This rule monitors for suspicious activity involving the access of multiple Office 365 Exchange mailboxes through APIs, specifically the Microsoft Graph API or Exchange Web Services. It detects instances where more than five unique mailboxes are accessed within a short timeframe (10 minutes). The detection leverages the 'MailItemsAccessed' operation and identifies API interactions through AppId and a regex pattern. Such behavior may suggest unauthorized access or data exfiltration attempts by attackers who could use compromised accounts to gain access to sensitive information. The rule is crucial for organizations to prevent potential data breaches and should be adjusted to fit specific operational contexts.