The project is called Monarch and the vision is called "One Outlook". Basically, Microsoft is building a new Outlook client that will be powered by the web. The app will be based on the Outlook website and desktop versions will get native OS integrations for things like offline storage, share targets, notifications, and more.
Microsoft wants to replace the existing desktop clients with one app built with web technologies. The project will deliver Outlook as a single product, with the same user experience and codebase whether that be on Windows or Mac. It'll also have a much smaller footprint and be accessible to all users whether they're free Outlook consumers or commercial business customers.The new Outlook is expected in 2022 and will initially replace the Windows 10 Mail & Calendar apps. Microsoft also plans to replace the Win32 Outlook client but that is a more complex endeavor that will require more time.
Via: Windows Central