My email address is invalid help me fix this?

I am trying to register for a new site but when i fil out the application the only thing is my email is invalid and it wont let me register i have double checked and entered several different addresses in the registration form that are all coming back as invalid even though i know they are i have had this problem before on other computers i dont understand i was able to fix it by going to internet options before but i forgot how to could someone please tell me how i make websites accept my email address Thanks