What is “complaint feedback-based blocking”?

Complaint feedback-based blocking reacts to recipient behavior:

How it works:

Recipients mark your email as spam. ISP aggregates complaint data. High complaint rates trigger blocking. Sender rejected until rates improve.

Complaint rate thresholds:

Industry concern: Above 0.1% (1 per 1,000). Serious risk: Above 0.3%. Blocking likely: Above 0.5%.

Feedback loop connection:

FBL reports show who complained. Enables removal before more complaints. Ignoring FBL data accelerates blocking.

Blocking signals:

"Rejected due to user complaints." "Too many spam reports from recipients." Sudden deliverability drop to specific provider.

Resolution:

Honor FBL unsubscribes immediately. Review list sources and acquisition. Improve content relevance. Consider re-permission campaigns.

Complaint-based blocking is democracy in action. Enough recipients voting "spam" gets you banned.