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diff --git a/README_FILES/DSN_README b/README_FILES/DSN_README new file mode 100644 index 0000000..efd7f4c --- /dev/null +++ b/README_FILES/DSN_README @@ -0,0 +1,98 @@ +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. + |