The best thing is, if you could send them with your server.. just send them once with free offers, such as ebooks according to the list type. Send them to other legit email services, such as aweber with ur own opt-in page. Just send those list only once and see what's the bounce rate, open rates, and clickrates are. After that not many will re-opt in to ur other mailing list, but it'll be 95% legit.