How do I fix the 550 5.2.1 bounce error?

Try reaching out through another channel (like a phone call or LinkedIn) to see if they have a new address If this is an internal colleague, check with your IT department to see if the account is active Stop sending to this address for now. It's better to remove it than to let it keep bouncing

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.

Published April 23, 2026 · Last verified May 31, 2026 · Maintained by TamingDNS

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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 (Hard bounce)
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 it's currently 'closed for business.' The account might be suspended, temporarily disabled, or set up to intentionally reject all incoming mail.

Common Causes

The account was suspended by the email provider (often for non-payment or inactivity)
The person has manually disabled their inbox for a while
The company has kept the domain but deactivated this specific employee's account
The mailbox has hit an old age or "retention" limit set by an admin

How to Fix This

Try reaching out through another channel (like a phone call or LinkedIn) to see if they have a new address
If this is an internal colleague, check with your IT department to see if the account is active
Stop sending to this address for now. It's better to remove it than to let it keep bouncing

📚 Official Documentation

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 → Browse all Microsoft 365 / Outlook error codes →

📋 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

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