“Know thy customer” is a time-honored percept for success in the marketing world. The majority of marketers collect email addresses, but lack the additional data that can help you better communicate with those subscribers. Rapleaf helps you learn more about your customers. They provide demographic and lifestyle data (age, gender, marital status, income, etc., click here to see all) on US consumer email addresses. Is it worth the expense and effort? Short answer is yes.