If you are doing a validation email, then there is no need to check anything. Either they give a proper email address and get the validation link, or they do not give a proper address and do not get a validation link.
var x = document.forms.email.value;
var filter = /^([a-zA-Z0-9_\.\-])+\@(csu.fullerton.edu)$/;
if (filter.test(x)) alert('YES! Correct email address');
else alert('NO! Incorrect email address');
This code only checks the address. It does not pass on the string if it is valid. There are tons of code samples for form validation, so you should have no problem finding something that works. On the server side, you will just need something to generate the validation email, and then a form that recognizes when a validation link has been clicked. Is it the back-end mechanism that you are asking about?