ESPs use a combination of algorithms, user feedback, and machine learning models to determine what emails to filter or block. Factors include:
Content Analysis: Scanning emails for keywords and phrases that are commonly associated with spam. Behavioral Analysis: Monitoring user behavior such as marking emails as spam or deleting without reading. Sender Reputation: Tracking the sender's history and reputation across various metrics. User Complaints: Considering the number of user complaints against a particular sender.