What’s the difference between blocklist and spam filter?

A blocklist is a database of IPs, domains, or URLs that have been identified as spam sources. It provides a simple yes or no answer: is this sender listed?

A spam filter is a complete system that makes placement decisions using multiple inputs. Blocklists are one input among many. Filters also analyze content, check authentication, evaluate engagement, and consider sender reputation.

Being on a blocklist typically adds points to your spam score rather than causing automatic rejection. The filter weighs that input alongside everything else. Some filters treat major blocklist hits as immediate blockers; others consider them one factor among many.

Blocklists are reactive, listing known bad actors. Filters are predictive, evaluating new messages based on patterns. Both work together to protect inboxes.

A blocklist is the wanted poster. The filter is the entire security team using that poster plus their own judgment.