The 550 5.4.1 bounce is common with Microsoft 365 and means the recipient address was rejected at the connection level. Learn what causes it and how to get delisted.
5.4.1
| Component | Value | Meaning |
|---|---|---|
| Class | 5 | Permanent failure |
| Subject | 4 | Network and routing |
| Detail | 1 | Recipient Address Rejected |
Per RFC 3463 Enhanced Mail System Status Codes. Class (X) = severity, Subject (Y) = category, Detail (Z) = specific condition.
The recipient server refused the connection or rejected the address at the connection level. Commonly seen with Microsoft 365 when the sending IP or domain is blocked by their anti-spam policy.
Microsoft 365 commonly returns 5.4.1 as "Recipient address rejected: Access denied" for policy-blocked senders. Use the Microsoft delist portal.
📖 Microsoft 365 / Outlook documentation →These are real bounce message formats you might receive. Paste yours into the Bounce Decoder for instant analysis.
550 5.4.1 Recipient address rejected: Access denied [AM0P190CA0026.EURP190.PROD.OUTLOOK.COM] 550 5.4.1 [x.x.x.x]: Client host rejected: cannot find your hostname
Paste your full NDR email, SMTP error line, or mail log fragment to get an instant plain-English diagnosis.
Open the Bounce Decoder →