421 4.7.1
421 4.7.1 Rate Limiting
Apple deferred the message because the sending IP exceeded the allowed connection or message rate.
Burst testing, seed list monitoring, or poorly tuned MTAs often trigger Apple’s rate limits. The block usually clears within a few hours.
Severity
WARNING
Provider
Apple Mail (iCloud)
Last Reviewed
2025-06-01
How to Fix 421 4.7.1
Follow these steps to resolve this Apple Mail (iCloud) SMTP error and restore normal delivery.
- ✓Lower the number of concurrent SMTP connections to iCloud servers.
- ✓Spread deliveries across a longer time window instead of a single burst.
- ✓Warm new IPs gradually and avoid blasting large seed lists.
- ✓Implement per-domain throttles so Apple traffic can be tuned independently.
Helpful Resources
More Apple Mail (iCloud) SMTP Codes
Keep these related troubleshooting guides handy while addressing 421 4.7.1.
Still experiencing Apple Mail (iCloud) delivery issues?
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