Path: utzoo!attcan!uunet!cs.utexas.edu!tut.cis.ohio-state.edu!att!cbnews!mark
From: mark@cbnews.ATT.COM (Mark Horton)
Newsgroups: comp.mail.uucp
Subject: Re: Domains vs. Routing (was Re: rewriting FROM: lines)
Message-ID: <7050@cbnews.ATT.COM>
Date: 1 Jun 89 21:21:49 GMT
References: <31051@sri-unix.SRI.COM> <160@zebra.UUCP> <6982@cbnews.ATT.COM> <882@adobe.UUCP>
Reply-To: mark@cbnews.ATT.COM (Mark Horton)
Organization: AT&T Bell Laboratories
Lines: 41

In article <882@adobe.UUCP> greid@adobe.COM (Glenn Reid) writes:
>The bangity!bangity!user stuff is pretty crude, but it was very
>reliable in terms of reversing the path and getting mail returned to
>the sender.  That's valuable, in my opinion.  And sorely missed in
>today's world.

That's why RFC976 says that there's supposed to be BOTH a return
address or name and a return route in the header:
	From cblpf!mark <date> remote from att
	From: mark@cblpf.att.com (Mark Horton)
The remote from is ugly, but necessary for upward compatibility.
By the time it arrives in your mailbox, it probably looks like
	From att!cblpf!mark <date>
	From: mark@cblpf.att.com (Mark Horton)

As a rule, you can reply using either the From_ line (the route)
or the From: line (the address or name.)  Mail/mailx, for example,
uses r for one and R for the other (possibly flipped.)  The return
route is also needed for upward compatibility, as well as redundancy
and troubleshooting.

Most of the time, you can just reply using the From: line and get
the right result.  Every once in awhile something is broken in the
header you get, and you get a broken From: line and have to reply
using the From_ line.  For example, mail through sun (and some other
places) arrives looking like
	From: sun!dasnet!user
and since I'm not directly connected to sun, the reply bounces.
(Some sites smart-host to figure out who sun is, our software doesn't.)

There is still much turmoil in the email world.  There are lots of
broken mailers out there.  And while the world is clearly building
momentum around RFC822 domains and getting its act together to
support them, X.400 and X.500 are starting to build critical mass.
Throw billing into the picture (who is going to pay for the mail
from random UUCP sites into the commercial X.400 world?) and the
whole picture gets a lot messier.

Gives all us postmasters something to do to earn our paychecks.

	Mark