421 5.3.2: System Not Accepting Messages
The 5.3.2 SMTP error means the receiving mail system is not currently accepting messages. Learn when this is permanent vs. temporary.
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421
5.3.2
System Not Accepting Messages
Common
🔢 Enhanced Status Code Breakdown: 5.3.2
| Component | Value | Meaning |
|---|---|---|
| Class | 5 | Permanent failure (Hard bounce) |
| Subject | 3 | Mail system status |
| Detail | 2 | System Not Accepting Messages |
Per RFC 3463 Enhanced Mail System Status Codes. Class (X) = severity, Subject (Y) = category, Detail (Z) = specific condition.
💬 What This Error Means
The receiving mail server is currently turned off or not accepting any messages. This usually happens during server maintenance or when a system has been shut down.
Common Causes
- Mail server deliberately shut down or taken offline
- Server configured to reject all incoming connections
- Network-level block preventing delivery
How to Fix This
- Your mail server will retry automatically
- If the issue persists beyond 24 hours, contact the recipient through another channel
- If this is your own server, check your mail server configuration
📚 Official Documentation
📋 Real-World Example Messages
These are real bounce message formats you might receive. Paste yours into the Bounce Decoder for instant analysis.
421 5.3.2 System not accepting network messages
🔗 Related Error Codes
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