X.6.9 · Message content or media
SMTP enhanced status code 5.6.9
UTF-8 header message cannot be transferred to one or more recipients, so the message must be rejected
X.6.9 means the transaction failed after the end of DATA because a UTF-8 header could not be sent to one or more recipients.
| Registry code | X.6.9 |
|---|---|
| Forms in use | 5.6.9 |
| Registry name | UTF-8 header message cannot be transferred to one or more recipients, so the message must be rejected |
| Subject | 6: Message content or media |
| Permanent or temporary | 5.x.x permanent failure: resending unchanged will not succeed |
| Associated basic codes | 550 |
| Defined in | [RFC 6531] |
What the registry says
This indicates that transaction failed after the final "." of the DATA command.
IANA SMTP Enhanced Status Codes registry, X.6.9
The basic codes it travels with
- 550 Requested action not taken: mailbox unavailable (e.g., mailbox not found, no access, or command rejected for policy reasons)
In practice
X.6.9 is returned after the message body has been sent, when the server finds UTF-8 headers it cannot pass on to one or more recipients. It shows up with internationalised From names or subjects on paths without SMTPUTF8. Sending with encoded headers or plain ASCII fixes it. Unlike most rejections, this one comes after the whole message was transferred, so the sending server has already spent the bandwidth.
What the sender should do
Send to those recipients without internationalised headers, or through a path that supports SMTPUTF8.
Would verifying the list have prevented 5.6.9?
No
This reply is about your sending setup, the message or the receiving system, not about whether the address exists, so verifying the list will not prevent it.
Common questions
- What does 5.6.9 mean?
- X.6.9 means the transaction failed after the end of DATA because a UTF-8 header could not be sent to one or more recipients.
- What should I do about 5.6.9?
- Send to those recipients without internationalised headers, or through a path that supports SMTPUTF8.
- Would an email verifier have caught 5.6.9?
- No. This reply is about your sending setup, the message or the receiving system, not about whether the address exists, so verifying the list will not prevent it.
Sources
- IANA: SMTP Enhanced Status Codes registry (checked 2026-11-05)
- RFC 3463: Enhanced Mail System Status Codes (checked 2026-11-05)
- RFC 5321: Simple Mail Transfer Protocol, section 4.2.3 (reply codes) (checked 2026-11-05)
Registry and provider wording is quoted exactly; guidance is written by the SimpleVerifier Team.
SimpleVerifier Team · Last checked against the sources 2026-11-05