554 5.7.9
554 5.7.9 Policy Violation
Yahoo blocked the message because it violated sending policies or formatting rules.
Improperly encoded subject lines, malformed headers, or risky content can trigger 5.7.9. It is often a signal to review MIME structure and compliance.
Severity
ERROR
Provider
Yahoo Mail
Last Reviewed
2025-06-01
How to Fix 554 5.7.9
Follow these steps to resolve this Yahoo Mail SMTP error and restore normal delivery.
- ✓Re-encode subject lines and headers using proper MIME or UTF-8 encoding.
- ✓Review message copy for phrases commonly associated with spam.
- ✓Confirm authentication passes and that DKIM canonicalization matches the message body.
- ✓Test the campaign with deliverability tools before resending.
Helpful Resources
More Yahoo Mail SMTP Codes
Keep these related troubleshooting guides handy while addressing 554 5.7.9.
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