I have one PC that had been upgraded to Windows 10 and has been using Windows Live Mail as the email client. I set up a POP3 account in the new Windows 10 Mail app and it works well except....
I cannot create new folders or subfolders. Right-clicking on the Inbox brings up two options [Remove from Favorites/Pin to Start].
Not sure if there is a setting somewhere that is causing issues - but my guess is yes.