Microsoft replacing windows Mail with a new Outlook app. It is built using the same scripts as Outlook on the web, but in an app framework. It supports multiple accounts, currently only Outlook.com, Microsoft 365 Work or School, and IMAP accounts. Microsoft 365 Work or School accounts must have a Microsoft 365 software subscription on their account to use new Outlook for Windows or new Outlook for Mac.

Gmail All Mail and Outlook’s Archive folder
Using Gmail's All Mail folder in new Outlook for Windows or classic Outlook for Windows. In the new Outlook, there is a folder named Archive and it appears to contain all of the messages in the All Mail folder in Gmail. Is new Outlook syncing All Mail?

Automatically Open New Outlook when Windows boots
How to enable New Outlook for Windows to run automatically when you boot the computer.
Enable or Disable Yellow Highlight on Flagged Messages
Outlook on the web introduced highlighting flagged messages, then the option appeared in Outlook 365 subscriptions. Now it's in Outlook 2019 and 2021. Outlook for Windows A recent update for Office 2019 enabled the option to display a yellow background on flagged messages,but did not enable the option to turn it off. Oops. Users with

"This account is not supported in Outlook" error message
New Outlook error: This account is not supported in Outlook due to the license provided by your work or school. Try to login with another account or go to Outlook on the web.

New Outlook for Windows
Office 365 subscribers in the beta channel and with an Office 365 business account in their profile, will have a switch in the upper right corner for Try the New Outlook.

Leave Messages Unread
How to change Outlook's Mark as Read settings and manually mark as read or unread.