Hi,

if you're facing problem because the mail id which you put in during registration is been deleted permanently and you're not able to open it in any way possible then I would advice you to go for the optional mail id. As, these days at the time of registration two mail ids are asked just for the sake of safety. And if in case you don't have that mail id or that form didn't asked for an additional one then just write a mail to the university and explain them your situation they're always there to help you and they respond quickly.