421 4.7.0: low IP reputation, rate limited

What it means

Gmail rates each sending IP on the mail it has seen from it, including how many recipients report that mail as spam. Yours is rated very low, so Gmail is limiting how much it accepts from that IP. This is the temporary form; Google also documents a permanent 550 5.7.1 with nearly the same wording. On shared IPs, such as those of an email service provider, other senders' mail counts as well. Reputation recovers only as Gmail sees better mail over time, so the work lies in what you send and to whom.

Common causes

• Recipients have reported mail from this IP as spam.
• Sending to old, purchased or scraped lists with many unknown addresses.
• A shared IP whose other senders send unwanted mail.
• A sudden rise in volume from an IP with little history.

How to fix it

1. 01Check IP reputation and spam rate in Google Postmaster Tools.
2. 02Pause or slow sending to Gmail, and send only to recipients who asked for your mail and engage with it.
3. 03Remove addresses that bounce or never engage, and stop buying or scraping lists.
4. 04If you are on a shared IP, ask your provider about its reputation or move to a better pool.
5. 05Raise volume gradually once the rate limiting stops.

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

Further reading

• Google Postmaster Tools guide
• Why your sender reputation dropped
• Blacklist checker