I'm using davmail + thunderbird to access my O365 emails + calendar. Works flawlessly for me but does mean you have to have a separate application running to pr

I'm using davmail + thunderbird to access my O365 emails + calendar. Works flawlessly for me but does mean you have to have a separate application running to provide the gateway. I run mine on the same machine as my email client but you could easily host it on a server and connect via that.