https://www.theverge.com/2017/10/16/16481190/microsoft-outlook-windows-mac-redesign-features

Microsoft is working on a big redesign for its Outlook for Mac and Windows apps. The software giant revealed teasers for the new design during an Ignite conference session last month, and the goal is to simplify the user interface on both Mac and Windows versions. A lot of the changes look very similar to the Outlook for iOS app, with a single-line ribbon and a smaller set of default commands. Reducing complexity is one of the key aims of the redesign, to make it easier for new and existing Outlook users to navigate the email app.

A new customizable ribbon will let Outlook for Mac and Windows users control which buttons are available, so you can tailor the email interface to your own common tasks. The left navigation panel will include quicker access to folders across multiple accounts, and looks like the switcher in Outlook for iOS.