421 4.7.28: Rate Limited: Unusual Volume
The 421 4.7.28 error means Gmail has rate limited you after seeing an unusual volume of mail tied to your IP, domain or a URL you linked. Here is how to clear it.
Published · Last verified · Maintained by TamingDNS
421
4.7.28
Rate Limited: Unusual Volume
Very Common
🔢 Enhanced Status Code Breakdown: 4.7.28
| Component | Value | Meaning |
|---|---|---|
| Class | 4 | Temporary failure (Soft bounce) |
| Subject | 7 | Security or policy |
| Detail | 28 | Rate Limited: Unusual Volume |
Per RFC 3463 Enhanced Mail System Status Codes. Class (X) = severity, Subject (Y) = category, Detail (Z) = specific condition.
💬 What This Error Means
Gmail has seen an unusual amount of mail tied to you and has temporarily throttled it. The trigger is whichever identifier Gmail attached the volume to, and its own sentence names it: your IP address, your whole netblock, your SPF domain, your DKIM domain, a URL inside your message, or repeated use of one Message-ID. Complaints are one reason Gmail treats volume as unsolicited, not the whole definition.
Common Causes
- A genuine spike in sending volume from your IP address or netblock
- Gmail classifying that volume as unsolicited, which recipient spam reports feed into
- Mail from a neighbour on shared sending infrastructure being counted against the same netblock
- A URL in your message body appearing across a lot of unwanted mail
How to Fix This
- Read the sentence in the bounce: it names which identifier Gmail limited, and that is what you have to fix
- Check Google Postmaster Tools for your spam rate and domain reputation, and keep the spam rate under 0.3%
- Slow the send. Your server will retry, and this clears once the rate falls back
- Only send to people who explicitly opted in, and make unsubscribing easier than reporting spam
📚 Official Documentation
Google-specific. Its documented 4.7.28 texts all describe an unusual rate of email, attributed to your IP, netblock, SPF domain, DKIM domain, a URL domain in the body, or a Message-ID quota. Note that IANA registers X.7.28 as "Mail flood detected", so Gmail's use is close to, but not the same as, the registered meaning.
📖 Google Workspace / Gmail documentation → Browse all Google Workspace / Gmail error codes →📋 Real-World Example Messages
These are real bounce message formats you might receive. Paste yours into the Bounce Decoder for instant analysis.
421 4.7.28 Gmail has detected an unusual rate of unsolicited email originating from your IP address 198.51.100.1. To protect our users from spam, email sent from your IP address has been temporarily rate limited.
🔗 Related Error Codes
🔧 Related Diagnostic Tools
These tools can help you diagnose and fix this type of bounce:
Got a bounce message to decode?
Paste your full NDR email, SMTP error line, or mail log fragment to get an instant plain-English diagnosis.
Open the Bounce Decoder →