This is a very quick way to get banned from Mailchimp. If you import addresses, you'd damn well better make sure they want to receive your emails. Mailchimp has zero tolerance.
To OP - first thing you've got to do is to make sure your lists are clean. I mean, actually verify every. single. address.
Tons of bounces are going to get you flagged in a New York minute by any email service provider. You want your mail blasts to be like smart bombs... not carpet bombs.
Once you've cleaned your list you can start looking at ESPs... I can 95% guarantee you're going to get banned by anyone you use sooner or later since you are using stolen emails. However, sign up for several providers & rotate. That number of addresses isn't going to be cheap - so if you aren't willing to invest some $$$, you may be best to sell them.