I’m just an eM Client 6 Pro user, and I did some searches about your question but was unable to find anything specific. I doubt seriously that Support here will be able to answer your question (not a knock on them at all, btw).
It appears more complicated than necessary, something Microsoft with their lack of wisdom is extremely good at doing - making things even more complicated when simplicity is what end users need.
Still, I offer this link as a possible place to start your quest to find an answer:
Hi,
For migrating the account, simply recreating it as an Exchange account in the automatic setup should be enough. It does usually take 5-10 minutes to obtain the server configuration while doing it, so take that into consideration and don’t cancel the process. The address for the Exchange server should read https://outlook.office365.com/EWS/Exc… after the automatic setup.
Hope that helps.
Dave