I can't make Office 2013 programs send anything via Windows 10 native mail app, it tells me to use outlook instead, but I don't want to use outlook, so I even uninstalled it. Now Office tells me there's no program to handel the MAPI protocol, what does it mean? Doesn't the native mail app work with that protocol?
It means what it says. Windows 10 Mail App doesn't support MAPI protocol. The only mail client available for Windows that supports this protocol is the Microsoft Office Outlook.