Same with my PC

I opened a case with Malwarebytes. They sent me a repair / reinstall tool. After running it, Malwarebytes Premium starting with Windows no longer interferes with Mail notifications.

I use Outlook.com

I also keep the Mail app open. Malwarebytes Premium does interfere, if it starts with Windows.

This was a problem for me for weeks. Here are the steps I used to get the notifications working again:

1. Used a powershell script to uninstall Mail/Calendar app. See:

How to Uninstall Windows...