Subject: Returned mail: see transcript for details

From: Mail Delivery Subsystem <[email-masked]>
Date: Tue, 20 Jan 2026 13:11:59 +0200

The original message was received at Tue, 20 Jan 2026 13:11:46 +0200
from sally.edelkey.net [213.138.147.136]

   ----- 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 [DU2PEPF0001E9C6.eurprd03.prod.outlook.com 2026-01-20T11:11:59.302Z 08DE564E915317C6])

   ----- 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 [DU2PEPF0001E9C6.eurprd03.prod.outlook.com 2026-01-20T11:11:59.302Z 08DE564E915317C6]
550 5.1.1 <[email-masked]>... User unknown
<<< 503 5.5.2 Need rcpt command [DU2PEPF0001E9C6.eurprd03.prod.outlook.com 2026-01-20T11:11:59.303Z 08DE564E915317C6]