Test what delivers results by using A/B testing. This works best when isolating variables as much as possible and comparing the results. You can do this in any number of ways: Use email templates that have slight differences such as the first impression being feature-based or price-based. Email at different times of day / week / month to determine when is best for open rates. Different email frequency for different lists. HTML templates vs Rich Text templates. Pass off to sales team for direct communication at different engagement points.