help needed for e-mail varification from my specific domain

i need a suggestion from u

i want when a user puts his/her e-mail address on the registration form, the must use an e-mail of a particular domain

(i.e. user1@diu.edu.bd
user2@diu.edu.bd
user3@diu.edu.bd )

otherwise any normal user (who don't have an e-mail id on -> diu.edu.bd) cannot not get registered  in my social website.

can it be done ? i thinks it is.

would u plz tell me how can i make it.

thank U
-Omar Sayem