How do ESPs detect and block spam campaigns internally?

ESPs actively monitor outbound mail to catch spam before it damages their infrastructure reputation. Multiple detection systems work together.

• Content analysis:
• Pattern matching against known spam templates
• Keyword and phrase analysis
• URL reputation checking
• Attachment scanning
• Image analysis for text-in-images
• Complaint monitoring:
• Real-time feedback loop data processing
• Per-campaign and per-account complaint tracking
• Threshold alerts triggering automatic review
• Spamtrap detection:
• Known trap addresses in ESP's monitoring
• Reports from anti-spam organizations
• Hits trigger immediate investigation
• Behavioral analysis:
• New accounts sending to old lists (suspicious)
• Unusual sending patterns
• High bounce rates suggesting bad lists
• Geographic anomalies in sending activity
• Machine learning systems:
• Models trained on confirmed spam examples
• Anomaly detection for novel patterns
• Continuous learning from feedback
• Response actions:
• Automatic throttling or pausing
• Quarantine for review
• Account suspension
• Customer notification and remediation requirements
• These systems run continuously. Legitimate senders rarely notice them; spammers hit walls quickly.