William:
Isn't this a violation of RFC 1035?
--Mark <admin(_at_)asarian-host(_dot_)net> wrote:
Yes.
Shouldn't SPF check on this MX record result in NXDOMAIN?
No. NXDOMAIN (RCODE 3) would be the result if there were no A or MX
records for expofreight.com at all; there are, however:
My point was that if an MX record contains 1.2.3.4 you could try looking it
up. It will give you NXDOMAIN and you would treat it just like they had
put MX 5 null.domain.invalid.
(in this case "you" are the SPF checker and "it" is the DNS resolver :)
You could throw out the MX rhs if it's all-numeric, but in my mind it's an
extra step. It happens rarely enough that it's OK to try and treat it as a
name and handle it just like a non-existent name.
--
Greg Connor <gconnor(_at_)nekodojo(_dot_)org>