Adding upstream version 3.4.23.upstream/3.4.23upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 98 insertions, 0 deletions

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+PPoossttffiixx DDSSNN SSuuppppoorrtt
+
+-------------------------------------------------------------------------------
+
+IInnttrroodduuccttiioonn
+
+Postfix version 2.3 introduces support for Delivery Status Notifications as
+described in RFC 3464. This gives senders control over successful and failed
+delivery notifications.
+
+Specifically, DSN support gives an email sender the ability to specify:
+
+  * What notifications are sent: success, failure, delay, or none. Normally,
+    Postfix informs the sender only when mail delivery is delayed or when
+    delivery fails.
+
+  * What content is returned in case of failure: only the message headers, or
+    the full message.
+
+  * An envelope ID that is returned as part of delivery status notifications.
+    This identifies the message submission transaction, and must not be
+    confused with the message ID, which identifies the message content.
+
+The implementation of DSN support involves extra parameters to the SMTP MAIL
+FROM and RCPT TO commands, as well as two Postfix sendmail command line options
+that provide a sub-set of the functions of the extra SMTP command parameters.
+
+This document has information on the following topics:
+
+  * Restricting the scope of "success" notifications
+  * Postfix sendmail command-line interface
+  * Postfix VERP support compatibility
+
+RReessttrriiccttiinngg tthhee ssccooppee ooff ""ssuucccceessss"" nnoottiiffiiccaattiioonnss
+
+Just like reports of undeliverable mail, DSN reports of successful delivery can
+give away more information about the internal infrastructure than desirable.
+Unfortunately, disallowing "success" notification requests requires disallowing
+other DSN requests as well. The RFCs do not offer the option to negotiate
+feature subsets.
+
+This is not as bad as it sounds. When you turn off DSN for remote inbound mail,
+remote senders with DSN support will still be informed that their mail reached
+your Postfix gateway successfully; they just will not get successful delivery
+notices from your internal systems. Remote senders lose very little: they can
+no longer specify how Postfix should report delayed or failed delivery.
+
+Use the smtpd_discard_ehlo_keyword_address_maps feature if you wish to allow
+DSN requests from trusted clients but not from random strangers (see below for
+how to turn this off for all clients):
+
+    /etc/postfix/main.cf:
+        smtpd_discard_ehlo_keyword_address_maps =
+            cidr:/etc/postfix/esmtp_access
+
+    /etc/postfix/esmtp_access:
+        # Allow DSN requests from local subnet only
+        192.168.0.0/28      silent-discard
+        0.0.0.0/0           silent-discard, dsn
+        ::/0                silent-discard, dsn
+
+If you want to disallow all use of DSN requests from the network, use the
+smtpd_discard_ehlo_keywords feature:
+
+    /etc/postfix/main.cf:
+        smtpd_discard_ehlo_keywords = silent-discard, dsn
+
+PPoossttffiixx sseennddmmaaiill ccoommmmaanndd--lliinnee iinntteerrffaaccee
+
+Postfix has two Sendmail-compatible command-line options for DSN support.
+
+  * The first option specifies what notifications are sent for mail that is
+    submitted via the Postfix sendmail(1) command line:
+
+        $ sseennddmmaaiill --NN ssuucccceessss,,ddeellaayy,,ffaaiilluurree ...... (one or more of these)
+        $ sseennddmmaaiill --NN nneevveerr ......                 (or just this by itself)
+
+    The built-in default corresponds with "delay,failure".
+
+  * The second option specifies an envelope ID which is reported in delivery
+    status notifications for mail that is submitted via the Postfix sendmail(1)
+    command line:
+
+        $ sseennddmmaaiill --VV eennvveellooppee--iidd ......
+
+    Note: this conflicts with VERP support in older Postfix versions, as
+    discussed in the next section.
+
+PPoossttffiixx VVEERRPP ssuuppppoorrtt ccoommppaattiibbiilliittyy
+
+With Postfix versions before 2.3, the sendmail(1) command uses the -V command-
+line option to request VERP-style delivery. In order to request VERP style
+delivery with Postfix 2.3 and later, you must specify -XV instead of -V.
+
+The Postfix 2.3 sendmail(1) command will recognize if you try to use -V for
+VERP-style delivery. It will do the right thing and will remind you of the new
+syntax.
+