Path: utzoo!mnetor!uunet!husc6!purdue!gatech!amdcad!rpw3
From: rpw3@amdcad.AMD.COM (Rob Warnock)
Newsgroups: comp.mail.misc
Subject: Re: operator precedence
Message-ID: <20960@amdcad.AMD.COM>
Date: 30 Mar 88 05:34:42 GMT
References: <23560@hi.unm.edu> <3395@psuvax1.psu.edu>
Reply-To: rpw3@amdcad.UUCP (Rob Warnock)
Organization: [Consultant] San Mateo, CA
Lines: 45
Keywords: '!' and '%', RFC886

>In article <23560@hi.unm.edu> kurt@hi.unm.edu (Kurt Zeilenga) writes:
>-What is considered defacto standard way(s) of rewriting "a!b%c"?

The "%" is neither a "!" nor a "@", and thus is (or *should* be) left
alone by any of the transport/routing programs. It *may* be interpreted
by "local" mail delivery systems, and in particular is handled by "sendmail",
and many SMTP mailers (although seldom by non-sendmail UUCP mailers).

The defacto standard way, and the reason for the "%" at all (as opposed
to "@"), is to defer any rewriting unless you are system "a", in which
case you have already stripped the "a!", and are trying to deliver mail
to a local "user" named "b%c". At this point (and *only* at this point),
you notice the "%", and re-write "b%c" as "b@c", and then do whatever
you do locally with "@" addresses (including sending it back out again).

If you are not "a", you send it via UUCP to "a" (if you know how :-).

The purpose of the "%" is to avoid the ambiguity that arises with mixed
"!" and "@".

By the way, "%" is often used in the SMTP world. The address "b%c@a"
means exactly the same as above: If you are system "a", the "b%c" is
a "local-part", which you can (but are not required to) re-write to "b@c".
So, for example, in SMTP-land you can often send a "mail-echo" be sending
to "me%my-system@other-system".


p.s.
Note that the usual example, "a!b@c", *cannot* be parsed corectly unless
you know what kind of transport it came in on. If it came in on SMTP, then
"a!b" is the "local-part", and you should send it to "a" via UUCP. If it
came in on UUCP, then "b@c" is the "user", and you should send it to "c"
with SMTP (or maybe UUCP, depending on your mail system). Such a mixed-mode
horror should *never* be generated locally! If you *have* to send to a "domain"
via a UUCP first hop, then use full-bang domain addressing: a!c.dom.ain!b
Mailers such as "smail" understand this form.


Rob Warnock
Systems Architecture Consultant

UUCP:	  {amdcad,fortune,sun,attmail}!redwood!rpw3
ATTmail:  !rpw3
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