5.6.7: non-ASCII address not allowed
An address in the envelope contains non-ASCII characters (an internationalised address), and the receiving server will not accept that for this sender or recipient.
- Standard
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 5.6.7
- Provider
- Standard SMTP codes
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- Either side, depending on the cause. Start with the checks below that are yours.
- What the server says
5.6.7 Non-ASCII addresses not permitted for that sender/recipient
What it means
RFC 6531 (SMTPUTF8) lets email addresses use characters beyond ASCII, such as accented letters or non-Latin scripts. When a server that supports enhanced codes refuses such an address in MAIL FROM or RCPT TO, it uses X.6.7, with reply code 553 for a recipient and 550 for a sender. It is a permanent refusal for that address, so 5.6.7 is the form you see. The answer is an ASCII address for the same person, or a sending path on which every server supports SMTPUTF8.
Common causes
- A recipient address with accented or non-Latin characters, sent to a server that requires ASCII.
- A sender address with non-ASCII characters, refused by a server that accepts only ASCII senders.
How to fix it
- 01Ask the recipient whether they have an ASCII address you can use.
- 02Send from an ASCII sender address.
- 03If you run the sending server, check that it and its relays support SMTPUTF8.
- 04Recipient admins: enable SMTPUTF8 on the receiving server if internationalised addresses should work.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 5.6.8UTF-8 reply needed but not allowed.To answer a VRFY or EXPN query the server would have to show a mailbox name in UTF-8, but the client did not say it can handle UTF-8 replies.
- 5.6.9Internationalised message cannot be delivered.The message has UTF-8 (internationalised) headers and could not be passed on to one or more recipients whose path cannot handle them, so it was rejected.
- 553Mailbox name not allowed.The server refused the address because the mailbox name is not allowed there, most often because it is written incorrectly.
- 5.1.3Recipient address is malformed.The recipient address breaks the rules for how an email address must be written, so the server refused it before checking whether it exists.
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