What happens when someone unsubscribes?
If one of your subscribers decides to stop receiving your messages, when they unsubscribe they would be removing themselves from your entire mailing list. This means that if a subscriber unsubscribes from a broadcast message sent to them, that subscriber also would not receive any messages from your mailing list going forward, including Campaign messages.
Can someone unsubscribe from all of my lists?
If you have multiple lists in your account, a subscriber could be subscribed to multiple lists. If a subscriber decides to stop receiving your messages and unsubscribe, they are presented with your unsubscribe page that will show all lists they're subscribed to. The subscriber will have the option to remove themselves from one, multiple, or all of your lists by selecting the radio button for each respective list and saving their settings.
What if someone unsubscribes from one list but not another?
If someone unsubscribes from your mailing list, then they will receive no further messages from that list; however, their subscriber status would not be impacted on any other lists they're subscribed to. This means that if someone unsubscribes from one of your lists, but still wished to remain on another, they will still be able to receive your messages from the list they're subscribed to.