The from address is now accepting mail, if I wasn't clear in my first post. It looks like at least one other mailserver was rejecting email for the same reason.
I'm curious if you consider that anti-spam measure to be productive? It's on the aggressive fringe of anti-spam measures...
“Compleχity is a symptom of confusion, not a cause.” —Jeff Hawkins
“The egg hatched...” “...the egg hatched... and a hundred baby spiders came out...”