By default, the suppression list will store anyone who meets the following criteria: they unsubscribe, hard bounce, someone marks your emails as spam, or soft bounces for multiple campaigns. To ensure these individuals are never emailed again, the email addresses in your suppression list will not be added to any of your subscribers lists.
Each client in your account has their own suppression list, which you can access at any time from the Manage Subscribers tab, pictured below:
Once you access your suppression list, you can easily add and remove addresses you'd like to be included. Here's the main screen for a suppression list:
If you need to import someone who is on the suppression list (and you have their explicit permission to do so) you can easily remove them from the suppression list. Simply view the list, find the email and use the checkbox to select them. Then hit the 'remove selected' button.
While all of your lists add any unsubscribes to the suppression list by default, you can turn this on or off on a list-by-list basis. If you'd like to ensure a particular subscriber list does not scrub any new subscribers against the suppression list or update it with any unsubscribes, head into the "Unsubscribe Options" for that list:
You'll now notice a setting at the top of Unsubscribe Options that lets you set how any unsubscribes are handled. If you'd like to ensure this list never uses the suppression list, select "Only unsubscribe from this list". If you'd like any unsubscribes to be added to the suppression list, which we recommend, select "Unsubscribe them from all this client's lists".
You can change this setting at any time. If you decide to change your subscriber list so that it hooks into the suppression list, you'll be given the option to make updates to both lists.
These options allow you to instantly add anyone who previously unsubscribed from that list to the suppression list. You'll also have the option to scrub all of the active subscribers in that list against the suppression list.