postfix-master/DSN_README.html

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   8 <title>Postfix DSN Support </title>
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  16 <h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Postfix
  17 DSN Support </h1>
  18
  19 <hr>
  20
  21 <h2>Introduction</h2>
  22
  23 <p> Postfix version 2.3 introduces support for Delivery Status
  24 Notifications as described in <a href="http://tools.ietf.org/html/rfc3464">RFC 3464</a>. This gives senders control
  25 over successful and failed delivery notifications.  </p>
  26
  27 <p> Specifically, DSN support gives an email sender the ability to
  28 specify: </p>
  29
  30 <ul>
  31
  32 <li> <p> What notifications are sent: success, failure, delay, or
  33 none. Normally, Postfix informs the sender only when mail delivery
  34 is delayed or when delivery fails.  </p>
  35
  36 <li> <p> What content is returned in case of failure: only the
  37 message headers, or the full message. </p>
  38
  39 <li> <p> An envelope ID that is returned as part of delivery status
  40 notifications. This identifies the message <i>submission</i>
  41 transaction, and must not be confused with the message ID, which
  42 identifies the message <i>content</i>. </p>
  43
  44 </ul>
  45
  46 <p> The implementation of DSN support involves extra parameters to
  47 the SMTP MAIL FROM and RCPT TO commands, as well as two Postfix
  48 sendmail command line options that provide a sub-set of the functions
  49 of the extra SMTP command parameters. </p>
  50
  51 <p> This document has information on the following topics: </p>
  52
  53 <ul>
  54
  55 <li> <a href="#scope">Restricting the scope of "success" notifications</a>
  56
  57 <li> <a href="#cli">Postfix sendmail command-line interface</a>
  58
  59 <li> <a href="#compat">Postfix VERP support compatibility</a>
  60
  61 </ul>
  62
  63 <h2> <a name="scope">Restricting the scope of "success" notifications</a> </h2>
  64
  65 <p> Just like reports of undeliverable mail, DSN reports of
  66 <i>successful</i> delivery can give away more information about the
  67 internal infrastructure than desirable.  Unfortunately, disallowing
  68 "success" notification requests requires disallowing other DSN
  69 requests as well. The RFCs do not offer the option to negotiate
  70 feature subsets. </p>
  71
  72 <p> This is not as bad as it sounds. When you turn off DSN for
  73 remote inbound mail, remote senders with DSN support will still be
  74 informed that their mail reached your Postfix gateway successfully;
  75 they just will not get successful delivery notices from your internal
  76 systems. Remote senders lose very little: they can no longer specify
  77 how Postfix should report delayed or failed delivery.  </p>
  78
  79 <p> Use the <a href="postconf.5.html#smtpd_discard_ehlo_keyword_address_maps">smtpd_discard_ehlo_keyword_address_maps</a> feature if you
  80 wish to allow DSN requests from trusted clients but not from random
  81 strangers (see below for how to turn this off for all clients):
  82 </p>
  83
  84 <blockquote>
  85 <pre>
  86 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
  87     <a href="postconf.5.html#smtpd_discard_ehlo_keyword_address_maps">smtpd_discard_ehlo_keyword_address_maps</a> =
  88         <a href="cidr_table.5.html">cidr</a>:/etc/postfix/esmtp_access
  89
  90 /etc/postfix/esmtp_access:
  91     # Allow DSN requests from local subnet only
  92     192.168.0.0/28      silent-discard
  93     0.0.0.0/0           silent-discard, dsn
  94     ::/0                silent-discard, dsn
  95 </pre>
  96 </blockquote>
  97
  98 <p> If you want to disallow all use of DSN requests from the network,
  99 use the <a href="postconf.5.html#smtpd_discard_ehlo_keywords">smtpd_discard_ehlo_keywords</a> feature: </p>
 100
 101 <blockquote>
 102 <pre>
 103 /etc/postfix/<a href="postconf.5.html">main.cf</a>:
 104     <a href="postconf.5.html#smtpd_discard_ehlo_keywords">smtpd_discard_ehlo_keywords</a> = silent-discard, dsn
 105 </pre>
 106 </blockquote>
 107
 108 <h2> <a name="cli">Postfix sendmail command-line interface</a> </h2>
 109
 110 <p> Postfix has two Sendmail-compatible command-line options for
 111 DSN support. </p>
 112
 113 <ul>
 114
 115 <li> <p>  The first option specifies what notifications are sent
 116 for mail that is submitted via the Postfix <a href="sendmail.1.html">sendmail(1)</a> command line:
 117 </p>
 118
 119 <blockquote>
 120 <pre>
 121 $ <b>sendmail -N success,delay,failure ...</b> (one or more of these)
 122 $ <b>sendmail -N never ...</b>                 (or just this by itself)
 123 </pre>
 124 </blockquote>
 125
 126 <p> The built-in default corresponds with "delay,failure". </p>
 127
 128 <li> <p> The second option specifies an envelope ID which is reported
 129 in delivery status notifications for mail that is submitted via the
 130 Postfix <a href="sendmail.1.html">sendmail(1)</a> command line: </p>
 131
 132 <blockquote>
 133 <pre>
 134 $ <b>sendmail -V <i>envelope-id</i> ...</b>
 135 </pre>
 136 </blockquote>
 137
 138 <p> Note: this conflicts with VERP support in older Postfix versions,
 139 as discussed in the next section. </p>
 140
 141 </ul>
 142
 143 <h2> <a name="compat">Postfix VERP support compatibility</a> </h2>
 144
 145 <p> With Postfix versions before 2.3, the <a href="sendmail.1.html">sendmail(1)</a> command uses
 146 the -V command-line option to request VERP-style delivery.  In order
 147 to request VERP style delivery with Postfix 2.3 and later, you must
 148 specify -XV instead of -V. </p>
 149
 150 <p> The Postfix 2.3 <a href="sendmail.1.html">sendmail(1)</a> command will recognize if you try
 151 to use -V for VERP-style delivery.  It will do the right thing and
 152 will remind you of the new syntax. </p>
 153
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