I use Outlook as my email, calendar, to-do, and notes client. It comes with my Microsoft Office 365 subscription. As of late, every few times I start Outlook I receive a message that I can switch to the New Outlook now or I will be forced to switch next time I start Classic Outlook! That happens regardless of me routinely uninstall the New Outlook app when I see that message. Well, I have tried the New Outlook app in the past and it is just OWA / Outlook.com loaded in a desktop window. If I wanted that, I will just open that interface in my web browser, but there is a reason why I use the desktop app and not the web version.

A bit of searching reveals a lot of complaining and few unreliable and complicated solutions. Well, there is a very simple solution, one provided by Microsoft itself. In your Classic Outlook:

1. Go to File > Options.
2. Click on the General tab and scroll the right pane all the way down.
3. Untick the checkbox next to “Automatically switch me to the new Outlook app”, then close the Options window by click on the “OK” button.

Resource

• Getting started with the new Outlook for Windows