How can i ask users to put a email [after they register] mandatory

I have a plugin which author doesn't take him anymore but for my is usefull,this plugin allow to make a new account with oauth and openid from It's a game... all good until here but after they make new accounts from that game they doesn't have an email , just a name
My question is : If i give you the code can you tell me what I can do to him ? or there is any plugin that can ask mandatory for an email after they make the account ? I don't want users with an account on website without an email.
I hope I explain good.