I've been going round in circles trying to fix this. I use Windows 10 and Internet Explorer 11, and when I click on a mailto: link on a website I'd like it to open Gmail. At the moment whenever I click on a link it opens Mail, one of the new apps that I don't use.
If I go to Control Panel\Programs\Default Programs\Set Associations and scroll down to the protocols I can see that MAILTO is set to Mail, but when I click on 'Change program...' the only options are to keep using Mail or 'Look for an app in the Store'. There's no option to select Internet Explorer and nothing useful in the Store.
If I got to Control Panel\Programs\Default Programs\Set Default Programs and select Mail, then 'Choose defaults for this program' I'm unable to untick MAILTO. I've already assigned .eml to Internet Explorer, to no avail. If I go back to Set Default Programs and select Internet Explorer, MAILTO is not listed in the default settings, nor is .eml.
In Internet Explorer if I enable the Google toolbar then navigate to the options there's a tickbox for 'Use Gmail for "Mail To" links', which I have already ticked, although I generally have the toolbar disabled. It seems to do nothing either way.
Previous to all of this the problem was that whenever I clicked on an email link in Internet Explorer it wanted to open Chrome, then it did nothing anyway. Email links wouldn't do anything at all when using Chrome. I've now uninstalled Chrome just to disassociate it from Mailto links, but the problem has simply moved to Mail, which can't be uninstalled.
Sorry for the long post. I was trying to anticipate any questions or suggestions. Any ideas what to try next?