R. Scott Perry wrote:
> Korey Verlsteffen wrote:
> >OK folks! I need your help. This is for all of you RFC experts out there.
> >My interpretation of RFC2821 (5. Address Resolutions and Mail Handling) is
> >that
> >
> >- If MX record(s) exist for a domain then the SMTP client should deliver to
> >those records in order of priority and if not sucessful (in the configured
> >amount of tries set in the SMTP client) return the mail back to sender. It
> >should never deliver to the A record of a domain if MX records exist but are
> >not responding.
> >
> >Am I correct in this interperation?
>
> I would say so. The key is that the A record *should* be used, but only if
> the MX records do not exist. If there are any MX records, the A record
> should not be used. I'm not sure of the status of RFC2821 (which just came
> out about 2 months ago), but it appears that prior RFCs should probably be
> interpreted the same way as well (although older ones aren't quite as clear).
Agreed, RFC2821 states in its Abstract
"It consolidates, updates and clarifies, but doesn't add new or change
existing functionality of the following:"
with a list of RFC's, one of which is RFC974.
In RFC974 under "Interpreting the List of MX RRs" it states
"It is possible that the list of MXs in the response to the query will
be empty. This is a special case. If the list is empty, mailers
should treat it as if it contained one RR, an MX RR with a preference
value of 0, and a host name of REMOTE. (I.e., REMOTE is its only MX)."
It doesn't have RFC2821's clarifying wording about
"... the "implicit MX" rule above applies only if there
are no MX records present."
but it's fairly clear that one should 'invent' an MX record *only* in
the case where no MX records are returned from the query.
--
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