Subject: Returned mail: see transcript for details

From: Mail Delivery Subsystem <[email-masked]>
Date: Mon, 18 Aug 2025 01:29:34 -0500

The original message was received at Mon, 18 Aug 2025 01:29:33 -0500
from m0132737.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 [SA2PEPF000015CC.namprd03.prod.outlook.com 2025-08-18T06:29:34.464Z 08DDDBEA2C25CBB2])

   ----- Transcript of session follows -----
... while talking to regalbeloit.mail.protection.outlook.com.:
>>> DATA
<<< 550 5.4.1 Recipient address rejected: Access denied. For more information see https://aka.ms/EXOSmtpErrors [SA2PEPF000015CC.namprd03.prod.outlook.com 2025-08-18T06:29:34.464Z 08DDDBEA2C25CBB2]
550 5.1.1 <[email-masked]>... User unknown
<<< 503 5.5.2 Need rcpt command [SA2PEPF000015CC.namprd03.prod.outlook.com 2025-08-18T06:29:34.464Z 08DDDBEA2C25CBB2]