What is the difference between multivariate testing and A/B testing?
With A/B testing you create different versions of your email and send each version to a different sample of your database. Then you analyze which version was the most successful in terms of conversion and send this best version to the remaining recipients. With multivariate testing you can test different placements in your email and see which combination of elements is the most successful. With AB testing the gain is smaller than with multivariate testing simply because multivariate testing allows you to generate a lot more variations of your email for less effort than traditional A/B testing.