Wouldn't it be utterly badass if, upon encountering a message that scored, say, a 15 or above in SpamAssassin, your MTA could not only tag it with a spam header but could, optionally, fling it back across the internet, with a flaming bag of soggy dogcrap attached, into the face of the sender? Maybe in version 3.0.
“We have the right to survive!”
“Not by killing others.”
— Deela and Kirk, “Wink of An Eye”, stardate 5710.5