A:) A protective barrier around an individual used to block out annoying people. This concept, while started for emails, is extended to more personal means of communication. B:) A more hip and modern version of shit-list
Person A: Hey, why don't you pick up that call.
Person B: Chris is on spam-filter until he gets his act together.
"I'm warning you, If you don't stop being such an ass, you're going right into my spam-filter"