Currently, the ability to set an email when you sign up is optional (in game). I believe that when you sign up it should be mandatory. My reasoning behind this is simple. Account recovery. Without a set email, if you lose your password, you have to contact an admin causing unnecessary work that could easily be avoided.

edit:
After a quick chat I had, this might not work. However I have an alternative.

Add some sort of notification/box that says something along the lines of, "Setting your email is a good way of recovering your account in the case you lose your password."