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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 16:18:56 +0000
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+<!doctype html public "-//W3C//DTD HTML 4.01 Transitional//EN"
+ "http://www.w3.org/TR/html4/loose.dtd">
+
+<html>
+
+<head>
+
+<title>Postfix Standard Configuration Examples</title>
+
+<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
+
+</head>
+
+<body>
+
+<h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Postfix Standard Configuration Examples</h1>
+
+<hr>
+
+<h2>Purpose of this document</h2>
+
+<p> This document presents a number of typical Postfix configurations.
+This document should be reviewed after you have followed the basic
+configuration steps as described in the <a href="BASIC_CONFIGURATION_README.html">BASIC_CONFIGURATION_README</a>
+document. In particular, do not proceed here if you don't already
+have Postfix working for local mail submission and for local mail
+delivery. </p>
+
+<p> The first part of this document presents standard configurations
+that each solve one specific problem. </p>
+
+<ul>
+
+<li><a href="#stand_alone">Postfix on a stand-alone Internet host</a>
+
+<li><a href="#null_client">Postfix on a null client</a>
+
+<li><a href="#local_network">Postfix on a local network</a>
+
+<li><a href="#firewall">Postfix email firewall/gateway</a>
+
+</ul>
+
+<p> The second part of this document presents additional configurations
+for hosts in specific environments. </p>
+
+<ul>
+
+<li><a href="#some_local">Delivering some but not all accounts locally</a>
+
+<li><a href="#intranet">Running Postfix behind a firewall</a>
+
+<li><a href="#backup">Configuring Postfix as primary or backup MX host for a remote
+site</a>
+
+<li><a href="#dialup">Postfix on a dialup machine</a>
+
+<li><a href="#fantasy">Postfix on hosts without a real
+Internet hostname</a>
+
+</ul>
+
+<h2><a name="stand_alone">Postfix on a stand-alone Internet host</a></h2>
+
+<p> Postfix should work out of the box without change on a stand-alone
+machine that has direct Internet access. At least, that is how
+Postfix installs when you download the Postfix source code via
+<a href="http://www.postfix.org/">http://www.postfix.org/</a>. </p>
+
+<p> You can use the command "<b>postconf -n</b>" to find out what
+settings are overruled by your <a href="postconf.5.html">main.cf</a>. Besides a few pathname
+settings, few parameters should be set on a stand-alone box, beyond
+what is covered in the <a href="BASIC_CONFIGURATION_README.html">BASIC_CONFIGURATION_README</a> document: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/<a href="postconf.5.html">main.cf</a>:
+ # Optional: send mail as user@domainname instead of user@hostname.
+ #<a href="postconf.5.html#myorigin">myorigin</a> = $<a href="postconf.5.html#mydomain">mydomain</a>
+
+ # Optional: specify NAT/proxy external address.
+ #<a href="postconf.5.html#proxy_interfaces">proxy_interfaces</a> = 1.2.3.4
+
+ # Alternative 1: don't relay mail from other hosts.
+ <a href="postconf.5.html#mynetworks_style">mynetworks_style</a> = host
+ <a href="postconf.5.html#relay_domains">relay_domains</a> =
+
+ # Alternative 2: relay mail from local clients only.
+ # <a href="postconf.5.html#mynetworks">mynetworks</a> = 192.168.1.0/28
+ # <a href="postconf.5.html#relay_domains">relay_domains</a> =
+</pre>
+</blockquote>
+
+<p> See also the section "<a href="#fantasy">Postfix on hosts without
+a real Internet hostname</a>" if this is applicable to your configuration.
+</p>
+
+<h2><a name="null_client">Postfix on a null client</a></h2>
+
+<p> A null client is a machine that can only send mail. It receives no
+mail from the network, and it does not deliver any mail locally. A
+null client typically uses POP, IMAP or NFS for mailbox access. </p>
+
+<p> In this example we assume that the Internet domain name is
+"example.com" and that the machine is named "hostname.example.com".
+As usual, the examples show only parameters that are not left at
+their default settings. </p>
+
+<blockquote>
+<pre>
+1 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
+2 <a href="postconf.5.html#myhostname">myhostname</a> = hostname.example.com
+3 <a href="postconf.5.html#myorigin">myorigin</a> = $<a href="postconf.5.html#mydomain">mydomain</a>
+4 <a href="postconf.5.html#relayhost">relayhost</a> = $<a href="postconf.5.html#mydomain">mydomain</a>
+5 <a href="postconf.5.html#inet_interfaces">inet_interfaces</a> = loopback-only
+6 <a href="postconf.5.html#mydestination">mydestination</a> =
+</pre>
+</blockquote>
+
+<p> Translation: </p>
+
+<ul>
+
+<li> <p> Line 2: Set <a href="postconf.5.html#myhostname">myhostname</a> to hostname.example.com, in case
+the machine name isn't set to a fully-qualified domain name (use
+the command "postconf -d <a href="postconf.5.html#myhostname">myhostname</a>" to find out what the machine
+name is). </p>
+
+<li> <p> Line 2: The <a href="postconf.5.html#myhostname">myhostname</a> value also provides the default
+value for the <a href="postconf.5.html#mydomain">mydomain</a> parameter (here, "<a href="postconf.5.html#mydomain">mydomain</a> = example.com").
+</p>
+
+<li> <p> Line 3: Send mail as "user@example.com" (instead of
+"user@hostname.example.com"), so that nothing ever has a reason
+to send mail to "user@hostname.example.com". </p>
+
+<li> <p> Line 4: Forward all mail to the mail server that is
+responsible for the "example.com" domain. This prevents mail from
+getting stuck on the null client if it is turned off while some
+remote destination is unreachable. Specify a real hostname
+here if your "example.com" domain has no MX record. </p>
+
+<li> <p> Line 5: Do not accept mail from the network. </p>
+
+<li> <p> Line 6: Disable local mail delivery. All mail goes to
+the mail server as specified in line 4. </p>
+
+</ul>
+
+<h2><a name="local_network">Postfix on a local network</a></h2>
+
+<p> This section describes a local area network environment of one
+main server and multiple other systems that send and receive email.
+As usual we assume that the Internet domain name is "example.com".
+All systems are configured to send mail as "user@example.com", and
+all systems receive mail for "user@hostname.example.com". The main
+server also receives mail for "user@example.com". We call this
+machine by the name of mailhost.example.com. </p>
+
+<p> A drawback of sending mail as "user@example.com" is that mail
+for "root" and other system accounts is also sent to the central
+mailhost. See the section "<a href="#some_local">Delivering some
+but not all accounts locally</a>" below for possible solutions.
+</p>
+
+<p> As usual, the examples show only parameters that are not left
+at their default settings. </p>
+
+<p> First we present the non-mailhost configuration, because it is
+the simpler one. This machine sends mail as "user@example.com" and
+is the final destination for "user@hostname.example.com". </p>
+
+<blockquote>
+<pre>
+1 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
+2 <a href="postconf.5.html#myorigin">myorigin</a> = $<a href="postconf.5.html#mydomain">mydomain</a>
+3 <a href="postconf.5.html#mynetworks">mynetworks</a> = 127.0.0.0/8 10.0.0.0/24
+4 <a href="postconf.5.html#relay_domains">relay_domains</a> =
+5 # Optional: forward all non-local mail to mailhost
+6 #<a href="postconf.5.html#relayhost">relayhost</a> = $<a href="postconf.5.html#mydomain">mydomain</a>
+</pre>
+</blockquote>
+
+<p> Translation: </p>
+
+<ul>
+
+<li> <p> Line 2: Send mail as "user@example.com". </p>
+
+<li> <p> Line 3: Specify the trusted networks. </p>
+
+<li> <p> Line 4: This host does not relay mail from untrusted networks. </p>
+
+<li> <p> Line 6: This is needed if no direct Internet access is
+available. See also below, "<a href="#firewall">Postfix behind
+a firewall</a>". </p>
+
+</ul>
+
+<p> Next we present the mailhost configuration. This machine sends
+mail as "user@example.com" and is the final destination for
+"user@hostname.example.com" as well as "user@example.com". </p>
+
+<blockquote>
+<pre>
+ 1 DNS:
+ 2 example.com IN MX 10 mailhost.example.com.
+ 3
+ 4 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
+ 5 <a href="postconf.5.html#myorigin">myorigin</a> = $<a href="postconf.5.html#mydomain">mydomain</a>
+ 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>
+ 7 <a href="postconf.5.html#mynetworks">mynetworks</a> = 127.0.0.0/8 10.0.0.0/24
+ 8 <a href="postconf.5.html#relay_domains">relay_domains</a> =
+ 9 # Optional: forward all non-local mail to firewall
+10 #<a href="postconf.5.html#relayhost">relayhost</a> = [firewall.example.com]
+</pre>
+</blockquote>
+
+<p> Translation: </p>
+
+<ul>
+
+<li> <p> Line 2: Send mail for the domain "example.com" to the
+machine mailhost.example.com. Remember to specify the "." at the
+end of the line. </p>
+
+<li> <p> Line 5: Send mail as "user@example.com". </p>
+
+<li> <p> Line 6: This host is the final mail destination for the
+"example.com" domain, in addition to the names of the machine
+itself. </p>
+
+<li> <p> Line 7: Specify the trusted networks. </p>
+
+<li> <p> Line 8: This host does not relay mail from untrusted networks. </p>
+
+<li> <p> Line 10: This is needed only when the mailhost has to
+forward non-local mail via a mail server on a firewall. The
+<tt>[]</tt> forces Postfix to do no MX record lookups. </p>
+
+</ul>
+
+<p> In an environment like this, users access their mailbox in one
+or more of the following ways:
+
+<ul>
+
+<li> <p> Mailbox access via NFS or equivalent. </p>
+
+<li> <p> Mailbox access via POP or IMAP. </p>
+
+<li> <p> Mailbox on the user's preferred machine. </p>
+
+</ul>
+
+<p> In the latter case, each user has an alias on the mailhost that
+forwards mail to her preferred machine: </p>
+
+<blockquote>
+<pre>
+/etc/aliases:
+ joe: joe@joes.preferred.machine
+ jane: jane@janes.preferred.machine
+</pre>
+</blockquote>
+
+<p> On some systems the alias database is not in /etc/aliases. To
+find out the location for your system, execute the command "<b>postconf
+<a href="postconf.5.html#alias_maps">alias_maps</a></b>". </p>
+
+<p> Execute the command "<b>newaliases</b>" whenever you change
+the aliases file. </p>
+
+<h2><a name="firewall">Postfix email firewall/gateway</a></h2>
+
+<p> The idea is to set up a Postfix email firewall/gateway that
+forwards mail for "example.com" to an inside gateway machine but
+rejects mail for "anything.example.com". There is only one problem:
+with "<a href="postconf.5.html#relay_domains">relay_domains</a> = example.com", the firewall normally also
+accepts mail for "anything.example.com". That would not be right.
+</p>
+
+<p> Note: this example requires Postfix version 2.0 and later. To find
+out what Postfix version you have, execute the command "<b>postconf
+<a href="postconf.5.html#mail_version">mail_version</a></b>". </p>
+
+<p> The solution is presented in multiple parts. This first part
+gets rid of local mail delivery on the firewall, making the firewall
+harder to break. </p>
+
+<blockquote>
+<pre>
+1 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
+2 <a href="postconf.5.html#myorigin">myorigin</a> = example.com
+3 <a href="postconf.5.html#mydestination">mydestination</a> =
+4 <a href="postconf.5.html#local_recipient_maps">local_recipient_maps</a> =
+5 <a href="postconf.5.html#local_transport">local_transport</a> = <a href="error.8.html">error</a>:local mail delivery is disabled
+6
+7 /etc/postfix/<a href="master.5.html">master.cf</a>:
+8 Comment out the local delivery agent
+</pre>
+</blockquote>
+
+<p> Translation: </p>
+
+<ul>
+
+<li> <p> Line 2: Send mail from this machine as "user@example.com",
+so that no reason exists to send mail to "user@firewall.example.com".
+</p>
+
+<li> <p> Lines 3-8: Disable local mail delivery on the firewall
+machine. </p>
+
+</ul>
+
+<p> For the sake of technical correctness the firewall must be able
+to receive mail for postmaster@[firewall ip address]. Reportedly,
+some things actually expect this ability to exist. The second part
+of the solution therefore adds support for postmaster@[firewall ip
+address], and as a bonus we do abuse@[firewall ip address] as well.
+All the mail to these two accounts is forwarded to an inside address.
+</p>
+
+<blockquote>
+<pre>
+1 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
+2 <a href="postconf.5.html#virtual_alias_maps">virtual_alias_maps</a> = <a href="DATABASE_README.html#types">hash</a>:/etc/postfix/virtual
+3
+4 /etc/postfix/virtual:
+5 postmaster postmaster@example.com
+6 abuse abuse@example.com
+</pre>
+</blockquote>
+
+<p> Translation: </p>
+
+<ul>
+
+<li> <p> Because <a href="postconf.5.html#mydestination">mydestination</a> is empty (see the previous example),
+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>
+are deemed local. So "localpart@[a.d.d.r]" can be matched as simply
+"localpart" in <a href="canonical.5.html">canonical(5)</a> and <a href="virtual.5.html">virtual(5)</a>. This avoids the need to
+specify firewall IP addresses in Postfix configuration files. </p>
+
+</ul>
+
+<p> The last part of the solution does the email forwarding, which
+is the real purpose of the firewall email function. </p>
+
+<blockquote>
+<pre>
+ 1 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
+ 2 <a href="postconf.5.html#mynetworks">mynetworks</a> = 127.0.0.0/8 12.34.56.0/24
+ 3 <a href="postconf.5.html#relay_domains">relay_domains</a> = example.com
+ 4 <a href="postconf.5.html#parent_domain_matches_subdomains">parent_domain_matches_subdomains</a> =
+ 5 <a href="postconf.5.html#debug_peer_list">debug_peer_list</a> smtpd_access_maps
+<br>
+ 6a # Postfix 2.10 and later support separate relay control and
+ 7a # spam control.
+ 8a <a href="postconf.5.html#smtpd_relay_restrictions">smtpd_relay_restrictions</a> =
+ 9a <a href="postconf.5.html#permit_mynetworks">permit_mynetworks</a> <a href="postconf.5.html#reject_unauth_destination">reject_unauth_destination</a>
+10a <a href="postconf.5.html#smtpd_recipient_restrictions">smtpd_recipient_restrictions</a> = ...spam blocking rules....
+<br>
+ 6b # Older configurations combine relay control and spam control. To
+ 7b # use this with Postfix &ge; 2.10 specify "<a href="postconf.5.html#smtpd_relay_restrictions">smtpd_relay_restrictions</a>=".
+ 8b <a href="postconf.5.html#smtpd_recipient_restrictions">smtpd_recipient_restrictions</a> =
+ 9b <a href="postconf.5.html#permit_mynetworks">permit_mynetworks</a> <a href="postconf.5.html#reject_unauth_destination">reject_unauth_destination</a>
+10b ...spam blocking rules....
+<br>
+11 <a href="postconf.5.html#relay_recipient_maps">relay_recipient_maps</a> = <a href="DATABASE_README.html#types">hash</a>:/etc/postfix/relay_recipients
+12 <a href="postconf.5.html#transport_maps">transport_maps</a> = <a href="DATABASE_README.html#types">hash</a>:/etc/postfix/transport
+13
+14 /etc/postfix/relay_recipients:
+15 user1@example.com x
+16 user2@example.com x
+17 . . .
+18
+19 /etc/postfix/transport:
+20 example.com <a href="smtp.8.html">smtp</a>:[inside-gateway.example.com]
+</pre>
+</blockquote>
+
+<p> Translation: </p>
+
+<ul>
+
+<li><p> Lines 1-10: Accept mail from local systems in $<a href="postconf.5.html#mynetworks">mynetworks</a>,
+and accept mail from outside for "user@example.com" but not for
+"user@anything.example.com". The magic is in lines 4-5. </p>
+
+<li> <p> Lines 11, 13-16: Define the list of valid addresses in the
+"example.com" domain that can receive mail from the Internet. This
+prevents the mail queue from filling up with undeliverable
+MAILER-DAEMON messages. If you can't maintain a list of valid
+recipients then you must specify "<a href="postconf.5.html#relay_recipient_maps">relay_recipient_maps</a> =" (that
+is, an empty value), or you must specify an "@example.com x"
+wild-card in the relay_recipients table. </p>
+
+<li> <p> Lines 12, 19-20: Route mail for "example.com" to the inside
+gateway machine. The <tt>[]</tt> forces Postfix to do no MX lookup.
+</p>
+
+</ul>
+
+<p>Specify <b>dbm</b> instead of <b>hash</b> if your system uses
+<b>dbm</b> files instead of <b>db</b> files. To find out what lookup
+tables Postfix supports, use the command "<b>postconf -m</b>". </p>
+
+<p> Execute the command "<b>postmap /etc/postfix/relay_recipients</b>"
+whenever you change the relay_recipients table. </p>
+
+<p> Execute the command "<b>postmap /etc/postfix/transport</b>"
+whenever you change the transport table. </p>
+
+<p> In some installations, there may be separate instances of Postfix
+processing inbound and outbound mail on a multi-homed firewall. The
+inbound Postfix instance has an SMTP server listening on the external
+firewall interface, and the outbound Postfix instance has an SMTP server
+listening on the internal interface. In such a configuration is it is
+tempting to configure $<a href="postconf.5.html#inet_interfaces">inet_interfaces</a> in each instance with just the
+corresponding interface address. </p>
+
+<p> In most cases, using <a href="postconf.5.html#inet_interfaces">inet_interfaces</a> in this way will not work,
+because as documented in the $<a href="postconf.5.html#inet_interfaces">inet_interfaces</a> reference manual, the
+<a href="smtp.8.html">smtp(8)</a> delivery agent will also use the specified interface address
+as the source address for outbound connections and will be unable to
+reach hosts on "the other side" of the firewall. The symptoms are that
+the firewall is unable to connect to hosts that are in fact up. See the
+<a href="postconf.5.html#inet_interfaces">inet_interfaces</a> parameter documentation for suggested work-arounds.</p>
+
+<h2><a name="some_local">Delivering some but not all accounts
+locally</a></h2>
+
+<p> A drawback of sending mail as "user@example.com" (instead of
+"user@hostname.example.com") is that mail for "root" and other
+system accounts is also sent to the central mailhost. In order to
+deliver such accounts locally, you can set up virtual aliases as
+follows: </p>
+
+<blockquote>
+<pre>
+1 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
+2 <a href="postconf.5.html#virtual_alias_maps">virtual_alias_maps</a> = <a href="DATABASE_README.html#types">hash</a>:/etc/postfix/virtual
+3
+4 /etc/postfix/virtual:
+5 root root@localhost
+6 . . .
+</pre>
+</blockquote>
+
+<p> Translation: </p>
+
+<ul>
+
+<li> <p> Line 5: As described in the <a href="virtual.5.html">virtual(5)</a> manual page, the
+bare name "root" matches "root@site" when "site" is equal to
+$<a href="postconf.5.html#myorigin">myorigin</a>, when "site" is listed in $<a href="postconf.5.html#mydestination">mydestination</a>, or when it
+matches $<a href="postconf.5.html#inet_interfaces">inet_interfaces</a> or $<a href="postconf.5.html#proxy_interfaces">proxy_interfaces</a>. </p>
+
+</ul>
+
+<p> Execute the command "<b>postmap /etc/postfix/virtual</b>" after
+editing the file. </p>
+
+<h2><a name="intranet">Running Postfix behind a firewall</a></h2>
+
+<p> The simplest way to set up Postfix on a host behind a firewalled
+network is to send all mail to a gateway host, and to let that mail
+host take care of internal and external forwarding. Examples of that
+are shown in the <a href="#local_network">local area network</a>
+section above. A more sophisticated approach is to send only external
+mail to the gateway host, and to send intranet mail directly. </p>
+
+<p> Note: this example requires Postfix version 2.0 and later. To find
+out what Postfix version you have, execute the command "<b>postconf
+<a href="postconf.5.html#mail_version">mail_version</a></b>". </p>
+
+<p> The following example presents additional configuration. You
+need to combine this with basic configuration information as
+discussed in the first half of this document. </p>
+
+<blockquote>
+<pre>
+ 1 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
+ 2 <a href="postconf.5.html#transport_maps">transport_maps</a> = <a href="DATABASE_README.html#types">hash</a>:/etc/postfix/transport
+ 3 <a href="postconf.5.html#relayhost">relayhost</a> =
+ 4 # Optional for a machine that isn't "always on"
+ 5 #<a href="postconf.5.html#fallback_relay">fallback_relay</a> = [gateway.example.com]
+ 6
+ 7 /etc/postfix/transport:
+ 8 # Internal delivery.
+ 9 example.com :
+10 .example.com :
+11 # External delivery.
+12 * <a href="smtp.8.html">smtp</a>:[gateway.example.com]
+</pre>
+</blockquote>
+
+<p> Translation: </p>
+
+<ul>
+
+<li> <p> Lines 2, 7-12: Request that intranet mail is delivered
+directly, and that external mail is given to a gateway. Obviously,
+this example assumes that the organization uses DNS MX records
+internally. The <tt>[]</tt> forces Postfix to do no MX lookup.
+</p>
+
+<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>.
+</p>
+
+<li> <p> Line 5: This prevents mail from being stuck in the queue
+when the machine is turned off. Postfix tries to deliver mail
+directly, and gives undeliverable mail to a gateway. </p>
+
+</ul>
+
+<p> Specify <b>dbm</b> instead of <b>hash</b> if your system uses
+<b>dbm</b> files instead of <b>db</b> files. To find out what lookup
+tables Postfix supports, use the command "<b>postconf -m</b>". </p>
+
+<p> Execute the command "<b>postmap /etc/postfix/transport</b>" whenever
+you edit the transport table. </p>
+
+<h2><a name="backup">Configuring Postfix as primary or backup MX host for a remote site</a></h2>
+
+<p> This section presents additional configuration. You need to
+combine this with basic configuration information as discussed in the
+first half of this document. </p>
+
+<p> When your system is SECONDARY MX host for a remote site this
+is all you need: </p>
+
+<blockquote>
+<pre>
+ 1 DNS:
+ 2 the.backed-up.domain.tld IN MX 100 your.machine.tld.
+ 3
+ 4 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
+ 5 <a href="postconf.5.html#relay_domains">relay_domains</a> = . . . the.backed-up.domain.tld
+<br>
+ 6a # Postfix 2.10 and later support separate relay control and
+ 7a # spam control.
+ 8a <a href="postconf.5.html#smtpd_relay_restrictions">smtpd_relay_restrictions</a> =
+ 9a <a href="postconf.5.html#permit_mynetworks">permit_mynetworks</a> <a href="postconf.5.html#reject_unauth_destination">reject_unauth_destination</a>
+10a <a href="postconf.5.html#smtpd_recipient_restrictions">smtpd_recipient_restrictions</a> = ...spam blocking rules....
+<br>
+ 6b # Older configurations combine relay control and spam control. To
+ 7b # use this with Postfix &ge; 2.10 specify "<a href="postconf.5.html#smtpd_relay_restrictions">smtpd_relay_restrictions</a>=".
+ 8b <a href="postconf.5.html#smtpd_recipient_restrictions">smtpd_recipient_restrictions</a> =
+ 9b <a href="postconf.5.html#permit_mynetworks">permit_mynetworks</a> <a href="postconf.5.html#reject_unauth_destination">reject_unauth_destination</a>
+10b ...spam blocking rules....
+<br>
+11 # You must specify your NAT/proxy external address.
+12 #<a href="postconf.5.html#proxy_interfaces">proxy_interfaces</a> = 1.2.3.4
+13
+14 <a href="postconf.5.html#relay_recipient_maps">relay_recipient_maps</a> = <a href="DATABASE_README.html#types">hash</a>:/etc/postfix/relay_recipients
+15
+16 /etc/postfix/relay_recipients:
+17 user1@the.backed-up.domain.tld x
+18 user2@the.backed-up.domain.tld x
+19 . . .
+</pre>
+</blockquote>
+
+<p> When your system is PRIMARY MX host for a remote site you
+need the above, plus: </p>
+
+<blockquote>
+<pre>
+20 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
+21 <a href="postconf.5.html#transport_maps">transport_maps</a> = <a href="DATABASE_README.html#types">hash</a>:/etc/postfix/transport
+22
+23 /etc/postfix/transport:
+24 the.backed-up.domain.tld relay:[their.mail.host.tld]
+</pre>
+</blockquote>
+
+<p> Important notes:
+
+<ul>
+
+<li><p>Do not list the.backed-up.domain.tld in <a href="postconf.5.html#mydestination">mydestination</a>.</p>
+
+<li><p>Do not list the.backed-up.domain.tld in <a href="postconf.5.html#virtual_alias_domains">virtual_alias_domains</a>.</p>
+
+<li><p>Do not list the.backed-up.domain.tld in <a href="postconf.5.html#virtual_mailbox_domains">virtual_mailbox_domains</a>.</p>
+
+<li> <p> Lines 1-9: Forward mail from the Internet for
+"the.backed-up.domain.tld" to the primary MX host for that domain.
+</p>
+
+<li> <p> Line 12: This is a must if Postfix receives mail via a
+NAT relay or proxy that presents a different IP address to the
+world than the local machine. </p>
+
+<li> <p> Lines 14-18: Define the list of valid addresses in the
+"the.backed-up.domain.tld" domain. This prevents your mail queue
+from filling up with undeliverable MAILER-DAEMON messages. If you
+can't maintain a list of valid recipients then you must specify
+"<a href="postconf.5.html#relay_recipient_maps">relay_recipient_maps</a> =" (that is, an empty value), or you must
+specify an "@the.backed-up.domain.tld x" wild-card in the
+relay_recipients table. </p>
+
+<li> <p> Line 24: The <tt>[]</tt> forces Postfix to do no MX lookup. </p>
+
+</ul>
+
+<p> Specify <b>dbm</b> instead of <b>hash</b> if your system uses
+<b>dbm</b> files instead of <b>db</b> files. To find out what lookup
+tables Postfix supports, use the command "<b>postconf -m</b>". </p>
+
+<p> Execute the command "<b>postmap /etc/postfix/transport</b>"
+whenever you change the transport table. </p>
+
+<p> NOTE for Postfix &lt; 2.2: Do not use the <a href="postconf.5.html#fallback_relay">fallback_relay</a> feature
+when relaying mail
+for a backup or primary MX domain. Mail would loop between the
+Postfix MX host and the <a href="postconf.5.html#fallback_relay">fallback_relay</a> host when the final destination
+is unavailable. </p>
+
+<ul>
+
+<li> In <a href="postconf.5.html">main.cf</a> specify "<tt><a href="postconf.5.html#relay_transport">relay_transport</a> = relay</tt>",
+
+<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
+end of the <tt>relay</tt> entry.
+
+<li> In transport maps, specify "<tt>relay:<i>nexthop...</i></tt>"
+as the right-hand side for backup or primary MX domain entries.
+
+</ul>
+
+<p> These are default settings in Postfix version 2.2 and later.
+</p>
+
+<h2><a name="dialup">Postfix on a dialup machine</a></h2>
+
+<p> This section applies to dialup connections that are down most
+of the time. For dialup connections that are up 24x7, see the <a
+href="#local_network">local area network</a> section above. </p>
+
+<p> This section presents additional configuration. You need to
+combine this with basic configuration information as discussed in the
+first half of this document. </p>
+
+<p> If you do not have your own hostname and IP address (usually
+with dialup, cable TV or DSL connections) then you should also
+study the section on "<a href="#fantasy">Postfix on hosts without
+a real Internet hostname</a>". </p>
+
+<ul>
+
+<li> Route all outgoing mail to your network provider.
+
+<p> If your machine is disconnected most of the time, there isn't
+a lot of opportunity for Postfix to deliver mail to hard-to-reach
+corners of the Internet. It's better to give the mail to a machine
+that is connected all the time. In the example below, the <tt>[]</tt>
+prevents Postfix from trying to look up DNS MX records. </p>
+
+<pre>
+/etc/postfix/<a href="postconf.5.html">main.cf</a>:
+ <a href="postconf.5.html#relayhost">relayhost</a> = [smtprelay.someprovider.com]
+</pre>
+
+<li> <p><a name="spontaneous_smtp">Disable spontaneous SMTP mail
+delivery (if using on-demand dialup IP only).</a> </p>
+
+<p> Normally, Postfix attempts to deliver outbound mail at its convenience.
+If your machine uses on-demand dialup IP, this causes your system
+to place a telephone call whenever you submit new mail, and whenever
+Postfix retries to deliver delayed mail. To prevent such telephone
+calls from being placed, disable spontaneous SMTP mail deliveries. </p>
+
+<pre>
+/etc/postfix/<a href="postconf.5.html">main.cf</a>:
+ <a href="postconf.5.html#defer_transports">defer_transports</a> = smtp (Only for on-demand dialup IP hosts)
+</pre>
+
+<li> <p>Disable SMTP client DNS lookups (dialup LAN only).</p>
+
+<pre>
+/etc/postfix/<a href="postconf.5.html">main.cf</a>:
+ <a href="postconf.5.html#disable_dns_lookups">disable_dns_lookups</a> = yes (Only for on-demand dialup IP hosts)
+</pre>
+
+<li> Flush the mail queue whenever the Internet link is established.
+
+<p> Put the following command into your PPP or SLIP dialup scripts: </p>
+
+<pre>
+/usr/sbin/sendmail -q (whenever the Internet link is up)
+</pre>
+
+<p> The exact location of the Postfix sendmail command is system-specific.
+Use the command "<b>postconf <a href="postconf.5.html#sendmail_path">sendmail_path</a></b>" to find out where the
+Postfix sendmail command is located on your machine. </p>
+
+<p> In order to find out if the mail queue is flushed, use something
+like: </p>
+
+<pre>
+#!/bin/sh
+
+# Start mail deliveries.
+/usr/sbin/sendmail -q
+
+# Allow deliveries to start.
+sleep 10
+
+# Loop until all messages have been tried at least once.
+while mailq | grep '^[^ ]*\*' &gt;/dev/null
+do
+ sleep 10
+done
+</pre>
+
+<p> If you have disabled <a href="#spontaneous_smtp">spontaneous
+SMTP mail delivery</a>, you also need to run the "<b>sendmail -q</b>"
+command every now and then while the dialup link is up, so that
+newly-posted mail is flushed from the queue. </p>
+
+</ul>
+
+<h2><a name="fantasy">Postfix on hosts without a real Internet
+hostname</a></h2>
+
+<p> This section is for hosts that don't have their own Internet
+hostname. Typically these are systems that get a dynamic IP address
+via DHCP or via dialup. Postfix will let you send and receive mail
+just fine between accounts on a machine with a fantasy name. However,
+you cannot use a fantasy hostname in your email address when sending
+mail into the Internet, because no-one would be able to reply to
+your mail. In fact, more and more sites refuse mail addresses with
+non-existent domain names. </p>
+
+<p> Note: the following information is Postfix version dependent.
+To find out what Postfix version you have, execute the command
+"<b>postconf <a href="postconf.5.html#mail_version">mail_version</a></b>". </p>
+
+<h3>Solution 1: Postfix version 2.2 and later </h3>
+
+<p> Postfix 2.2 uses the <a href="generic.5.html">generic(5)</a> address mapping to replace
+local fantasy email addresses by valid Internet addresses. This
+mapping happens ONLY when mail leaves the machine; not when you
+send mail between users on the same machine. </p>
+
+<p> The following example presents additional configuration. You
+need to combine this with basic configuration information as
+discussed in the first half of this document. </p>
+
+<blockquote>
+<pre>
+1 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
+2 <a href="postconf.5.html#smtp_generic_maps">smtp_generic_maps</a> = <a href="DATABASE_README.html#types">hash</a>:/etc/postfix/generic
+3
+4 /etc/postfix/generic:
+5 his@localdomain.local hisaccount@hisisp.example
+6 her@localdomain.local heraccount@herisp.example
+7 @localdomain.local hisaccount+local@hisisp.example
+</pre>
+</blockquote>
+
+<p> When mail is sent to a remote host via SMTP: </p>
+
+<ul>
+
+<li> <p> Line 5 replaces <i>his@localdomain.local</i> by his ISP
+mail address, </p>
+
+<li> <p> Line 6 replaces <i>her@localdomain.local</i> by her ISP
+mail address, and </p>
+
+<li> <p> Line 7 replaces other local addresses by his ISP account,
+with an address extension of +<i>local</i> (this example assumes
+that the ISP supports "+" style address extensions). </p>
+
+</ul>
+
+<p>Specify <b>dbm</b> instead of <b>hash</b> if your system uses
+<b>dbm</b> files instead of <b>db</b> files. To find out what lookup
+tables Postfix supports, use the command "<b>postconf -m</b>". </p>
+
+<p> Execute the command "<b>postmap /etc/postfix/generic</b>"
+whenever you change the generic table. </p>
+
+<h3>Solution 2: Postfix version 2.1 and earlier </h3>
+
+<p> The solution with older Postfix systems is to use valid
+Internet addresses where possible, and to let Postfix map valid
+Internet addresses to local fantasy addresses. With this, you can
+send mail to the Internet and to local fantasy addresses, including
+mail to local fantasy addresses that don't have a valid Internet
+address of their own.</p>
+
+<p> The following example presents additional configuration. You
+need to combine this with basic configuration information as
+discussed in the first half of this document. </p>
+
+<blockquote>
+<pre>
+ 1 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
+ 2 <a href="postconf.5.html#myhostname">myhostname</a> = hostname.localdomain
+ 3 <a href="postconf.5.html#mydomain">mydomain</a> = localdomain
+ 4
+ 5 <a href="postconf.5.html#canonical_maps">canonical_maps</a> = <a href="DATABASE_README.html#types">hash</a>:/etc/postfix/canonical
+ 6
+ 7 <a href="postconf.5.html#virtual_alias_maps">virtual_alias_maps</a> = <a href="DATABASE_README.html#types">hash</a>:/etc/postfix/virtual
+ 8
+ 9 /etc/postfix/canonical:
+10 your-login-name your-account@your-isp.com
+11
+12 /etc/postfix/virtual:
+13 your-account@your-isp.com your-login-name
+</pre>
+</blockquote>
+
+<p> Translation: </p>
+
+<ul>
+
+<li> <p> Lines 2-3: Substitute your fantasy hostname here. Do not
+use a domain name that is already in use by real organizations
+on the Internet. See <a href="https://tools.ietf.org/html/rfc2606">RFC 2606</a> for examples of domain
+names that are guaranteed not to be owned by anyone. </p>
+
+<li> <p> Lines 5, 9, 10: This provides the mapping from
+"your-login-name@hostname.localdomain" to "your-account@your-isp.com".
+This part is required. </p>
+
+<li> <p> Lines 7, 12, 13: Deliver mail for "your-account@your-isp.com"
+locally, instead of sending it to the ISP. This part is not required
+but is convenient.
+
+</ul>
+
+<p>Specify <b>dbm</b> instead of <b>hash</b> if your system uses
+<b>dbm</b> files instead of <b>db</b> files. To find out what lookup
+tables Postfix supports, use the command "<b>postconf -m</b>". </p>
+
+<p> Execute the command "<b>postmap /etc/postfix/canonical</b>"
+whenever you change the canonical table. </p>
+
+<p> Execute the command "<b>postmap /etc/postfix/virtual</b>"
+whenever you change the virtual table. </p>
+
+</body>
+
+</html>