SMTP response codes for Symantec Messaging Gateway

Products

• Messaging Gateway

Issue/Introduction

Symantec Messaging Gateway (SMG) uses Simple Mail Transfer Protocol (SMTP) response codes to provide feedback about email delivery issues. These codes help administrators understand why emails were delayed or rejected and identify the necessary steps to resolve them. This article summarizes common SMTP response codes generated by SMG, grouped into temporary and permanent errors, with links to detailed explanations for each code.

Resolution

Temporary errors:

Temporary errors, also known as soft bounces, indicate transient issues that may resolve without intervention. However, if these errors persist, they require further investigation.

• 421 4.4.0 [internal] failed to connect: no mail servers for this domain could be reached at this time
• 421 4.4.2 Service timed out
• 421 4.4.4 [internal] domain does not resolve
• 450 4.4.1 [internal] Connection Timed Out
• 451 4.4.2 [internal] no banner
• 451 4.4.2 [internal] no BODY response
• 451 4.4.2 [internal] no RSET response
• 451 4.4.2 [internal] no HELO/EHLO response
• 451 4.4.2 [internal] no MAIL FROM response
• 451 4.4.2 [internal] no RCPT TO response
• 451 4.4.2 [internal] no DATA response

Permanant errors:

Permanent errors, or hard bounces, indicate issues that prevent delivery and require corrective action to ensure successful email transmission.

• 501 5.5.2 MAIL FROM syntax error
• 501 5.5.2 RCPT TO syntax error
• 552 5.3.4 message size limit exceeded
• 554 5.1.2 Recipient address rejected: User unknown

Note: For additional troubleshooting, you can refer to the below article:
Troubleshoot email delivery issues using telnet