Keith Moore wrote:
"whatever it needs to do ... given a domain name" and "an address
for the domain name" means to me "lookup both A and AAAA records"
in a mixed IPv4/IPv6 world.
Okay, maybe 974 does say that. But has been pointed out a couple
of times, the world has changed a lot since then.
Interpreting RFC 974 published 1986 in a way as if it was meant to
cover the later invention IPv6 is shaky, after all its status is
"HISTORIC" for a reason. We could also claim that RFC 974 wants
us to check WKS before doing something with addresses not limited
to AAAA.
Extending "implicit MX" to AAAA while ignoring WKS is like keeping
forwarding after deprecating the reverse routes: broken by design.
Frank