That's a great question! The good news is our system is designed to automatically remove any unsubscribes from any lists in your account. They are also recognized and will not be re-added in any new upload. Instead you will be given the option to view and download a list of unsubscribed contacts that were attempted to be re-added through your upload. For more information, we also have this article in our Help Center that helps go over what happens when a contact unsubscribes.