strange resolver behavour

[Ian Smith]

On Tue, 12 Oct 2010, Tom Evans wrote:
 > On Tue, Oct 12, 2010 at 10:05 AM, Ian Smith <smithi at nimnet.asn.au> wrote:
 > > On Mon, 11 Oct 2010, Eugene Grosbein wrote:
 > >  > Hi!
 > >  >
 > >  > FreeBSD 8.1-STABLE:
 > >  >
 > >  > # host koin-nkz.com.
 > >  > koin-nkz.com has address 62.231.164.101
 > >  > Host koin-nkz.com not found: 3(NXDOMAIN)
 > >  >
 > >  > This domain does not have MX records but NXDOMAIN seems to wrong return
 > >  > code to me. Think about MTA that does look-up for MX first,
 > >  > obtains NXDOMAIN and rejects mail.
 > >
 > > If a domain has no MX server, how's an MTA supposed to do mail with it?
 > >
 > 
 > The same way as has been done since they invented the MX record type -
 > if no MX record exists, fallback to an A record. See RFC 5321, section
 > 5.1.

Well thanks Tom, I did - but which A record?

Taking the '5.3. Master file example' in RFC1035, what is the A response 
for 'ISI.EDU.' where the domain itself has no specific A RR?  Would it 
be that of VENERA.ISI.EDU, or that of the first A listed, ie A.ISI.EDU?

And in either case - assuming a domain without any MX RR as above - why 
would that A response be expected to address a mail server?

cc Doug for obvious reasons, ie I'm likely missing something obvious :)

cheers, Ian

(BTW I'd begun to reply off-list, as neither your private copy nor your 
reply to the list indicated cc'ing the other .. googlemail quaintness?)