A year ago, word leaked about Project Monarch, Microsoft's effort to consolidate its many different versions of its Outlook mail and calendar product. At that time, as first reported by Windows Central, Microsoft was planning to roll out its so-called "One Outlook" product and strategy in 2021. Monarch is still happening, but now it seems the bulk of the new One Outlook strategy and deliverables will be rolling out this year instead.
Microsoft currently has different versions of Outlook for Windows, Mac, the Web, iOS, and Android devices (based on the Acompli technology it acquired), all of which its officials (confusingly) tend to refer to as plain-old "Outlook." The new One Outlook -- which also is expected to be branded as plain-old "Outlook" once it's available -- will work on the Windows Desktop (Win32/UWP; Intel and Arm), on the Web, and the macOS Desktop. The new Outlook will look and feel a lot like Outlook for the Web, I hear.
Microsoft has been testing Monarch/One Outlook for several months internally with increasingly large rings of employees. My sources say the company is planning to make an official announcement about One Outlook this spring. Microsoft could be ready to get a test version of the new Outlook to Windows Insiders in the Dev and Beta channels by late March or early April 2022, my contacts say. By late July or August this year, Microsoft is hoping to be able to get it to Insiders in the Slow Channel, though this target date could slip until the fall, my contacts said.
The original leak about Monarch indicated that Microsoft was considering replacing the built-in Mail/Calendar client in Windows with the new Outlook. It seems like this is still the strategy, but it may happen more gradually than originally expected, my contacts say.
When Microsoft makes available the next feature update for Windows 10 and 11 around October 2022, the new Outlook will be an option and be pinned alongside the existing Mail and Calendar app, my sources say. Microsoft will likely try to get Windows users to try the new Outlook but doesn't seem like it will force users to migrate to it this calendar year. I'm not sure if next year at some point Microsoft will require Windows users to go with the new Outlook and remove the existing Mail and Calendar app.