No regexp in the world will tell you if an email address is real.

Of course - I doubt anyone (smart) has ever claimed that to be the case.

However, they can, if implemented correctly, tell you if the email address is syntactically valid.

Why check it's an email at all if you're just going to presume it works?

Think about the repercussions of not using a validation email. Anyone can sign anyone else up. That's even more unacceptable IMHO.

How many emails to asdasdasd@example.com or sdfsdf@gmail.com are you willing to pay for (the nickels add up)? What if someone uses my email address to sign up for your service?