The correct answer is Active synchronization because it allows emails, calendars, and contact information to be updated in real-time across all user devices, which is essential for maintaining continuous availability and seamless user experience. Email relays are used primarily for routing emails between servers, Latency optimization primarily deals with reducing delays in network communication and is more related to the overall performance rather than synchronization features, and Email throttling is the practice of limiting the number of emails sent to avoid overwhelming servers, hence not directly related to the synchronization and availability requirements of the company.