Keith Moore writes:
Can one, for example, do some SRV DNS lookup?
What would form the lookup key?
Exactly.
It doesn't have anything inherent to do with the user's From address
The way the wind seems to be blowing, SPF will change that during the
next year or two. For better or worse.
I hope you're wrong. Because if there's anything worse than spammers, it's
people who try to impose half-baked solutions to spam on the rest of ous.
Keith