Exact response pattern
421 4.7.0 Temporarily deferred because of user complaints or unusual volumeTemporaryMicrosoftReputation
What it means
Microsoft is temporarily slowing or deferring the sending IP or domain.
Likely causes
- Complaint signals.
- Unusual volume.
- New IP or sudden traffic pattern.
Recommended response
- Review SNDS data.
- Reduce volume and concurrency.
- Check list quality and complaint controls.
- Ramp gradually after acceptance improves.
Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.