Hello Claire Harris and BTD and welcome to the forum.
I wish I could tell you that the Mail App in Windows 10, was feature rich and robust and would do everything you ever wanted with respect to a mail client, but.....
I can't, well I could but it would be less than truthful.
What I've found to be a better substitute is actually the old Windows Live Mail client which is part of Windows Essentials.
You can get that from here
http://windows.microsoft.com/en-us/windows-live/essentials
And if you'd like choose only to install the Live Mail App and forego the others.
I keep hoping that the Mail App that is native to Windows 10 will at some point become a more usable mail client, as it seems to get an update or two practically every week, but so far it doesn't seem to be quite there yet.