421 4.7.28
421 4.7.28 DKIM Domain Rate Limit
Gmail rate limited mail signed with this DKIM domain after seeing abuse elsewhere.
The same DKIM domain can be used across multiple senders. If any stream misbehaves, Gmail slows every message signed with that domain.
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.
- ✓Review all platforms and brands using the DKIM domain for compromise.
- ✓Segment transactional and marketing streams onto separate DKIM domains.
- ✓Rotate signing keys when a partner or vendor no longer sends on your behalf.
- ✓Track DKIM domain reputation inside Google Postmaster Tools.
Helpful Resources
More Gmail SMTP Codes
Keep these related troubleshooting guides handy while addressing 421 4.7.28.
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