Exchange ActiveSync (EAS) is a protocol developed by Microsoft that enables the synchronization of emails, contacts, calendars, tasks, and notes between a mail server and mobile devices. It allows users to access and manage their mailbox data in real-time on smartphones and tablets, ensuring that any changes made on one device are reflected across all connected devices. EAS uses HTTP and XML to communicate and supports features like remote wipe, device security policies, and selective synchronization. It is widely used in enterprise environments to provide secure and efficient mobile access to Microsoft Exchange or other compatible mail servers, enhancing productivity while maintaining security controls.