144 <p> This section describes a local area network environment of one
 145 main server and multiple other systems that send and receive email.
 146 As usual we assume that the Internet domain name is "example.com".
 147 All systems are configured to send mail as "user@example.com", and
 148 all systems receive mail for "user@hostname.example.com".  The main
 149 server also receives mail for "user@example.com". We call this
 150 machine by the name of mailhost.example.com. </p>
 151
 152 <p> A drawback of sending mail as "user@example.com" is that mail
 153 for "root" and other system accounts is also sent to the central
 154 mailhost. See the section "<a href="#some_local">Delivering some
 155 but not all accounts locally</a>" below for possible solutions.
 156 </p>
 157
 158 <p> As usual, the examples show only parameters that are not left
 159 at their default settings. </p>
 160
 161 <p> First we present the non-mailhost configuration, because it is
 162 the simpler one. This machine sends mail as "user@example.com" and
 163 is final destination for "user@hostname.example.com". </p>
 164
 165 <blockquote>
 166 <pre>
 167 1 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 168 2     <a href="postconf.5.html#myorigin">myorigin</a> = $<a href="postconf.5.html#mydomain">mydomain</a>
 169 3     <a href="postconf.5.html#mynetworks">mynetworks</a> = 127.0.0.0/8 10.0.0.0/24
 170 4     <a href="postconf.5.html#relay_domains">relay_domains</a> =
 171 5     # Optional: forward all non-local mail to mailhost
 172 6     #<a href="postconf.5.html#relayhost">relayhost</a> = $<a href="postconf.5.html#mydomain">mydomain</a>
 173 </pre>
 174 </blockquote>
 175
 176 <p> Translation: </p>
 177
 178 <ul>
 179
 180 <li> <p> Line 2: Send mail as "user@example.com". </p>
 181
 182 <li> <p> Line 3: Specify the trusted networks. </p>
 183
 184 <li> <p> Line 4: This host does not relay mail from untrusted networks. </p>
 185
 186 <li> <p> Line 6: This is needed if no direct Internet access is
 187 available.  See also below, "<a href="#firewall">Postfix behind
 188 a firewall</a>". </p>
 189
 190 </ul>
 191
 192 <p> Next we present the mailhost configuration.  This machine sends
 193 mail as "user@example.com" and is final destination for
 194 "user@hostname.example.com" as well as "user@example.com". </p>
 195
 196 <blockquote>
 197 <pre>
 198  1 DNS:
 199  2     example.com    IN    MX  10 mailhost.example.com.
 200  3
 201  4 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 202  5     <a href="postconf.5.html#myorigin">myorigin</a> = $<a href="postconf.5.html#mydomain">mydomain</a>
 203  6     <a href="postconf.5.html#mydestination">mydestination</a> = $<a href="postconf.5.html#myhostname">myhostname</a> localhost.$<a href="postconf.5.html#mydomain">mydomain</a> localhost $<a href="postconf.5.html#mydomain">mydomain</a>
 204  7     <a href="postconf.5.html#mynetworks">mynetworks</a> = 127.0.0.0/8 10.0.0.0/24
 205  8     <a href="postconf.5.html#relay_domains">relay_domains</a> =
 206  9     # Optional: forward all non-local mail to firewall
 207 10     #<a href="postconf.5.html#relayhost">relayhost</a> = [firewall.example.com]
 208 </pre>
 209 </blockquote>
 210
 211 <p> Translation: </p>
 212
 213 <ul>
 214
 215 <li> <p> Line 2: Send mail for the domain "example.com" to the
 216 machine mailhost.example.com.  Remember to specify the "." at the
 217 end of the line. </p>
 218
 219 <li> <p> Line 5: Send mail as "user@example.com". </p>
 220
 221 <li> <p> Line 6: This host is the final mail destination for the
 222 "example.com" domain, in addition to the names of the machine
 223 itself. </p>
 224
 225 <li> <p> Line 7: Specify the trusted networks. </p>
 226
 227 <li> <p> Line 8: This host does not relay mail from untrusted networks. </p>
 228
 229 <li> <p> Line 10: This is needed only when the mailhost has to
 230 forward non-local mail via a mail server on a firewall.  The
 231 <tt>[]</tt> forces Postfix to do no MX record lookups. </p>
 232
 233 </ul>
 234
 235 <p> In an environment like this, users access their mailbox in one
 236 or more of the following ways:
 237
 238 <ul>
 239
 240 <li> <p> Mailbox access via NFS or equivalent.  </p>
 241
 242 <li> <p> Mailbox access via POP or IMAP. </p>
 243
 244 <li> <p> Mailbox on the user's preferred machine. </p>
 245
 246 </ul>
 247
 248 <p> In the latter case, each user has an alias on the mailhost that
 249 forwards mail to her preferred machine: </p>
 250
 251 <blockquote>
 252 <pre>
 253 /etc/aliases:
 254     joe:    joe@joes.preferred.machine
 255     jane:   jane@janes.preferred.machine
 256 </pre>
 257 </blockquote>
 258
 259 <p> On some systems the alias database is not in /etc/aliases.  To
 260 find out the location for your system, execute the command "<b>postconf
 261 <a href="postconf.5.html#alias_maps">alias_maps</a></b>". </p>
 262
 263 <p> Execute the command "<b>newaliases</b>" whenever you change
 264 the aliases file.  </p>
 265
 266 <h2><a name="firewall">Postfix email firewall/gateway</a></h2>
 267
 268 <p> The idea is to set up a Postfix email firewall/gateway that
 269 forwards mail for "example.com" to an inside gateway machine but
 270 rejects mail for "anything.example.com". There is only one problem:
 271 with "<a href="postconf.5.html#relay_domains">relay_domains</a> = example.com", the firewall normally also
 272 accepts mail for "anything.example.com".  That would not be right.
 273 </p>
 274
 275 <p> Note: this example requires Postfix version 2.0 and later. To find
 276 out what Postfix version you have, execute the command "<b>postconf
 277 <a href="postconf.5.html#mail_version">mail_version</a></b>". </p>
 278
 279 <p> The solution is presented in multiple parts. This first part
 280 gets rid of local mail delivery on the firewall, making the firewall
 281 harder to break. </p>
 282
 283 <blockquote>
 284 <pre>
 285 1 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 286 2     <a href="postconf.5.html#myorigin">myorigin</a> = example.com
 287 3     <a href="postconf.5.html#mydestination">mydestination</a> =
 288 4     <a href="postconf.5.html#local_recipient_maps">local_recipient_maps</a> =
 289 5     <a href="postconf.5.html#local_transport">local_transport</a> = <a href="error.8.html">error</a>:local mail delivery is disabled
 290 6
 291 7 /etc/postfix/<a href="master.5.html">master.cf</a>:
 292 8     Comment out the local delivery agent
 293 </pre>
 294 </blockquote>
 295
 296 <p> Translation: </p>
 297
 298 <ul>
 299
 300 <li> <p> Line 2: Send mail from this machine as "user@example.com",
 301 so that no reason exists to send mail to "user@firewall.example.com".
 302 </p>
 303
 304 <li> <p> Lines 3-8: Disable local mail delivery on the firewall
 305 machine. </p>
 306
 307 </ul>
 308
 309 <p> For the sake of technical correctness the firewall must be able
 310 to receive mail for postmaster@[firewall ip address]. Reportedly,
 311 some things actually expect this ability to exist. The second part
 312 of the solution therefore adds support for postmaster@[firewall ip
 313 address], and as a bonus we do abuse@[firewall ip address] as well.
 314 All the mail to these two accounts is forwarded to an inside address.
 315 </p>
 316
 317 <blockquote>
 318 <pre>
 319 1 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 320 2     <a href="postconf.5.html#virtual_alias_maps">virtual_alias_maps</a> = hash:/etc/postfix/virtual
 321 3
 322 4 /etc/postfix/virtual:
 323 5     postmaster      postmaster@example.com
 324 6     abuse           abuse@example.com
 325 </pre>
 326 </blockquote>
 327
 328 <p> Translation: </p>
 329
 330 <ul>
 331
 332 <li> <p> Because <a href="postconf.5.html#mydestination">mydestination</a> is empty (see the previous example),
 333 only address literals matching $<a href="postconf.5.html#inet_interfaces">inet_interfaces</a> or $<a href="postconf.5.html#proxy_interfaces">proxy_interfaces</a>
 334 are deemed local.  So "localpart@[a.d.d.r]" can be matched as simply
 335 "localpart" in <a href="canonical.5.html">canonical(5)</a> and <a href="virtual.5.html">virtual(5)</a>. This avoids the need to
 336 specify firewall IP addresses into Postfix configuration files. </p>
 337
 338 </ul>
 339
 340 <p> The last part of the solution does the email forwarding, which
 341 is the real purpose of the firewall email function. </p>
 342
 343 <blockquote>
 344 <pre>
 345  1 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 346  2     <a href="postconf.5.html#mynetworks">mynetworks</a> = 127.0.0.0/8 12.34.56.0/24
 347  3     <a href="postconf.5.html#relay_domains">relay_domains</a> = example.com
 348  4     <a href="postconf.5.html#parent_domain_matches_subdomains">parent_domain_matches_subdomains</a> =
 349  5         <a href="postconf.5.html#debug_peer_list">debug_peer_list</a> smtpd_access_maps
 350  6     <a href="postconf.5.html#smtpd_recipient_restrictions">smtpd_recipient_restrictions</a> =
 351  7         <a href="postconf.5.html#permit_mynetworks">permit_mynetworks</a> <a href="postconf.5.html#reject_unauth_destination">reject_unauth_destination</a>
 352  8
 353  9     <a href="postconf.5.html#relay_recipient_maps">relay_recipient_maps</a> = hash:/etc/postfix/relay_recipients
 354 10     <a href="postconf.5.html#transport_maps">transport_maps</a> = hash:/etc/postfix/transport
 355 11
 356 12 /etc/postfix/relay_recipients:
 357 13     user1@example.com   x
 358 14     user2@example.com   x
 359 15      . . .
 360 16
 361 17 /etc/postfix/transport:
 362 18     example.com   <a href="smtp.8.html">smtp</a>:[inside-gateway.example.com]
 363 </pre>
 364 </blockquote>
 365
 366 <p> Translation: </p>
 367
 368 <ul>
 369
 370 <li><p> Lines 1-7: Accept mail from local systems in $<a href="postconf.5.html#mynetworks">mynetworks</a>,
 371 and accept mail from outside for "user@example.com" but not for
 372 "user@anything.example.com". The magic is in lines 4-5. </p>
 373
 374 <li> <p> Lines 9, 12-14: Define the list of valid addresses in the
 375 "example.com" domain that can receive mail from the Internet. This
 376 prevents the mail queue from filling up with undeliverable
 377 MAILER-DAEMON messages. If you can't maintain a list of valid
 378 recipients then you must specify "<a href="postconf.5.html#relay_recipient_maps">relay_recipient_maps</a> =" (that
 379 is, an empty value), or you must specify an "@example.com  x"
 380 wild-card in the relay_recipients table. </p>
 381
 382 <li> <p> Lines 10, 17-18: Route mail for "example.com" to the inside
 383 gateway machine. The <tt>[]</tt> forces Postfix to do no MX lookup.
 384 </p>
 385
 386 </ul>
 387
 388 <p>Specify <b>dbm</b> instead of <b>hash</b> if your system uses
 389 <b>dbm</b> files instead of <b>db</b> files. To find out what lookup
 390 tables Postfix supports, use the command "<b>postconf -m</b>".  </p>
 391
 392 <p> Execute the command "<b>postmap /etc/postfix/relay_recipients</b>"
 393 whenever you change the relay_recipients table. </p>
 394
 395 <p> Execute the command "<b>postmap /etc/postfix/transport</b>"
 396 whenever you change the transport table. </p>
 397
 398 <p> In some installations, there may be separate instances of Postfix
 399 processing inbound and outbound mail on a multi-homed firewall. The
 400 inbound Postfix instance has an SMTP server listening on the external
 401 firewall interface, and the outbound Postfix instance has an SMTP server
 402 listening on the internal interface. In such a configuration is it is
 403 tempting to configure $<a href="postconf.5.html#inet_interfaces">inet_interfaces</a> in each instance with just the
 404 corresponding interface address. </p>
 405
 406 <p> In most cases, using <a href="postconf.5.html#inet_interfaces">inet_interfaces</a> in this way will not work,
 407 because as documented in the $<a href="postconf.5.html#inet_interfaces">inet_interfaces</a> reference manual, the
 408 <a href="smtp.8.html">smtp(8)</a> delivery agent will also use the specified interface address
 409 as the source address for outbound connections and will be unable to
 410 reach hosts on "the other side" of the firewall. The symptoms are that
 411 the firewall is unable to connect to hosts that are in fact up. See the
 412 <a href="postconf.5.html#inet_interfaces">inet_interfaces</a> parameter documentation for suggested work-arounds.</p>
 413
 414 <h2><a name="some_local">Delivering some but not all accounts
 415 locally</a></h2>
 416
 417 <p> A drawback of sending mail as "user@example.com" (instead of
 418 "user@hostname.example.com") is that mail for "root" and other
 419 system accounts is also sent to the central mailhost.  In order to
 420 deliver such accounts locally, you can set up virtual aliases as
 421 follows:  </p>
 422
 423 <blockquote>
 424 <pre>
 425 1 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 426 2     <a href="postconf.5.html#virtual_alias_maps">virtual_alias_maps</a> = hash:/etc/postfix/virtual
 427 3
 428 4 /etc/postfix/virtual:
 429 5     root     root@localhost
 430 6     . . .
 431 </pre>
 432 </blockquote>
 433
 434 <p> Translation: </p>
 435
 436 <ul>
 437
 438 <li> <p> Line 5: As described in the <a href="virtual.5.html">virtual(5)</a> manual page, the
 439 bare name "root" matches "root@site" when "site" is equal to
 440 $<a href="postconf.5.html#myorigin">myorigin</a>, when "site" is listed in $<a href="postconf.5.html#mydestination">mydestination</a>, or when it
 441 matches $<a href="postconf.5.html#inet_interfaces">inet_interfaces</a> or $<a href="postconf.5.html#proxy_interfaces">proxy_interfaces</a>. </p>
 442
 443 </ul>
 444
 445 <p> Execute the command "<b>postmap /etc/postfix/virtual</b>" after
 446 editing the file. </p>
 447
 448 <h2><a name="intranet">Running Postfix behind a firewall</a></h2>
 449
 450 <p> The simplest way to set up Postfix on a host behind a firewalled
 451 network is to send all mail to a gateway host, and to let that mail
 452 host take care of internal and external forwarding. Examples of that
 453 are shown in the <a href="#local_network">local area network</a>
 454 section above. A more sophisticated approach is to send only external
 455 mail to the gateway host, and to send intranet mail directly. </p>
 456
 457 <p> Note: this example requires Postfix version 2.0 and later. To find
 458 out what Postfix version you have, execute the command "<b>postconf
 459 <a href="postconf.5.html#mail_version">mail_version</a></b>". </p>
 460
 461 <p> The following example presents additional configuration. You
 462 need to combine this with basic configuration information as
 463 discussed the first half of this document. </p>
 464
 465 <blockquote>
 466 <pre>
 467  1 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 468  2     <a href="postconf.5.html#transport_maps">transport_maps</a> = hash:/etc/postfix/transport
 469  3     <a href="postconf.5.html#relayhost">relayhost</a> =
 470  4     # Optional for a machine that isn't "always on"
 471  5     #<a href="postconf.5.html#fallback_relay">fallback_relay</a> = [gateway.example.com]
 472  6
 473  7 /etc/postfix/transport:
 474  8     # Internal delivery.
 475  9     example.com      :
 476 10     .example.com     :
 477 11     # External delivery.
 478 12     *                <a href="smtp.8.html">smtp</a>:[gateway.example.com]
 479 </pre>
 480 </blockquote>
 481
 482 <p> Translation: </p>
 483
 484 <ul>
 485
 486 <li> <p> Lines 2, 7-12: Request that intranet mail is delivered
 487 directly, and that external mail is given to a gateway. Obviously,
 488 this example assumes that the organization uses DNS MX records
 489 internally.  The <tt>[]</tt> forces Postfix to do no MX lookup.
 490 </p>
 491
 492 <li> <p> Line 3: IMPORTANT: do not specify a <a href="postconf.5.html#relayhost">relayhost</a> in <a href="postconf.5.html">main.cf</a>.
 493 </p>
 494
 495 <li> <p> Line 5: This prevents mail from being stuck in the queue
 496 when the machine is turned off.  Postfix tries to deliver mail
 497 directly, and gives undeliverable mail to a gateway.  </p>
 498
 499 </ul>
 500
 501 <p> Specify <b>dbm</b> instead of <b>hash</b> if your system uses
 502 <b>dbm</b> files instead of <b>db</b> files. To find out what lookup
 503 tables Postfix supports, use the command "<b>postconf -m</b>". </p>
 504
 505 <p> Execute the command "<b>postmap /etc/postfix/transport</b>" whenever
 506 you edit the transport table. </p>
 507
 508 <h2><a name="backup">Configuring Postfix as primary or backup MX host for a remote site</a></h2>
 509
 510 <p> This section presents additional configuration. You need to
 511 combine this with basic configuration information as discussed the
 512 first half of this document. </p>
 513
 514 <p> When your system is SECONDARY MX host for a remote site this
 515 is all you need: </p>
 516
 517 <blockquote>
 518 <pre>
 519  1 DNS:
 520  2     the.backed-up.domain.tld        IN      MX 100 your.machine.tld.
 521  3
 522  4 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 523  5     <a href="postconf.5.html#relay_domains">relay_domains</a> = . . . the.backed-up.domain.tld
 524  6     <a href="postconf.5.html#smtpd_recipient_restrictions">smtpd_recipient_restrictions</a> =
 525  7         <a href="postconf.5.html#permit_mynetworks">permit_mynetworks</a> <a href="postconf.5.html#reject_unauth_destination">reject_unauth_destination</a>
 526  8
 527  9     # You must specify your NAT/proxy external address.
 528 10     #<a href="postconf.5.html#proxy_interfaces">proxy_interfaces</a> = 1.2.3.4
 529 11
 530 12     <a href="postconf.5.html#relay_recipient_maps">relay_recipient_maps</a> = hash:/etc/postfix/relay_recipients
 531 13
 532 14 /etc/postfix/relay_recipients:
 533 15     user1@the.backed-up.domain.tld   x
 534 16     user2@the.backed-up.domain.tld   x
 535 17      . . .
 536 </pre>
 537 </blockquote>
 538
 539 <p> When your system is PRIMARY MX host for a remote site you
 540 need the above, plus: </p>
 541
 542 <blockquote>
 543 <pre>
 544 18 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 545 19     <a href="postconf.5.html#transport_maps">transport_maps</a> = hash:/etc/postfix/transport
 546 20
 547 21 /etc/postfix/transport:
 548 22     the.backed-up.domain.tld       relay:[their.mail.host.tld]
 549 </pre>
 550 </blockquote>
 551
 552 <p> Important notes:
 553
 554 <ul>
 555
 556 <li><p>Do not list the.backed-up.domain.tld in <a href="postconf.5.html#mydestination">mydestination</a>.</p>
 557
 558 <li><p>Do not list the.backed-up.domain.tld in <a href="postconf.5.html#virtual_alias_domains">virtual_alias_domains</a>.</p>
 559
 560 <li><p>Do not list the.backed-up.domain.tld in <a href="postconf.5.html#virtual_mailbox_domains">virtual_mailbox_domains</a>.</p>
 561
 562 <li> <p> Lines 1-7: Forward mail from the Internet for
 563 "the.backed-up.domain.tld" to the primary MX host for that domain.
 564 </p>
 565
 566 <li> <p> Line 10: This is a must if Postfix receives mail via a
 567 NAT relay or proxy that presents a different IP address to the
 568 world than the local machine. </p>
 569
 570 <li> <p> Lines 12-16: Define the list of valid addresses in the
 571 "the.backed-up.domain.tld" domain.  This prevents your mail queue
 572 from filling up with undeliverable MAILER-DAEMON messages. If you
 573 can't maintain a list of valid recipients then you must specify
 574 "<a href="postconf.5.html#relay_recipient_maps">relay_recipient_maps</a> =" (that is, an empty value), or you must
 575 specify an "@the.backed-up.domain.tld  x" wild-card in the
 576 relay_recipients table. </p>
 577
 578 <li> <p> Line 22: The <tt>[]</tt> forces Postfix to do no MX lookup. </p>
 579
 580 </ul>
 581
 582 <p> Specify <b>dbm</b> instead of <b>hash</b> if your system uses
 583 <b>dbm</b> files instead of <b>db</b> files. To find out what lookup
 584 tables Postfix supports, use the command "<b>postconf -m</b>". </p>
 585
 586 <p> Execute the command "<b>postmap /etc/postfix/transport</b>"
 587 whenever you change the transport table. </p>
 588
 589 <p> NOTE for Postfix &lt; 2.2: Do not use the <a href="postconf.5.html#fallback_relay">fallback_relay</a> feature
 590 when relaying mail
 591 for a backup or primary MX domain. Mail would loop between the
 592 Postfix MX host and the <a href="postconf.5.html#fallback_relay">fallback_relay</a> host when the final destination
 593 is unavailable. </p>
 594
 595 <ul>
 596
 597 <li> In <a href="postconf.5.html">main.cf</a> specify "<tt><a href="postconf.5.html#relay_transport">relay_transport</a> = relay</tt>",
 598
 599 <li> In <a href="master.5.html">master.cf</a> specify "<tt>-o <a href="postconf.5.html#fallback_relay">fallback_relay</a> =</tt>" at the
 600 end of the <tt>relay</tt> entry.
 601
 602 <li> In transport maps, specify "<tt>relay:<i>nexthop...</i></tt>"
 603 as the right-hand side for backup or primary MX domain entries.
 604
 605 </ul>
 606
 607 <p> These are default settings in Postfix version 2.2 and later.
 608 </p>
 609
 610 <h2><a name="dialup">Postfix on a dialup machine</a></h2>
 611
 612 <p> This section applies to dialup connections that are down most
 613 of the time. For dialup connections that are up 24x7, see the <a
 614 href="#local_network">local area network</a> section above.  </p>
 615
 616 <p> This section presents additional configuration. You need to
 617 combine this with basic configuration information as discussed the
 618 first half of this document. </p>
 619
 620 <p> If you do not have your own hostname and IP address (usually
 621 with dialup, cable TV or DSL connections) then you should also
 622 study the section on "<a href="#fantasy">Postfix on hosts without
 623 a real Internet hostname</a>".  </p>
 624
 625 <ul>
 626
 627 <li> Route all outgoing mail to your network provider.
 628
 629 <p> If your machine is disconnected most of the time, there isn't
 630 a lot of opportunity for Postfix to deliver mail to hard-to-reach
 631 corners of the Internet. It's better to give the mail to a machine
 632 that is connected all the time. In the example below, the <tt>[]</tt>
 633 prevents Postfix from trying to look up DNS MX records.  </p>
 634
 635 <pre>
 636 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 637     <a href="postconf.5.html#relayhost">relayhost</a> = [smtprelay.someprovider.com]
 638 </pre>
 639
 640 <li> <p><a name="spontaneous_smtp">Disable spontaneous SMTP mail
 641 delivery (if using on-demand dialup IP only).</a> </p>
 642
 643 <p> Normally, Postfix attempts to deliver outbound mail at its convenience.
 644 If your machine uses on-demand dialup IP, this causes your system
 645 to place a telephone call whenever you submit new mail, and whenever
 646 Postfix retries to deliver delayed mail. To prevent such telephone
 647 calls from being placed, disable spontaneous SMTP mail deliveries. </p>
 648
 649 <pre>
 650 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 651     <a href="postconf.5.html#defer_transports">defer_transports</a> = smtp (Only for on-demand dialup IP hosts)
 652 </pre>
 653
 654 <li> <p>Disable SMTP client DNS lookups (dialup LAN only).</p>
 655
 656 <pre>
 657 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 658     <a href="postconf.5.html#disable_dns_lookups">disable_dns_lookups</a> = yes (Only for on-demand dialup IP hosts)
 659 </pre>
 660
 661 <li> Flush the mail queue whenever the Internet link is established.
 662
 663 <p> Put the following command into your PPP or SLIP dialup scripts: </p>
 664
 665 <pre>
 666 /usr/sbin/sendmail -q (whenever the Internet link is up)
 667 </pre>
 668
 669 <p> The exact location of the Postfix sendmail command is system-specific.
 670 Use the command "<b>postconf <a href="postconf.5.html#sendmail_path">sendmail_path</a></b>" to find out where the
 671 Postfix sendmail command is located on your machine. </p>
 672
 673 <p> In order to find out if the mail queue is flushed, use something
 674 like: </p>
 675
 676 <pre>
 677 #!/bin/sh
 678
 679 # Start mail deliveries.
 680 /usr/sbin/sendmail -q
 681
 682 # Allow deliveries to start.
 683 sleep 10
 684
 685 # Loop until all messages have been tried at least once.
 686 while mailq | grep '^[^ ]*\*' &gt;/dev/null
 687 do
 688     sleep 10
 689 done
 690 </pre>
 691
 692 <p> If you have disabled <a href="#spontaneous_smtp">spontaneous
 693 SMTP mail delivery</a>, you also need to run the "<b>sendmail -q</b>"
 694 command every now and then while the dialup link is up, so that
 695 newly-posted mail is flushed from the queue. </p>
 696
 697 </ul>
 698
 699 <h2><a name="fantasy">Postfix on hosts without a real Internet
 700 hostname</a></h2>
 701
 702 <p> This section is for hosts that don't have their own Internet
 703 hostname.  Typically these are systems that get a dynamic IP address
 704 via DHCP or via dialup. Postfix will let you send and receive mail
 705 just fine between accounts on a machine with a fantasy name. However,
 706 you cannot use a fantasy hostname in your email address when sending
 707 mail into the Internet, because no-one would be able to reply to
 708 your mail. In fact, more and more sites refuse mail addresses with
 709 non-existent domain names. </p>
 710
 711 <p> Note: the following information is Postfix version dependent.
 712 To find out what Postfix version you have, execute the command
 713 "<b>postconf <a href="postconf.5.html#mail_version">mail_version</a></b>". </p>
 714
 715 <h3>Solution 1: Postfix version 2.2 and later </h3>
 716
 717 <p> Postfix 2.2 uses the <a href="generic.5.html">generic(5)</a> address mapping to replace
 718 local fantasy email addresses by valid Internet addresses.  This
 719 mapping happens ONLY when mail leaves the machine; not when you
 720 send mail between users on the same machine. </p>
 721
 722 <p> The following example presents additional configuration. You
 723 need to combine this with basic configuration information as
 724 discussed the first half of this document. </p>
 725
 726 <blockquote>
 727 <pre>
 728 1 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 729 2     <a href="postconf.5.html#smtp_generic_maps">smtp_generic_maps</a> = hash:/etc/postfix/generic
 730 3
 731 4 /etc/postfix/generic:
 732 5     his@localdomain.local             hisaccount@hisisp.example
 733 6     her@localdomain.local             heraccount@herisp.example
 734 7     @localdomain.local                hisaccount+local@hisisp.example
 735 </pre>
 736 </blockquote>
 737
 738 <p> When mail is sent to a remote host via SMTP: </p>
 739
 740 <ul>
 741
 742 <li> <p> Line 5 replaces <i>his@localdomain.local</i> by his ISP
 743 mail address, </p>
 744
 745 <li> <p> Line 6 replaces <i>her@localdomain.local</i> by her ISP
 746 mail address, and </p>
 747
 748 <li> <p> Line 7 replaces other local addresses by his ISP account,
 749 with an address extension of +<i>local</i> (this example assumes
 750 that the ISP supports "+" style address extensions). </p>
 751
 752 </ul>
 753
 754 <p>Specify <b>dbm</b> instead of <b>hash</b> if your system uses
 755 <b>dbm</b> files instead of <b>db</b> files. To find out what lookup
 756 tables Postfix supports, use the command "<b>postconf -m</b>".  </p>
 757
 758 <p> Execute the command "<b>postmap /etc/postfix/generic</b>"
 759 whenever you change the generic table. </p>
 760
 761 <h3>Solution 2: Postfix version 2.1 and earlier </h3>
 762
 763 <p> The solution with older Postfix systems is to use valid
 764 Internet addresses where possible, and to let Postfix map valid
 765 Internet addresses to local fantasy addresses. With this, you can
 766 send mail to the Internet and to local fantasy addresses, including
 767 mail to local fantasy addresses that don't have a valid Internet
 768 address of their own.</p>
 769
 770 <p> The following example presents additional configuration. You
 771 need to combine this with basic configuration information as
 772 discussed the first half of this document. </p>
 773
 774 <blockquote>
 775 <pre>
 776  1 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 777  2     <a href="postconf.5.html#myhostname">myhostname</a> = hostname.localdomain
 778  3     <a href="postconf.5.html#mydomain">mydomain</a> = localdomain
 779  4
 780  5     <a href="postconf.5.html#canonical_maps">canonical_maps</a> = hash:/etc/postfix/canonical
 781  6
 782  7     <a href="postconf.5.html#virtual_alias_maps">virtual_alias_maps</a> = hash:/etc/postfix/virtual
 783  8
 784  9 /etc/postfix/canonical:
 785 10     your-login-name    your-account@your-isp.com
 786 11
 787 12 /etc/postfix/virtual:
 788 13     your-account@your-isp.com       your-login-name
 789 </pre>
 790 </blockquote>
 791
 792 <p> Translation: </p>
 793
 794 <ul>
 795
 796 <li> <p> Lines 2-3: Substitute your fantasy hostname here. Do not
 797 use a domain name that is already in use by real organizations
 798 on the Internet. See <a href="http://tools.ietf.org/html/rfc2606">RFC 2606</a> for examples of domain
 799 names that are guaranteed not to be owned by anyone. </p>
 800
 801 <li> <p> Lines 5, 9, 10: This provides the mapping from
 802 "your-login-name@hostname.localdomain" to "your-account@your-isp.com".
 803 This part is required. </p>
 804
 805 <li> <p> Lines 7, 12, 13: Deliver mail for "your-account@your-isp.com"
 806 locally, instead of sending it to the ISP. This part is not required
 807 but is convenient.
 808
 809 </ul>
 810
 811 <p>Specify <b>dbm</b> instead of <b>hash</b> if your system uses
 812 <b>dbm</b> files instead of <b>db</b> files. To find out what lookup
 813 tables Postfix supports, use the command "<b>postconf -m</b>".  </p>
 814
 815 <p> Execute the command "<b>postmap /etc/postfix/canonical</b>"
 816 whenever you change the canonical table. </p>
 817
 818 <p> Execute the command "<b>postmap /etc/postfix/virtual</b>"
 819 whenever you change the virtual table. </p>
 820
 821 </body>
 822
 823 </html>