Subject: Returned mail: see transcript for details

From: Mail Delivery Subsystem <[email-masked]>
Date: Mon, 29 Sep 2025 06:01:38 GMT

The original message was received at Mon, 29 Sep 2025 06:01:37 GMT
from m0223512.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 [DU2PEPF0001E9BF.eurprd03.prod.outlook.com 2025-09-29T06:01:38.177Z 08DDFADB8AC35B1E])

   ----- Transcript of session follows -----
... while talking to nibe-com.mail.protection.outlook.com.:
>>> DATA
<<< 550 5.4.1 Recipient address rejected: Access denied. For more information see https://aka.ms/EXOSmtpErrors [DU2PEPF0001E9BF.eurprd03.prod.outlook.com 2025-09-29T06:01:38.177Z 08DDFADB8AC35B1E]
550 5.1.1 <[email-masked]>... User unknown
<<< 503 5.5.2 Need rcpt command [DU2PEPF0001E9BF.eurprd03.prod.outlook.com 2025-09-29T06:01:38.177Z 08DDFADB8AC35B1E]