To ensure an email is never sent to certain email addresses (say, addresses that have claimed you sent spam or otherwise complained), mark them as an excluded subscriber. If that address is marked as an excluded subscriber, it is another barrier to ensure they will never be emailed. This is especially useful when importing multiple lists that might have duplicates of one email address across several lists.
You can exclude subscribers by selecting the “Subscribers” tab, navigating to “Advanced Options” and selecting “Excluded Subscribers.”
You have the option to exclude either are a specific email address, any address that begins with a certain phrase, or an address that ends with a certain phrase. For example, if you wanted to make sure no one with a “@gmail.com” email address received anything from you, you would select “Ends with” from the drop down menu and type in that phrase.
Then, select which list or lists you would like this exclusion to apply to and click “Add.”
If you want to ensure this address is never added to any subscriber list, make sure you check every list before clicking “Add.” After clicking this button, you will be directed to the Exclusion List which shows all Email Matching Patterns you've designated (either specific email addresses, "Ends with" patterns or "Begins with" patterns, depending which options you've created from the drop down).
If you wish to undo the exclusion you’ve set, click “Delete Selected.” You will be asked if you’re sure you want to delete this exclusion before the deletion is finalized.