Retailers have attracted more email subscribers but engagement has decreased over time. While the proportion of active subscribers increased 8% from 2013-2015, the proportion who last engaged over a year ago also increased 7%. Additionally, marketers continue to spend less on email despite its good ROI. While email provides a relatively cheap way to generate orders, marketers don't increase spending to maintain subscriber interest levels. Finally, factors inhibiting successful campaigns have shifted from resource limitations to issues with data quality and a lack of relevant, targeted content.