421 4.7.30: DKIM did not pass, rate limited
Gmail is rate limiting your mail because it failed DKIM, which Google requires of bulk senders along with SPF.
- Gmail
- Provider
- Temporary (4xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 421 4.7.30
- 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 4.7.30 Your email has been rate limited because DKIM authentication didn't pass for this message.
What it means
Under Google's sender guidelines, anyone sending more than 5,000 messages a day to Gmail accounts must pass DKIM as well as SPF. This message did not pass DKIM: it had no signature, the signature did not verify, or the public key could not be found in DNS. Gmail has rate limited it. This is the temporary form, also listed in Google's sender guidelines FAQ, and the permanent form is 550 5.7.30. A signature that breaks on the way, because a gateway or a list added a footer for example, fails the same way as a missing one.
Common causes
- DKIM signing is not turned on at the sending service.
- The selector's public key is missing from DNS or does not match the private key.
- Something changed the message after it was signed, such as a footer or rewritten links.
How to fix it
- 01Turn on DKIM signing at every service that sends for your domain.
- 02Publish the selector record each service gives you, and check it with a DKIM lookup.
- 03Stop gateways or tools from changing the message after it is signed, or have them sign after their changes.
- 04Send a test to a Gmail address and confirm dkim=pass in the Authentication-Results header.
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 5.7.30DKIM did not pass, blocked.Gmail rejected the message because it failed DKIM, which Gmail requires of bulk senders along with SPF.
- 421 4.7.27SPF did not pass, rate limited.Gmail is rate limiting your mail because it failed SPF, which Gmail requires of bulk senders, those sending more than 5,000 messages a day to Gmail.
- 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.
Further reading
All 108 Gmail codesEvery code in the wikiPaste your own bounce