Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.3 alpha 5/22/85; site cbosgd.UUCP
Path: utzoo!linus!gatech!cbosgd!mark
From: mark@cbosgd.UUCP (Mark Horton)
Newsgroups: net.mail
Subject: Re: Mail routing -- problems showing up
Message-ID: <1478@cbosgd.UUCP>
Date: Sat, 14-Sep-85 12:50:46 EDT
Article-I.D.: cbosgd.1478
Posted: Sat Sep 14 12:50:46 1985
Date-Received: Sat, 14-Sep-85 20:20:39 EDT
References: <1383@peora.UUCP> <9546@ucbvax.ARPA>
Organization: AT&T Bell Laboratories, Columbus, Oh
Lines: 76

In article <1632@peora.UUCP> jer@peora.UUCP (J. Eric Roskos) writes:
>You don't have to, though.  Here if I want to write to a mailnet site, I
>write
>	To: sam_smith@tops10site.mailnet
>
>The router looks in its domain table, where it sees
>
>    .MAILNET,>ucbvax,,%P!%U%%%D@MIT-MULTICS.ARPA
>
>It translates the %P to the path to ucbvax (which is what >ucbvax stands
>for); it inserts sam_smith where the %U is, it generates a % where %%
>is (I guess I should have used a $), it puts tops10site.mailnet where
>the %D is, and that gives
>
>    pesnta!hplabs!ucbvax!sam_smith%tops10site.mailnet@MIT-MULTICS.ARPA
>
>And that gets the message there right now, using plain old UUCP mailers.

This method may happen to work today, with the particular path you
mention, but it's extremely dangerous, because you're generating an
address has a ! to the left of an @.

Let's suppose that next month hplabs installs smail or any other
piece of software that conforms to RFC822, that is, gives @ priority
over !.

Now your mail will appear on hplabs addressed to
	ucbvax!sam_smith%tops10site.mailnet@MIT-MULTICS.ARPA
and hplabs will in turn send it off to MIT-MULTICS.ARPA for
	ucbvax!sam_smith@tops10site.mailnet
which sends it to tops10site.mailnet for
	ucbvax!sam_smith
which fails.

So you say "why don't we just require hplabs to hack their mailer
so that mail coming in from uucp will give ! priority?"  There are
four problems with this:

(1) This is anarchistic UUCP - you can't require hplabs to do anything.
Any assumptions you make that every other host on the net will do "x"
are bound to be false of some significant percentage of the net, unless
"x" is something everyone has always done and always will.

(2) RFC822 is a documented standard and ! routing is not.  The chances are
excellent that AT&T will soon endorse @ having priority over !.

(3) What happens if you want to send mail to a remote UUCP host?  That is,
let's suppose that tops10site really runs UNIX (so let's call them unixsite)
and has a UUCP link to foovax.  You want to send to
	foovax!user@unixsite.mailnet
which has you generating the path
	pesnta!hplabs!ucbvax!foovax!sam_smith%unixsite.mailnet@MIT-MULTICS.ARPA
What would you have ucbvax do with this string?  Especially if it happens
to have a connection to foovax?

(4) What is hplabs supposed to do with the following address typed by a
user on hplabs?
	ucbvax!fred@F.ISI.ARPA
It didn't come in via rmail, so you can't assume bang priority.  It didn't
come in via SMTP, so you can't assume @ priority.  Is fred on ISI or ucbvax?

In general, you can do the same thing with standard conforming syntax
such as
	pesnta!hplabs!ucbvax!MIT-MULTICS.ARPA!foovax!sam_smith%unixsite.mailnet
or better yet
	pesnta!hplabs!ucbvax!unixsite.mailnet!foovax!sam_smith
(These examples assume that ucbvax is properly configured as a gateway,
which I'm not sure is true right now.  They would work using seismo as
the gateway.)

While smail is nearly ready (we're hoping for an October posting), I'd
be interested to hear more about your nameserver.  What we have is not
a nameserver - it's a table driven routing program that uses pathalias
and sendmail.  A true nameserver might be a useful thing to have.

	Mark