Gmail 421 4.7.30
Rate limited: DKIM did not pass
Gmail 421 4.7.30 means: rate limited: DKIM did not pass. It is a temporary failure, so your server retries it. Gmail requires bulk senders to pass DKIM. Publish the DKIM key your sending service gives you and check that signatures survive any footer or tracking tool.
Gmail’s exact wording
Quoted from Google Workspace Admin Help: Gmail SMTP errors and codes, checked 2026-11-05. Placeholders are Gmail’s own.
Reply text
Your email has been rate limited because DKIM authentication didn't pass for this message. Gmail requires all email bulk senders to authenticate their email with DKIM. Authentication results: DKIM = Did not pass. To set up DKIM for your sending domains, visit Set up DKIM. To learn more about Gmail requirements for bulk email senders, visit Email sender guidelines.
| Who sends it | Gmail and Google Workspace |
|---|---|
| Basic code | 421: <domain> Service not available, closing transmission channel (RFC) |
| Enhanced code | 4.7.30: REQUIRETLS support required |
| Permanent or temporary | Temporary (4xx) |
| Verifying the list prevents it | No |
In practice
Gmail requires bulk senders to sign with DKIM. This deferral means no DKIM signature passed. Common causes are DKIM never set up on the sending service, a DNS key published at the wrong selector, and a gateway or footer tool changing the message after it was signed. Send a test to a Gmail account and look at the Authentication-Results header with Show original.
What the sender should do
Gmail requires bulk senders to pass DKIM. Publish the DKIM key your sending service gives you and check that signatures survive any footer or tracking tool.
Would verifying the list have prevented Gmail 421 4.7.30?
No
This reply is about your sending setup, the message or the receiving system, not about whether the address exists, so verifying the list will not prevent it.
Common questions
- What does Gmail 421 4.7.30 mean?
- Gmail 421 4.7.30 means: rate limited: DKIM did not pass. It is a temporary failure, so your server retries it. Gmail requires bulk senders to pass DKIM. Publish the DKIM key your sending service gives you and check that signatures survive any footer or tracking tool.
- Should I retry after Gmail 421 4.7.30?
- Your sending server retries it automatically, because it is a temporary (4xx) failure. Investigate only if it keeps coming back over several hours.
- Would verifying my list have prevented Gmail 421 4.7.30?
- No. This reply is about your sending setup, the message or the receiving system, not about whether the address exists, so verifying the list will not prevent it.
Sources
- Google Workspace Admin Help: Gmail SMTP errors and codes (checked 2026-11-05)
- IANA: SMTP Enhanced Status Codes registry (checked 2026-11-05)
- RFC 5321: Simple Mail Transfer Protocol, section 4.2.3 (reply codes) (checked 2026-11-05)
Registry and provider wording is quoted exactly; guidance is written by the SimpleVerifier Team.
SimpleVerifier Team · Last checked against the sources 2026-11-05