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Path: utzoo!linus!decvax!genrad!grkermit!masscomp!clyde!burl!hou3c!ron@brl-vgr.ARPA
From: ron@brl-vgr.ARPA
Newsgroups: net.mail.headers
Subject: Re:  "Return-Path" vs. "From"
Message-ID: <243@hou3c.UUCP>
Date: Tue, 7-Feb-84 10:37:43 EST
Article-I.D.: hou3c.243
Posted: Tue Feb  7 10:37:43 1984
Date-Received: Thu, 9-Feb-84 22:32:44 EST
Sender: ka@hou3c.UUCP (Kenneth Almquist)
Lines: 33
To: Nathaniel Mishkin 
Cc: Mark Crispin , Ellis@yale.arpa

The confusion factor is minimized by not looking at RETURN-PATH.
If you must, configure your mail reader such that the RETURN-PATH
lines are deleted.  The reason in you case (although I am not certain)
is probably one of human engineering.  At BRL, for the sake of user
friendliness, a user is allowed to specify any return address in his
FROM or SENDER line that will legally get the letter back to him
(the validation on this is interesting but too lengthy to discuss here).
However, the return path is always set to the address that the system
determines is the mail invoker really is associated with.  This also
allows getting around the multiple FROM list problem.  For example:
I can send a letter with "FROM: Ronald.Natalie@BRL" but the mail system
recognizes me as the "ron" user on the BRL-VGR host and my return path
gets marked as "ron@Brl-Vgr".

RETURN-PATH should probably not be in the header at all, except that
mail does get out of the SMTP environment and it's nice to propagate
the information along to the non-SMTP environments.

The other major use (other than setting return path to null to avoid
error messages entirely) is with large mailing lists.  If you look
carefully at the large lists maintained at BRL (INFO-{MICRO,UNIX,CPM,APPLE},
UNIX-WIZARDS, MSGGROUP).  You will find that although these appear to
be simple mail exploders (an incoming letter immediately gets turned around
and sent out to the list), a transformation occurs.  The RETURN-PATH
is changed from what it was to the appropriate -REQUEST list.  This keeps
the list submitters from seeing errors that are beyond their control
to fix and forwards them to the people who might be able to fix them who
would ordinarily have seen them.

-Ron