A suppression list is a list that contains email addresses that you wish to permanently exclude from future emails. There is a couple of steps you need to do to create a suppression list. First, you have to upload the list that needs to be excluded from any further campaigns. Next, select all email addresses in that list and mark them as unsubscribed. You don’t have to worry about the duplicates, Sender.net recognizes them and does not double count it.