Normally I open my email accounts via my browser as Windows 10 is slow to bring everything up to date and I don't like the format of grouping mail together, however for quickness sometimes I go straight to Mail via Windows 10 as I don't have to log in. If I want to send a new message from Windows 10 Mail the screen just closes and I'm back to my desktop. This has happened a few times recently but not in the past. I haven;t checked to see if the same thing applies with my Yahoo account but it is happening with my Outlook account.