Gmail 4.7.28: temporarily rate limited
By Jose Pollman · Published
Soft bounceYour sending reputationGmail / Google Workspace
The error
421-4.7.28 Gmail has detected an unusual rate of mail originating from your IP address.
450 4.7.28 Our system has detected an unusual rate of unsolicited mail originating from your IP addressWhat it means
Gmail has seen an unusual volume from your IP and is throttling it. This is temporary and the mail is not lost — your server should retry.
The receiver is refusing your mail because of how your sending IP or domain behaves, not because of this particular message.
Why it happens
Usually a genuine spike: a newsletter to a list that has not been mailed in months, a migration to a new IP with no warm-up, or a compromised account sending in bulk. Gmail throttles first and blocks later, so this is the warning shot before 5.7.28.
How to fix it
- Let the queue retry — do not requeue everything at once, which makes it worse.
- Check for a compromised account or an open relay before assuming the volume was intentional.
- If you moved to a new IP, warm it up: start low and increase daily over two to four weeks.
- Register at Google Postmaster Tools to see your reputation and spam rate for the domain.
Official documentation: Google: Gmail SMTP error codes.
Related guides
- Gmail 550 5.7.25: the sending IP has no PTR record — Gmail blocked the message because the IP it arrived from has no reverse DNS record, or the record it has does not resolve back to that same IP.
- Gmail 550 5.7.26: this mail is unauthenticated — Gmail rejected the message because it could not verify that you sent it. Gmail requires every sender to pass either SPF or DKIM, aligned with the domain in your From address, and this message passed neither.
- 4.7.0: temporarily refused on policy grounds — The receiver is temporarily refusing your mail for policy reasons — most often rate limiting, greylisting, or a TLS requirement that was not met.