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Bounce Decoder: 501 5.1.3

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501 5.1.3 — Invalid Address Syntax

The 501 5.1.3 bounce error means the email address format is invalid. Learn what causes this SMTP error and how to correct address formatting.

🔴
Permanent Failure (Hard Bounce)
SMTP Code
501
Enhanced Code
5.1.3
Category
Invalid Address Syntax
Frequency
Common

🔢 Enhanced Status Code Breakdown: 5.1.3

Component Value Meaning
Class 5 Permanent failure
Subject 1 Addressing
Detail 3 Invalid Address Syntax

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

💬 What This Error Means

The email address format is invalid and doesn't conform to RFC 5321 rules. This is usually a formatting or encoding problem.

Common Causes

  • Missing @ symbol or domain part
  • Spaces or invalid characters in the address
  • Double dots or dot at start/end of local part
  • Encoding issue during import or copy/paste

How to Fix This

  • Verify the address format: [email protected]
  • Remove any spaces, angle brackets, or unusual characters
  • Ensure the address was imported or copied correctly from the source

📋 Real-World Example Messages

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

501 5.1.3 Bad recipient address syntax
501 5.1.3 Invalid address format

🔗 Related Error Codes

550 5.1.0
Other Address Status
550 5.1.1
Mailbox Does Not Exist

📚 Official Documentation

↗ RFC 5321 — Address syntax
🔍

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