Path: utzoo!utgpu!attcan!uunet!husc6!purdue!decwrl!vixie
From: vixie@decwrl.dec.com (Paul Vixie)
Newsgroups: comp.mail.uucp
Subject: Re: using Path: for mail replies
Message-ID: <63@volition.dec.com>
Date: 20 Aug 88 09:40:06 GMT
References: <676@bacchus.DEC.COM> <881@vsi1.UUCP> <10135@e.ms.uky.edu> <60@minya.UUCP> <8528@swan.ulowell.edu> <879@ncrcan.Toronto.NCR.COM>
Organization: DEC Western Research Lab
Lines: 44

This has been dealt with extensively in years past; apparently we need another
round on this topic.

# >Nope.  Here's the Path: line as it arrived here:
# >Path: ulowell!bbn!uwmcsd1!ig!agate!ucbvax!decwrl!decvax!ima!minya!jc
# 
# gawd!  How could anyone want to reply using that path?!?
# 
# >A reply from here would go to mit-eddie!minya!jc.  Not a news path.
# 
# Much better. Score one for smart mailers choosing the best path.

What was the "From:" line?

"Path:" lines should be changed in the next release of B/C/TMN News, so
that they don't look so much like UUCP bang-paths.  People get the mistaken
impression that these are useful ways to get mail back to the sender of
an article.  In fact, it often works.

The problems?  (1) the path is almost guaranteed suboptimal.  Netnews
articles flow in eddies and currents, and the path an article took to
get to your system is always longer than what you'd plan if you were
only sending one piece of text from point A to point B.  (2) the path
may include news-only links, or it may include several Internet/NNTP
sites, which are mostly all one mail hop away from each other -- do you
want to send to a!b!c!d when "a" can talk to "d" directly, and when "a"
can speak NetNews but not Mail to "b"?

The solution?  Use the "From:" or "Reply-To:" lines.  They are designed
to be used as targets of "reply".  (At least in Netnews they are.)  You
can either install "smail" and let it find the route in the mail transport
using pathalias-generated data, or you can use the "mailpaths" file in
the "News B 2.11" software, pointing your "internet" to some well-known
host near you that _does_ run something like "smail".

The point of all this?  Since you aren't supposed to use "Path:" lines
to send your e-mail replies to news articles, there is _never_ any good
reason for _anyone_ to optimize their pass-through MTA to deal with this
type of traffic.  This means re-routing MTA's.  It means Rutgers.
-- 
Paul Vixie
Digital Equipment Corporation	Work:  vixie@dec.com	Play:  paul@vixie.UUCP
Western Research Laboratory	 uunet!decwrl!vixie	   uunet!vixie!paul
Palo Alto, California, USA	  +1 415 853 6600	   +1 415 864 7013