The document discusses the role of email within an inbound marketing strategy and provides key metrics for measuring email marketing effectiveness. It begins by listing facts about email marketing ROI and engagement. It then outlines key elements of an effective email, such as having a specific goal, segmenting lists, and testing. The document also describes different types of emails like newsletters, stand-alone, and transactional emails. It concludes by defining important email marketing metrics to track, including open rates, click-through rates, bounce rates, and conversion rates.