I am developing an application that will be limited to users at colleges/universities, and I want to prevent non-university users from registering, to the extent possible. Since users have to provide a valid email address when registering, I could require them to use a ".edu" address (the user has to click a link in a confirmation email to complete registration).

The question is: do all colleges/universities in the United States issue ".edu" email addresses to their students and faculty members? I would settle for 99% or higher. But if only, say, 80% do, then I would not implement this requirement since I would lose too many potential users.

Thanks in advance.