In Forrester's 37-criteria evaluation of email marketing vendors, we identified the six significant providers in this category — Epsilon, ExactTarget, Experian CheetahMail, Responsys, StrongMail, and Yesmail Interactive — from a pool of 48, and researched, analyzed, and scored them. This report details our findings about how each vendor measures up and plots where they stand in relation to each other to help interactive marketers select the right partner for their email marketing efforts.