What is content-based spam filtering?

Content-based spam filtering analyzes the actual message to identify spam characteristics. It examines the subject line, body text, HTML structure, embedded links, and attachments. The goal is to detect spam based on what the message says and how it is constructed.

Content filters look for known spam phrases, suspicious URL patterns, excessive images with little text, deceptive HTML tricks, and attachment types commonly used in malware delivery. They may use pattern matching, heuristic rules, or machine learning models.

This approach catches spam that might come from new or unknown senders who have no reputation data yet. It also detects compromised accounts sending spam from previously legitimate addresses.

Content filtering works alongside reputation filtering. A sender with good reputation but suspicious content may still be flagged. A sender with poor reputation sending clean content may still be blocked.

Content filtering is the inspector who reads the manifest and checks the cargo, regardless of how the ship's captain is dressed.