Provided by: qmail_1.06-6.2~deb10u1build0.16.04.1_amd64 bug


       envelopes - sender/recipient lists attached to messages


       Electronic mail messages are delivered in envelopes.

       An  envelope  lists a sender and one or more recipients.  Usually these envelope addresses
       are the same as the addresses listed in the message header:

          (envelope) from djb to root
          From: djb
          To: root

       In more complicated situations, though, the envelope addresses may differ from the  header


       When  a  message  is  delivered  to  several  people  at  different locations, it is first
       photocopied and placed into several envelopes:

          (envelope) from djb to root
          From: djb                          Copy #1 of message
          To: root,

          (envelope) from djb to
          From: djb                          Copy #2 of message
          To: root,

       When a message is delivered to several people at the same  location,  the  sender  doesn't
       have  to  photocopy it.  He can instead stuff it into one envelope with several addresses;
       the recipients will make the photocopy:

          (envelope) from djb to,
          From: djb
          To:,, joe, frde

       Bounced mail is sent back to the envelope sender address.  The bounced mail  doesn't  list
       an envelope sender, so bounce loops are impossible:

          (envelope) from <> to djb
          From: MAILER-DAEMON
          To: djb
          Subject: unknown user frde

       The recipient of a message may make another copy and forward it in a new envelope:

          (envelope) from djb to joe
          From: djb                          Original message
          To: joe

          (envelope) from joe to fred
          From: djb                          Forwarded message
          To: joe

       A mailing list works almost the same way:

          (envelope) from djb to sos-list
          From: djb                          Original message
          To: sos-list

          (envelope) from sos-owner to
          From: djb                          Forwarded message
          To: sos-list                       to recipient #1

          (envelope) from sos-owner to frde
          From: djb                          Forwarded message
          To: sos-list                       to recipient #2

       Notice  that the mailing list is set up to replace the envelope sender with something new,
       sos-owner.  So bounces will come back to sos-owner:

          (envelope) from <> to sos-owner
          From: MAILER-DAEMON
          To: sos-owner
          Subject: unknown user frde

       It's a good idea to set up an extra address, sos-owner, like this: the  original  envelope
       sender  (djb)  has no way to fix bad sos-list addresses, and of course bounces must not be
       sent to sos-list itself.


       Envelope sender and envelope recipient addresses are transmitted and recorded  in  several

       When  a  user  injects mail through qmail-inject, he can supply a Return-Path line or a -f
       option for the envelope sender; by default the envelope sender is  his  login  name.   The
       envelope  recipient  addresses  can  be taken from the command line or from various header
       fields, depending on the options to qmail-inject.  Similar comments apply to sendmail.

       When a message is transferred from one machine  to  another  through  SMTP,  the  envelope
       sender  is  given  in  a  MAIL  FROM command, the envelope recipients are given in RCPT TO
       commands, and the message is supplied separately by a DATA command.

       When a message is delivered by qmail to a single local recipient, qmail-local records  the
       recipient in Delivered-To and the envelope sender in Return-Path.  It uses Delivered-To to
       detect mail forwarding loops.

       sendmail normally records the envelope sender in Return-Path.  It does not record envelope
       recipient  addresses, on the theory that they are redundant: you received the mail, so you
       must have been one of the envelope recipients.

       Note that, if the header doesn't have any recipient addresses, sendmail will move envelope
       recipient  addresses  back  into  the header.  This situation occurs if all addresses were
       originally listed as Bcc, since Bcc is automatically removed.  When sendmail sees this, it
       creates  a new Apparently-To header field with the envelope recipient addresses.  This has
       the strange effect that each blind-carbon-copy recipient will see a list of all recipients
       on the same machine.

       When a message is stored in mbox format, the envelope sender is recorded at the top of the
       message as a UUCP-style From (no colon) line.  Note that this line is less  reliable  than
       the Return-Path line added by qmail-local or sendmail.


       qmail-header(5), qmail-local(8), qmail-inject(8)