envelopes(5)       Headers, Tables, and Macros       envelopes(5)



NAME
     envelopes - sender/recipient lists attached to messages

INTRODUCTION
     Electronic mail messages are delivered in envelopes.

     An envelope lists a sender and one or more recipients.  Usu-
     ally 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 addresses.

ENVELOPE EXAMPLES
     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, god@brl.mil

        (envelope) from djb to god@brl.mil
        From: djb                          Copy #2 of message
        To: root, god@brl.mil

     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 god@brl.mil, angel@brl.mil
        From: djb
        To: god@brl.mil, angel@brl.mil, 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



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envelopes(5)       Headers, Tables, and Macros       envelopes(5)



        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 god@brl.mil
        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  enve-
     lope  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.

HOW ENVELOPE ADDRESSES ARE STORED
     Envelope  sender and envelope recipient addresses are trans-
     mitted and recorded in several ways.

     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 enve-
     lope  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 com-
     mands, and the message is supplied separately by a DATA com-
     mand.




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envelopes(5)       Headers, Tables, and Macros       envelopes(5)



     When  a  message  is  delivered  by  qmail to a single local
     recipient, qmail-alias 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  auto-
     matically  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-car-
     bon-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-alias or sendmail.

SEE ALSO
     qmail-header(5), qmail-alias(8), qmail-inject(8)




























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