I might be wrong, but I don't think there is a way. The closest thing you can do (im hoping this applies to what you are doing) is send an e-mail to the address with an activation code or something, then the user will have to enter their real e-mail address if they actually want to use whatever service it is you are offering.
What exactly do you mean valid address? Do you mean does it appear to be correct according to a set of rules you create? Or do you mean does it actually exist on the email server? They are two different things.