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From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: Rewriting From: lines
Message-ID: <1988Dec14.180452.733@utzoo.uucp>
Organization: U of Toronto Zoology
References: <1227@vsi1.UUCP> <871@acer.stl.stc.co.uk> <944@dlhpedg.co.uk> <1296@ucsd.EDU> <10510@swan.ulowell.edu> <504@pacbell.PacBell.COM> <1306@ucsd.EDU> <10670@swan.ulowell.edu>
Date: Wed, 14 Dec 88 18:04:52 GMT

In article <10670@swan.ulowell.edu> page@swan.ulowell.edu (Bob Page) writes:
>>Regrettably, that is not always true, and sometimes the From: line
>>contains a path, which must, by definition, be updated.
>
>When it leaves a site with a From: line of user, or host!user, are
>either of those an address or a path?  ...
>I still say leave it alone under all circumstances.  There's no reason
>you should propagate someone else's error.  Keep the path info in From_.

I have to agree with this.  The first and foremost principle of mail
relaying is (should be!) what it says in the Hippocratic Oath:  "First,
Do No Harm".  Corollary:  it is much more important that mail relaying be
predictable than that it be smart.  The receiving and transmitting ends
can always add smartness, but they can't restore lost predictability.

Trying to guess whether a From: line is an address or a path violates
both of these rules.  It introduces unpredictable behavior, since by
definition it's guesswork.  And it has the potential to do major harm,
because an address which is misinterpreted as a path will probably cause
later sites to guess "path" too, resulting in an indecipherable mess in
the situation (our current one) where some sites munge paths and some don't.

The most predictable, and least harmful, approach is to prepend a new From_
line and leave From: alone.  (Trying to stuff your site name into an existing
From_ line rather than just prepending a new one is not as safe, but it's
better than a lot of the alternatives.)
-- 
SunOSish, adj:  requiring      |     Henry Spencer at U of Toronto Zoology
32-bit bug numbers.            | uunet!attcan!utzoo!henry henry@zoo.toronto.edu