674 lines
22 KiB
HTML
674 lines
22 KiB
HTML
<!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 Basic Configuration </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 Basic Configuration </h1>
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<hr>
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<h2> Introduction </h2>
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<p> Postfix has several hundred configuration parameters that are
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controlled via the main.cf file. Fortunately, all parameters have
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sensible default values. In many cases, you need to configure only
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two or three parameters before you can start to play with the mail
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system. Here's a quick introduction to the syntax: </p>
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<ul>
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<li> <p> <a href="#syntax">Postfix configuration files</a></p>
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</ul>
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<p> The text below assumes that you already have Postfix installed
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on the system, either by compiling the source code yourself (as
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described in the INSTALL file) or by installing an already compiled
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version. </p>
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<p> This document covers basic Postfix configuration. Information
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about how to configure Postfix for specific applications such as
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mailhub, firewall or dial-up client can be found in the
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STANDARD_CONFIGURATION_README file. But don't go there until you
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already have covered the material presented below. </p>
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<p> The first parameters of interest specify the machine's identity
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and role in the network. </p>
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<ul>
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<li> <p> <a href="#myorigin"> What domain name to use in outbound mail </a> </p>
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<li> <p> <a href="#mydestination"> What domains to receive mail for </a> </p>
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<li> <p> <a href="#relay_from"> What clients to relay mail from </a> </p>
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<li> <p> <a href="#relay_to"> What destinations to relay mail to </a> </p>
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<li> <p> <a href="#relayhost"> What delivery method: direct or
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indirect </a> </p>
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</ul>
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<p> The default values for many other configuration parameters are
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derived from just these. </p>
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<p> The next parameter of interest controls the amount of mail sent
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to the local postmaster: </p>
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<ul>
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<li> <p> <a href="#notify"> What trouble to report to the postmaster
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</a> </p>
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</ul>
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<p> Be sure to set the following correctly if you're behind a proxy or
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network address translator, and you are running a backup MX host
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for some other domain: </p>
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<ul>
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<li> <p> <a href="#proxy_interfaces"> Proxy/NAT external network
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addresses </a> </p>
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</ul>
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<p> Postfix daemon processes run in the background, and log problems
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and normal activity to the syslog daemon. Here are a few things
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that you need to be aware of: </p>
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<ul>
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<li> <p> <a href="#syslog_howto"> What you need to know about
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Postfix logging </a> </p>
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</ul>
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<p> If your machine has unusual security requirements you may
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want to run Postfix daemon processes inside a chroot environment. </p>
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<ul>
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<li> <p> <a href="#chroot_setup"> Running Postfix daemon processes
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chrooted </a> </p>
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</ul>
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<p> If you run Postfix on a virtual network interface, or if your
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machine runs other mailers on virtual interfaces, you'll have to
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look at the other parameters listed here as well: </p>
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<ul>
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<li> <p> <a href="#myhostname"> My own hostname </a> </p>
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<li> <p> <a href="#mydomain"> My own domain name </a> </p>
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<li> <p> <a href="#inet_interfaces"> My own network addresses </a> </p>
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</ul>
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<h2> <a name="syntax">Postfix configuration files</a></h2>
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<p> By default, Postfix configuration files are in /etc/postfix.
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The two most important files are main.cf and master.cf; these files
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must be owned by root. Giving someone else write permission to
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main.cf or master.cf (or to their parent directories) means giving
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root privileges to that person. </p>
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<p> In /etc/postfix/main.cf you will have to set up a minimal number
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of configuration parameters. Postfix configuration parameters
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resemble shell variables, with two important differences: the first
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one is that Postfix does not know about quotes like the UNIX shell
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does.</p>
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<p> You specify a configuration parameter as: </p>
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<blockquote>
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<pre>
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/etc/postfix/main.cf:
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parameter = value
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</pre>
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</blockquote>
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<p> and you use it by putting a "$" character in front of its name: </p>
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<blockquote>
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<pre>
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/etc/postfix/main.cf:
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other_parameter = $parameter
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</pre>
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</blockquote>
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<p> You can use $parameter before it is given a value (that is the
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second main difference with UNIX shell variables). The Postfix
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configuration language uses lazy evaluation, and does not look at
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a parameter value until it is needed at runtime. </p>
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<p> Postfix uses database files for access control, address rewriting
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and other purposes. The DATABASE_README file gives an introduction
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to how Postfix works with Berkeley DB, LDAP or SQL and other types.
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Here is a common example of how Postfix invokes a database: </p>
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<blockquote>
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<pre>
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/etc/postfix/main.cf:
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virtual_alias_maps = hash:/etc/postfix/virtual
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</pre>
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</blockquote>
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<p> Whenever you make a change to the main.cf or master.cf file,
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execute the following command as root in order to refresh a running
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mail system: </p>
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<blockquote>
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<pre>
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# postfix reload
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</pre>
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</blockquote>
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<h2> <a name="myorigin"> What domain name to use in outbound mail </a> </h2>
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<p> The myorigin parameter specifies the domain that appears in
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mail that is posted on this machine. The default is to use the
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local machine name, $myhostname, which defaults to the name of the
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machine. Unless you are running a really small site, you probably
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want to change that into $mydomain, which defaults to the parent
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domain of the machine name. </p>
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<p> For the sake of consistency between sender and recipient addresses,
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myorigin also specifies the domain name that is appended
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to an unqualified recipient address. </p>
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<p> Examples (specify only one of the following): </p>
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<blockquote>
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<pre>
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/etc/postfix/main.cf:
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myorigin = $myhostname (default: send mail as "user@$myhostname")
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myorigin = $mydomain (probably desirable: "user@$mydomain")
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</pre>
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</blockquote>
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<h2><a name="mydestination"> What domains to receive mail for </a>
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</h2>
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<p> The mydestination parameter specifies what domains this
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machine will deliver locally, instead of forwarding to another
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machine. The default is to receive mail for the machine itself.
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See the VIRTUAL_README file for how to configure Postfix for
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hosted domains. </p>
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<p> You can specify zero or more domain names, "/file/name" patterns
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and/or "type:table" lookup tables (such as hash:, btree:, nis:, ldap:,
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or mysql:), separated by whitespace and/or commas. A "/file/name"
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pattern is replaced by its contents; "type:table" requests that a
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table lookup is done and merely tests for existence: the lookup
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result is ignored. </p>
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<p> IMPORTANT: If your machine is a mail server for its entire
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domain, you must list $mydomain as well. </p>
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<p> Example 1: default setting. </p>
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<blockquote>
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<pre>
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/etc/postfix/main.cf:
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mydestination = $myhostname localhost.$mydomain localhost
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</pre>
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</blockquote>
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<p> Example 2: domain-wide mail server. </p>
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<blockquote>
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<pre>
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/etc/postfix/main.cf:
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mydestination = $myhostname localhost.$mydomain localhost $mydomain
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</pre>
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</blockquote>
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<p> Example 3: host with multiple DNS A records. </p>
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<blockquote>
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<pre>
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/etc/postfix/main.cf:
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mydestination = $myhostname localhost.$mydomain localhost
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www.$mydomain ftp.$mydomain
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</pre>
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</blockquote>
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<p> Caution: in order to avoid mail delivery loops, you must list all
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hostnames of the machine, including $myhostname, and localhost.$mydomain. </p>
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<h2> <a name="relay_from"> What clients to relay mail from </a> </h2>
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<p> By default, Postfix will forward mail from clients in authorized
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network blocks to any destination. Authorized networks are defined
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with the mynetworks configuration parameter. The default is to
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authorize all clients in the IP subnetworks that the local machine
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is attached to. </p>
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<p> IMPORTANT: If your machine is connected to a wide area network
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then your default mynetworks setting may be too friendly. </p>
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<p> Examples (specify only one of the following): </p>
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<blockquote>
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<pre>
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/etc/postfix/main.cf:
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mynetworks_style = subnet (default: authorize subnetworks)
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mynetworks_style = host (safe: authorize local machine only)
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mynetworks = 127.0.0.0/8 (safe: authorize local machine only)
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mynetworks = 127.0.0.0/8 168.100.189.2/32 (authorize local machine)
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</pre>
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</blockquote>
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<p> You can specify the trusted networks in the main.cf file, or
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you can let Postfix do the work for you. The default is to let
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Postfix do the work. The result depends on the mynetworks_style
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parameter value.
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<ul>
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<li> <p> Specify "mynetworks_style = host" when Postfix should
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forward mail from only the local machine. </p>
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<li> <p> Specify "mynetworks_style = subnet" (the default) when
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Postfix should forward mail from SMTP clients in the same IP
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subnetworks as the local machine. On Linux, this works correctly
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only with interfaces specified with the "ifconfig" command. </p>
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<li> <p> Specify "mynetworks_style = class" when Postfix should
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forward mail from SMTP clients in the same IP class A/B/C networks
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as the local machine. Don't do this with a dialup site - it would
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cause Postfix to "trust" your entire provider's network. Instead,
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specify an explicit mynetworks list by hand, as described below.
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</p>
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</ul>
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<p> Alternatively, you can specify the mynetworks list by hand,
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in which case Postfix ignores the mynetworks_style setting.
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To specify the list of trusted networks by hand, specify network
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blocks in CIDR (network/mask) notation, for example: </p>
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<blockquote>
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<pre>
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/etc/postfix/main.cf:
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mynetworks = 168.100.189.0/28, 127.0.0.0/8
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</pre>
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</blockquote>
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<p> You can also specify the absolute pathname of a pattern file instead
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of listing the patterns in the main.cf file. </p>
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<h2> <a name="relay_to"> What destinations to relay mail to </a> </h2>
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<p> By default, Postfix will forward mail from strangers (clients outside
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authorized networks) to authorized destinations only. Authorized
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destinations are defined with the relay_domains configuration
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parameter. The default is to authorize all domains (and subdomains)
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of the domains listed with the mydestination parameter. </p>
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<p> Examples (specify only one of the following): </p>
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<blockquote>
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<pre>
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/etc/postfix/main.cf:
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relay_domains = $mydestination (default)
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relay_domains = (safe: never forward mail from strangers)
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relay_domains = $mydomain (forward mail to my domain and subdomains)
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</pre>
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</blockquote>
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<h2> <a name="relayhost"> What delivery method: direct or
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indirect </a> </h2>
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<p> By default, Postfix tries to deliver mail directly to the
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Internet. Depending on your local conditions this may not be possible
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or desirable. For example, your system may be turned off outside
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office hours, it may be behind a firewall, or it may be connected
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via a provider who does not allow direct mail to the Internet. In
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those cases you need to configure Postfix to deliver mail indirectly
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via a relay host. </p>
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<p> Examples (specify only one of the following): </p>
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<blockquote>
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<pre>
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/etc/postfix/main.cf:
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relayhost = (default: direct delivery to Internet)
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relayhost = $mydomain (deliver via local mailhub)
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relayhost = [mail.$mydomain] (deliver via local mailhub)
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relayhost = [mail.isp.tld] (deliver via provider mailhub)
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</pre>
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</blockquote>
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<p> The form enclosed with <tt>[]</tt> eliminates DNS MX lookups.
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Don't worry if you don't know what that means. </p>
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<p> The STANDARD_CONFIGURATION_README file has more hints and tips
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for firewalled and/or dial-up networks. </p>
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<h2> <a name="notify"> What trouble to report to the postmaster</a> </h2>
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<p> You should set up a postmaster alias in the aliases(5) table
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that directs mail to a human person. The postmaster address is
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required to exist, so that people can report mail delivery problems.
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While you're updating the aliases(5) table, be sure to direct mail
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for the super-user to a human person too. </p>
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<blockquote>
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<pre>
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/etc/aliases:
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postmaster: you
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root: you
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</pre>
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</blockquote>
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<p> Execute the command "newaliases" after changing the aliases
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file. Instead of /etc/aliases, your alias file may be located
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elsewhere. Use the command "postconf alias_maps" to find out.</p>
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<p> The Postfix system reports problems to the postmaster alias.
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You may not be interested in all types of trouble reports, so this
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reporting mechanism is configurable. The default is to report only
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serious problems (resource, software) to postmaster: </p>
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<p> Default setting: </p>
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<blockquote>
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<pre>
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/etc/postfix/main.cf:
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notify_classes = resource, software
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</pre>
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</blockquote>
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<p> The meaning of the classes is as follows: </p>
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<blockquote>
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<dl>
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<dt> bounce </dt> <dd> Inform the postmaster of undeliverable
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mail. Either send the postmaster a copy of undeliverable mail that
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is returned to the sender, or send a transcript of the SMTP session
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when Postfix rejected mail. For privacy reasons, the postmaster
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copy of undeliverable mail is truncated after the original message
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headers. This implies "2bounce" (see below). See also the
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luser_relay feature. The notification is sent to the address
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specified with the bounce_notice_recipient configuration parameter
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(default: postmaster). </dd>
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<dt> 2bounce </dt> <dd> When Postfix is unable to return undeliverable
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mail to the sender, send it to the postmaster instead (without
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truncating the message after the primary headers). The notification
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is sent to the address specified with the 2bounce_notice_recipient
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configuration parameter (default: postmaster). </dd>
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<dt> delay </dt> <dd> Inform the postmaster of delayed mail. In
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this case, the postmaster receives message headers only. The
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notification is sent to the address specified with the
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delay_notice_recipient configuration parameter (default: postmaster).
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</dd>
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<dt> policy </dt> <dd> Inform the postmaster of client requests
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that were rejected because of (UCE) policy restrictions. The
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postmaster receives a transcript of the SMTP session. The notification
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is sent to the address specified with the error_notice_recipient
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configuration parameter (default: postmaster). </dd>
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<dt> protocol </dt> <dd> Inform the postmaster of protocol errors
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(client or server side) or attempts by a client to execute
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unimplemented commands. The postmaster receives a transcript of
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the SMTP session. The notification is sent to the address specified
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with the error_notice_recipient configuration parameter (default:
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postmaster). </dd>
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<dt> resource </dt> <dd> Inform the postmaster of mail not delivered
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due to resource problems (for example, queue file write errors).
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The notification is sent to the address specified with the
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error_notice_recipient configuration parameter (default: postmaster).
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</dd>
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<dt> software </dt> <dd> Inform the postmaster of mail not delivered
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due to software problems. The notification is sent to the address
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specified with the error_notice_recipient configuration parameter
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(default: postmaster). </dd>
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</dl>
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</blockquote>
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<h2><a name="proxy_interfaces"> Proxy/NAT external network
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addresses</a> </h2>
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<p> Some mail servers are connected to the Internet via a network
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address translator (NAT) or proxy. This means that systems on the
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Internet connect to the address of the NAT or proxy, instead of
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connecting to the network address of the mail server. The NAT or
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proxy forwards the connection to the network address of the mail
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server, but Postfix does not know this. </p>
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<p> If you run a Postfix server behind a proxy or NAT, you need to
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configure the proxy_interfaces parameter and specify all the external
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proxy or NAT addresses that Postfix receives mail on. You may
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specify symbolic hostnames instead of network addresses. </p>
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<p> IMPORTANT: You must specify your proxy/NAT external addresses
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when your system is a backup MX host for other domains, otherwise
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mail delivery loops will happen when the primary MX host is down.
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</p>
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<p> Example: host behind NAT box running a backup MX host. </p>
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<blockquote>
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<pre>
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/etc/postfix/main.cf:
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proxy_interfaces = 1.2.3.4 (the proxy/NAT external network address)
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</pre>
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</blockquote>
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<h2> <a name="syslog_howto"> What you need to know about
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Postfix logging </a> </h2>
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<p> Postfix daemon processes run in the background, and log problems
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and normal activity to the syslog daemon. The syslogd process sorts
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events by class and severity, and appends them to logfiles. The
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logging classes, levels and logfile names are usually specified in
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/etc/syslog.conf. At the very least you need something like: </p>
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<blockquote>
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<pre>
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/etc/syslog.conf:
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mail.err /dev/console
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mail.debug /var/log/maillog
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</pre>
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</blockquote>
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<p> After changing the syslog.conf file, send a "HUP" signal to
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the syslogd process. </p>
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<p> IMPORTANT: many syslogd implementations will not create files.
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You must create files before (re)starting syslogd. </p>
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<p> IMPORTANT: on Linux you need to put a "-" character before the
|
|
pathname, e.g., -/var/log/maillog, otherwise the syslogd process
|
|
will use more system resources than Postfix. </p>
|
|
|
|
<p> Hopefully, the number of problems will be small, but it is a good
|
|
idea to run every night before the syslog files are rotated: </p>
|
|
|
|
<blockquote>
|
|
<pre>
|
|
# postfix check
|
|
# egrep '(reject|warning|error|fatal|panic):' /some/log/file
|
|
</pre>
|
|
</blockquote>
|
|
|
|
<ul>
|
|
|
|
<li> <p> The first line (postfix check) causes Postfix to report
|
|
file permission/ownership discrepancies. </p>
|
|
|
|
<li> <p> The second line looks for problem reports from the mail
|
|
software, and reports how effective the relay and junk mail access
|
|
blocks are. This may produce a lot of output. You will want to
|
|
apply some postprocessing to eliminate uninteresting information.
|
|
</p>
|
|
|
|
</ul>
|
|
|
|
<p> The <a href="DEBUG_README.html#logging"> DEBUG_README </a>
|
|
document describes the meaning of the "warning" etc. labels in
|
|
Postfix logging. </p>
|
|
|
|
<h2> <a name="chroot_setup"> Running Postfix daemon processes
|
|
chrooted </a> </h2>
|
|
|
|
<p> Postfix daemon processes can be configured (via the master.cf
|
|
file) to run in a chroot jail. The processes run at a fixed low
|
|
privilege and with file system access limited to the Postfix queue
|
|
directories (/var/spool/postfix). This provides a significant
|
|
barrier against intrusion. The barrier is not impenetrable (chroot
|
|
limits file system access only), but every little bit helps.</p>
|
|
|
|
<p>With the exception of Postfix daemons that deliver mail locally
|
|
and/or that execute non-Postfix commands, every Postfix daemon can
|
|
run chrooted.</p>
|
|
|
|
<p>Sites with high security requirements should consider to chroot
|
|
all daemons that talk to the network: the smtp(8) and smtpd(8)
|
|
processes, and perhaps also the lmtp(8) client. The author's own
|
|
porcupine.org mail server runs all daemons chrooted that can be
|
|
chrooted. </p>
|
|
|
|
<p>The default /etc/postfix/master.cf file specifies that no Postfix
|
|
daemon runs chrooted. In order to enable chroot operation, edit
|
|
the file /etc/postfix/master.cf, and follow instructions in the
|
|
file. When you're finished, execute "postfix reload" to make the
|
|
change effective. </p>
|
|
|
|
<p>Note that a chrooted daemon resolves all filenames relative to
|
|
the Postfix queue directory (/var/spool/postfix). For successful
|
|
use of a chroot jail, most UNIX systems require you to bring in
|
|
some files or device nodes. The examples/chroot-setup directory in
|
|
the source code distribution has a collection of scripts that help
|
|
you set up Postfix chroot environments on different operating
|
|
systems.</p>
|
|
|
|
<p> Additionally, you almost certainly need to configure syslogd
|
|
so that it listens on a socket inside the Postfix queue directory.
|
|
Examples of syslogd command line options that achieve this for
|
|
specific systems: </p>
|
|
|
|
<p> FreeBSD: <tt>syslogd -l /var/spool/postfix/var/run/log</tt> </p>
|
|
|
|
<p> Linux, OpenBSD: <tt>syslogd -a /var/spool/postfix/dev/log</tt> </p>
|
|
|
|
<h2><a name="myhostname"> My own hostname </a> </h2>
|
|
|
|
<p> The myhostname parameter specifies the fully-qualified domain
|
|
name of the machine running the Postfix system. $myhostname
|
|
appears as the default value in many other Postfix configuration
|
|
parameters. </p>
|
|
|
|
<p> By default, myhostname is set to the local machine name. If
|
|
your local machine name is not in fully-qualified domain name form,
|
|
or if you run Postfix on a virtual interface, you will have to
|
|
specify the fully-qualified domain name that the mail system should
|
|
use. </p>
|
|
|
|
<p> Alternatively, if you specify mydomain in main.cf, then Postfix
|
|
will use its value to generate a fully-qualified default value
|
|
for the myhostname parameter. </p>
|
|
|
|
<p> Examples (specify only one of the following): </p>
|
|
|
|
<blockquote>
|
|
<pre>
|
|
/etc/postfix/main.cf:
|
|
myhostname = host.local.domain (machine name is not FQDN)
|
|
myhostname = host.virtual.domain (virtual interface)
|
|
myhostname = virtual.domain (virtual interface)
|
|
</pre>
|
|
</blockquote>
|
|
|
|
<h2><a name="mydomain"> My own domain name</a> </h2>
|
|
|
|
<p> The mydomain parameter specifies the parent domain of
|
|
$myhostname. By default, it is derived from $myhostname
|
|
by stripping off the first part (unless the result would be a
|
|
top-level domain). </p>
|
|
|
|
<p> Conversely, if you specify mydomain in main.cf, then Postfix
|
|
will use its value to generate a fully-qualified default value
|
|
for the myhostname parameter. </p>
|
|
|
|
<p> Examples (specify only one of the following): </p>
|
|
|
|
<blockquote>
|
|
<pre>
|
|
/etc/postfix/main.cf:
|
|
mydomain = local.domain
|
|
mydomain = virtual.domain (virtual interface)
|
|
</pre>
|
|
</blockquote>
|
|
|
|
<h2><a name="inet_interfaces">My own network addresses</a> </h2>
|
|
|
|
<p>The inet_interfaces parameter specifies all network interface
|
|
addresses that the Postfix system should listen on; mail addressed
|
|
to "user@[network address]" will be delivered locally,
|
|
as if it is addressed to a domain listed in $mydestination.</p>
|
|
|
|
<p> You can override the inet_interfaces setting in the Postfix
|
|
master.cf file by prepending an IP address to a server name. </p>
|
|
|
|
<p> The default is to listen on all active interfaces. If you run
|
|
mailers on virtual interfaces, you will have to specify what
|
|
interfaces to listen on. </p>
|
|
|
|
<p> IMPORTANT: If you run MTAs on virtual interfaces you must
|
|
specify explicit inet_interfaces values for the MTA that receives
|
|
mail for the machine itself: this MTA should never listen on the
|
|
virtual interfaces or you would have a mailer loop when a virtual
|
|
MTA is down. </p>
|
|
|
|
<p> Example: default setting. </p>
|
|
|
|
<blockquote>
|
|
<pre>
|
|
/etc/postfix/main.cf:
|
|
inet_interfaces = all
|
|
</pre>
|
|
</blockquote>
|
|
|
|
<p> Example: host running one or more virtual mailers. For
|
|
each Postfix instance, specify only one of the following. </p>
|
|
|
|
<blockquote>
|
|
<pre>
|
|
/etc/postfix/main.cf:
|
|
inet_interfaces = virtual.host.tld (virtual Postfix)
|
|
inet_interfaces = $myhostname localhost... (non-virtual Postfix)
|
|
</pre>
|
|
</blockquote>
|
|
|
|
<p> Note: you need to stop and start Postfix after changing this
|
|
parameter. </p>
|
|
|
|
</body>
|
|
|
|
</html>
|