Very unfortunate situation.
I get it... it isn't logical for Microsoft to support 2 (well, actually 3) email applications.
It's just that Windows Live Mail is one of the best applications ever to come from Microsoft and Windows 10 Mail is one of the worst applications to come from Microsoft.
I have an Office 360 subscription. I guess I'll switch from Windows Live Mail to Outlook. Outlook is a well designed application. It's just that Outlook is kind-of overkill for my needs.