What’s a “false positive” and “false negative”?

A false positive occurs when a legitimate message is incorrectly classified as spam. The recipient wanted the email, but the filter blocked it. False positives frustrate users and damage sender relationships.

A false negative occurs when spam successfully reaches the inbox. The filter failed to detect it. False negatives expose users to unwanted or potentially malicious content.

Filter tuning involves balancing these two error types. Aggressive filtering reduces false negatives but increases false positives. Lenient filtering does the opposite. Finding the optimal threshold is an ongoing challenge.

Users can correct both types. Moving a message from spam to inbox signals a false positive. Reporting an inbox message as spam signals a false negative. These corrections help filters learn and improve.

False positives are friendly ships turned away by mistake. False negatives are hostile vessels that slipped through. Neither is desirable.