5.6.9: internationalised 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.
- Standard
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 5.6.9
- 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
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
5.6.9 UTF-8 header message cannot be transferred to one or more recipients…
What it means
RFC 6531 allows UTF-8 in message headers when every server along the way supports SMTPUTF8. When a server finds, after the whole message has been sent, that one or more recipients cannot receive such a message, it rejects it with X.6.9. RFC 6531 pairs this with reply 554 (transaction failed), while the registry lists 550. It is permanent for this message, so 5.6.9 is the form you see. RFC 6531 encourages servers to spot the problem earlier, at the RCPT stage, so this code at the end of the transfer is the fallback.
Common causes
- Non-ASCII characters in headers such as Subject, From or To, sent towards a server without SMTPUTF8.
- An internationalised address in the headers for a recipient whose server handles only ASCII.
How to fix it
- 01Use ASCII addresses in the headers for recipients on servers without SMTPUTF8.
- 02Make sure your software encodes non-ASCII header text the classic way (RFC 2047 encoded words) when the next server lacks SMTPUTF8.
- 03Check that every relay on your sending path supports SMTPUTF8.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
Related codes
- 5.6.7Non-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.
- 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.
- 554Transaction failed.The server permanently refused the transaction, often after receiving the message data or straight away when the connection opened.
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