Email On Acid concentrates 100% on email marketing. Basic subscription offers you every feature in the (unlimited) email and spam testing list and a few extras such as use of the email inspiration library and the email optimizer tool. The All Access subscription adds advanced email analytics to the Basic package. Advanced options include open and click tracking, Mozify, heat mapping, geolocation reports and many other top features. Whatever the subscription (and rates are very reasonable), the monthly fee remains fixed forever.