What Is a Contact's Quality and How Is It Measured?
You might notice the attribute Quality listed in your contact list. In this column, you'll see each contact has a number of stars selected, between 0 and 5. This is a measurement of your contact's engagement with your mailings. The more a contact engages with your emails, the more stars they will receive. Engagement includes opens, clicks, conversions and the total number of campaigns received.
An active contact with zero stars hasn't received any mailings yet and hasn't had a chance to carry out any possible activites. All receipients that have received at least one mailing automatically receive one star.
You can find more details about individual contact activity at their profile page. To get to this, simply select their name from the contact list.