I don't see this as a moderator job.
It's a Robot job.
Extract 'from' address
Compare address with subscribers
if no hit, then return to sender as error.
Thanks go to all the people staying on topic lately.
Two spams is nothing. BTW the idiocy of that guy
with the four items was in sending items 1..3 at all.
Item 4 itself was pretty OK, a wire recorder, wasn't it?
John A.