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...
“The egg hatched...” “...the egg hatched... and a hundred baby spiders came out...” (blade runner)
“Who are you?” “A friend. I'm here to prevent you from making a mistake.” “You have no idea what I'm doing here, friend.” “In specific terms, no, but I swore an oath to protect the world...” (continuum)
“It's a goal you won't understand until later. Your job is to make sure he doesn't achieve the goal.” (bsg)