550 5.7.1: unicode character in a header
Gmail rejected the message because a header that must stay plain ASCII contains a Unicode character.
- Gmail
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 550 5.7.1
- Provider
- Gmail and Google Workspace
- 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
550 5.7.1 The message contains a unicode character in a disallowed header.
What it means
Headers were designed for ASCII. Non-ASCII text, such as accented names or emoji in a subject, has to be encoded as RFC 2047 encoded words unless both servers support internationalized mail (SMTPUTF8, RFC 6531 and 6532). Some headers may not carry raw Unicode at all, and this message had a Unicode character in one of them. Google links the reply to its article on blocked messages and file types. The usual cause is sending software that writes non-ASCII text into headers without encoding it.
Common causes
- A display name or subject with accented letters or emoji written into the header without encoding.
- A custom header carrying raw non-ASCII data.
- Software that assumes SMTPUTF8 support it never negotiated.
How to fix it
- 01Find the header with the raw character by inspecting the message source.
- 02Have the sending software encode non-ASCII header text as RFC 2047 encoded words, which mail libraries do on their own.
- 03Remove non-ASCII characters from custom headers, or encode their values.
- 04Resend once the header is fixed.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Gmail SMTP errors and codes (Google Workspace Admin Help)knowledge.workspace.google.com
Related codes
- 550 5.7.1Encoded word in a header where it is not allowed.Gmail rejected the message because a header contains RFC 2047 encoded-word text in a place where that encoding is not allowed.
- 550Mailbox unavailable.The receiving server permanently refused the message for this recipient: the mailbox does not exist, cannot be reached, or the server rejected the message by policy.
- 5.7.1Delivery not authorised.The receiving server refuses the message because this sender is not allowed to send to this recipient, as a result of filtering by host or by recipient.
5.7.1 at other providers
- 550 5.7.1Not authorized to send to this recipient.You do not have permission to send to this recipient, typically a group restricted to certain senders or a recipient protected by a mail flow rule.
- 550 5.7.1Public folder does not accept external mail.An external sender wrote to a mail-enabled public folder in Microsoft 365, which by default accepts mail only from authenticated senders.
- 550 5.7.1Sending IP blocked by Proofpoint Dynamic Reputation.Proofpoint’s IP reputation system has your sending IP on its block list because it has seen spam or viruses from it, so Proofpoint customers refuse your mail.
- 550 5.7.1SPF check failed.The recipient’s Cisco Secure Email gateway checked SPF, found your server not authorised for the sender domain, and its policy rejects that result.
- 550 5.7.1Rejected under your domain’s DMARC policy.Your message failed DMARC, your domain’s DMARC record asks receivers to reject such mail, and the recipient’s Cisco gateway did so.
- 550 5.7.1DMARC verification failed permanently.The Cisco gateway hit a permanent failure while verifying DMARC for your message, and the recipient’s policy rejects such mail. Cisco does not say what produces that failure.
Further reading
All 108 Gmail codesEvery code in the wikiPaste your own bounce