The person who indicated it would take 20 lines of code to fix didn't know what they were talking about.
Read this thread (http://answers.microsoft.com/en-us/windows/forum/windows_8-ecoms/windows-8-mail-not-working-properly-as-default/005c9131-40fe-4fdd-8280-fa36998e0dc1?page=1) where the Microsoft Forum Moderator involved with the Mail app indicated that the mail app does not support MAPI and so it does not support the SendTo function. You can complain as much as you want and as many times as you want, but that was over 2 years ago and they still are not supporting it and will not.
The Mail app is not an email client program. It is webmail wrapped in a fancy wrapper. They told us years ago that they are not going to invest in any email program that does not have "revenue value". So they dumped Outlook Express and produced a hideous alternative with WLM and now they have this cruddy Mail app. But they aren't going to change.
steve