Email Marketing takes care of unsubscribes for you, automatically! But, sometimes people write to you instead of clicking the Unsubscribe button in your email. In that case, you are responsible for suppressing those contacts, out of your Subscribers list. But don't worry, Email Marketing makes that a snap!
How Do People Unsubscribe from Emails
Can I Block Someone without Them Unsubscribing?
Using the Display Names Feature to Give Unsubscribers List Options