A Delivery Status Notification (DSN) is an automated email generated by a mail system to report whether a message was delivered, delayed, or could not be delivered. A failure notice may include returned message data or parts of the original email to help diagnose the problem.
DSNs matter in security because their system-generated appearance can make them seem trustworthy, while included or nested content may still be unsafe. Attackers can exploit this by placing deceptive text, links, or contact details in content that a legitimate service later returns in a delivery report. Users should verify requests through an independent channel, and defenders should inspect returned content and nested MIME parts rather than trusting a notice solely because it came from an automated system.