I have seen that already, there are sites that have two boxes when we are about to register and one of the box are optional for offers but if someone mistaken it and received emails, he can always disable it in the account setting of the gambling site his playing or he can also mark it as spam in the email provider that he was using.
Not sure if paradice.in do this but most newsletters have an unsubscribe link in the footer of the email in case you don't want to receive any more emails from them.
Although I agree with the replies above that forcing users to subscribe to their newsletter when they register with their emails is annoying but at least they wete transparent and didn't try to hide it. Many other casinos do it without asking for your permission or even mention it in the sign up pages.