https://www.theverge.com/2018/9/4/17819636/microsoft-resdesigned-outlook-windows-web

Microsoft first unveiled a redesign of its Outlook email app last fall, and now that visual overhaul for the software is available publicly starting today. Microsoft is making it available for the Windows app version of Outlook, as well as the web version. Similar to Google’s recent Gmail redesign, Microsoft will let you toggle the redesign on with the press of a button or revert back to the classic look if you aren’t too keen on the changes.

The company is stressing control and customizability with the refreshed Outlook, so many of the new features and visual changes are optional and can be stripped away if you want a simplified interface that’s far less cluttered than past versions of the software. If you want a more complex system, you can add items to the Outlook ribbon, while a left navigation panel will let you manage multiple accounts, access folders, and switch between your email inbox, calendar, and address book.