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.