421 4.7.0
421 4.7.0 Too Many Errors
SFR closed the connection after accumulating too many SMTP errors in a short period.
Protocol mistakes (bad HELO, premature QUIT, missing TLS) cause repeated 421 events. If the pattern continues, SFR escalates to SFR_IN codes.
Severity
WARNING
Provider
SFR
Last Reviewed
2025-06-01
How to Fix 421 4.7.0
Follow these steps to resolve this SFR SMTP error and restore normal delivery.
- ✓Validate SMTP command order and enforce STARTTLS where required.
- ✓Ensure your MTA respects SFR’s two-connection limit per IP.
- ✓Retry with exponential backoff to avoid hitting an automatic two-hour suspension.
- ✓Monitor logs for authentication failures or unexpected 5xx responses.
Helpful Resources
More SFR SMTP Codes
Keep these related troubleshooting guides handy while addressing 421 4.7.0.
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