A subscriber unsubscribes. Will the subscriber be automatically unsubscribed?

Yes, a subscriber who uses the unsubscribe link in your newsletter to unsubscribe from a subsequent newsletter is automatically unsubscribed from your list of active subscribers.

In the overview of your subscribers (under Subscribers → View), you will no longer find this subscriber in the category of active subscribers, but in the category of unsubscribes.

You can only send newsletters to active subscribers.