Firstly, we remove duplicates for every campaign you send, so if a recipient is subscribed to multiple lists and you send a campaign to all of those lists, they will only ever receive one copy of your email.
What about unsubscribes? If you send a campaign to multiple lists, and an individual is subscribed to more than one of those lists, they will be removed from each list if they unsubscribe from the campaign.
If you send a campaign to a single list, and an individual is subscribed to multiple lists, they will only be removed from the list you sent to. They will remain in the other subscriber lists until they unsubscribe from a campaign sent to that list. This ensures your subscribers can join different types of lists, unsubscribe from one but still receive from the other.
Also, when you upload subscribers into an existing list, all bounced and unsubscribed recipients WILL NOT be added to the list. We remember everyone that ever unsubscribed. The only way an unsubscribed individual can get back into your list is to subscribe again from your web site or if you manually change their status.