I am not arguing that the implicit MX should go for IPv4(*). I am just
arguing that it shouldn't appear for IPv6.
Ah, okay. Thank you for the clarification (and I probably should have
understood originally that's what you meant).
In case there's any uncertainty, that's also what I'm arguing. The
time to deprecate fallback to A would have been about 1988, not today.
But since everyone's going to have to add AAAA records anyway to move
to IPv6, it seems to me this is the least painful time to make them add
MXes for their mail servers as well.
R's,
John