X.6.7 · Message content or media
SMTP enhanced status code 5.6.7
Non-ASCII addresses not permitted for that sender/recipient
X.6.7 means a non-ASCII (internationalised) address was used with a server or sender that does not allow it, as defined in RFC 6531.
| Registry code | X.6.7 |
|---|---|
| Forms in use | 5.6.7 |
| Registry name | Non-ASCII addresses not permitted for that sender/recipient |
| Subject | 6: Message content or media |
| Permanent or temporary | 5.x.x permanent failure: resending unchanged will not succeed |
| Associated basic codes | 553, 550 |
| Defined in | [RFC 6531] |
What the registry says
This indicates the reception of a MAIL or RCPT command that non-ASCII addresses are not permitted
IANA SMTP Enhanced Status Codes registry, X.6.7
The basic codes it travels with
- 553 Requested action not taken: mailbox name not allowed (e.g., mailbox syntax incorrect)
- 550 Requested action not taken: mailbox unavailable (e.g., mailbox not found, no access, or command rejected for policy reasons)
In practice
X.6.7 is part of internationalised email under RFC 6531. A server that does not support SMTPUTF8 will refuse an address with non-ASCII characters, such as accented letters in the local part. If the recipient also has an ASCII address, use that. Otherwise both systems need SMTPUTF8 support. Internationalised addresses are still uncommon, and many servers and sending tools do not support them. Collecting an ASCII address alongside a non-ASCII one avoids the problem.
What the sender should do
Use an ASCII address for that recipient, or make sure both sides support SMTPUTF8.
Would verifying the list have prevented 5.6.7?
Partly
The reply is not only about one address, but providers weigh how often a sender hits addresses that do not exist. Removing bad addresses before sending lowers that signal.
Common questions
- What does 5.6.7 mean?
- X.6.7 means a non-ASCII (internationalised) address was used with a server or sender that does not allow it, as defined in RFC 6531.
- What should I do about 5.6.7?
- Use an ASCII address for that recipient, or make sure both sides support SMTPUTF8.
- Would an email verifier have caught 5.6.7?
- Partly. The reply is not only about one address, but providers weigh how often a sender hits addresses that do not exist. Removing bad addresses before sending lowers that signal.
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