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Deliverability Letter

554 5.4.14 (ATTR34)

554 5.4.14 ATTR34 Hop Count Exceeded

Mail Loop

Microsoft detected a mail routing loop and stopped the delivery.

Misconfigured forwards or hybrid routing can create loops. Microsoft drops the message when the hop count exceeds its safety threshold.

Severity

ERROR

Provider

Microsoft 365 / Outlook

Reference

ATTR34

Last Reviewed

2025-06-01

How to Fix 554 5.4.14 (ATTR34)

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

  • ✓Inspect forwarding rules for both sender and recipient tenants.
  • ✓Verify connectors and smart hosts do not route mail back to Exchange Online.
  • ✓Check third-party security appliances that might re-inject mail incorrectly.
  • ✓Work with recipient admins to resolve policy conflicts causing the loop.

Helpful Resources

More Microsoft 365 / Outlook SMTP Codes

Keep these related troubleshooting guides handy while addressing 554 5.4.14 (ATTR34).

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