Subject: Returned mail: see transcript for details

From: Mail Delivery Subsystem <[email-masked]>
Date: Fri, 19 Dec 2025 12:42:00 GMT

The original message was received at Fri, 19 Dec 2025 12:41:58 GMT
from m0341351.ppops.net [127.0.0.1]

   ----- The following addresses had permanent fatal errors -----
<[email-masked]>
    (reason: 550 5.4.1 Recipient address rejected: Access denied. For more information see https://aka.ms/EXOSmtpErrors [SJ5PEPF000001F2.namprd05.prod.outlook.com 2025-12-19T12:41:59.815Z 08DE3B53F8B9E116])

   ----- Transcript of session follows -----
... while talking to danaher.mail.protection.outlook.com.:
>>> DATA
<<< 550 5.4.1 Recipient address rejected: Access denied. For more information see https://aka.ms/EXOSmtpErrors [SJ5PEPF000001F2.namprd05.prod.outlook.com 2025-12-19T12:41:59.815Z 08DE3B53F8B9E116]
550 5.1.1 <[email-masked]>... User unknown
<<< 503 5.5.2 Need rcpt command [SJ5PEPF000001F2.namprd05.prod.outlook.com 2025-12-19T12:41:59.815Z 08DE3B53F8B9E116]