Definition of an Email Marked Spam
Because an email is marked as spam doesn't necessary mean that it is spam. And this doesn't mean that the email was of poor quality or sent to the wrong people. Sometimes people click or mark an email as spam by accident or for other reasons.
Any email address that marks an email we send out as spam, we remove that email address from our email list. Our philosophy is that if they don't want the email we don't want to keep sending it to them. This also make sure your email list is clean and prevents it from going into the spam folder with other email subscribers.