Subject: Re: [dnsext] Bundling of Domain Names and DNAME

From: Alfred Hönes <[email-masked]>
Date: Tue, 8 Dec 2009 02:53:12 +0100 (MEZ)

Kevin,
you are right; I have been too hastily; the restriction on non-CNAME
in [E]SMTP does _not_ apply to the primary email addresses, but to
-   the domain names returned by MX RRs (see RFC 5321, Section 5.1,
    page 69), and to
-   domain names given in the EHLO command (see RFC 5321,
    Section 2.3.5, bottom of page 13).

RFC 5321 points to RFC 1035 and RFC 2181, Section 10.3 for these
purposes.  RFC 5321 does not update these RFCs.  However, for MX,
RFC 1035 normatively refers to RFC 974, which has been obsoleted
by RFC 2821, which has been obsoleted by RFC 5321 ... :-)

Regarding lack of DNAME discussion in RFC 5321:  That was out of
scope for the effort for RFC 5321 that only had been allowed to
perform "clarifications" to RFC 2821 and not impose "new" requirements.
IIRC, when the effort for RFC 5321 started, the "rehabilitation" of
DNAME (now performed by draft-ietf-dnsext-rfc2672bis-dname, Sect. 4)
was not yet known to the IESG; the wisdom at that time was that
DNAME had been 'banned' together with A6 (per RFCs 3363/3364).

If you would like to have DNAME considerations in 5321bis, feel free
to contact the YAM WG that currently works on an evaluation document
for the IESG in order to get a sign-off for some changes the IESG
might admit for a Full Standard successor to RFC 5321 -- or ask the
chairs to do that 'officially'.  But please keep in mind:
It might be advisable to personally contact and convince many IESG
members of the necessity to change even less significant details.  :-(
Beware that the politically correct form of examples, the trouble
with normative downrefs (since not all related documents already
are at Draft Standards level), and similar deep issues are of much
greater interest to the current IESG, because there are more experts
for such questions there than for the protocol itself. :-)

Kind regards,
  Alfred.

-- 

+------------------------+--------------------------------------------+
| TR-Sys Alfred Hoenes   |  Alfred Hoenes   Dipl.-Math., Dipl.-Phys.  |
| Gerlinger Strasse 12   |  Phone: (+49)7156/9635-0, Fax: -18         |
| D-71254  Ditzingen     |  E-Mail:  [email-masked]                     |
+------------------------+--------------------------------------------+

---

From: Tony Finch <[email-masked]>
Date: Tue, 8 Dec 2009 22:56:49 +0000

On Tue, 8 Dec 2009, Alfred H?nes wrote:

> in [E]SMTP does _not_ apply to the primary email addresses,

It does not now, but it did apply in the past (see RFC 1123 section
5.2.2) and some SMTP senders still implement that old requirement.
However SMTP receivers have not cared either way for a very long time
(if ever).

Tony.
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