Sometimes a contact may request that you unsubscribe them from future emails, or perhaps you no longer want to email a contact going forward. Here's how you can complete this --
From the Contact List View:
Select the checkbox to the left of one or more contact's names.
Click the Actions dropdown > show more > Unsubscribe Contacts.
Confirm the unsubscribe in the modal box that appears.
From a Contact Record:
Click the Actions dropdown > Unsubscribe Contact.