Greg Connor wrote:
Yes, the exists: mechanism explicitly checks *only* A records, even if
the MTA connection is via IPv6. This is to maintain compatibility
with already existing DNS blacklists and whitelists.
Any reason not to query for ANY?
It is remotely possible that a directory structure might have TXT records
for a label but not A records. In that case, the TXT might contain
descriptive info about the IP (or whatever you are requesting) but not be
an "active listing". I would say if there is no A record it should be
considered not to exist for purposes of exists: even if there is other data
there. So, if someone does an ANY query, they should explicitly check for
an A in the reply.
Hm. In the interest of future-proofing, it might be nice to specify ANY.
Imagine twenty years from now when IPv4 is finally seen by most as
antique, and AAAA is the normal query. Perhaps the MARID system will not
seem so baroque then as it might otherwise.