Outlook customers can apply categories to events, messages, contacts, tasks, and group posts in a consistent way to enhance organization and discovery. The calendar API lets you access and define a user's master list of categories, which opens up additional creative scenarios. For example, an athletic club can organize a sports tournament and offer an app that differentiates emails and events for each sport with their own color category. For last-minute news such as unforeseen timetable changes, the app can also set the importance property of those events and emails to alert customers.