Email marketing firm Silverpop, released study results about the efficacy of email campaigns. Silverpop took a look at emails that were sent during 2011 and the first quarter of 2012. The email messages analyzed were sent by Silverpop's clients, by over 1,100 different brands. They looked at several different types of email messages, including transactional messages, promotional emails, content-based newsletters, and notifications. The data that they found pertaining to click-through rates, open rates and unsusubscribe rates were very informative.