Send with Excel

I have mostly converted from Outlook to the new Windows 10 Mail app. I just noticed today that when I Send from Excel, it uses Outlook… Help, I prefer to stay in one mail ecosystem. How can I make Excel use Mail instead of Outlook. I do have Mail as the default Mail app, not Outlook! Where does Excel find the mail app to use?

I could uninstall Outlook but there are occasions where I have to use it to move mail between accounts and folders. For some reason Mail won’t let me move email from my Verizon account to a folder in my Hotmail account – I can do this in Outlook.