Blocked Emails Hotmail |work| -

| Error Code | Common Meaning | Recommended Action | | :--- | :--- | :--- | | | Unauthenticated or blocked sender. | Check SPF/DKIM/DMARC records. | | 550 5.7.509 | IP blocked due to poor reputation. | Request delisting via sender portal. | | 421 4.7.0 | Temporary rate limiting. | Slow down sending volume; warm up IP. | | 550 5.7.511 | Domain blocked. | The sending domain is blacklisted by Microsoft. |

Even with a good IP reputation, specific content triggers can block an email. Microsoft's "SmartScreen" technology scans for: blocked emails hotmail