This analytic rule detects unauthorized access to emails in Office 365 Exchange via the Microsoft Graph API, specifically targeting actions performed by an OAuth application with a known Client ID, '00000003-0000-0000-c000-000000000000'. The detection focuses on the 'MailItemsAccessed' operation within the Exchange workload. Unauthorized access may signify potential data breaches, where attackers can exfiltrate sensitive information and further compromise user accounts, which poses a significant risk to the organization's cybersecurity. The detection logic utilizes the Splunk query language to analyze events recorded in the 'o365_management_activity' log, filtering for the designated AppId and relevant operation. Alerting on these events is crucial, as it enables cybersecurity teams to investigate and respond to potential threats in real-time, ultimately helping to prevent severe breaches that could leverage access to sensitive communications.