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Bounce Decoder: 550 5.2.4

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550 5.2.4 — Mailing List Expansion Problem

The 550 5.2.4 SMTP error indicates a problem expanding a mailing list or distribution group. Learn what causes this and how to fix it.

🔴
Permanent Failure (Hard Bounce)
SMTP Code
550
Enhanced Code
5.2.4
Category
Mailing List Expansion Problem
Frequency
Common

🔢 Enhanced Status Code Breakdown: 5.2.4

Component Value Meaning
Class 5 Permanent failure
Subject 2 Mailbox status
Detail 4 Mailing List Expansion Problem

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

💬 What This Error Means

The receiving server could not expand a mailing list or distribution group that the message was addressed to. This is a server-side configuration problem with the list.

Common Causes

  • A distribution group or mailing list has an invalid or missing member
  • The list expansion exceeded the server's configured limit
  • Circular list membership (list A includes list B which includes list A)
  • The list owner account is disabled

How to Fix This

  • Check the mailing list configuration in your email admin panel
  • Remove invalid or disabled accounts from the distribution group
  • Look for circular group memberships
  • Contact your mail server administrator

🏢 Provider-Specific Variations

Microsoft 365 / Outlook

Microsoft 365 returns 5.2.4 when a distribution group cannot be expanded, often due to a disabled owner or a group with no members.

📖 Microsoft 365 / Outlook documentation →

📋 Real-World Example Messages

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

550 5.2.4 Mailing list expansion problem

🔗 Related Error Codes

550 5.2.0
Other Mailbox Status
550 5.2.1
Mailbox Disabled

📚 Official Documentation

↗ Microsoft 365 NDR codes
🔍

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