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authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-27 12:06:34 +0000
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+<!doctype html public "-//W3C//DTD HTML 4.01 Transitional//EN"
+ "http://www.w3.org/TR/html4/loose.dtd">
+
+<head>
+
+<title>Postfix SASL Howto</title>
+
+<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
+
+</head>
+
+<body>
+
+<h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Postfix SASL Howto</h1>
+
+<hr>
+
+<h2><a name="intro">How Postfix uses SASL authentication</a></h2>
+
+<p> SMTP servers need to decide whether an SMTP client is authorized
+to send mail to remote destinations, or only to destinations that
+the server itself is responsible for. Usually, SMTP servers accept
+mail to remote destinations when the client's IP address is in the
+"same network" as the server's IP address. </p>
+
+<p> SMTP clients outside the SMTP server's network need a different
+way to get "same network" privileges. To address this need, Postfix
+supports SASL authentication (RFC 4954, formerly RFC 2554). With
+this a remote SMTP client can authenticate to the Postfix SMTP
+server, and the Postfix SMTP client can authenticate to a remote
+SMTP server. Once a client is authenticated, a server can give it
+"same network" privileges. </p>
+
+<p> Postfix does not implement SASL itself, but instead uses existing
+implementations as building blocks. This means that some SASL-related
+configuration files will belong to Postfix, while other
+configuration files belong to the specific SASL
+implementation that Postfix will use. This document covers both the
+Postfix and non-Postfix configuration. </p>
+
+<p> NOTE: People who go to the trouble of installing Postfix may
+have the expectation that Postfix is more secure than some other
+mailers. The Cyrus SASL library contains a lot of code. With this,
+Postfix becomes as secure as other mail systems that use the Cyrus
+SASL library. Dovecot provides an alternative that may be worth
+considering. </p>
+
+<p> You can read more about the following topics: </p>
+
+<ul>
+
+<li><a href="#server_sasl">Configuring SASL authentication in the
+Postfix SMTP server</a></li>
+
+<li><a href="#client_sasl">Configuring SASL authentication in the Postfix SMTP/LMTP client</a></li>
+
+<li><a href="#postfix_build">Building Postfix with SASL support</a></li>
+
+<li><a href="#cyrus_legacy">Using Cyrus SASL version 1.5.x</a></li>
+
+<li><a href="#credits">Credits</a></li>
+
+</ul>
+
+<h2><a name="server_sasl">Configuring SASL authentication in the
+Postfix SMTP server</a></h2>
+
+<p> As mentioned earlier, SASL is implemented separately from
+Postfix. For this reason, configuring SASL authentication in the
+Postfix SMTP server involves two different steps: </p>
+
+<ul>
+
+<li> <p> Configuring the SASL implementation to offer a list of
+mechanisms that are suitable for SASL authentication and, depending
+on the SASL implementation used, configuring authentication backends
+that verify the remote SMTP client's authentication data against
+the system password file or some other database. </p> </li>
+
+<li> <p> Configuring the Postfix SMTP server to enable SASL
+authentication, and to authorize clients to relay mail or to control
+what envelope sender addresses the client may use. </p> </li>
+
+</ul>
+
+<p> Successful authentication in the Postfix SMTP server requires
+a functional SASL framework. Configuring SASL should therefore
+always be the first step, before configuring Postfix. </p>
+
+<p> You can read more about the following topics: </p>
+
+<ul>
+
+<li><a href="#server_which">Which SASL Implementations are
+supported?</a></li>
+
+<li><a href="#server_dovecot">Configuring Dovecot SASL</a>
+
+<ul>
+
+<li><a href="#server_dovecot_comm">Postfix to Dovecot SASL
+communication</a></li>
+
+</ul> </li>
+
+<li><a href="#server_cyrus">Configuring Cyrus SASL</a>
+
+<ul>
+
+<li><a href="#server_cyrus_name">Cyrus SASL configuration file
+name</a></li>
+
+<li><a href="#server_cyrus_location">Cyrus SASL configuration
+file location</a></li>
+
+<li><a href="#server_cyrus_comm">Postfix to Cyrus SASL
+communication</a></li>
+
+</ul> </li>
+
+<li><a href="#server_sasl_enable">Enabling SASL authentication and
+authorization in the Postfix SMTP server</a>
+
+<ul>
+
+<li><a href="#server_sasl_authc">Enabling SASL authentication in
+the Postfix SMTP server</a></li>
+
+<li><a href="#smtpd_sasl_security_options">Postfix SMTP Server
+policy - SASL mechanism properties</a></li>
+
+<li><a href="#server_sasl_authz">Enabling SASL authorization in the
+Postfix SMTP server</a></li>
+
+<li><a href="#server_sasl_other">Additional SMTP Server SASL
+options</a></li>
+
+</ul></li>
+
+<li><a href="#server_test">Testing SASL authentication in the Postfix
+SMTP server</a></li>
+
+</ul>
+
+
+<h3><a name="server_which">Which SASL Implementations are
+supported?</a></h3>
+
+<p> Currently the Postfix SMTP server supports the Cyrus SASL and
+Dovecot SASL implementations. </p>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> Current Postfix versions have a plug-in architecture that can
+support multiple SASL implementations. Before Postfix version 2.3,
+Postfix had support only for Cyrus SASL. </p>
+
+</blockquote>
+
+<p> To find out what SASL implementations are compiled into Postfix,
+use the following commands: </p>
+
+<blockquote>
+<pre>
+% <strong><code>postconf -a</code></strong> (SASL support in the SMTP server)
+% <strong><code>postconf -A</code></strong> (SASL support in the SMTP+LMTP client)
+</pre>
+</blockquote>
+
+<p> These commands are available only with Postfix version 2.3 and
+later. </p>
+
+<h3><a name="server_dovecot">Configuring Dovecot SASL</a></h3>
+
+<p> Dovecot is a POP/IMAP server that has its own configuration to
+authenticate POP/IMAP clients. When the Postfix SMTP server uses
+Dovecot SASL, it reuses parts of this configuration. Consult the
+<a href="http://wiki.dovecot.org">Dovecot documentation</a> for how
+to configure and operate the Dovecot authentication server. </p>
+
+<h4><a name="server_dovecot_comm">Postfix to Dovecot SASL communication</a></h4>
+
+<p> Communication between the Postfix SMTP server and Dovecot SASL
+happens over a UNIX-domain socket or over a TCP socket. We will
+be using a UNIX-domain socket for better privacy. </p>
+
+<p> The following fragment for Dovecot version 2 assumes that the
+Postfix queue is under <code>/var/spool/postfix/</code>. </p>
+
+<blockquote>
+<pre>
+ 1 conf.d/10-master.conf:
+ 2 service auth {
+ 3 ...
+ 4 unix_listener /var/spool/postfix/private/auth {
+ 5 mode = 0660
+ 6 # Assuming the default Postfix user and group
+ 7 user = postfix
+ 8 group = postfix
+ 9 }
+10 ...
+11 }
+12
+13 conf.d/10-auth.conf
+14 auth_mechanisms = plain login
+</pre>
+</blockquote>
+
+<p> Line 4 places the Dovecot SASL socket in
+<code>/var/spool/postfix/private/auth</code>, lines 5-8 limit
+read+write permissions to user and group <code>postfix</code> only,
+and line 14 provides <code>plain</code> and <code>login</code> as
+mechanisms for the Postfix SMTP server. </p>
+
+<p> Proceed with the section "<a href="#server_sasl_enable">Enabling
+SASL authentication and authorization in the Postfix SMTP server</a>"
+to turn on and use SASL in the Postfix SMTP server. </p>
+
+<h3><a name="server_cyrus">Configuring Cyrus SASL</a></h3>
+
+<p> The Cyrus SASL framework supports a wide variety of applications
+(POP, IMAP, SMTP, etc.). Different applications may require different
+configurations. As a consequence each application may have its own
+configuration file. </p>
+
+<p> The first step configuring Cyrus SASL is to determine name and
+location of a configuration file that describes how the Postfix
+SMTP server will use the SASL framework. </p>
+
+<h4><a name="server_cyrus_name">Cyrus SASL configuration file name</a></h4>
+
+<p> The name of the configuration file (default: <code>smtpd.conf</code>)
+is configurable. It is a concatenation from a value that the Postfix
+SMTP server sends to the Cyrus SASL library, and the suffix
+<code>.conf</code>, added by Cyrus SASL. </p>
+
+<p> The value sent by Postfix is the name of the server component
+that will use Cyrus SASL. It defaults to <code>smtpd</code> and
+is configured with one of the following variables: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ # Postfix 2.3 and later
+ smtpd_sasl_path = smtpd
+
+ # Postfix &lt; 2.3
+ smtpd_sasl_application_name = smtpd
+</pre>
+</blockquote>
+
+<h4><a name="server_cyrus_location">Cyrus SASL configuration file
+location</a></h4>
+
+<p> The location where Cyrus SASL searches for the named file depends
+on the Cyrus SASL version and the OS/distribution used. </p>
+
+<p> You can read more about the following topics: </p>
+
+<ul>
+
+<li> <p> Cyrus SASL version 2.x searches for the configuration file
+in <code>/usr/lib/sasl2/</code>. </p> </li>
+
+<li> <p> Cyrus SASL version 2.1.22 and newer additionally search
+in <code>/etc/sasl2/</code>. </p> </li>
+
+<li> <p> Some Postfix distributions are modified and look for the
+Cyrus SASL configuration file in <code>/etc/postfix/sasl/</code>,
+<code>/var/lib/sasl2/</code> etc. See the distribution-specific
+documentation to determine the expected location. </p> </li>
+
+</ul>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> Cyrus SASL searches <code>/usr/lib/sasl2/</code> first. If it
+finds the specified configuration file there, it will not examine
+other locations. </p>
+
+</blockquote>
+
+<h4><a name="server_cyrus_comm">Postfix to Cyrus SASL communication</a></h4>
+
+<p> As the Postfix SMTP server is linked with the Cyrus SASL library
+<code>libsasl</code>, communication between Postfix and Cyrus SASL
+takes place by calling functions in the SASL library. </p>
+
+<p> The SASL library may use an external password verification
+service, or an internal plugin to connect to authentication backends
+and verify the SMTP client's authentication data against the system
+password file or other databases. </p>
+
+<p> The following table shows typical combinations discussed in
+this document: </p>
+
+<blockquote>
+
+<table border="1">
+
+<tr>
+
+<th align="center">authentication backend</th>
+
+<th align="center">password verification service / plugin</th>
+
+</tr>
+
+<tr>
+
+<td>/etc/shadow</td>
+
+<td><a href="#saslauthd">saslauthd</a></td>
+
+</tr>
+
+<tr>
+
+<td>PAM</td>
+
+<td><a href="#saslauthd">saslauthd</a></td>
+
+</tr>
+
+<tr>
+
+<td>IMAP server</td>
+
+<td><a href="#saslauthd">saslauthd</a></td>
+
+</tr>
+
+<tr>
+
+<td>sasldb</td>
+
+<td><a href="#auxprop_sasldb">sasldb</a></td>
+
+</tr>
+
+<tr>
+
+<td>MySQL, PostgreSQL, SQLite</td>
+
+<td><a href="#auxprop_sql">sql</a></td>
+
+</tr>
+
+<tr>
+
+<td>LDAP</td>
+
+<td><a href="#auxprop_ldapdb">ldapdb</a></td>
+
+</tr>
+
+</table>
+
+</blockquote>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> Read the Cyrus SASL documentation for other backends it can
+use. </p>
+
+</blockquote>
+
+<h4><a name="saslauthd">saslauthd - Cyrus SASL password verification service</a></h4>
+
+<p> Communication between the Postfix SMTP server (read: Cyrus SASL's
+<code>libsasl</code>) and the <code>saslauthd</code> server takes
+place over a UNIX-domain socket. </p>
+
+<p> <code>saslauthd</code> usually establishes the UNIX domain
+socket in <code>/var/run/saslauthd/</code> and waits for authentication
+requests. The Postfix SMTP server must have read+execute permission
+to this directory or authentication attempts will fail. </p>
+
+<blockquote>
+
+<strong>Important</strong>
+
+<p> Some distributions require the user <code>postfix</code> to be
+member of a special group e.g. <code>sasl</code>, otherwise it
+will not be able to access the <code>saslauthd</code> socket
+directory. </p>
+
+</blockquote>
+
+<p> The following example configures the Cyrus SASL library to
+contact <code>saslauthd</code> as its password verification service:
+</p>
+
+<blockquote>
+<pre>
+/etc/sasl2/smtpd.conf:
+ pwcheck_method: saslauthd
+ mech_list: PLAIN LOGIN
+</pre>
+</blockquote>
+
+<blockquote>
+
+<strong>Important</strong>
+
+<p> Do not specify any other mechanisms in <code>mech_list</code>
+than <code>PLAIN</code> or <code>LOGIN</code> when using
+<code>saslauthd</code>! It can only handle these two mechanisms,
+and authentication will fail if clients are allowed to choose other
+mechanisms. </p>
+
+</blockquote>
+
+<blockquote>
+
+<strong>Important</strong>
+
+<p> Plaintext mechanisms (<code>PLAIN</code>, <code>LOGIN</code>)
+send credentials unencrypted. This information should be protected
+by an additional security layer such as a TLS-encrypted SMTP session
+(see: TLS_README). </p>
+
+</blockquote>
+
+<p> Additionally the <code>saslauthd</code> server itself must be
+configured. It must be told which authentication backend to turn
+to for password verification. The backend is selected with a
+<code>saslauthd</code> command-line option and will be shown in the
+following examples. </p>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> Some distributions use a configuration file to provide saslauthd
+command line options to set e.g. the authentication backend. Typical
+locations are <code>/etc/sysconfig/saslauthd</code> or
+<code>/etc/default/saslauthd</code>. </p>
+
+</blockquote>
+
+<h4><a name="saslauthd_shadow">Using saslauthd with /etc/shadow</a></h4>
+
+<p> Access to the <code>/etc/shadow</code> system password file
+requires <code>root</code> privileges. The Postfix SMTP server
+(and in consequence <code>libsasl</code> linked to the server) runs
+with the least privilege possible. Direct access to
+<code>/etc/shadow</code> would not be possible without breaking the
+Postfix security architecture. </p>
+
+<p> The <code>saslauthd</code> socket builds a safe bridge. Postfix,
+running as limited user <code>postfix</code>, can access the
+UNIX-domain socket that <code>saslauthd</code> receives commands
+on; <code>saslauthd</code>, running as privileged user <code>root</code>,
+has the privileges required to access the shadow file. </p>
+
+<p> The <code>saslauthd</code> server verifies passwords against the
+authentication backend <code>/etc/shadow</code> if started like this: </p>
+
+<blockquote>
+<pre>
+% <strong><code>saslauthd -a shadow</code></strong>
+</pre>
+</blockquote>
+
+<p> See section "<a href="#testing_saslauthd">Testing saslauthd
+authentication</a>" for test instructions. </p>
+
+<h4><a name="saslauthd_pam">Using saslauthd with PAM</a></h4>
+
+<p> Cyrus SASL can use the PAM framework to authenticate credentials.
+<code>saslauthd</code> uses the PAM framework when started like
+this: </p>
+
+<blockquote>
+<pre>
+% <strong><code>saslauthd -a pam</code></strong>
+</pre>
+</blockquote>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> PAM configuration for the Postfix SMTP server is usually given
+in <code>/etc/pam.d/smtp</code> and is beyond the scope of this
+document. </p>
+
+</blockquote>
+
+<p> See section "<a href="#testing_saslauthd">Testing saslauthd
+authentication</a>" for test instructions. </p>
+
+<h4><a name="saslauthd_imap">Using saslauthd with an IMAP server</a></h4>
+
+<p> <code>saslauthd</code> can verify the SMTP client credentials
+by using them to log into an IMAP server. If the login succeeds,
+SASL authentication also succeeds. <code>saslauthd</code> contacts
+an IMAP server when started like this: </p>
+
+<blockquote>
+<pre>
+% <strong><code>saslauthd -a rimap -O imap.example.com</code></strong>
+</pre>
+</blockquote>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> The option "<code>-O imap.example.com</code>" specifies the
+IMAP server <code>saslauthd</code> should contact when it verifies
+credentials. </p>
+
+</blockquote>
+
+<blockquote>
+
+<strong>Important</strong>
+
+<p> <code>saslauthd</code> sends IMAP login information unencrypted.
+Any IMAP session leaving the local host should be protected by an
+additional security layer such as an SSL tunnel. </p>
+
+</blockquote>
+
+<p> See section "<a href="#testing_saslauthd">Testing saslauthd
+authentication</a>" for test instructions. </p>
+
+<h4><a name="testing_saslauthd">Testing saslauthd authentication</a></h4>
+
+<p> Cyrus SASL provides the <code>testsaslauthd</code> utility to
+test <code>saslauthd</code> authentication. The username and password
+are given as command line arguments. The example shows the response
+when authentication is successful: </p>
+
+<blockquote>
+<pre>
+% <strong><code>testsaslauthd -u <em>username</em> -p <em>password</em></code></strong>
+0: OK "Success."
+</pre>
+</blockquote>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> Sometimes the <code>testsaslauthd</code> program is not distributed
+with a the Cyrus SASL main package. In that case, it may be
+distributed with <code>-devel</code>, <code>-dev</code> or
+<code>-debug</code> packages. </p>
+
+</blockquote>
+
+<p> Specify an additional "<code>-s smtp</code>" if <code>saslauthd</code>
+was configured to contact the PAM authentication framework, and
+specify an additional "<code>-f <em>/path/to/socketdir/mux</em></code>"
+if <code>saslauthd</code> establishes the UNIX-domain socket in a
+non-default location. </p>
+
+<p> If authentication succeeds, proceed with the section "<a
+href="#server_sasl_enable">Enabling SASL authentication and authorization
+in the Postfix SMTP server</a>". </p>
+
+<h4><a name="auxprop">Cyrus SASL Plugins - auxiliary property
+plugins</a></h4>
+
+<p> Cyrus SASL uses a plugin infrastructure (called <code>auxprop</code>)
+to expand <code>libsasl</code>'s capabilities. Currently Cyrus
+SASL sources provide three authentication plugins. </p>
+
+<blockquote>
+
+<table border="1">
+
+<tr> <th>Plugin </th> <th>Description </th> </tr>
+
+<tr> <td><a href="#auxprop_sasldb">sasldb</a></td> <td> Accounts
+are stored stored in a Cyrus SASL Berkeley DB database </td> </tr>
+
+<tr> <td><a href="#auxprop_sql">sql</a></td> <td> Accounts are
+stored in a SQL database </td> </tr>
+
+<tr> <td><a href="#auxprop_ldapdb">ldapdb</a></td> <td> Accounts
+are stored stored in an LDAP database </td> </tr>
+
+</table>
+
+</blockquote>
+
+<blockquote>
+
+<strong>Important</strong>
+
+<p> These three plugins support shared-secret mechanisms i.e.
+CRAM-MD5, DIGEST-MD5 and NTLM. These mechanisms send credentials
+encrypted but their verification process requires the password to
+be available in plaintext. Consequently passwords cannot (!) be
+stored in encrypted form. </p>
+
+</blockquote>
+
+<h4><a name="auxprop_sasldb">The sasldb plugin</a></h4>
+
+<p> The sasldb auxprop plugin authenticates SASL clients against
+credentials that are stored in a Berkeley DB database. The database
+schema is specific to Cyrus SASL. The database is usually located
+at <code>/etc/sasldb2</code>. </p>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> The <code>sasldb2</code> file contains passwords in
+plaintext, and should have read+write access only to user
+<code>postfix</code> or a group that <code>postfix</code> is member
+of. </p>
+
+</blockquote>
+
+<p> The <code>saslpasswd2</code> command-line utility creates
+and maintains the database: </p>
+
+<blockquote>
+<pre>
+% <strong>saslpasswd2 -c -u <em>example.com</em> <em>username</em></strong>
+Password:
+Again (for verification):
+</pre>
+</blockquote>
+
+<p> This command creates an account
+<code><em>username@example.com</em></code>. </p>
+
+<blockquote>
+
+<strong>Important</strong>
+
+<p> users must specify <code><em>username@example.com</em></code>
+as login name, not <code><em>username</em></code>. </p>
+
+</blockquote>
+
+<p> Run the following command to reuse the Postfix <code>mydomain</code>
+parameter value as the login domain: </p>
+
+<blockquote>
+<pre>
+% <strong>saslpasswd2 -c -u `postconf -h mydomain` <em>username</em></strong>
+Password:
+Again (for verification):
+</pre>
+</blockquote>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> Run <code>saslpasswd2</code> without any options for further
+help on how to use the command. </p>
+
+</blockquote>
+
+<p> The <code>sasldblistusers2</code> command lists all existing
+users in the sasldb database: </p>
+
+<blockquote>
+<pre>
+% <strong>sasldblistusers2</strong>
+username1@example.com: password1
+username2@example.com: password2
+</pre>
+</blockquote>
+
+<p> Configure libsasl to use sasldb with the following instructions: </p>
+
+<blockquote>
+<pre>
+/etc/sasl2/smtpd.conf:
+ pwcheck_method: auxprop
+ auxprop_plugin: sasldb
+ mech_list: PLAIN LOGIN CRAM-MD5 DIGEST-MD5 NTLM
+</pre>
+</blockquote>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> In the above example adjust <code>mech_list</code> to the
+mechanisms that are applicable for your environment. </p>
+
+</blockquote>
+
+<h4><a name="auxprop_sql">The sql plugin</a></h4>
+
+<p> The sql auxprop plugin is a generic SQL plugin. It provides
+access to credentials stored in a MySQL, PostgreSQL or SQLite
+database. This plugin requires that SASL client passwords are
+stored as plaintext. </p>
+
+<blockquote>
+
+<strong>Tip</strong>
+
+<p> If you must store encrypted passwords, you cannot use the sql
+auxprop plugin. Instead, see section "<a href="#saslauthd_pam">Using
+saslauthd with PAM</a>", and configure PAM to look up the encrypted
+passwords with, for example, the <code>pam_mysql</code> module.
+You will not be able to use any of the methods that require access
+to plaintext passwords, such as the shared-secret methods CRAM-MD5
+and DIGEST-MD5. </p>
+
+</blockquote>
+
+<p> The following example configures libsasl to use the sql plugin
+and connects it to a PostgreSQL server: </p>
+
+<blockquote>
+<pre>
+/etc/sasl2/smtpd.conf:
+ pwcheck_method: auxprop
+ auxprop_plugin: sql
+ mech_list: PLAIN LOGIN CRAM-MD5 DIGEST-MD5 NTLM
+ sql_engine: pgsql
+ sql_hostnames: 127.0.0.1, 192.0.2.1
+ sql_user: username
+ sql_passwd: secret
+ sql_database: dbname
+ sql_select: SELECT password FROM users WHERE user = '%u@%r'
+</pre>
+</blockquote>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> Set appropriate permissions if <code>smtpd.conf</code> contains
+a password. The file should be readable by the <code>postfix</code>
+user. </p>
+
+</blockquote>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> In the above example, adjust <code>mech_list</code> to the
+mechanisms that are applicable for your environment. </p>
+
+</blockquote>
+
+<p> The sql plugin has the following configuration options: </p>
+
+<blockquote>
+
+<dl>
+
+<dt>sql_engine</dt>
+
+<dd>
+
+<p> Specify <code>mysql</code> to connect to a MySQL server,
+<code>pgsql</code> for a PostgreSQL server or <code>sqlite</code>
+for an SQLite database </p>
+
+</dd>
+
+<dt>sql_hostnames</dt>
+
+<dd>
+
+<p> Specify one or more servers (hostname or hostname:port) separated
+by commas. </p>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> With MySQL servers, specify <code>localhost</code> to connect
+over a UNIX-domain socket, and specify <code>127.0.0.1</code> to
+connect over a TCP socket. </p>
+
+</blockquote>
+
+</dd>
+
+<dt>sql_user</dt>
+
+<dd>
+
+<p> The login name to gain access to the database. </p>
+
+</dd>
+
+<dt>sql_passwd</dt>
+
+<dd>
+
+<p> The password to gain access to the database. </p>
+
+</dd>
+
+<dt>sql_database</dt>
+
+<dd>
+
+<p> The name of the database to connect to. </p>
+
+</dd>
+
+<dt>sql_select</dt>
+
+<dd>
+
+<p> The SELECT statement that should retrieve the plaintext password
+from a database table. </p>
+
+<blockquote>
+
+<strong>Important</strong>
+
+<p> Do not enclose the statement in quotes! Use single quotes to
+escape macros! </p>
+
+</blockquote>
+
+</dd>
+
+</dl>
+
+</blockquote>
+
+<p> The sql plugin provides macros to build <code>sql_select</code>
+statements. They will be replaced with arguments sent from the client. The
+following macros are available: </p>
+
+<blockquote>
+
+<dl>
+
+<dt>%u</dt>
+
+<dd>
+
+<p> The name of the user whose properties are being selected. </p>
+
+</dd>
+
+<dt>%p</dt>
+
+<dd>
+
+<p> The name of the property being selected. While this could technically be
+anything, Cyrus SASL will try userPassword and cmusaslsecretMECHNAME (where
+MECHNAME is the name of a SASL mechanism). </p>
+
+</dd>
+
+<dt>%r</dt>
+
+<dd>
+
+<p> The name of the realm to which the user belongs. This could be
+the KERBEROS realm, the fully-qualified domain name of the computer
+the SASL application is running on, or the domain after the "@" in a
+username. </p>
+
+</dd>
+
+</dl>
+
+</blockquote>
+
+<h4><a name="auxprop_ldapdb">The ldapdb plugin</a></h4>
+
+<p> The ldapdb auxprop plugin provides access to credentials stored
+in an LDAP server. This plugin requires that SASL client passwords are
+stored as plaintext. </p>
+
+<blockquote>
+
+<strong>Tip</strong>
+
+<p> If you must store encrypted passwords, you cannot use the ldapdb
+auxprop plugin. Instead, you can use "<code>saslauthd -a ldap</code>"
+to query the LDAP database directly, with appropriate configuration
+in <code>saslauthd.conf</code>, <a
+href="http://git.cyrusimap.org/cyrus-sasl/tree/saslauthd/LDAP_SASLAUTHD">as
+described here</a>. You will not be able to use any of the
+methods that require access to plaintext passwords, such as the
+shared-secret methods CRAM-MD5 and DIGEST-MD5. </p>
+
+</blockquote>
+
+<p> The ldapdb plugin implements proxy authorization. This means
+that the ldapdb plugin uses its own username and password to
+authenticate with the LDAP server, before it asks the LDAP server
+for the remote SMTP client's password. The LDAP server then decides
+if the ldapdb plugin is authorized to read the remote SMTP client's
+password. </p>
+
+<p> In a nutshell: Configuring ldapdb means authentication and
+authorization must be configured twice - once in the Postfix SMTP
+server to authenticate and authorize the remote SMTP client, and
+once in the LDAP server to authenticate and authorize the ldapdb
+plugin. </p>
+
+<p> This example configures libsasl to use the ldapdb plugin and
+the plugin to connect to an LDAP server: </p>
+
+<blockquote>
+<pre>
+/etc/sasl2/smtpd.conf:
+ pwcheck_method: auxprop
+ auxprop_plugin: ldapdb
+ mech_list: PLAIN LOGIN NTLM CRAM-MD5 DIGEST-MD5
+ ldapdb_uri: ldap://localhost
+ ldapdb_id: proxyuser
+ ldapdb_pw: password
+ ldapdb_mech: DIGEST-MD5
+</pre>
+</blockquote>
+
+<blockquote>
+
+<strong>Important</strong>
+
+<p> Set appropriate permissions if <code>smtpd.conf</code> contains a
+password. The file should be readable by the <code>postfix</code>
+user. </p>
+
+</blockquote>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> The shared-secret mechanisms (CRAM-MD5, etc.) require that the
+SASL client passwords are stored as plaintext. </p>
+
+</blockquote>
+
+<p> The following is a summary of applicable <code>smtpd.conf</code>
+file entries: </p>
+
+<blockquote>
+
+<dl>
+
+<dt>auxprop_plugin</dt>
+
+<dd> <p> Specify <code>ldapdb</code> to enable the plugin. </p> </dd>
+
+<dt>ldapdb_uri</dt>
+
+<dd> <p> Specify either <code>ldapi://</code> for to connect over
+a UNIX-domain socket, <code>ldap://</code> for an unencrypted TCP
+connection or <code>ldaps://</code> for an encrypted TCP connection.
+</p> </dd>
+
+<dt>ldapdb_id</dt>
+
+<dd> <p> The login name to authenticate the ldapdb plugin to the
+LDAP server (proxy authorization). </p> </dd>
+
+<dt>ldapdb_pw</dt>
+
+<dd> <p> The password (in plaintext) to authenticate the ldapdb
+plugin to the LDAP server (proxy authorization). </p> </dd>
+
+<dt>ldapdb_mech</dt>
+
+<dd> <p> The mechanism to authenticate the ldapdb plugin to the
+LDAP server. </p>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> Specify a mechanism here that is supported by the LDAP server.
+</p>
+
+</blockquote>
+
+</dd>
+
+<dt>ldapdb_rc (optional)</dt>
+
+<dd> <p> The path to a file containing individual configuration
+options for the ldapdb LDAP client (libldap). This allows to specify
+a TLS client certificate which in turn can be used to use the SASL
+EXTERNAL mechanism. </p>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> This mechanism supports authentication over an encrypted transport
+layer, which is recommended if the plugin must connect to an OpenLDAP
+server on a remote machine. </p>
+
+</blockquote>
+
+</dd>
+
+<dt>ldapdb_starttls (optional)</dt>
+
+<dd> <p> The TLS policy for connecting to the LDAP server. Specify
+either <code>try</code> or <code>demand</code>. If the option is
+<code>try</code> the plugin will attempt to establish a TLS-encrypted
+connection with the LDAP server, and will fallback to an unencrypted
+connection if TLS fails. If the policy is <code>demand</code> and
+a TLS-encrypted connection cannot be established, the connection
+fails immediately. </p> </dd>
+
+</dl>
+
+</blockquote>
+
+<p> When the ldapdb plugin connects to the OpenLDAP server and
+successfully authenticates, the OpenLDAP server decides if the
+plugin user is authorized to read SASL account information. </p>
+
+<p> The following configuration gives an example of authorization configuration
+in the OpenLDAP slapd server: </p>
+
+<blockquote>
+<pre>
+/etc/openldap/slapd.conf:
+ authz-regexp
+ uid=(.*),cn=.*,cn=auth
+ ldap:///dc=example,dc=com??sub?cn=$1
+ authz-policy to
+</pre>
+</blockquote>
+
+<p> Here, the <code>authz-regexp</code> option serves for authentication
+of the ldapdb user. It maps its login name to a DN in the LDAP
+directory tree where <code>slapd</code> can look up the SASL account
+information. The <code>authz-policy</code> options defines the
+authentication policy. In this case it grants authentication
+privileges "<code>to</code>" the ldapdb plugin. </p>
+
+<p> The last configuration step is to tell the OpenLDAP <code>slapd</code>
+server where ldapdb may search for usernames matching the one given
+by the mail client. The example below adds an additional attribute
+ldapdb user object (here: <code>authzTo</code> because the authz-policy
+is "<code>to</code>") and configures the scope where the login name
+"proxyuser" may search: </p>
+
+<blockquote>
+<pre>
+dn: cn=proxyuser,dc=example,dc=com
+changetype: modify
+add: authzTo
+authzTo: dn.regex:uniqueIdentifier=(.*),ou=people,dc=example,dc=com
+</pre>
+</blockquote>
+
+<p> Use the <code>ldapmodify</code> or <code>ldapadd</code> command
+to add the above attribute. </p>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> Read the chapter "Using SASL" in the <a
+href="http://www.openldap.org/doc/admin">OpenLDAP Admin Guide</a>
+for more detailed instructions to set up SASL authentication in
+OpenLDAP. </p>
+
+</blockquote>
+
+<h3><a name="server_sasl_enable">Enabling SASL authentication and
+authorization in the Postfix SMTP server</a></h3>
+
+<p> By default the Postfix SMTP server uses the Cyrus SASL
+implementation. If the Dovecot SASL implementation should be used,
+specify an <code>smtpd_sasl_type</code> value of <code>dovecot</code>
+instead of <code>cyrus</code>: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ smtpd_sasl_type = dovecot
+</pre>
+</blockquote>
+
+<p> Additionally specify how Postfix SMTP server can find the Dovecot
+authentication server. This depends on the settings that you have
+selected in the section "<a href="#server_dovecot_comm">Postfix to
+Dovecot SASL communication</a>". </p>
+
+<ul>
+
+<li> <p> If you configured Dovecot for UNIX-domain socket communication,
+configure Postfix as follows: </p>
+
+<pre>
+/etc/postfix/main.cf:
+ smtpd_sasl_path = private/auth
+</pre>
+
+<strong>Note</strong>
+
+<p> This example uses a pathname relative to the Postfix queue
+directory, so that it will work whether or not the Postfix SMTP
+server runs chrooted. </p>
+
+<li> <p> If you configured Dovecot for TCP socket communication,
+configure Postfix as follows. If Dovecot runs on a different machine,
+replace 127.0.0.1 by that machine's IP address. </p>
+
+<pre>
+/etc/postfix/main.cf:
+ smtpd_sasl_path = inet:127.0.0.1:12345
+</pre>
+
+<strong>Note</strong>
+
+<p> If you specify a remote IP address, information
+will be sent as plaintext over the network. </p>
+
+</ul>
+
+<h4><a name="server_sasl_authc">Enabling SASL authentication
+in the Postfix SMTP server</a></h4>
+
+<p> Regardless of the SASL implementation type, enabling SMTP
+authentication in the Postfix SMTP server always requires setting
+the <code>smtpd_sasl_auth_enable</code> option: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ smtpd_sasl_auth_enable = yes
+</pre>
+</blockquote>
+
+<p> After a "postfix reload", SMTP clients will see the additional
+capability AUTH in an SMTP session, followed by a list of
+authentication mechanisms the server supports: </p>
+
+<blockquote>
+<pre>
+% <strong>telnet server.example.com 25</strong>
+...
+220 server.example.com ESMTP Postfix
+<strong>EHLO client.example.com</strong>
+250-server.example.com
+250-PIPELINING
+250-SIZE 10240000
+250-AUTH DIGEST-MD5 PLAIN CRAM-MD5
+...
+</pre>
+</blockquote>
+
+<p> However not all clients recognize the AUTH capability as defined
+by the SASL authentication RFC. Some historical implementations expect the
+server to send an "<code>=</code>" as separator between the AUTH
+verb and the list of mechanisms that follows it. </p>
+
+<p> The <code>broken_sasl_auth_clients</code> configuration option
+lets Postfix repeat the AUTH statement in a form that these broken
+clients understand: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ broken_sasl_auth_clients = yes
+</pre>
+</blockquote>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> Enable this option for Outlook up to and including version 2003
+and Outlook Express up to version 6. This option does not hurt other
+clients. </p>
+
+</blockquote>
+
+<p> After "postfix reload", the Postfix SMTP server will propagate
+the AUTH capability twice - once for compliant and once for broken
+clients: </p>
+
+<blockquote>
+<pre>
+% <strong>telnet server.example.com 25</strong>
+...
+220 server.example.com ESMTP Postfix
+<strong>EHLO client.example.com</strong>
+250-server.example.com
+250-PIPELINING
+250-SIZE 10240000
+250-AUTH DIGEST-MD5 PLAIN CRAM-MD5
+250-AUTH=DIGEST-MD5 PLAIN CRAM-MD5
+...
+</pre>
+</blockquote>
+
+<h4><a name="smtpd_sasl_security_options">Postfix SMTP Server policy
+- SASL mechanism properties</a></h4>
+
+<p> The Postfix SMTP server supports policies that limit the SASL
+mechanisms that it makes available to clients, based on the properties
+of those mechanisms. The next two sections give examples of how
+these policies are used. </p>
+
+<blockquote>
+
+<table border="1">
+
+<tr> <th>Property</th> <th>Description</th> </tr>
+
+<tr> <td>noanonymous</td> <td> Don't use mechanisms that permit
+anonymous authentication. </td> </tr>
+
+<tr> <td>noplaintext</td> <td> Don't use mechanisms that transmit
+unencrypted username and password information. </td> </tr>
+
+<tr> <td>nodictionary</td> <td> Don't use mechanisms that are
+vulnerable to dictionary attacks. </td> </tr>
+
+<tr> <td>forward_secrecy</td> <td> Require forward secrecy between
+sessions (breaking one session does not break earlier sessions).
+</td> </tr>
+
+<tr> <td>mutual_auth</td> <td> Use only mechanisms that authenticate
+both the client and the server to each other. </td> </tr>
+
+</table>
+
+</blockquote>
+
+<h4><a name="id396877">Unencrypted SMTP session</a></h4>
+
+<p> The default policy is to allow any mechanism in the Postfix SMTP server
+except for those based on anonymous authentication: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ # Specify a list of properties separated by comma or whitespace
+ smtpd_sasl_security_options = noanonymous
+</pre>
+</blockquote>
+
+<blockquote>
+
+<strong>Important</strong>
+
+<p> Always set at least the <code>noanonymous</code> option.
+Otherwise, the Postfix SMTP server can give strangers the same
+authorization as a properly-authenticated client. </p>
+
+</blockquote>
+
+<h4><a name="id396969">Encrypted SMTP session (TLS)</a></h4>
+
+<p> A separate parameter controls Postfix SASL mechanism policy
+during a TLS-encrypted SMTP session. The default is to copy the
+settings from the unencrypted session: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ smtpd_sasl_tls_security_options = $smtpd_sasl_security_options
+</pre>
+</blockquote>
+
+<p> A more sophisticated policy allows plaintext mechanisms, but
+only over a TLS-encrypted connection: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ smtpd_sasl_security_options = noanonymous, noplaintext
+ smtpd_sasl_tls_security_options = noanonymous
+</pre>
+</blockquote>
+
+<p> To offer SASL authentication only after a TLS-encrypted session has been
+established specify this: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ smtpd_tls_auth_only = yes
+</pre>
+</blockquote>
+
+<h4><a name="server_sasl_authz">Enabling SASL authorization in the Postfix
+SMTP server</a></h4>
+
+<p> After the client has authenticated with SASL, the Postfix SMTP
+server decides what the remote SMTP client will be authorized
+for. Examples of possible SMTP clients authorizations are: </p>
+
+<ul>
+
+<li> <p> Send a message to a remote recipient. </p> </li>
+
+<li> <p> Use a specific envelope sender in the MAIL FROM command. </p> </li>
+
+</ul>
+
+<p> These permissions are not enabled by default. </p>
+
+<h4><a name="server_sasl_authz_relay">Mail relay authorization</a></h4>
+
+<p> With <code>permit_sasl_authenticated</code> the Postfix SMTP
+server can allow
+SASL-authenticated SMTP clients to send mail to remote destinations.
+Examples:
+</p>
+
+<blockquote>
+<pre>
+# With Postfix 2.10 and later, the mail relay policy is
+# preferably specified under smtpd_relay_restrictions.
+/etc/postfix/main.cf:
+ smtpd_relay_restrictions =
+ permit_mynetworks
+ <strong>permit_sasl_authenticated</strong>
+ reject_unauth_destination
+</pre>
+
+<pre>
+# Older configurations combine relay control and spam control under
+# smtpd_recipient_restrictions. To use this example with Postfix &ge;
+# 2.10 specify "smtpd_relay_restrictions=".
+/etc/postfix/main.cf:
+ smtpd_recipient_restrictions =
+ permit_mynetworks
+ <strong>permit_sasl_authenticated</strong>
+ reject_unauth_destination
+ ...other rules...
+</pre>
+</blockquote>
+
+<h4><a name="server_sasl_authz_envelope">Envelope sender address
+authorization</a></h4>
+
+<p> By default an SMTP client may specify any envelope sender address
+in the MAIL FROM command. That is because the Postfix SMTP server
+only knows the remote SMTP client hostname and IP address, but not
+the user who controls the remote SMTP client. </p>
+
+<p> This changes the moment an SMTP client uses SASL authentication.
+Now, the Postfix SMTP server knows who the sender is. Given a table
+of envelope sender addresses and SASL login names, the Postfix SMTP
+server can decide if the SASL authenticated client is allowed to
+use a particular envelope sender address: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ <strong>smtpd_sender_login_maps = hash:/etc/postfix/controlled_envelope_senders</strong>
+
+ smtpd_recipient_restrictions =
+ ...
+ <strong>reject_sender_login_mismatch</strong>
+ permit_sasl_authenticated
+ ...
+</pre>
+</blockquote>
+
+<p> The <code>controlled_envelope_senders</code> table specifies
+the binding between a sender envelope address and the SASL login
+names that own that address: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/controlled_envelope_senders
+ # envelope sender owners (SASL login names)
+ john@example.com john@example.com
+ helpdesk@example.com john@example.com, mary@example.com
+ postmaster admin@example.com
+ @example.net barney, fred, john@example.com, mary@example.com
+</pre>
+</blockquote>
+
+<p> With this, the <code>reject_sender_login_mismatch</code>
+restriction above will reject the sender address in the MAIL FROM
+command if <code>smtpd_sender_login_maps</code> does not specify
+the SMTP client's login name as an owner of that address. </p>
+
+<p> See also <code>reject_authenticated_sender_login_mismatch</code>,
+<code>reject_known_sender_login_mismatch</code>, and
+<code>reject_unauthenticated_sender_login_mismatch</code> for additional
+control over the SASL login name and the envelope sender. </p>
+
+<h4><a name="server_sasl_other">Additional SMTP Server SASL options</a></h4>
+
+<p> Postfix provides a wide range of SASL authentication configuration
+options. The next section lists a few that are discussed frequently.
+See postconf(5) for a complete list. </p>
+
+<h4><a name="sasl_access">Per-account access control</a></h4>
+
+<p> Postfix can implement policies that depend on the SASL login
+name (Postfix 2.11 and later). Typically this is used to HOLD or
+REJECT mail from accounts whose credentials have been compromised.
+</p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ smtpd_recipient_restrictions =
+ permit_mynetworks
+ check_sasl_access hash:/etc/postfix/sasl_access
+ permit_sasl_authenticated
+ ...
+
+/etc/postfix/sasl_access:
+ # Use this when smtpd_sasl_local_domain is empty.
+ username HOLD
+ # Use this when smtpd_sasl_local_domain=example.com.
+ username@example.com HOLD
+</pre>
+</blockquote>
+
+<h4><a name="id397172">Default authentication domain</a></h4>
+
+<p> Postfix can append a domain name (or any other string) to a
+SASL login name that does not have a domain part, e.g. "<code>john</code>"
+instead of "<code>john@example.com</code>": </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ smtpd_sasl_local_domain = example.com
+</pre>
+</blockquote>
+
+<p> This is useful as a default setting and safety net for misconfigured
+clients, or during a migration to an authentication method/backend
+that requires an authentication REALM or domain name, before all
+SMTP clients are configured to send such information. </p>
+
+<h4><a name="id397205">Hiding SASL authentication from clients or
+networks</a></h4>
+
+<p> Some clients insist on using SASL authentication if it is offered, even
+when they are not configured to send credentials - and therefore
+they will always fail and disconnect. </p>
+
+<p> Postfix can hide the AUTH capability from these clients/networks: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ smtpd_sasl_exceptions_networks = !192.0.2.171/32, 192.0.2.0/24
+</pre>
+</blockquote>
+
+<h4><a name="id397226">Adding the SASL login name to mail headers</a></h4>
+
+<p> To report SASL login names in Received: message headers (Postfix
+version 2.3 and later): </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ smtpd_sasl_authenticated_header = yes
+</pre>
+</blockquote>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> The SASL login names will be shared with the entire world. </p>
+
+</blockquote>
+
+<h3><a name="server_test">Testing SASL authentication in the Postfix SMTP Server</a></h3>
+
+<p> To test the server side, connect (for example, with
+<code>telnet</code>) to the Postfix SMTP server port and you should
+be able to have a conversation as shown below. Information sent by
+the client (that is, you) is shown in <strong>bold</strong> font.
+</p>
+
+<blockquote>
+<pre>
+% <strong>telnet server.example.com 25</strong>
+...
+220 server.example.com ESMTP Postfix
+<strong>EHLO client.example.com</strong>
+250-server.example.com
+250-PIPELINING
+250-SIZE 10240000
+250-ETRN
+250-AUTH DIGEST-MD5 PLAIN CRAM-MD5
+250 8BITMIME
+<strong>AUTH PLAIN AHRlc3QAdGVzdHBhc3M=</strong>
+235 Authentication successful
+</pre>
+</blockquote>
+
+<p> To test this over a connection that is encrypted with TLS, use
+<code>openssl s_client</code> instead of <code>telnet</code>:
+
+<blockquote>
+<pre>
+% <strong>openssl s_client -connect server.example.com:25 -starttls smtp</strong>
+...
+220 server.example.com ESMTP Postfix
+<strong>EHLO client.example.com</strong>
+...see above example for more...
+</pre>
+</blockquote>
+
+<p> Instead of <code>AHRlc3QAdGVzdHBhc3M=</code>, specify the
+base64-encoded form of <code>\0username\0password</code> (the \0
+is a null byte). The example above is for a user named `<code>test</code>'
+with password `<code>testpass</code>'. </p>
+<blockquote>
+
+<strong>Caution</strong>
+
+<p> When posting logs of the SASL negotiations to public lists,
+please keep in mind that username/password information is trivial
+to recover from the base64-encoded form. </p>
+
+</blockquote>
+
+<p> You can use one of the following commands to generate base64
+encoded authentication information: </p>
+
+<ul>
+
+<li> <p> Using a recent version of the <b>bash</b> shell: </p>
+
+<blockquote>
+<pre>
+% <strong>echo -ne '\000username\000password' | openssl base64</strong>
+</pre>
+</blockquote>
+
+<p> Some other shells support similar syntax. </p>
+
+<li> <p> Using the <b>printf</b> command: </p>
+
+<blockquote>
+<pre>
+% <strong>printf '\0%s\0%s' '<em>username</em>' '<em>password</em>' | openssl base64</strong>
+% <strong>printf '\0%s\0%s' '<em>username</em>' '<em>password</em>' | mmencode</strong>
+</pre>
+</blockquote>
+
+<p> The <strong>mmencode</strong> command is part of the metamail
+software. </p>
+
+<li> <p> Using Perl <b>MIME::Base64</b> (from http://www.cpan.org/): </p>
+
+<blockquote>
+<pre>
+% <strong>perl -MMIME::Base64 -e \
+ 'print encode_base64("\0<em>username</em>\0<em>password</em>");'</strong>
+</pre>
+</blockquote>
+
+<p> If the username or password contain "@", you must specify "\@". </p>
+
+<li> <p> Using the <b>gen-auth</b> script: </p>
+
+<blockquote>
+<pre>
+% <strong>gen-auth plain</strong>
+username: <strong><em>username</em></strong>
+password:
+</pre>
+</blockquote>
+
+<p> The <strong>gen-auth</strong> Perl script was written by John
+Jetmore and can be found at http://jetmore.org/john/code/gen-auth. </p>
+
+</ul>
+
+<h2><a name="client_sasl">Configuring SASL authentication in the Postfix SMTP/LMTP client</a></h2>
+
+<p> The Postfix SMTP and the LMTP client can authenticate with a
+remote SMTP server via the Cyrus SASL framework. At this time, the
+Dovecot SASL implementation does not provide client functionality.
+</p>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> The examples in this section discuss only the SMTP client.
+Replace <code>smtp_</code> with <code>lmtp_</code> to get the
+corresponding LMTP client configuration. </p>
+
+</blockquote>
+
+<p> You can read more about the following topics: </p>
+
+<ul>
+
+<li><a href="#client_sasl_enable">Enabling SASL authentication in
+the Postfix SMTP/LMTP client</a></li>
+
+<li><a href="#client_sasl_sender">Configuring sender-dependent SASL
+authentication</a></li>
+
+<li><a href="#client_sasl_policy">Postfix SMTP/LMTP client policy
+- SASL mechanism <em>properties</em></a></li>
+
+<li><a href="#client_sasl_filter">Postfix SMTP/LMTP client policy
+- SASL mechanism <em>names</em></a></li>
+
+</ul>
+
+<h3><a name="client_sasl_enable">Enabling SASL authentication in the
+Postfix SMTP/LMTP client</a></h3>
+
+<p> This section shows a typical scenario where the Postfix SMTP
+client sends all messages via a mail gateway server that requires
+SASL authentication. </p>
+
+<blockquote>
+
+<strong> Trouble solving tips: </strong>
+
+<ul>
+
+<li> <p> If your SASL logins fail with "SASL authentication failure:
+No worthy mechs found" in the mail logfile, then see the section
+"<a href="SASL_README.html#client_sasl_policy">Postfix SMTP/LMTP
+client policy - SASL mechanism <em>properties</em></a>".
+
+<li> <p> For a solution to a more obscure class of SASL authentication
+failures, see "<a href="SASL_README.html#client_sasl_filter">Postfix
+SMTP/LMTP client policy - SASL mechanism <em>names</em></a>".
+
+</ul>
+
+</blockquote>
+
+<p> To make the example more readable we introduce it in two parts.
+The first part takes care of the basic configuration, while the
+second part sets up the username/password information. </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ smtp_sasl_auth_enable = yes
+ smtp_tls_security_level = encrypt
+ smtp_sasl_tls_security_options = noanonymous
+ relayhost = [mail.isp.example]
+ # Alternative form:
+ # relayhost = [mail.isp.example]:submission
+ smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
+</pre>
+</blockquote>
+
+<ul>
+
+<li> <p> The <code>smtp_sasl_auth_enable</code> setting enables
+client-side authentication. We will configure the client's username
+and password information in the second part of the example. </p>
+</li>
+
+<li> <p> The <code>smtp_tls_security_level</code> setting ensures
+that the connection to the remote smtp server will be encrypted, and
+<code>smtp_sasl_tls_security_options</code> removes the prohibition on
+plaintext passwords. </p>
+
+<li> <p> The <code>relayhost</code> setting forces the Postfix SMTP
+to send all remote messages to the specified mail server instead
+of trying to deliver them directly to their destination. </p> </li>
+
+<li> <p> In the <code>relayhost</code> setting, the "<code>[</code>"
+and "<code>]</code>" prevent the Postfix SMTP client from looking
+up MX (mail exchanger) records for the enclosed name. </p> </li>
+
+<li> <p> The <code>relayhost</code> destination may also specify a
+non-default TCP port. For example, the alternative form
+<code>[mail.isp.example]:submission</code> tells Postfix to connect
+to TCP network port 587, which is reserved for email client
+applications. </p> </li>
+
+<li> <p> The Postfix SMTP client is compatible with SMTP servers
+that use the non-standard "<code>AUTH=<em>method.</em>...</code>"
+syntax in response to the EHLO command; this requires no additional
+Postfix client configuration. </p> </li>
+
+<li> <p> The Postfix SMTP client does not support the obsolete
+"wrappermode" protocol, which uses TCP port <code>465</code> on the
+SMTP server. See TLS_README for a solution that uses the
+<code>stunnel</code> command. </p> </li>
+
+<li> <p> With the <code>smtp_sasl_password_maps</code> parameter,
+we configure the Postfix SMTP client to send username and password
+information to the mail gateway server. As discussed in the next
+section, the Postfix SMTP client supports multiple ISP accounts.
+For this reason the username and password are stored in a table
+that contains one username/password combination for each mail gateway
+server. </p>
+
+</ul>
+
+<blockquote>
+<pre>
+/etc/postfix/sasl_passwd:
+ # destination credentials
+ [mail.isp.example] username:password
+ # Alternative form:
+ # [mail.isp.example]:submission username:password
+</pre>
+</blockquote>
+
+<blockquote>
+
+<strong>Important</strong>
+
+<p> Keep the SASL client password file in <code>/etc/postfix</code>,
+and make the file read+write only for <code>root</code> to protect
+the username/password combinations against other users. The Postfix
+SMTP client will still be able to read the SASL client passwords.
+It opens the file as user <code>root</code> before it drops privileges,
+and before entering an optional chroot jail. </p>
+
+</blockquote>
+
+<ul>
+
+<li> <p> Use the <code>postmap</code> command whenever you
+change the <code>/etc/postfix/sasl_passwd</code> file. </p> </li>
+
+<li> <p> If you specify the "<code>[</code>" and "<code>]</code>"
+in the <code>relayhost</code> destination, then you must use the
+same form in the <code>smtp_sasl_password_maps</code> file. </p>
+</li>
+
+<li> <p> If you specify a non-default TCP Port (such as
+"<code>:submission</code>" or "<code>:587</code>") in the
+<code>relayhost</code> destination, then you must use the same form
+in the <code>smtp_sasl_password_maps</code> file. </p> </li>
+
+</ul>
+
+<h3><a name="client_sasl_sender">Configuring Sender-Dependent SASL
+authentication</a></h3>
+
+<p> Postfix supports different ISP accounts for different sender
+addresses (version 2.3 and later). This can be useful when one
+person uses the same machine for work and for personal use, or when
+people with different ISP accounts share the same Postfix server.
+</p>
+
+<p> To make this possible, Postfix supports per-sender SASL passwords
+and per-sender relay hosts. In the example below, the Postfix SMTP
+client will search the SASL password file by sender address before
+it searches that same file by destination. Likewise, the Postfix
+trivial-rewrite(8) daemon will search the per-sender relayhost file,
+and use the default <code>relayhost</code> setting only as a final
+resort. </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ smtp_sender_dependent_authentication = yes
+ sender_dependent_relayhost_maps = hash:/etc/postfix/sender_relay
+ smtp_sasl_auth_enable = yes
+ smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
+ relayhost = [mail.isp.example]
+ # Alternative form:
+ # relayhost = [mail.isp.example]:submission
+</pre>
+</blockquote>
+
+<blockquote>
+<pre>
+/etc/postfix/sasl_passwd:
+ # Per-sender authentication; see also /etc/postfix/sender_relay.
+ user1@example.com username1:password1
+ user2@example.net username2:password2
+ # Login information for the default relayhost.
+ [mail.isp.example] username:password
+ # Alternative form:
+ # [mail.isp.example]:submission username:password
+</pre>
+</blockquote>
+
+<blockquote>
+<pre>
+/etc/postfix/sender_relay:
+ # Per-sender provider; see also /etc/postfix/sasl_passwd.
+ user1@example.com [mail.example.com]:submission
+ user2@example.net [mail.example.net]
+</pre>
+</blockquote>
+
+<ul>
+
+<li> <p> If you are creative, then you can try to combine the two
+tables into one single MySQL database, and configure different
+Postfix queries to extract the appropriate information. </p>
+
+<li> <p> Specify dbm instead of hash if your system uses dbm files
+instead of db files. To find out what lookup tables Postfix supports,
+use the command "postconf -m". </p>
+
+<li> <p> Execute the command "postmap /etc/postfix/sasl_passwd"
+whenever you change the sasl_passwd table. </p>
+
+<li> <p> Execute the command "postmap /etc/postfix/sender_relay"
+whenever you change the sender_relay table. </p>
+
+</ul>
+
+<h3><a name="client_sasl_policy">Postfix SMTP/LMTP client policy -
+SASL mechanism <em>properties</em></a></h3>
+
+<p> Just like the Postfix SMTP server, the SMTP client has a policy
+that determines which SASL mechanisms are acceptable, based on their
+properties. The next two sections give examples of how these policies
+are used. </p>
+
+<blockquote>
+
+<table border="1">
+
+<tr> <th>Property</th> <th>Description</th> </tr>
+
+<tr> <td>noanonymous</td> <td> Don't use mechanisms that permit
+anonymous authentication. </td> </tr>
+
+<tr> <td>noplaintext</td> <td> Don't use mechanisms that transmit
+unencrypted username and password information. </td> </tr>
+
+<tr> <td>nodictionary</td> <td> Don't use mechanisms that are
+vulnerable to dictionary attacks. </td> </tr>
+
+<tr> <td>mutual_auth</td> <td> Use only mechanisms that authenticate
+both the client and the server to each other. </td> </tr>
+
+</table>
+
+</blockquote>
+
+<h4>Unencrypted SMTP session</h4>
+
+<p> The default policy is stricter than that of the Postfix SMTP
+server - plaintext mechanisms are not allowed (nor is any anonymous
+mechanism): </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ smtp_sasl_security_options = noplaintext, noanonymous
+</pre>
+</blockquote>
+
+<p> This default policy, which allows no plaintext passwords, leads
+to authentication failures if the remote server only offers plaintext
+authentication mechanisms (the SMTP server announces "<code>AUTH
+PLAIN LOGIN</code>"). In such cases the SMTP client will log the
+following error message: </p>
+
+<blockquote>
+<pre>
+SASL authentication failure: No worthy mechs found
+</pre>
+</blockquote>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> This same error message will also be logged when the
+<code>libplain.so</code> or <code>liblogin.so</code> modules are
+not installed in the <code>/usr/lib/sasl2</code> directory. </p>
+
+</blockquote>
+
+<p> The insecure approach is to lower the security standards and
+permit plaintext authentication mechanisms: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ smtp_sasl_security_options = noanonymous
+</pre>
+</blockquote>
+
+<p> The more secure approach is to protect the plaintext username
+and password with TLS session encryption. To find out if the remote
+SMTP server supports TLS, connect to the server and see if it
+announces STARTTLS support as shown in the example. Information
+sent by the client (that is, you) is shown in <strong>bold</strong>
+font. </p>
+
+<blockquote>
+<pre>
+% <strong>telnet server.example.com 25</strong>
+...
+220 server.example.com ESMTP Postfix
+<strong>EHLO client.example.com</strong>
+250-server.example.com
+250-PIPELINING
+250-SIZE 10240000
+250-STARTTLS
+...
+</pre>
+</blockquote>
+
+<p> Instead of port 25 (smtp), specify port 587 (submission) where
+appropriate. </p>
+
+<h4>Encrypted SMTP session (TLS)</h4>
+
+<p> To turn on TLS in the Postfix SMTP client, see TLS_README for
+configuration details. </p>
+
+<p> The smtp_sasl_tls_security_options parameter controls Postfix
+SASL mechanism policy during a TLS-encrypted SMTP session. The
+default is to copy the settings from the unencrypted session: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ smtp_sasl_tls_security_options = $smtp_sasl_security_options
+</pre>
+</blockquote>
+
+<p> A more sophisticated policy allows plaintext mechanisms, but
+only over a TLS-encrypted connection: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ smtp_sasl_security_options = noanonymous, noplaintext
+ smtp_sasl_tls_security_options = noanonymous
+</pre>
+</blockquote>
+
+<h3><a name="client_sasl_filter">Postfix SMTP/LMTP client policy -
+SASL mechanism <em>names</em></a></h3>
+
+<p> Given the SASL security options of the previous section, the
+Cyrus SASL library will choose the most secure authentication
+mechanism that both the SMTP client and server implement. Unfortunately,
+that authentication mechanism may fail because the client or server
+is not configured to use that mechanism.</p>
+
+<p> To prevent this, the Postfix SMTP client can filter the names
+of the authentication mechanisms from the remote SMTP server. Used
+correctly, the filter hides unwanted mechanisms from the Cyrus SASL
+library, forcing the library to choose from the mechanisms the
+Postfix SMTP client filter passes through. </p>
+
+<p> The following example filters out everything but the mechanisms
+<code>PLAIN</code> and <code>LOGIN</code>: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ smtp_sasl_mechanism_filter = plain, login
+</pre>
+</blockquote>
+
+<blockquote>
+
+<strong>Note</strong>
+
+<p> If the remote server does not offer any of the mechanisms on
+the filter list, authentication will fail. </p>
+
+</blockquote>
+
+<p> We close this section with an example that passes every mechanism
+except for <code>GSSAPI</code> and <code>LOGIN</code>: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/main.cf:
+ smtp_sasl_mechanism_filter = !gssapi, !login, static:all
+</pre>
+</blockquote>
+
+<h2><a name="postfix_build">Building Postfix with SASL support</a></h2>
+
+<p> As mentioned elsewhere, Postfix supports two SASL implementations:
+Cyrus SASL (SMTP client and server) and Dovecot SASL (SMTP server
+only). Both implementations can be built into Postfix simultaneously.
+</p>
+
+<ul>
+
+<li><a href="#build_dovecot">Building Dovecot SASL support</a></li>
+
+<li><a href="#sasl_support">Building Cyrus SASL support</a></li>
+
+</ul>
+
+<h3><a name="build_dovecot">Building Dovecot SASL support</a></h3>
+
+<p> These instructions assume that you build Postfix from source
+code as described in the INSTALL document. Some modification may
+be required if you build Postfix from a vendor-specific source
+package. </p>
+
+<p> Support for the Dovecot version 1 SASL protocol is available
+in Postfix 2.3 and later. At the time of writing, only server-side
+SASL support is available, so you can't use it to authenticate the
+Postfix SMTP client to your network provider's server. </p>
+
+<p> Dovecot uses its own daemon process for authentication. This
+keeps the Postfix build process simple, because there is no need
+to link extra libraries into Postfix. </p>
+
+<p> To generate the necessary Makefiles, execute the following in
+the Postfix top-level directory: </p>
+
+<blockquote>
+<pre>
+% <strong>make tidy</strong> # if you have left-over files from a previous build
+% <strong>make makefiles CCARGS='-DUSE_SASL_AUTH \
+ -DDEF_SERVER_SASL_TYPE=\"dovecot\"'</strong>
+</pre>
+</blockquote>
+
+<p> After this, proceed with "<code>make</code>" as described in
+the INSTALL document. </p>
+
+<strong>Note</strong>
+
+<ul>
+
+<li>
+
+<p> The <code>-DDEF_SERVER_SASL_TYPE=\"dovecot\"</code> is not
+necessary; it just makes Postfix configuration a little more
+convenient because you don't have to specify the SASL plug-in type
+in the Postfix main.cf file (but this may cause surprises when you
+switch to a later Postfix version that is built with the default
+SASL type of <code>sasl</code>). </p>
+
+</li>
+
+<li>
+
+<p> If you also want support for LDAP or TLS (or for Cyrus SASL),
+you need to merge their <code>CCARGS</code> and <code>AUXLIBS</code>
+options into the above command line; see the LDAP_README and
+TLS_README for details. </p>
+
+<blockquote>
+<pre>
+% <strong>make tidy</strong> # if you have left-over files from a previous build
+% <strong>make makefiles CCARGS='-DUSE_SASL_AUTH \
+ -DDEF_SERVER_SASL_TYPE=\"dovecot\" \
+ ...<i>CCARGS options for LDAP or TLS etc.</i>...' \
+ AUXLIBS='...<i>AUXLIBS options for LDAP or TLS etc.</i>...'</strong>
+</pre>
+</blockquote>
+
+</li>
+
+</ul>
+
+<h3><a name="sasl_support">Building Cyrus SASL support</a></h3>
+
+<h4><a name="build_sasl">Building the Cyrus SASL library</a></h4>
+
+<p> Postfix works with cyrus-sasl-1.5.x or cyrus-sasl-2.1.x, which are
+available from ftp://ftp.andrew.cmu.edu/pub/cyrus-mail/. </p>
+
+<blockquote>
+
+<strong>Important</strong>
+
+<p> If you install the Cyrus SASL libraries as per the default, you will have
+to create a symlink <code>/usr/lib/sasl</code> -&gt;
+<code>/usr/local/lib/sasl</code> for version 1.5.x or
+<code>/usr/lib/sasl2</code> -&gt; <code>/usr/local/lib/sasl2</code>
+for version 2.1.x. </p>
+
+</blockquote>
+
+<p> Reportedly, Microsoft Outlook (Express) requires the non-standard LOGIN
+and/or NTLM authentication mechanism. To enable these authentication
+mechanisms, build the Cyrus SASL libraries with: </p>
+
+<blockquote>
+<pre>
+% <strong>./configure --enable-login --enable-ntlm</strong>
+</pre>
+</blockquote>
+
+<h4><a name="build_postfix">Building Postfix with Cyrus SASL support</a></h4>
+
+<p> These instructions assume that you build Postfix from source
+code as described in the INSTALL document. Some modification may
+be required if you build Postfix from a vendor-specific source
+package. </p>
+
+<p> The following assumes that the Cyrus SASL include files are in
+<code>/usr/local/include</code>, and that the Cyrus SASL libraries are in
+<code>/usr/local/lib</code>. </p>
+
+<p> On some systems this generates the necessary <code>Makefile</code>
+definitions: </p>
+
+<dl>
+
+<dt>Cyrus SASL version 2.1.x</dt>
+
+<dd>
+
+<pre>
+% <strong>make tidy</strong> # if you have left-over files from a previous build
+% <strong>make makefiles CCARGS="-DUSE_SASL_AUTH -DUSE_CYRUS_SASL \
+ -I/usr/local/include/sasl" AUXLIBS="-L/usr/local/lib -lsasl2"</strong>
+</pre>
+
+</dd>
+
+<dt>Cyrus SASL version 1.5.x</dt>
+
+<dd>
+
+<pre>
+% <strong>make tidy</strong> # if you have left-over files from a previous build
+% <strong>make makefiles CCARGS="-DUSE_SASL_AUTH -DUSE_CYRUS_SASL \
+ -I/usr/local/include" AUXLIBS="-L/usr/local/lib -lsasl"</strong>
+</pre>
+
+</dd>
+
+</dl>
+
+<p> On Solaris 2.x you need to specify run-time link information,
+otherwise the ld.so run-time linker will not find the SASL shared
+library: </p>
+
+<dl>
+
+<dt>Cyrus SASL version 2.1.x</dt>
+
+<dd>
+
+<pre>
+% <strong>make tidy</strong> # remove left-over files from a previous build
+% <strong>make makefiles CCARGS="-DUSE_SASL_AUTH -DUSE_CYRUS_SASL \
+ -I/usr/local/include/sasl" AUXLIBS="-L/usr/local/lib \
+ -R/usr/local/lib -lsasl2"</strong>
+</pre>
+
+</dd>
+
+<dt>Cyrus SASL version 1.5.x</dt>
+
+<dd>
+
+<pre>
+% <strong>make tidy</strong> # if you have left-over files from a previous build
+% <strong>make makefiles CCARGS="-DUSE_SASL_AUTH -DUSE_CYRUS_SASL \
+ -I/usr/local/include" AUXLIBS="-L/usr/local/lib \
+ -R/usr/local/lib -lsasl"</strong>
+</pre>
+
+</dd>
+
+</dl>
+
+<h2><a name="cyrus_legacy">Using Cyrus SASL version 1.5.x</a></h2>
+
+<p> Postfix supports Cyrus SASL version 1.x, but you shouldn't use
+it unless you are forced to. The makers of Cyrus SASL write: </p>
+
+<blockquote> <i> This library is being deprecated and applications
+should transition to using the SASLv2 library</i> (source: <a
+href="http://cyrusimap.web.cmu.edu/downloads.html">Project Cyrus:
+Downloads</a>). </blockquote>
+
+<p> If you still need to set it up, here's a quick rundown: </p>
+
+<p> Read the regular section on SMTP server configurations for the
+Cyrus SASL framework. The differences are: </p>
+
+<ul>
+
+<li> <p> Cyrus SASL version 1.5.x searches for configuration
+(<code>smtpd.conf</code>) in <code>/usr/lib/sasl/</code> only. You
+must place the configuration in that directory. Some systems may
+have modified Cyrus SASL and put the files into e.g.
+<code>/var/lib/sasl/</code>. </p> </li>
+
+<li> <p> Use the <code>saslpasswd</code> command instead of
+<code>saslpasswd2</code> to create users in <code>sasldb</code>.
+</p> </li>
+
+<li> <p> Use the <code>sasldblistusers</code> command instead of
+<code>sasldblistusers2</code> to find users in <code>sasldb</code>.
+</p> </li>
+
+<li> <p> In the <code>smtpd.conf</code> file you can't use
+<code>mech_list</code> to limit the range of mechanisms offered.
+Instead, remove their libraries from <code>/usr/lib/sasl/</code>
+(and remember remove those files again when a system update
+re-installs new versions). </p> </li>
+
+</ul>
+
+<h2><a name="credits">Credits</a></h2>
+
+<ul>
+
+<li> Postfix SASL support was originally implemented by Till Franke
+of SuSE Rhein/Main AG. </li>
+
+<li> Wietse trimmed down the code to only the bare necessities.
+ </li>
+
+<li> Support for Cyrus SASL version 2 was contributed by Jason Hoos.
+</li>
+
+<li> Liviu Daia added smtpd_sasl_application_name, separated
+reject_sender_login_mismatch into
+reject_authenticated_sender_login_mismatch and
+reject_unauthenticated_sender_login_mismatch, and revised the docs.
+ </li>
+
+<li> Wietse made another iteration through the code to add plug-in
+support for multiple SASL implementations, and for reasons that
+have been lost, also changed smtpd_sasl_application_name into
+smtpd_sasl_path. </li>
+
+<li> The Dovecot SMTP server-only plug-in was originally implemented
+by Timo Sirainen of Procontrol, Finland. </li>
+
+<li> Patrick Ben Koetter revised this document for Postfix 2.4 and
+made much needed updates. </li>
+
+<li> Patrick Ben Koetter revised this document again for Postfix
+2.7 and made much needed updates. </li>
+
+</ul>
+
+</body>
+
+</html>
+