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RE: domain name definition in RFC2821

2006-04-22 02:18:39

--On Saturday, 22 April, 2006 01:27 -0700 Yuri Inglikov
<Yuri(_dot_)Inglikov(_at_)microsoft(_dot_)com> wrote:

By the way the "ws." syntax appears "invalid" according to
every RFC I read.

Except the base DNS specs and RFC 1123, which makes accepting it
mandatory everywhere.

See also below.


-----Original Message-----
From: Valdis(_dot_)Kletnieks(_at_)vt(_dot_)edu 
Sent: Saturday, April 22, 2006 1:13 AM
To: william(at)
Cc: Yuri Inglikov; ietf-smtp(_at_)imc(_dot_)org
Subject: Re: domain name definition in RFC2821

postmaster(_at_)ws ?

ws.                     21600   IN      MX      10

Gaak.  I hope that's not a wildcard MX. ;)

A 4AM re-reading of 2821 seems to indicate that's a *legal*

It really has been since RFC 1123, although it has also been
considered bad practice.  2821 is obviously not clear enough on
the subject; the working version of 2821bis is now crystal-clear
after a little patching this morning.

 But I suspect there are *so* many software packages
that will try to convert '@ws' to a FQDN at message submission
time as per 2821, section 6.3:

   The following changes to a message being processed MAY be
applied    when necessary by an originating SMTP server, or
one used as the    target of SMTP as an initial posting

   -  Addition of a message-id field when none appears

   -  Addition of a date, time or time zone when none appears

   -  Correction of addresses to proper FQDN format

(For instance, on my Fedora Linux box, the default resolv.conf
setting of 'options ndots:1' means that 'ws' will be
canonalized to a FQDN, while 'ws.' will behave the way Yuri
apparently expects 'ws' to work.  Now try to explain to your
average end user why 'postmaster(_at_)ws' and 'postmaster(_at_)ws(_dot_)' do
different things....

That is, indeed, an issue.  But, again, 1123 is crystal-clear on
the subject.  And the 2821bis  working draft is now consistent
with it.

Yuri, since you seem to be looking for the bottom line here, I
suggest it is:

(1) Anywhere that "Domain" is permitted as a piece of syntax,
"Domain." is permitted.   Not supporting it is bad news.  If you
are working on this at Microsoft, note that IE supports the
trailing dot in domain names, so failure to support it in email
would presumably violate the law of least astonishment, provide
a surprising user experience, etc.

(2) Because of the widespread historical support for a single
apparent label as an abbreviation of some sort (most often an
indication that a search rule, alias substitution, or completion
algorithm external to SMTP should be applied)
should be discouraged.  If someone needs to reference a TLD as a
mail address, or a TLD in any other way than as part of an FQDN
with more labels, it should appear with the trailing period,
i.e., as
I believe that advice is consistent with RFC 1123