Tony Hansen wrote:
Before we can put the issue of AAAA implicit MX to bed, we need to get
an answer to the question of how much AAAA implicit MX is already
being used in the real world.
I'm not sure that this is that significant anyway.
For a sending server, if it tries an implicit AAAA when it shouldn't,
then it's no biggy, it's just wasting its own resources
For a receiving server, it shouldn't (assuming any level of sensible
internal authorisation procedures) take long to add an MX record if the
standard requires it.