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Standards, Environments, and Macros envelopes(5)
NNNNAAAAMMMMEEEE
envelopes - sender/recipient lists attached to messages
IIIINNNNTTTTRRRROOOODDDDUUUUCCCCTTTTIIIIOOOONNNN
Electronic mail messages are delivered in _e_n_v_e_l_o_p_e_s.
An envelope lists a _s_e_n_d_e_r and one or more _r_e_c_i_p_i_e_n_t_s. 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.
EEEENNNNVVVVEEEELLLLOOOOPPPPEEEE EEEEXXXXAAAAMMMMPPPPLLLLEEEESSSS
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
SunOS 5.11 Last change: 1
Standards, Environments, 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
envelope sender with something new, ssssoooossss----oooowwwwnnnneeeerrrr. So bounces
will come back to ssssoooossss----oooowwwwnnnneeeerrrr:
(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, ssssoooossss----oooowwwwnnnneeeerrrr, like
this: the original envelope sender (ddddjjjjbbbb) has no way to fix
bad ssssoooossss----lllliiiisssstttt addresses, and of course bounces must not be
sent to ssssoooossss----lllliiiisssstttt itself.
HHHHOOOOWWWW EEEENNNNVVVVEEEELLLLOOOOPPPPEEEE AAAADDDDDDDDRRRREEEESSSSSSSSEEEESSSS AAAARRRREEEE SSSSTTTTOOOORRRREEEEDDDD
Envelope sender and envelope recipient addresses are
transmitted and recorded in several ways.
When a user injects mail through qqqqmmmmaaaaiiiillll----iiiinnnnjjjjeeeecccctttt, he can supply
a RRRReeeettttuuuurrrrnnnn----PPPPaaaatttthhhh line or a -ffff 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 qqqqmmmmaaaaiiiillll----iiiinnnnjjjjeeeecccctttt. Similar comments apply to sssseeeennnnddddmmmmaaaaiiiillll.
When a message is transferred from one machine to another
through SMTP, the envelope sender is given in a MMMMAAAAIIIILLLL FFFFRRRROOOOMMMM
command, the envelope recipients are given in RRRRCCCCPPPPTTTT TTTTOOOO com-
mands, and the message is supplied separately by a DDDDAAAATTTTAAAA com-
mand.
SunOS 5.11 Last change: 2
Standards, Environments, and Macros envelopes(5)
When a message is delivered by qqqqmmmmaaaaiiiillll to a single local reci-
pient, qqqqmmmmaaaaiiiillll----llllooooccccaaaallll records the recipient in DDDDeeeelllliiiivvvveeeerrrreeeedddd----TTTToooo and
the envelope sender in RRRReeeettttuuuurrrrnnnn----PPPPaaaatttthhhh. It uses DDDDeeeelllliiiivvvveeeerrrreeeedddd----TTTToooo to
detect mail forwarding loops.
sssseeeennnnddddmmmmaaaaiiiillll normally records the envelope sender in RRRReeeettttuuuurrrrnnnn----
PPPPaaaatttthhhh. 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, sssseeeennnnddddmmmmaaaaiiiillll will move envelope recipient addresses
back into the header. This situation occurs if all
addresses were originally listed as BBBBcccccccc, since BBBBcccccccc is
automatically removed. When sssseeeennnnddddmmmmaaaaiiiillll sees this, it creates
a new AAAAppppppppaaaarrrreeeennnnttttllllyyyy----TTTToooo 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 mmmmbbbbooooxxxx format, the envelope sender
is recorded at the top of the message as a UUCP-style FFFFrrrroooommmm
(no colon) line. Note that this line is less reliable than
the RRRReeeettttuuuurrrrnnnn----PPPPaaaatttthhhh line added by qqqqmmmmaaaaiiiillll----llllooooccccaaaallll or sssseeeennnnddddmmmmaaaaiiiillll.
SSSSEEEEEEEE AAAALLLLSSSSOOOO
qmail-header(5), qmail-local(8), qmail-inject(8)
SunOS 5.11 Last change: 3