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+<html>
+
+<head>
+
+<title>Postfix VERP Howto</title>
+
+<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
+
+</head>
+
+<body>
+
+<h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Postfix VERP Howto</h1>
+
+<hr>
+
+<h2>Postfix VERP support</h2>
+
+<p> Postfix versions 1.1 and later support variable envelope return
+path addresses on request. When VERP style delivery is requested,
+each recipient of a message receives a customized copy of the
+message, with his/her own recipient address encoded in the envelope
+sender address. </p>
+
+<p> For example, when VERP style delivery is requested, Postfix
+delivers mail from "<tt>owner-listname@origin</tt>" for a recipient
+"<tt>user@domain</tt>", with a sender address that encodes the
+recipient as follows: </p>
+
+<blockquote>
+<pre>
+owner-listname+user=domain@origin
+</pre>
+</blockquote>
+
+<p> Thus, undeliverable mail can reveal the undeliverable recipient
+address without requiring the list owner to parse bounce messages.
+</p>
+
+<p> The VERP concept was popularized by the qmail MTA and by the ezmlm
+mailing list manager. See <a href="http://cr.yp.to/proto/verp.txt">http://cr.yp.to/proto/verp.txt</a> for the
+ideas behind this concept. </p>
+
+<p> Topics covered in this document: </p>
+
+<ul>
+
+<li> <a href="#config"> Postfix VERP configuration parameters </a>
+
+<li> <a href="#majordomo"> Using VERP with majordomo etc. mailing lists </a>
+
+<li> <a href="#smtp"> VERP support in the Postfix SMTP server</a>
+
+<li> <a href="#sendmail"> VERP support in the Postfix sendmail command </a>
+
+<li> <a href="#qmqp"> VERP support in the Postfix QMQP server </a>
+
+</ul>
+
+<h2> <a name="config"> Postfix VERP configuration parameters </a> </h2>
+
+With Postfix, the whole process is controlled by four configuration
+parameters.
+
+<dl>
+
+<dt> <a href="postconf.5.html#default_verp_delimiters">default_verp_delimiters</a> (default value: +=)
+
+ <dd> <p> What VERP delimiter characters Postfix uses when VERP
+ style delivery is requested but no explicit delimiters are
+ specified. </p>
+
+<dt> <a href="postconf.5.html#verp_delimiter_filter">verp_delimiter_filter</a> (default: -+=)
+
+ <dd> <p> What characters Postfix accepts as VERP delimiter
+ characters on the sendmail command line and in SMTP commands.
+ Many characters must not be used as VERP delimiter characters,
+ either because they already have a special meaning in email
+ addresses (such as the @ or the %), because they are used as
+ part of a username or domain name (such as alphanumerics), or
+ because they are non-ASCII or control characters. And who
+ knows, some characters may tickle bugs in vulnerable software,
+ and we would not want that to happen. </p> </dd>
+
+<dt> <a href="postconf.5.html#smtpd_authorized_verp_clients">smtpd_authorized_verp_clients</a> (default value: none)
+
+ <dd> <p> What SMTP clients are allowed to request VERP style
+ delivery. The Postfix QMQP server uses its own access control
+ mechanism, and local submission (via /usr/sbin/sendmail etc.)
+ is always authorized. To authorize a host, list its name, IP
+ address, subnet (net/mask) or parent .domain. </p>
+
+ <p> With Postfix versions 1.1 and 2.0, this parameter is called
+ <a href="postconf.5.html#authorized_verp_clients">authorized_verp_clients</a> (default: $<a href="postconf.5.html#mynetworks">mynetworks</a>). </p> </dd>
+
+<dt> <a href="postconf.5.html#disable_verp_bounces">disable_verp_bounces</a> (default: no)
+
+ <dd> <p> Send one bounce report for multi-recipient VERP mail,
+ instead of one bounce report per recipient. The default,
+ one per recipient, is what ezmlm needs. </p> </dd>
+
+</dl>
+
+<h2> <a name="majordomo"> Using VERP with majordomo etc. mailing lists </a> </h2>
+
+<p> In order to make VERP useful with majordomo etc. mailing lists,
+you would configure the list manager to submit mail according
+to one of the following two forms: </p>
+
+<p> Postfix 2.3 and later: </p>
+
+<blockquote>
+<pre>
+% sendmail -XV -f owner-listname other-arguments...
+
+% sendmail -XV+= -f owner-listname other-arguments...
+</pre>
+</blockquote>
+
+<p> Postfix 2.2 and earlier (Postfix 2.3 understands the old syntax
+for backwards compatibility, but will log a warning that reminds
+you of the new syntax): </p>
+
+<blockquote>
+<pre>
+% sendmail -V -f owner-listname other-arguments...
+
+% sendmail -V+= -f owner-listname other-arguments...
+</pre>
+</blockquote>
+
+<p> The first form uses the default <a href="postconf.5.html">main.cf</a> VERP delimiter characters.
+The second form allows you to explicitly specify the VERP delimiter
+characters. The example shows the recommended values. </p>
+
+<p> This text assumes that you have set up an owner-listname alias
+that routes undeliverable mail to a real person: </p>
+
+<blockquote>
+<pre>
+/etc/aliases:
+ owner-listname: yourname+listname
+</pre>
+</blockquote>
+
+<p> In order to process bounces we are going to make extensive use
+of address extension tricks. </p>
+
+<p> You need to tell Postfix that + is the separator between an
+address and its optional address extension, that address extensions
+are appended to .forward file names, and that address extensions
+are to be discarded when doing alias expansions: </p>
+
+<blockquote>
+<pre>
+/etc/postfix/<a href="postconf.5.html">main.cf</a>:
+ <a href="postconf.5.html#recipient_delimiter">recipient_delimiter</a> = +
+ <a href="postconf.5.html#forward_path">forward_path</a> = $home/.forward${<a href="postconf.5.html#recipient_delimiter">recipient_delimiter</a>}${extension},
+ $home/.forward
+ <a href="postconf.5.html#propagate_unmatched_extensions">propagate_unmatched_extensions</a> = canonical, virtual
+</pre>
+</blockquote>
+
+<p> (the last two parameter settings are default settings). </p>
+
+<p> You need to set up a file named .forward+listname with the
+commands that process all the mail that is sent to the owner-listname
+address: </p>
+
+<blockquote>
+<pre>
+~/.forward+listname:
+ "|/some/where/command ..."
+</pre>
+</blockquote>
+
+<p> With this set up, undeliverable mail for user@domain will be returned
+to the following address: </p>
+
+<blockquote>
+<pre>
+owner-listname+user=domain@your.domain
+</pre>
+</blockquote>
+
+<p> which is processed by the command in your .forward+listname file.
+The message should contain, among others, a To: header with the
+encapsulated recipient sender address: </p>
+
+<blockquote>
+<pre>
+To: owner-listname+user=domain@your.domain
+</pre>
+</blockquote>
+
+<p> It is left as an exercise for the reader to parse the To: header
+line and to pull out the user=domain part from the recipient address.
+</p>
+
+<h2> <a name="smtp"> VERP support in the Postfix SMTP server </a> </h2>
+
+<p> The Postfix SMTP server implements a command XVERP to enable
+VERP style delivery. The syntax allows two forms: </p>
+
+<blockquote>
+<pre>
+MAIL FROM:&lt;sender@domain&gt; XVERP
+
+MAIL FROM:&lt;sender@domain&gt; XVERP=+=
+</pre>
+</blockquote>
+
+<p> The first form uses the default <a href="postconf.5.html">main.cf</a> VERP delimiters, the
+second form overrides them explicitly. The values shown are the
+recommended ones. </p>
+
+<p> You can use the <a href="postconf.5.html#smtpd_command_filter">smtpd_command_filter</a> feature to append XVERP
+to SMTP commands from legacy software. This requires Postfix 2.7
+or later. </p>
+
+<blockquote>
+<pre>
+/etc/postfix/<a href="postconf.5.html">main.cf</a>:
+ <a href="postconf.5.html#smtpd_command_filter">smtpd_command_filter</a> = <a href="pcre_table.5.html">pcre</a>:/etc/postfix/append_verp.pcre
+ <a href="postconf.5.html#smtpd_authorized_verp_clients">smtpd_authorized_verp_clients</a> = $<a href="postconf.5.html#mynetworks">mynetworks</a>
+
+/etc/postfix/append_verp.<a href="pcre_table.5.html">pcre</a>:
+ /^(MAIL FROM:&lt;listname@example\.com&gt;.*)/ $1 XVERP
+</pre>
+</blockquote>
+
+<h2> <a name="sendmail"> VERP support in the Postfix sendmail command </a> </h2>
+
+<p> The Postfix sendmail command has a -V flag to request VERP style
+delivery. Specify one of the following two forms: </p>
+
+<p> Postfix 2.3 and later:</p>
+<blockquote>
+<pre>
+% sendmail -XV -f owner-listname ....
+
+% sendmail -XV+= -f owner-listname ....
+</pre>
+</blockquote>
+
+<p> Postfix 2.2 and earlier (Postfix 2.3 understands the old syntax
+for backwards compatibility, but will log a warning that reminds
+you of the new syntax): </p>
+
+<blockquote>
+<pre>
+% sendmail -V -f owner-listname ....
+
+% sendmail -V+= -f owner-listname ....
+</pre>
+</blockquote>
+
+<p> The first form uses the default <a href="postconf.5.html">main.cf</a> VERP delimiters, the
+second form overrides them explicitly. The values shown are the
+recommended ones. </p>
+
+<h2> <a name="qmqp"> VERP support in the Postfix QMQP server </a> </h2>
+
+<p> When the Postfix QMQP server receives mail with an envelope
+sender address of the form: </p>
+
+<blockquote>
+<pre>
+listname-@your.domain-@[]
+</pre>
+</blockquote>
+
+<p> Postfix generates sender addresses
+"<tt>listname-user=domain@your.domain</tt>", using "-=" as the VERP
+delimiters because qmail/ezmlm expect this. </p>
+
+<p> More generally, a sender address of "<tt>prefix@origin-@[]</tt>"
+requests VERP style delivery with sender addresses of the form
+"<tt>prefixuser=domain@origin</tt>". However, Postfix allows only
+VERP delimiters that are specified with the <a href="postconf.5.html#verp_delimiter_filter">verp_delimiter_filter</a>
+parameter. In particular, the "=" delimiter is required for qmail
+compatibility (see the qmail addresses(5) manual page for details).
+
+</body>
+
+</html>