421 4.7.0: no 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.
- Gmail
- Provider
- Temporary (4xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 421 4.7.0
- 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
421 4.7.0 The IP address sending this message does not have a PTR record…
What it means
Gmail checks that every sending IP has a PTR record (reverse DNS) and that the hostname in it resolves forward to the same IP, a pairing often called forward-confirmed reverse DNS. Your IP failed that check, so Gmail has rate limited mail from it as a protection against spam. Google's sender guidelines make valid forward and reverse DNS a requirement for all senders. The reply is temporary, so some mail may get through on retries, but the limit stays until DNS is fixed. The PTR record is set by whoever controls the IP address, usually your hosting or cloud provider, and not in your domain's own DNS zone.
Common causes
- The sending IP has no PTR record at all.
- The PTR hostname does not resolve back to the sending IP.
- Mail leaves through an IP you did not expect, such as a new server or a NAT address, that was never given reverse DNS.
How to fix it
- 01Look up the sending IP with a PTR lookup to see what reverse DNS it has.
- 02Ask your hosting or cloud provider to set a PTR record for the IP, pointing to a hostname you control.
- 03Create an A or AAAA record for that hostname that points back to the same IP.
- 04It also helps to use that hostname in your server's HELO or EHLO greeting. Then let queued mail retry.
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
- 451 4.7.23No 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.
- 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.
- 421Service not available.The receiving server is closing the connection and will not take mail right now. The reply is temporary, so the sending server keeps the message and tries again later.
- 5.7.0Security or policy refusal, unspecified.The message or session was refused for a security or policy reason that the server did not describe more precisely, or chose not to reveal.
Further reading
All 108 Gmail codesEvery code in the wikiPaste your own bounce