Gmail 421 4.7.0
Rate limited or connection closed
Gmail 421 4.7.0 means: rate limited or connection closed. It is a temporary failure, so your server retries it. Gmail uses 421 4.7.0 for several different reasons, so read the full text: a missing PTR record, TLS required by the recipient domain, an IP not on the recipient's allowlist, or low IP or domain reputation. Fix the named cause and let the queue retry; reputation deferrals clear only once the mail stops looking risky.
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
Connection expired, try reconnecting. For more information, go to About SMTP error messages.
Reply text
IP not in whitelist for RCPT domain, closing connection. For more information, go to Allowlists, denylists, and approved senders.
Reply text
Try again later, closing connection. (command) For more information, go to About SMTP error messages.
Reply text
The IP address sending this message does not have a PTR record, or the corresponding forward DNS entry does not point to the sending IP. To protect our users from spam, email sent from your IP address has been temporarily rate limited. For more information, go to Email sender guidelines.
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TLS required for RCPT domain, closing connection. For more information, go to Email encryption in transit.
Reply text
This message is suspicious due to the very low reputation of the sending IP address. To protect our users from spam, email sent from your IP address has been temporarily rate limited. For more information, go to Why has Gmail blocked my messages?.
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This message is suspicious due to the very low reputation of the sending domain. To best protect our users from spam, the message has been blocked. For more information, go to Why has Gmail blocked my messages?.
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This message is suspicious due to the nature of the content or the links within. To best protect our users from spam, the message has been blocked. For more information, go to Why has Gmail blocked my messages?.
| Who sends it | Gmail and Google Workspace |
|---|---|
| Basic code | 421: <domain> Service not available, closing transmission channel (RFC) |
| Enhanced code | 4.7.0: Other or undefined security status |
| Permanent or temporary | Temporary (4xx) |
| Verifying the list prevents it | Partly |
In practice
Gmail uses 421 4.7.0 for at least eight different reasons, listed separately in its reference: an expired connection, an IP not on the recipient domain's allowlist, a generic try-again-later, a sending IP without a matching PTR record, TLS required by the recipient domain, and suspicious mail because of low IP reputation, low domain reputation, or content and links. The reputation versions are the ones senders hit most, and they clear only when the signals improve. The PTR and TLS versions are configuration fixes.
What the sender should do
Gmail uses 421 4.7.0 for several different reasons, so read the full text: a missing PTR record, TLS required by the recipient domain, an IP not on the recipient's allowlist, or low IP or domain reputation. Fix the named cause and let the queue retry; reputation deferrals clear only once the mail stops looking risky.
Would verifying the list have prevented Gmail 421 4.7.0?
Partly
The reply is not only about one address, but providers weigh how often a sender hits addresses that do not exist. Removing bad addresses before sending lowers that signal.
Common questions
- What does Gmail 421 4.7.0 mean?
- Gmail 421 4.7.0 means: rate limited or connection closed. It is a temporary failure, so your server retries it. Gmail uses 421 4.7.0 for several different reasons, so read the full text: a missing PTR record, TLS required by the recipient domain, an IP not on the recipient's allowlist, or low IP or domain reputation. Fix the named cause and let the queue retry; reputation deferrals clear only once the mail stops looking risky.
- Should I retry after Gmail 421 4.7.0?
- 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 4.7.0?
- Partly. The reply is not only about one address, but providers weigh how often a sender hits addresses that do not exist. Removing bad addresses before sending lowers that signal.
The same code elsewhere
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