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Path: utzoo!watmath!clyde!cuae2!ihnp4!alberta!sask!reid
From: reid@sask.UUCP
Newsgroups: comp.mail.uucp
Subject: Forcing mail routing and brackets in mail addresses
Message-ID: <577@sask.UUCP>
Date: Fri, 16-Jan-87 13:25:35 EST
Article-I.D.: sask.577
Posted: Fri Jan 16 13:25:35 1987
Date-Received: Mon, 19-Jan-87 01:54:11 EST
Organization: University of Saskatchewan
Lines: 46
Keywords: mail, routing, RFC822


A couple of recent postings (sorry, I don't have references) have brought up
two points about the mail routing system.  One poster suggested the
possibility of using brackets to force the mail system to parse addresses
the way the sender meant them, and another wondered about the possibility of
forcing sites that usually re-route mail to refrain from doing so.

First, I know from maintaining a mailing list and having to debug the paths
how frustrating it can be to have another site re-route mail when you don't
want it to.  I would like to see an extra field added to the "Received:"
header (which gets added by every site the mail goes through) so that we can
tell if bounced mail was re-routed, and if so where.

Getting back to the point:

The mail standard which seems to be in use here is described in the RFC822
document.  Section 6.2.3. of this document, along with the sections that
describe syntax, allow for "domain literals", which are strings enclosed in
square brackets ("[", "]").  These are supposed to be passed uninterpreted
to the destination host.  Thus, [user@host_a]@host_b should be routed to
host_b, which will then deliver it to user@host_a (if it can).  As far as I
can tell, these should nest correctly.

To bypass sites that automatically re-route mail, try:

...!re-routing-host!next-host![path-you-don't-want-re-routed!user]

or

[path!user]@first-host-after-re-routing-host

If the mail systems are RFC822 compliant (big if, in some cases) the
re-routing host can only mess with the path as far as the next site on the
line; since it would have sent it there anyways your path comes out the way
you wanted.

RFC822 makes it clear that this is a hack added to allow people to work
around bad mail systems; seems like they designed it for just this case.  Of
course, all of this depends on sites along the line being properly RFC822.

 - irving "the best I can give you is a wild guess" reid -
-- 
reid@sask.uucp                          {alberta, ihnp4, utcsri}!sask!reid

East is East and West is West and maybe their agents will get in touch and
the twain shall do lunch.