Provided by: qmail_1.06-4_i386 bug

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.  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 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
          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  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.

HOW ENVELOPE ADDRESSES ARE STORED

       Envelope  sender  and  envelope recipient addresses are transmitted 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  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.

SEE ALSO

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

                                                                  envelopes(5)