In my list of defaults I have assigned mine for email. I have many applications and would like to know which ones might require an email assignment. I keep on getting an error message requesting an assignment several times a day. But it does not indicate which app needs the assignment.
What's the name of the programs/apps you see the problem in? There's quite a few that may support that, usually in a Sent To item on a drop-down menu. It the programs were installed before an E-Mail Client it probably wasn't made known to those programs, especially if they are third-party [not Microsoft]. A lot of programs will 'read' what is installed during their setup process.