On Thu, 2003-11-20 at 01:04, Dominik Ruf wrote:
> * Kirill Miazine <km-lists@???> [2003-11-19 22:50]:
> > * John Dalbec [2003-11-19 16:14]:
> > > What RFC allows an MX record (example.com -> mail.example.com say) to exist
> > > without an A record for example.com existing?
> > No RFC forbids such behaviour.
>
> How about that one? ;-)
> http://www.dns.net/dnsrd/rfc/rfc2181.html#10.3.%20MX%20and%20NS%20Records
>
> | The domain name used as the value of a NS resource record, or part of
> | the value of a MX resource record must not be an alias. [...]
> | This domain name must have as its value one or more address records.
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> | Currently those will be A records, however in the future other record
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> | types giving addressing information may be acceptable. It can also have
> | other RRs, but never a CNAME RR.
That's *not* what was asked though. The passage you quoted from RFC2181
states that the RHS of an MX should be an A. The question was to do with
the *L*HS, which is not at all required to have a resolvable A RR.
Indeed, it is quite common for situations to exist such as:
lists.example.com MX foo.example.com
where `lists.example.com' does not have a corresponding A RR.
> Additionally, I'm pretty sure any domain whose MX RR entry doesn't have
> an A RR will be welcome by the rfc-ignorant.org team for listing in at
> least their postmaster.rfc-ignorant.org DNSBL. *eg*
Whether you're pretty sure or not, it's entirely irrelevant to the point
at hand. RFCI will not list anyone on the basis that the LHS of their MX
doesn't have an A RR.
Adam
