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Deliverability Letter

550 5.7.606

550 5.7.606 Banned Sending IP

IP Block

Microsoft blocked the sending IP address via Exchange Online Protection.

5.7.606 often includes an AS number. You must submit a mitigation request at sender.office.com after resolving the abuse.

Severity

CRITICAL

Provider

Microsoft 365 / Outlook

Reference

Mitigation Portal

Last Reviewed

2025-06-01

How to Fix 550 5.7.606

Follow these steps to resolve this Microsoft 365 / Outlook SMTP error and restore normal delivery.

  • ✓Visit https://sender.office.com/ and submit a mitigation ticket with evidence.
  • ✓Fix the behaviour (malware, open relay, spam) before asking for delisting.
  • ✓Rotate traffic to clean IPs while the review is in progress.
  • ✓Set up ongoing monitoring so issues are caught before Microsoft blocks again.

Helpful Resources

More Microsoft 365 / Outlook SMTP Codes

Keep these related troubleshooting guides handy while addressing 550 5.7.606.

421 4.7.0 – 421 4.7.0 Temporary System Problem
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451 4.4.4 (ATTR5) – 451 4.4.4 ATTR5 Temporary Server Error
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451 4.7.500 (S77719) – 451 4.7.500 Server Busy (S77719)
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452 4.5.3 (ATTR38) – 452 4.5.3 ATTR38 Mixed Regions
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