An MX lookup just returns the name of the MX. There might be
A and AAAA records in the additional section, but there also
might not, and as I understand it, the order of records in a
section of a DNS response has always been considered to be
arbitrary. So I agree, these tea leaves aren't worth reading.
And that, of course, is exactly why the relevant section of 5321
carefully avoids saying anything specific or normative about
order of attempts.
Having reread 5321, I was surprised to see that it says that it says that
the order of the A or AAAA records for a single name does matter.
Was that left over from olden days, or a recent addition? Seems wrong
either way.
Regards,
John Levine, johnl(_at_)taugh(_dot_)com, Taughannock Networks, Trumansburg NY
"I dropped the toothpaste", said Tom, crestfallenly.