We are currently also think about switching to O365, using the cool stuff like Teams (Skype for Business), e.g.:
Some of the features require also mail setup.
We have over 60 Notes databases which will stay on our running Domino 9.0.2 system.
Some of those databases using group mail functionalities, this must stay as well inside our domino environment. We will only move user mail files.
Do you also have 2 separate e-mail domain running? One for domino and one for O365?
Do you already have experience with document links inside emails. Are those also work within outlook?
I would love to here more of your experiences.