How do I fix the 421 4.3.2 bounce error?

Your mail server will retry automatically — no action needed If it persists beyond 12 hours, the issue is likely on the recipient side

Bounce Decoder: 421 4.3.2

ANALYSIS TOOLS

DIAGNOSTIC TOOLS

BUILDER TOOLS

The 421 4.3.2 soft bounce means the receiving mail server is temporarily unavailable. Learn what causes this and when to retry.

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Temporary Failure (Soft Bounce)

SMTP Code
421

Enhanced Code
4.3.2

Category
System Not Accepting Mail

Frequency
Common

Component	Value	Meaning
Class	4	Persistent transient failure (temporary)
Subject	3	Mail system status
Detail	2	System Not Accepting Mail

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

The receiving mail server is temporarily unavailable or not accepting connections. This is usually a brief outage or maintenance window.

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

421 4.3.2 Service temporarily unavailable
421 4.3.2 All server ports are busy

                    421 4.4.1                

                    421 4.4.2                

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Paste your full NDR email, SMTP error line, or mail log fragment to get an instant plain-English diagnosis.