550 5.7.511
550 5.7.511 Banned Sender
Exchange Online Protection banned the sending IP or domain for abuse.
5.7.511 is Microsoft’s strongest block for IP reputation problems. You must show remediation before Microsoft removes the ban.
Severity
CRITICAL
Provider
Microsoft 365 / Outlook
Reference
Mitigation Portal
Last Reviewed
2025-06-01
How to Fix 550 5.7.511
Follow these steps to resolve this Microsoft 365 / Outlook SMTP error and restore normal delivery.
- ✓Forward the original NDR to delist@messaging.microsoft.com with full headers.
- ✓Document corrective actions (list cleaning, compromised account remediation, etc.).
- ✓Pause traffic until Microsoft confirms the unblock to avoid extended bans.
- ✓Warm a fallback IP in case the review process takes several days.
More Microsoft 365 / Outlook SMTP Codes
Keep these related troubleshooting guides handy while addressing 550 5.7.511.
Still experiencing Microsoft 365 / Outlook delivery issues?
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