Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!usc!polyslo!unmvax!unmvax.cs.unm.edu!mike
From: mike@unmvax.cs.unm.edu (Michael I. Bushnell)
Newsgroups: comp.mail.misc
Subject: Re: Replying to mail... is there a general theory?
Message-ID: <219@unmvax.unm.edu>
Date: 12 Jul 89 19:06:56 GMT
References: <3483@portia.Stanford.EDU> <207@unmvax.unm.edu> <1581@marvin.Solbourne.COM>
Sender: news@unmvax.unm.edu
Reply-To: mike@unmvax.cs.unm.edu (Michael I. Bushnell)
Organization: University of No Money, Albuquerque, New Mexico
Lines: 61

In article <1581@marvin.Solbourne.COM> dce@Solbourne.com (David Elliott) writes:
>In article <207@unmvax.unm.edu> mike@unmvax.cs.unm.edu (Michael I. Bushnell) writes:
>>Actually, you should use, in order of preference, the following:
>>  Reply-To:
>>  From:
>>  Sender:

>What about Return-Path:?  I modified my MH configuration files
>to prefer that because it seems to be right more of the time
>than any of the others.

>For example, when stuff gets sent through sites like pyramid
>and nbires, the From: line gets left alone, but Return-Path:
>is modified.  The problem is that other sites may modify From:,
>so the path might appear to be uunet!mips.com!mdove, when the
>actual path taken would have been mips!pyramid!uunet!nbires.

The standard for UUCP mail is for From: to be modified when passing
through each machine.  This arranges for the return address to be
correct.  The standard on the Internet is for From: to be left
absolutely alone.  The best thing to do in gatewaying is as following:

UUCP -> Internet gatewaying:

From: foo!bar!baz    maps to      From: foo!bar!baz@my.internet.site.name


Internet -> UUCP gatewaying:

From: user@his.host.name     maps to   From: myuucpname!user%his.host.name


This all works quite well and integrates nicely with the two
standards.  Note that Reply-To: is modified roughly as above.

Unfortunately, there is no standard for how Return-Path: gets modified
when gatewaying.  Alas.

From RFC 822:

The "Reply-To" field is added by the originator and serves to direct
replies, whereas the "Return-Path" field is used to identify a path
back to the originator.

You see, Return-Path: is not a "path to use for returns/replies".
It's just a path (hopefully) back to the sender.  Internet sites form
it with route-addrs, UUCP sites form it with ! paths, and there isn't
an easy way to map around, and still guarantee that UUCP sites always
get ! and Internet sites never do...you see...not everyone on the
internet understands ! and not everyone in UUCPland understands @ or
route-addrs.  

I have found Return-Path: to be wrong in virtually every case that
involved gatewaying between the two networks.  I have *never* seen the
From: line to be incorrect.  Sometimes inefficient, but never
incorrect. 

   Michael I. Bushnell       \     This above all; to thine own self be true
     Silence == Death         \    And it must follow, as the night the day,
  mike@unmvax.cs.unm.edu      /\   Thou canst not be false to any man.
Telephone: +1 505 292 0001   /  \  Farewell:  my blessing season this in thee!