Gmail and Google Workspace · permanent error
550 5.7.1: duplicate headers
Gmail rejected the message because a header that may appear only once, such as Subject or Date, appears more than once.
- 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 This message is not RFC 5322 compliant because it has duplicate headers.
What it means
RFC 5322 allows some headers to appear only once per message: Date, From, Sender, Reply-To, To, Cc, Bcc, Message-ID, In-Reply-To, References and Subject. Gmail rejects messages that repeat one of them. Google documents a general wording about duplicate headers and a second one that names the repeated header. It usually happens when a gateway, list or script adds a header the message already had, instead of replacing it.
Common causes
- A gateway or script that adds To, Subject or Date without removing the existing one.
- A template that writes a header the mail library also adds.
- Forwarding software that copies headers from the original message.
How to fix it
- 01Check the bounce, or the raw message, for the header that repeats.
- 02Change the step that adds the header so it replaces the existing value.
- 03Let the mail library set standard headers instead of writing them yourself.
- 04Resend once each header appears only once.
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
- Email sender guidelines (Gmail Help)support.google.com
Related codes
- 550 5.7.1More than one sender in From.Gmail rejected the message because its From header lists more than one address, or the message has more than one From header.
- 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