Keith Moore writes:
The missing MX records for the 286 domains are the result of lazy or
clueless mail administrators.
While I think that deprecating A fallback would be a good idea, I
don't buy that admins currently using it are lazy or clueless. What
they're doing is explicitly permitted by the current standards.
Judging by the 38 domains I visually inspected, the usage is:
50% cluelessness or error
25% informed choice
25% indeterminate
I've no reason to think that a larger sample would be very different,
but I'm too lazy to collect one.
Arnt