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Bounce Decoder: 550 5.2.1

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550 5.2.1 — Mailbox Disabled

The 550 5.2.1 bounce means the recipient mailbox exists but is disabled or suspended. Learn what this SMTP error means and what to do.

🔴
Permanent Failure (Hard Bounce)
SMTP Code
550
Enhanced Code
5.2.1
Category
Mailbox Disabled
Frequency
Very Common

🔢 Enhanced Status Code Breakdown: 5.2.1

Component Value Meaning
Class 5 Permanent failure
Subject 2 Mailbox status
Detail 1 Mailbox Disabled

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

💬 What This Error Means

The mailbox exists but is not currently accepting messages. The account is suspended, disabled, or configured to reject all incoming mail.

Common Causes

  • Account suspended by the mail provider
  • The recipient disabled incoming mail
  • Account decommissioned but domain still exists
  • Mailbox over retention policy limits

How to Fix This

  • Try an alternative contact method for this person
  • If you manage the server, check account status in your email admin panel
  • Remove this address from active mailing lists

🏢 Provider-Specific Variations

Microsoft 365 / Outlook

Microsoft 365 uses 5.2.1 when an Exchange Online mailbox has been disabled or the account has been deactivated.

📖 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 5.2.1 Mailbox not enabled for receiving
550 5.2.1 The email account that you tried to reach is disabled

🔗 Related Error Codes

550 5.1.1
Mailbox Does Not Exist
550 5.2.0
Other Mailbox Status

📚 Official Documentation

↗ Microsoft 365 NDR codes
🔍

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