Ubuntu Manpage: envelopes - sender/recipient lists attached to messages

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.

NAME

INTRODUCTION

ENVELOPE EXAMPLES

HOW ENVELOPE ADDRESSES ARE STORED

SEE ALSO