Email marketing has become a popular and cost-effective method for reaching prospects and generating revenue. Like any marketing expense, it is important to understand the return that you are making with such an investment. Ideally, you want to be generating a return on investment that exceeds the performance you could achieve by using those expense dollars in other areas of the company or investing them. To measure ROI, you need to carefully track your response and conversion rates so that you know which sales can be tracked back to a particular campaign.