Subject: Delivery Status Notification (Failure)
From: Mail Delivery Subsystem <[email-masked]>
To: [email-masked]
Date: Tue, 02 Jun 2026 10:00:00 +0000

Delivery failure.
Final-Recipient: rfc822; [email-masked]
Action: failed
Status: 5.1.1
Diagnostic-Code: smtp; 550 5.1.1 User unknown