421 4.7.28
421 4.7.28 SPF Domain Rate Limit
Gmail slowed mail because the SPF domain is authorising IPs that are sending spam.
Overly broad SPF records (e.g., “include:*”) can expose your domain to abuse. Gmail rate limits all IPs in the record when abuse is detected.
Severity
WARNING
Provider
Gmail
Reference
Mitigation Portal
Last Reviewed
2025-06-01
How to Fix 421 4.7.28
Follow these steps to resolve this Gmail SMTP error and restore normal delivery.
- ✓Remove unused IP ranges and vendors from the SPF record.
- ✓Flatten nested SPF includes so you can audit each address space.
- ✓Create dedicated SPF records per business unit or use case.
- ✓Coordinate with partners to ensure their traffic meets Google standards.
Helpful Resources
More Gmail SMTP Codes
Keep these related troubleshooting guides handy while addressing 421 4.7.28.
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