How do ESPs prevent cross-customer contamination (reputation-wise)?

Cross-customer contamination occurs when one sender's bad behavior damages shared infrastructure reputation, affecting other senders. ESPs use multiple strategies to prevent this.

IP pool segmentation:

Separate pools for different sender tiers

High-quality senders share IPs only with other high-quality senders

New or unproven senders use separate pools

Problem senders isolated to limit blast radius

Quality monitoring:

Continuous tracking of bounce, complaint, and engagement rates per customer

Automated alerts when metrics degrade

Proactive intervention before problems spread

Rapid response:

Automatic throttling or pausing of accounts with sudden metric spikes

Quick removal of clearly bad actors

Fast delisting response when shared IPs get blocklisted

Dedicated resources:

Enterprise customers may receive dedicated IPs or pools

Complete isolation eliminates contamination risk for top senders

Abuse detection:

Content scanning for spam patterns

Send pattern analysis for suspicious behavior

Account verification and validation processes

Contractual obligations with enforcement

Good harbormasters don't let one leaky ship contaminate the whole fleet. Inspection, quarantine, and separate berths keep the port safe for legitimate traders.