The O365 Email Suspicious Search Behavior rule detects potentially malicious activities in Office 365 mailboxes by identifying users who either search for suspicious keywords or conduct an unusually high volume of mailbox queries within a short timeframe. Such behavior raises alerts for possible account compromise, where an attacker may be enumerating or discovering user data post-breach. The Splunk query used in this rule examines the Office 365 Universal Audit Log for search queries initiated by users, evaluating the legitimacy of the searches based on predefined suspicious terms. If a user exceeds a defined threshold of queries or searches for multiple suspect terms, the system flags these activities for further investigation, allowing security teams to respond swiftly to potential threats.