Sometimes people forget that they signed up for your list. If someone accuses you of spamming (sending unsolicited email), and you put them on your list with their permission, you can pull up their subscription date and time, as well as the IP address from which they signed up. This information will determine if they joined your list voluntarily.
Click on 'List' in the primary menu. From 'View/Find Members' click the 'Find' tab. Enter the person's email address exactly, or search for their account using other information you've collected about them.
Once you've located their account, click 'View Details.' Then copy and paste the 'Creator' and 'Date Created' details into your reply to them. Finally, select 'Unsubscribe' so they do not receive any more campaigns.
Please note that if you are indeed spamming (i.e., if you are signing up members without their explicit consent), you are violating the terms and conditions of this service. Such situations will be dealt with as per the License Agreement for this service.