To: Eric Thomas <ERIC@VM.SE.LSOFT.COM>
Cc: drums@cs.utk.edu
Subject: Re: CNAME/1123 breakage 
In-Reply-To: Your message of "Sun, 13 Oct 1996 05:10:16 +0200."
Date: Sun, 13 Oct 1996 17:58:38 +1000
Message-Id: <27477.845193518@munnari.OZ.AU>
From: Robert Elz <kre@munnari.oz.au>

    Date:        Sun, 13 Oct 1996 05:10:16 +0200
    From:        Eric Thomas <ERIC@VM.SE.LSOFT.COM>

    I'm  talking  about  a  *remote*  CNAME, not  one  for  the  local  host.

A remote CNAME to you is a local CNAME to me...

    All  I'm saying is that  mail clients like
    Eudora  or Pegasus  aren't going  to respect  the 1123  CNAME requirement

I wouldn't expect they would.   I woudn't expect they would actually
attempt to be Internet mail delivery agents.   Certainly here all the
Eudora mail users simply dump their mail on a mailserver that does
the delivery.

I don't think there's much doubt but that mail submission is a special
case, and that the rules there need to be different, in lots of ways.
This is where a dedicated protocol has been mooted from time to time.

However, if a Eudora/pegasus/qvnet/... mailer is going to actually do
end to end mail delivery, then it had better plan on following the
rules.   That includes nameserver lookups - the dest name needs to
be looked up to find its MX record in that case anyway, if there is
a CNAME, the nameservers should return the CNAME as a by product of
doing the MX lookup (or the A lookup if the canonical name has no MX),
the translation comes for free here.

For now, please let's leave aside the case of dumb clients that just
want to get the mail to a real server, and concentrate on the heart
of the protocol, which is where the real server does delivery across
the internet.   At that point, if a CNAME is found in a delivery
address it MUST be translated to the canonical name.   If you fail
to do it, and the mail fails, it is your fault, you cannot place any
of the blame at all on the remote server.

    HOME.EASE.LSOFT.COM  is one  of our  machines and  it certainly
    knows to accept mail  for this address.

Does it (home.dc.LSOFT.COM I presume) know how to accept mail for
lsoft-home.cs.mu.oz.au?   That is a CNAME for the same canonical
name?

CNAMEs have lots of uses, one is so that I (the owner of the domain
containing the CNAME) can create an alias for any other host on the
Internet it suits my purposes to create - because the name I create is
defined to be exatly the same thing as the canonical name, and to
be translated to the canonical name whenever it appears anywhere on
the net where it would be visible (like in RCPT To commands), this
is a nice safe way to create local short-hand names for remote hosts
that are used frequently.

Please don't go breaking what works now to suit some fancied demand
that so far doesn't look to have any basis in reality.

kre