On Sat, Sep 04, 2004 at 09:07:05AM +0200, Ralf Doeblitz wrote:
So, instead of saying "fall back to the A record", IMHO you should think
of it as "there's no MX record overriding the A record".
No, RFC2821 is quite specific about this (as RFC974 was before that):
If no MX records are found, but an A RR is found, the A RR is treated as
if it was associated with an implicit MX RR, with a preference of 0,
pointing to that host.
This is an implementation-technique. It is, in a way, a hack. It is
just a way of saying one should use the A record if no MX records are
present --> MX records override A records.
Just a little bit further: "If one or more MX RRs are found for a given
name, SMTP systems MUST NOT utilize any A RRs associated with that
name unless they are located using the MX RRs".
Again, MX records override the A record(s).
This means definitely "fall back to A if no MX is present" and not the
other way around.
This sounds quite negative, as if A records are something that should
be avoided when thinking about SMTP. That is just not true.
The bottom line is that an A record is sufficient to get email delivered.
MX records are not designed to replace the A record (for email) but to
provide more flexibility.
Alex
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