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Re: Last Call: draft-klensin-rfc2821bis

2008-03-24 11:54:06
John C Klensin <john-ietf(_at_)jck(_dot_)com> wrote:
--On Saturday, 22 March, 2008 23:02 -0700 Douglas Otis
<dotis(_at_)mail-abuse(_dot_)org> wrote:

The "update" of RFC2821 is making a _significant_
architectural change to SMTP by explicitly stating AAAA
records are within a list of SMTP server discovery records.

Well, to be very precise, 2821 is ambiguous on the subject.


Some people have read (and implemented) it as if the text said
"address records", implying a default MX for the AAAA case as
well as the A one.   Others have read it more narrowly and only
supporting the default for A RRs.    To the extent to which
2821bis is expected to eliminate ambiguities that were present
in 2821, it had to say something on this subject.

   It might, however, be best to simply document the ambiguity.
I suspect that implementation reports would show some implementations
querying for both AAAA and A RRs, while others query only for A RRs.
I am not convinced that 2821bis _should_ try to resolve this.

I don't think we have a choice. it is obvious that this ambiguity can lead to
interoperability problems, and that means this has to be resolved if the
document is to obtain draft standard status.

If it says "address records" (as the current text does),

   Actually, it says "address RR" (if I understand what text we're
discussing). I believe we're discussing Section 5.1 of

where it says
" The lookup first attempts to locate an MX record associated with the
" name.  If a CNAME record is found instead, the resulting name is
" processed as if it were the initial name.  If no MX records are
" found, but an address RR (i.e., either an IPv4 A RR or an IPv6 AAAA
" RR, or their successors) is found, the address RR is treated as if it
" was associated with an implicit MX RR, with a preference of 0,
" pointing to that host.

(Please correct me if I misunderstand what text we're discussing.)

you (and perhaps Mark and others) dislike the consequences and
claim "significant architectural change". If it is changed to
explicitly indicate that only A RRs can be used to imply an
MX record, then I assume that those who read 2821 the other way
and are now supporting AAAA records to generate an implied MX
would claim "significant architectural change".

   Indeed, that seems likely (though not demonstrated).

   But regardeless, we're on shaky ground if we try to force either
kind of implementation to change. May I suggest a different starting

On the contrary, it is expected that options can be eliminated from
documents moving to draft, especially if in doing so an interoperability
problem is removed.

   I think there's very strong consensus that the presence of an
MX RR demonstrates the intention to receive email addressed to the
domain in question. I don't think there's any consensus that the
presence of an AAAA or A RR demonstrates such an intent.

Perhaps, but the fact remains that MX-less configurations are currently legal
and in use.

   There is, however, considerable history that the presence of an
address RR _in_combination_with_ a process listening on port 25
of the IP address in question indicates a willingness to receive
email for a domain identical to the domain of that address RR.


   Whether or not we have any consensus that this historical
practice should be deprecated (I would vote YES!), rfc2821-bis
is not, IMHO, the right place to deprecate it.

On this we agree. We haven't gone through any sort of consensus process on this
and since there is no justification for deprecating use of A-record-only
configurations as part of a move to draft this cannot be done at time.

   (If I may digress a bit, let me explain that this implied-MX rule
is a real pain to me as an ISP, in that we maintain a SMTP server
on the same IP address as a number of virtual web services; and
the implied-MX rule brings us rather significant spam traffic that
I'd _much_ rather be sending to a different IP address than the web-
server for the domain in question.)

   Getting back to my point, what would be wrong with changing this
language in Section 5.1 to document the ambiguity instead of trying
(probably unsuccessfully) to prescibe a single way of resolving it?

See above. This would be fine if the document were intended for proposed but it
is not. I suppose we could ask for an exception to be made but frankly I see no
grounds for granting one.


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