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From: gds@mit-eddie.UUCP (Greg Skinner)
Newsgroups: net.mail
Subject: Re: Mail routing -- problems showing up
Message-ID: <4941@mit-eddie.UUCP>
Date: Mon, 12-Aug-85 17:36:12 EDT
Article-I.D.: mit-eddi.4941
Posted: Mon Aug 12 17:36:12 1985
Date-Received: Wed, 14-Aug-85 20:54:07 EDT
References: <3018@nsc.UUCP> <2875@topaz.ARPA> <4787@mit-eddie.UUCP> <16110@watmath.UUCP>
Distribution: net
Organization: MIT Lusers and Hosers Inc., Cambridge, Ma.
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First off, let me make myself clear.

What I want to be able to do is source-route over different networks.
That is to say, I want to be able to specify, via whatever means
possible, the route my message takes over whatever networks I see fit to
route it through.  Excepting in the case where it is illegal to use
intermediate networks to transport my messages, I would like to set the
precedence of certain network operators (more on this later) so that my
messages take the specified routes.

Now, about rfc822, source routing, etc.

Within a context which understands rfc822, the type of source routing
which you give example of <@site1,@site2:user@site3> works.  However,
over multiple contexts rfc822 source routing does not work, because the
non-rfc822 environments most likely will not be able to put the commands
together to deliver the mail given the source route.  As an example, if
I specify my route to be:

<@seismo,@ihnp4:gregbo@houxm>

what guarantees do I have that seismo knows how to put together the uux
command to deliver the mail to ihnp4?  Maybe it does, maybe it doesn't.
It's possible that seismo will return to mail to me with a

ihnp4:  Host unknown

since ihnp4 is not on the ARPAnet.  However, let's assume that seismo is
running sendmail and does know that ihnp4 should be looked up in its
uuname tables.  But then, how do I know that ihnp4 is running sendmail,
and can convert gregbo@houxm to what an address looks like in ihnp4's
context?  (Note:  this is just an illustration, and should not be
confused with any actual hosts or machines.)

Also, it was my impression that quoted strings were not broken up into
source routes in SMTP, so that if a user sends mail to
"ihnp4!houxm!gregbo"@seismo, the command that is created is

<@seismo:ihnp4!houxm!gregbo>

and seismo is left to cope with the entire formerly-quoted-string for
it's own interpretation, rather than have it pre-interpreted by the
ARPAnet.  So, I don't believe it is SMTP's job to create end-to-end
source routes for mail messages.

On the subject of quotes -- quotes were never intended as delimiters for
source routes.  In rfc822, quotes are used to make tokens out of phrases
like "John Smith" or "I. Furious User".  The spec mentions nothing about
the use of "'s to explicitly specify routes, just as the spec mentions
nothing about % as an internetworking character.  By using "'s in
addresses, one can specify an address such as "John Smith"@somehost,
assuming that somehost is capable of mapping "John Smith" to a mailbox
or process.  Some mailers took the liberty of allowing users to quote a
part of an address on the lhs of the @, because the lhs may have had a
character in it which had a special interpretation on the host (for
example, on tops20 a ! is a comment character).  Everything to the left
of the @ is left intact for interpretation by the rhs of the @.

In conclusion, there is no provision for source routing outside of an
rfc822 context specified by rfc822.  Whether or not source routing
should be allowed outside of the originating context is a subject for
much debate, but I hold that it is feasible, especially when sending
messages over multiple networks (when it is legal to do so).  Domains
provide one way of doing this, peter's pathalias scheme seems not to
have much knowledge of such things.  My proposal, to treat network
characters as operators, with grouping of expressions to specify
precedence for how addresses are interpreted, is also a subject for much
debate, as it has not been proven that such interpretation of addresses
is necessary.  However, I intend to give it some more thought, and will
probably post the same article maybe a year from now if domains or
pathalias don't provide neat solutions for the internetworking of mail
messages.
-- 
Do not meddle in the affairs of wizards,
for they are subtle and quick to anger.

Greg Skinner (gregbo)
{decvax!genrad, allegra, ihnp4}!mit-eddie!gds
gds@mit-eddie.mit.edu