Ted Hardie wrote:
But I think the key question is actually different. Look at this
text in RFC 2821:
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; the "implicit MX" rule
above applies only if there are no MX records present. If MX records
are present, but none of them are usable, this situation MUST be
reported as an error.
If I put in an MX record pointing to a guaranteed non-present
FQDN, someone complying with that text will throw an error rather than
keep seeking for an A/AAAA. Is *that* useful? If so, then
sink.arpa/1.0.0.257.in-addr.arpa as an MX record entry may be.
Yes, I understand the RFC. That section is what allows this topic to be
discussed in the first place. sink.arpa may very well be the interim
solution, too. It definitely looks better than "0 .". It just seems
like an ugly, smelly hack when the fundamental problem lies with
allowing the implicit MX. It implies that I should, for the benefit of
everyone, create a sink.arpa MX for every A record, where the effort
could be better spent dropping the implicit MX rule and requiring an MX
record for hosts that really do accept mail.
/Jason
