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+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).
+