To opt-out your contacts from your campaigns, firstly go to admin, then 'Activity' and click the 'Opt-Outs' tab.
Then, click the 'Add Opt Out' button
That will then take you to this screen, where you should paste in the domains or the email addresses you wish to opt-out, making sure they are separated by one per line, or with a semicolon.
After completing these steps, the opted contacts will be displayed with a red strike through them.
Another way to add opt-outs by either entering the email addresses into the Email Addresses box. Also, you can opt contacts out in bulk by entering all the contacts into an Excel spreadsheet and then import them all into the Email addresses box.