421 4.7.0
421 4.7.0 Temporary System Problem
Exchange Online is temporarily unavailable. Retry the delivery later.
421 4.7.0 usually reflects a transient Microsoft service interruption. Respect the retry interval or Microsoft may extend the deferral.
Severity
WARNING
Provider
Microsoft 365 / Outlook
Reference
Mitigation Portal
Last Reviewed
2025-06-01
How to Fix 421 4.7.0
Follow these steps to resolve this Microsoft 365 / Outlook SMTP error and restore normal delivery.
- ✓Implement exponential backoff when retrying the message.
- ✓Monitor the Microsoft 365 Service Health dashboard for incidents.
- ✓Spread retries across multiple connectors to avoid overwhelming a single region.
- ✓Document the timeline in case recipients open a support ticket.
Helpful Resources
More Microsoft 365 / Outlook SMTP Codes
Keep these related troubleshooting guides handy while addressing 421 4.7.0.
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