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Re: domain name definition in RFC2821

2007-03-21 18:17:02

--On Tuesday, March 20, 2007 17:41 +0100 Frank Ellermann <nobody(_at_)xyzzy(_dot_)claranet(_dot_)de> wrote:

(1) I replace the existing text in 2.3.5 by a comment
reminding people that single-label domains MUST NOT
appear between SMTP servers unless they refer to TLDs
and that any implementation intending to use single-label
domains as abbreviations must be sure to have a mechanism
for distinguishing between such abbreviations and FQDNs.

The only permitted way (in RFC 3696) to distinguish this is
to ask the root server, but that would be "suboptimal" for
crap like "HELO oemcomputer" (without dot).

(2) I tune the 2.3.5 text slightly to clearly permit the
trailing period on single-label domains, i.e., for TLDs

It's IMO more about "require" than "permit".

My instinct and understanding right now is that the first
option reflects the dominant current practice as we
understand it and ought to be the choice here.  Anyone
who disagrees should please speak up quickly and clearly.

I can't say that I disagree, but RFC 3696 "forbids" (as far
as that's possible in an informational RFC) to "hardwire"
TLDs in an application, with a compelling rationale.  If
the TLDs are not hardwired there have to be DNS queries.

First, if there were any disagreement between 3696 and 2821, then 3696 is simply wrong. For that case, one should heap abuse on the careless author and try to organize an effort to do a revision. But I don't think there is any disagreement in what you are suggesting: while I wouldn't particularly recommend this plan for other reasons, treating a one-label domain part in an email address and initiating some sort of search procedure in a submission server seems plausible. If that procedure involves a lookup to check if the name is identical to a TLD one is not a big deal... especially since, in the important cases, it would usually be resolved in a local cache. I think there are better ways to handle the issue -- such as looking up the relevant names of hosts on the LAN in some appropriate way first -- but "how to do DNS searching" is well outside the scope of 2821bis.

Are you sure that you want this (and sure that the DNSOP
folks will let you... :-) ?

I'm just trying to figure out what to do to get the error and ambiguity out of 2821bis. And, so far, the situation seems to favor solution (1).