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diff --git a/README_FILES/VERP_README b/README_FILES/VERP_README new file mode 100644 index 0000000..a721ece --- /dev/null +++ b/README_FILES/VERP_README @@ -0,0 +1,186 @@ +PPoossttffiixx VVEERRPP HHoowwttoo + +------------------------------------------------------------------------------- + +PPoossttffiixx VVEERRPP ssuuppppoorrtt + +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. + +For example, when VERP style delivery is requested, Postfix delivers mail from +"owner-listname@origin" for a recipient "user@domain", with a sender address +that encodes the recipient as follows: + + owner-listname+user=domain@origin + +Thus, undeliverable mail can reveal the undeliverable recipient address without +requiring the list owner to parse bounce messages. + +The VERP concept was popularized by the qmail MTA and by the ezmlm mailing list +manager. See http://cr.yp.to/proto/verp.txt for the ideas behind this concept. + +Topics covered in this document: + + * Postfix VERP configuration parameters + * Using VERP with majordomo etc. mailing lists + * VERP support in the Postfix SMTP server + * VERP support in the Postfix sendmail command + * VERP support in the Postfix QMQP server + +PPoossttffiixx VVEERRPP ccoonnffiigguurraattiioonn ppaarraammeetteerrss + +With Postfix, the whole process is controlled by four configuration parameters. + +default_verp_delimiters (default value: +=) + What VERP delimiter characters Postfix uses when VERP style delivery is + requested but no explicit delimiters are specified. + +verp_delimiter_filter (default: -+=) + 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. + +smtpd_authorized_verp_clients (default value: none) + 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. + + With Postfix versions 1.1 and 2.0, this parameter is called + authorized_verp_clients (default: $mynetworks). + +disable_verp_bounces (default: no) + 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. + +UUssiinngg VVEERRPP wwiitthh mmaajjoorrddoommoo eettcc.. mmaaiilliinngg lliissttss + +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: + +Postfix 2.3 and later: + + % sendmail -XV -f owner-listname other-arguments... + + % sendmail -XV+= -f owner-listname other-arguments... + +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): + + % sendmail -V -f owner-listname other-arguments... + + % sendmail -V+= -f owner-listname other-arguments... + +The first form uses the default main.cf VERP delimiter characters. The second +form allows you to explicitly specify the VERP delimiter characters. The +example shows the recommended values. + +This text assumes that you have set up an owner-listname alias that routes +undeliverable mail to a real person: + + /etc/aliases: + owner-listname: yourname+listname + +In order to process bounces we are going to make extensive use of address +extension tricks. + +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: + + /etc/postfix/main.cf: + recipient_delimiter = + + forward_path = $home/.forward${recipient_delimiter}${extension}, + $home/.forward + propagate_unmatched_extensions = canonical, virtual + +(the last two parameter settings are default settings). + +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: + + ~/.forward+listname: + "|/some/where/command ..." + +With this set up, undeliverable mail for user@domain will be returned to the +following address: + + owner-listname+user=domain@your.domain + +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: + + To: owner-listname+user=domain@your.domain + +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. + +VVEERRPP ssuuppppoorrtt iinn tthhee PPoossttffiixx SSMMTTPP sseerrvveerr + +The Postfix SMTP server implements a command XVERP to enable VERP style +delivery. The syntax allows two forms: + + MAIL FROM:<sender@domain> XVERP + + MAIL FROM:<sender@domain> XVERP=+= + +The first form uses the default main.cf VERP delimiters, the second form +overrides them explicitly. The values shown are the recommended ones. + +You can use the smtpd_command_filter feature to append XVERP to SMTP commands +from legacy software. This requires Postfix 2.7 or later. + + /etc/postfix/main.cf: + smtpd_command_filter = pcre:/etc/postfix/append_verp.pcre + smtpd_authorized_verp_clients = $mynetworks + + /etc/postfix/append_verp.pcre: + /^(MAIL FROM:<listname@example\.com>.*)/ $1 XVERP + +VVEERRPP ssuuppppoorrtt iinn tthhee PPoossttffiixx sseennddmmaaiill ccoommmmaanndd + +The Postfix sendmail command has a -V flag to request VERP style delivery. +Specify one of the following two forms: + +Postfix 2.3 and later: + + % sendmail -XV -f owner-listname .... + + % sendmail -XV+= -f owner-listname .... + +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): + + % sendmail -V -f owner-listname .... + + % sendmail -V+= -f owner-listname .... + +The first form uses the default main.cf VERP delimiters, the second form +overrides them explicitly. The values shown are the recommended ones. + +VVEERRPP ssuuppppoorrtt iinn tthhee PPoossttffiixx QQMMQQPP sseerrvveerr + +When the Postfix QMQP server receives mail with an envelope sender address of +the form: + + listname-@your.domain-@[] + +Postfix generates sender addresses "listname-user=domain@your.domain", using "- +=" as the VERP delimiters because qmail/ezmlm expect this. + +More generally, a sender address of "prefix@origin-@[]" requests VERP style +delivery with sender addresses of the form "prefixuser=domain@origin". However, +Postfix allows only VERP delimiters that are specified with the +verp_delimiter_filter parameter. In particular, the "=" delimiter is required +for qmail compatibility (see the qmail addresses(5) manual page for details). + |