I think you don't listen, neither everyone else out there!!!!!!!
The question was NOT just how to sync Android with Windows.
The question IS how to sync Android Calendar ( which is neither Google, neither outlook) with windows 10 calendar (which is Microsoft, not outlook).
Stop referring to download Google calendar or outlook calendar, because thats not what the majority of us are asking for help about.
Obviously we dont want to use Google calendar nor Outlook calendar.
Its about using IMAM/POP3 e-mail with Windows 10 mail client which is not a problem to Sync with Android Mail client.
The problem becomes when we want to USE WINDOWS 10 Calendar synchronizing with OUR ANDROID's CALENDAR (NOT THE GOOGLE< NOT THE OUTLOOK)
And to everyone who is going to say that this is not possible - IT IS!