Definition - What does Spam Blocker mean?
Because many types of spam blockers are simply modified filters, a spam blocker also may be known as a spam filter.
Techopedia explains Spam Blocker
Spam blockers and filters have lists that contain address that are either allowed to pass through or blocked. Addresses that are allowed to pass are placed on the "white list," while those that are supposed to be blocked are placed in the "black list."