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Deliverability Letter

550 5.7.64

550 5.7.64 TenantLevelReputation

Tenant Policy

The recipient tenant has blocked your domain or IP because of poor reputation or user reports.

TenantLevelReputation is controlled by each organisation. Even if Microsoft accepts the mail, the tenant can still refuse it.

Severity

ERROR

Provider

Microsoft 365 / Outlook

Reference

Mitigation Portal

Last Reviewed

2025-06-01

How to Fix 550 5.7.64

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

  • ✓Engage directly with the tenant to understand the reason for the block.
  • ✓Provide evidence of opt-in and remediation to regain trust.
  • ✓Improve targeting so that only engaged users at that tenant receive mail.
  • ✓Request an allow entry once compliance improvements are in place.

Helpful Resources

More Microsoft 365 / Outlook SMTP Codes

Keep these related troubleshooting guides handy while addressing 550 5.7.64.

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)
WARNING
452 4.5.3 (ATTR38) – 452 4.5.3 ATTR38 Mixed Regions
WARNING

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