421 4.7.29: Rate Limited: No TLS Connection
Gmail returns 421 4.7.29 when your server connects without TLS. It is a configuration fix on your side, not a reputation problem or an IP warm-up.
Published · Last verified · Maintained by TamingDNS
421
4.7.29
Rate Limited: No TLS Connection
Common
🔢 Enhanced Status Code Breakdown: 4.7.29
| Component | Value | Meaning |
|---|---|---|
| Class | 4 | Temporary failure (Soft bounce) |
| Subject | 7 | Security or policy |
| Detail | 29 | Rate Limited: No TLS Connection |
Per RFC 3463 Enhanced Mail System Status Codes. Class (X) = severity, Subject (Y) = category, Detail (Z) = specific condition.
💬 What This Error Means
Your server connected to Gmail without encryption. Gmail requires bulk senders to use TLS/SSL for SMTP connections and rate limits anyone who doesn't. This is not a reputation decision and waiting will not clear it: the connection has to change.
Common Causes
- Your MTA is not offering or negotiating STARTTLS on outbound connections
- An expired or invalid certificate on your side is causing the TLS handshake to fail, so delivery falls back to plaintext
- A relay, appliance or smart host in front of your MTA is stripping STARTTLS
How to Fix This
- Enable outbound TLS on your mail server. On Postfix that is smtp_tls_security_level = may, at minimum
- Check your certificate is valid and not expired, since a failed handshake can silently fall back to plaintext
- Confirm no relay or firewall in the path is stripping the STARTTLS advertisement
- Re-send after the fix. This clears immediately once the connection is encrypted
📚 Official Documentation
Google documents 421 4.7.29 as "Your email has been rate limited because you're not using a TLS connection", and requires all bulk senders to use TLS/SSL for SMTP. It is not a new-sender hold. IANA separately registers X.7.29 as "ARC validation failure", so this code does not carry its registered meaning at Gmail.
📖 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 4.7.29 Your email has been rate limited because you're not using a TLS connection. Gmail requires all bulk email senders to use TLS/SSL for SMTP connections.
🔗 Related Error Codes
🔧 Related Diagnostic Tools
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