451 4.7.23: no PTR record, rate limited
Gmail is rate limiting mail from your IP because its reverse DNS record is missing or does not resolve back to the same address.
- Gmail
- Provider
- Temporary (4xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 451 4.7.23
- Provider
- Gmail and Google Workspace
- Temporary or permanent
- TemporaryThe sending server keeps the message and tries again later.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
451 4.7.23 The sending IP address for this message doesn't have a PTR record…
What it means
This is Gmail's dedicated code for the reverse DNS requirement in its sender guidelines. Every sending IP needs a PTR record, and the hostname in that record must resolve forward to the same IP. Yours fails one of those checks, so mail from it is temporarily rate limited. Google's sender guidelines FAQ lists the code among the temporary failures it sends when a sender requirement is not met, and the permanent form is 550 5.7.25. The reply includes the IP that Gmail saw, which helps when mail leaves through more than one address. The PTR record is set by the IP's owner, usually your hosting provider.
Common causes
- The sending IP has no PTR record.
- The PTR hostname has no A or AAAA record, or it points to a different IP.
- Mail leaves through an unexpected IP, such as a new server or a NAT address, without reverse DNS.
How to fix it
- 01Look up the IP shown in the bounce with a PTR lookup.
- 02Ask your hosting or cloud provider to set a PTR record for it, pointing to a hostname you control.
- 03Add an A or AAAA record for that hostname pointing back to the same IP.
- 04Let deferred mail retry once both records resolve.
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 FAQ (Gmail Help)support.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.
- 451Local error in processing.The receiving server hit a problem on its own side while handling the message and stopped. The reply is temporary, so the sending server will try again.
Further reading
All 108 Gmail codesEvery code in the wikiPaste your own bounce