What’s the difference between spam filtering and reputation systems?

Spam filtering is the immediate decision made about each individual message: inbox, spam folder, or rejection. It happens in real time during or shortly after delivery.

Reputation systems are the long-term memory that informs those decisions. They track sender behavior over weeks, months, and years. A sender with strong reputation earns the benefit of the doubt. A sender with poor reputation faces heightened scrutiny on every message.

Reputation systems feed into spam filters but are not the same thing. Services like Sender Score, Google Postmaster Tools, and Microsoft SNDS provide visibility into reputation metrics. The filters themselves use that reputation data alongside content analysis and authentication checks.

Reputation is your credit score. Filtering is the bank deciding whether to approve each transaction.