Simple: everyone out there uses Yahoo Mail, and when they click on a mailto: link, it opens Outlook or something, which asks them to configure account, so they

Simple: everyone out there uses Yahoo Mail, and when they click on a mailto: link, it opens Outlook or something, which asks them to configure account, so they close it and then go to their Yahoo Mail and type the address. (This will happen until everyone clicks Yes to registerProtocolHandler requests.)