Another anti-spoof RFC proposal
http://serverauthority.net/draft-lorenzen-marid-mxout-00.txt
Seems most, if not all of it is covered by SPF, though it requires
a SPF record for every A record to achieve, I think.
It relies on reverse DNS (which is not a good long-term solution), and
uses ip addresses for informational purposes (where I would suggest
tagged information in TXT records like SPF in order to ensure a long
life for the protocol). I agree, that it is less useful than SPF and
doesn't do anything that SPF doesn't. Also, it requires several DNS
lookups for a check.
Lars Dybdahl.