Subject: Returned mail: see transcript for details

From: Mail Delivery Subsystem <[email-masked]>
Date: Thu, 11 Sep 2025 09:12:23 +0300

The original message was received at Thu, 11 Sep 2025 09:12:10 +0300
from harmaja.edelkey.net [213.138.147.141]

   ----- 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 [DB3PEPF0000885F.eurprd02.prod.outlook.com 2025-09-11T06:12:23.506Z 08DDF095E6D1E394])

   ----- Transcript of session follows -----
... while talking to halton-com.mail.protection.outlook.com.:
>>> DATA
<<< 550 5.4.1 Recipient address rejected: Access denied. For more information see https://aka.ms/EXOSmtpErrors [DB3PEPF0000885F.eurprd02.prod.outlook.com 2025-09-11T06:12:23.506Z 08DDF095E6D1E394]
550 5.1.1 <[email-masked]>... User unknown
<<< 503 5.5.2 Need rcpt command [DB3PEPF0000885F.eurprd02.prod.outlook.com 2025-09-11T06:12:23.506Z 08DDF095E6D1E394]