Exact response pattern
550 5.7.606 Access denied, banned sending IPPermanentMicrosoftReputation
What it means
Microsoft has denied the sender under an IP or policy restriction.
Likely causes
- IP reputation.
- Abuse or compromised account.
- Policy enforcement.
Recommended response
- Stop traffic from the affected source.
- Secure accounts.
- Review SNDS and request review only after remediation.
Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.