I believe it has a lot to do with the fact that new Outlook operates on email in their cloud, and that means they can … process your email as they see fit.
Remember that adding an account to new outlook means all your email gets uploaded to O365 servers. It no longer interacts locally. That includes external services like Gmail etc.
Remember that adding an account to new outlook means all your email gets uploaded to O365 servers. It no longer interacts locally. That includes external services like Gmail etc.