The 550 5.1.1 bounce error means the recipient email address does not exist. Learn why it happens, what Google and Microsoft return, and how to fix it.
5.1.1
| Component | Value | Meaning |
|---|---|---|
| Class | 5 | Permanent failure |
| Subject | 1 | Addressing |
| Detail | 1 | Mailbox Does Not Exist |
Per RFC 3463 Enhanced Mail System Status Codes. Class (X) = severity, Subject (Y) = category, Detail (Z) = specific condition.
The recipient's mail server says this email address doesn't exist. The account may have been deleted, the address might be mistyped, or the person may have changed providers.
Google returns: "The email account that you tried to reach does not exist. Please try double-checking the recipient's email address for typos or unnecessary spaces."
📖 Google Workspace / Gmail documentation →Microsoft 365 returns: "Recipient not found by SMTP address lookup." Check the address in the GAL if sending to an internal mailbox.
📖 Microsoft 365 / Outlook documentation →Yahoo returns: "No such user here." This is final — the address does not exist on their system.
📖 Yahoo / AOL documentation →These are real bounce message formats you might receive. Paste yours into the Bounce Decoder for instant analysis.
From: Mail Delivery Subsystem <[email protected]> Subject: Delivery Status Notification (Failure) Content-Type: message/delivery-status Final-Recipient: rfc822; [email protected] Action: failed Status: 5.1.1 Diagnostic-Code: smtp; 550 5.1.1 The email account that you tried to reach does not exist.
550 5.1.1 User unknown 550 5.1.1 <[email protected]>: Recipient address rejected: User unknown in virtual mailbox table
Paste your full NDR email, SMTP error line, or mail log fragment to get an instant plain-English diagnosis.
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