So, you need a groupware/email provider and app recommendations?
Thunderbird will likely be the most recommended client as it does all 3 of the things you need. So, it gets points for being easy. And you can try it out on Windows before to see if you like it.
There are other OK clients. Overall I am not a big fan of Thunderbird or most of the other options. I settled for Claws, but it is not for everyone.
Proton is highly recommended, along with Disroot and Tutanota and Mailbox and many others.
As for Android syncing, it is all pretty easy. I use Mailbox and on my Android FairEmail, Davx5, Icsx5, and Etar to keep everything synced.