How do I fix the 421 4.7.29 bounce error?

Implement a gradual IP warmup schedule over 4–6 weeks Start with low volumes to engaged recipients to build reputation Let your server retry automatically — the hold is temporary

Bounce Decoder: 421 4.7.29

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421 4.7.29 — Blocked: Local Policy (New Sender)

The 421 4.7.29 error means Google is temporarily blocking your new IP or domain. Learn how to implement IP warmup and fix this new sender hold.

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Temporary Failure (Soft Bounce)

SMTP Code
421

Enhanced Code
4.7.29

Category
Blocked: Local Policy (New Sender)

Frequency
Common

🔢 Enhanced Status Code Breakdown: `4.7.29`

Component	Value	Meaning
Class	4	Persistent transient failure (temporary)
Subject	7	Security or policy
Detail	29	Blocked: Local Policy (New Sender)

Per RFC 3463 Enhanced Mail System Status Codes. Class (X) = severity, Subject (Y) = category, Detail (Z) = specific condition.

💬 What This Error Means

Your message was temporarily rejected by the receiving server's local policy — typically a new-sender hold applied to IPs or domains without an established sending history.

Common Causes

New sending IP with no delivery history
Rapid volume increase from previously low-volume sender
Local anti-spam policy on the recipient server

How to Fix This

Implement a gradual IP warmup schedule over 4–6 weeks
Start with low volumes to engaged recipients to build reputation
Let your server retry automatically — the hold is temporary

🏢 Provider-Specific Variations

Google Workspace / Gmail

Google 421 4.7.29 is issued for new senders. Warm up your IP gradually, starting with your most engaged recipients and increasing volume weekly.

📖 Google Workspace / Gmail documentation →

📋 Real-World Example Messages

These are real bounce message formats you might receive. Paste yours into the Bounce Decoder for instant analysis.

421-4.7.29 Our system has detected that this message does not meet IPv6 sending guidelines

🔗 Related Error Codes

                    421 4.7.28                

Blocked: High Complaint Rate

                    421 4.7.0                

Temporary Policy Rejection

📚 Official Documentation

↗ Google Postmaster Tools ↗ IP Warmup best practices

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