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Re: MX to CNAME and (mis)interptretation of 2821

2007-12-14 08:30:44

From: Ned Freed
As for updating the specification, I have no problem with adding
>> a statement that the result of an MX lookup MUST NOT be a
>> CNAME if there is consensus to do so. I strongly object,
however, to adding statements along the lines of "this document
>> doesn't update this other RFC". That's a path to madness.

Trevor Paquette wrote:

I really like this idea. This will solve the problem of
misinterpretation of the RFC.

I doubt that because this issue predated RFC 2821.

While hugely successful over the years, one of the problems with the style of RFC documents (by design) is that they tend to serve a wide range of audiences. Specifically, they tend to blend both functional design specifications with technical design specifications. The former typically serves management, operations, possible marketing. The latter typically serves development and implementation details.

So it depends on who is reading the RFC.

That said, I do not advocate any change to RFC 2821bis, but if there is something to point out, IMO, it should be addressed to two parties:

 - DNS operators MUST NOT add CNAME records in MX records as this
   can create extra unnecessary queries.

 - SMTP DNS resolvers SHOULD be prepared for MX lookups
   resolving to CNAME records.

This targets both audiences.


Hector Santos, CTO