Yahoo TS03 temporary deferral

Exact response pattern421 4.7.0 [TS03] All messages from this IP are temporarily deferred

TemporaryYahoo/AOLReputation

What it means

Yahoo is temporarily deferring all traffic from the source IP.

Likely causes

Reputation deterioration.
Complaint or unknown-user pressure.
Unstable warm-up.

Recommended response

Pause or sharply reduce traffic.
Audit recipients and complaints.
Resume slowly after recovery.

Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.

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