As far as I know you need to have a valid adress in every email and you should get permission (with time-stamp and IP to be sure) to send the mail aswell as add an unsubscribe-link in every email you send. To be sure that you get permission and that it's not some moron adding his ex to 5 gazillion newsletters, make sure that you use double opt-in, that is: when someone opts in to your list, you send him a confirmation email. If he signed up with a time-stamp and confirmed the link, he wants your emails. And if he doesn't want them anymore he'll just click the unsubscribe link. Just keep a valid adress in your emails and you should do fine.
