Gmail and Google Workspace · permanent error
550 5.7.1: IPv6 sender without PTR or authentication
Gmail rejected mail that arrived over IPv6 because the sending address lacks a matching PTR record, or the message failed authentication.
- 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 does not meet IPv6 sending guidelines regarding PTR records and authentication.
What it means
For mail arriving over IPv6, Gmail wants two things: a PTR record for the sending IPv6 address whose hostname resolves back to it, and a message that authenticates. One of them is missing. Google's sender guidelines call this an IPv6 authorization error and say it can mean the PTR record for the sending server is not using IPv6. A server can start sending over IPv6 without anyone noticing, once its host gets an IPv6 address, so mail fails even though the IPv4 setup is complete.
Common causes
- The server sends over IPv6, but its IPv6 address has no PTR record.
- The IPv6 PTR hostname does not resolve back to the same address.
- SPF covers only IPv4 addresses, so mail sent over IPv6 fails SPF.
How to fix it
- 01Check which IPv6 address your server sends from, and look up its PTR record.
- 02Ask your provider to set an IPv6 PTR record, and add a matching AAAA record for the hostname.
- 03Add the IPv6 address or range to your SPF record, and sign with DKIM.
- 04If you cannot fix IPv6 quickly, set the mail server to send over IPv4 only.
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 5.7.25No PTR record, blocked.Gmail rejected the message because the sending IP has no reverse DNS record, or the hostname in that record does not point back to the IP.
- 421 4.7.0No PTR record for the sending IP.Gmail is rate limiting mail from your IP because it has no reverse DNS name, or that name does not point back to the same IP.
- 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