[jamesbrownuhh]

Already a largely solved problem. If you try enumerating email addresses by running through queries at Hotmail or Yahoo, for example, they'll shut the doors on you in a matter of seconds. Think you can just use thousands of IPs instead? Go for it - they trust 'new' and rarely-seen IP addresses even less, and bring up the shutters all the faster. It's not a new problem, and there's lots of best practice to learn from, for anyone who wants to do it right.