421 4.7.28
421 4.7.28 URL Rate Limit
Gmail throttled the campaign because the URLs inside are appearing in spam.
When Gmail detects large volumes of spam pointing to your URLs, it slows or blocks other messages that reference the same links.
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.
- ✓Audit messages to ensure no compromised accounts are spamming your links.
- ✓Avoid URL shorteners or open redirects that mask the destination.
- ✓Rotate or retire URLs that appear on blocklists and remediate the cause.
- ✓Monitor third-party affiliates to ensure they are not abusing your brand.
Helpful Resources
More Gmail SMTP Codes
Keep these related troubleshooting guides handy while addressing 421 4.7.28.
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