PHP/MYSQL change to registration system

I run [login to view URL], a free college classifieds. I need to change our registration system. Currently: anyone can register. When they register, an email is sent to them. They check their email and click a link to validate their account. I want to change it so that only school emails that end in .edu extension will be accepted. So if a user registers [login to view URL] email, they get the normal email validation. But if a user enters a NON .edu email, like yahoo or hotmail, it will be put into a queue for admin (me) to approve. See the image below in my attachment. Also, once a user registers a .edu email and they change their email to a free email, then their school (.edu) email must stay in the database. (currently if a user changes their .edu email, the .edu email is erased from the database). This is pretty simple and easy.