[ih] MX and A records

[johnl at iecc.com (John Levine)]

MX records were invented in 1986 in RFCS 973 and 974, replacing MD and
MF and as far as I can tell obsoleting MB, MG, and MR.

It looks like there wasn't a rule to fall back to A if there were no
MD and MF, or if there was it didn't make it into the RFC.  RFC 974
does describe fallback from MX to A.

Was that expected to be a transitional thing until MX was more widely
implemented, or was it expected to be permanent?  Or didn't anybody
think about it either way?

R's,
John