pch.net publishes a SPF record:
"v=spf1 ip4:204.61.210.70/32 mx mx:woodynet.net a:sprockets.gibbard.org
a:ghosthacked.net ~all"
Besides going from soft-fail (~all) to fail (-all), they are already
giving you the tools you need to validate a MAIL FROM: claim.
Rubens
Thats all very well and good, but advising people who do not validate
with spf to whitelist by domain name is an over-simplification.