ONLINE
Deliverability Letter

450 4.7.1

SFR_IN_104 Unknown Users

Invalid Recipient

Too many messages were addressed to non-existent SFR users.

SFR counts unknown users aggressively. Hit the threshold and you receive a two-hour block that resets with each offense.

Severity

ERROR

Provider

SFR

Reference

SFR_IN_104

Last Reviewed

2025-06-01

How to Fix 450 4.7.1

Follow these steps to resolve this SFR SMTP error and restore normal delivery.

  • ✓Remove hard bounces from all SFR domains immediately.
  • ✓Use confirmed opt-in for French lists to avoid typos.
  • ✓Clean legacy data sets before new campaigns, especially after mergers.
  • ✓Segment SFR addresses and monitor bounce rates separately.

Helpful Resources

More SFR SMTP Codes

Keep these related troubleshooting guides handy while addressing 450 4.7.1.

421 4.7.0 – 421 4.7.0 Too Many Errors
WARNING
450 4.7.1 – SFR_IN_101 Spam Complaints
ERROR
450 4.7.1 – SFR_IN_102 Virus or Malware Detected
CRITICAL
450 4.7.1 – SFR_IN_103 Too Many SMTP Errors
WARNING

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