Lucas Is an Email Administrator

Multiple Choice

Lucas is an Email administrator. He is extremely sick and tired of spam and convinces his boss to let him focus entirely on the email system for awhile. He puts into place a list of countermeasures that include: Spam prevention software at the edge of his network, DNSBLs (DNS Based Black Lists) , and Mail Exchanger Callbacks. Still the SPAM comes in.
He decides the next best thing to try is a system that slows down connections to known SPAM relays to at least reduce the volume of traffic that just gets blasted in. What is this technique known as?

A) SPAM Cannibal
B) Sender Policy Framework
C) Teergrubbing (Tar Pit)
D) SMTP Cannonball