A recent survey , as reported in MarketingVox found that email has a higher ROI than any other type of campaign according to the results  posted by Return Path, who conducted the survey.

Marketers use a wide variety of techniques to improve response in their retention and acquisition email programs, with varying results, according to a MarketingProfs survey, the results of which are analyzed (premium article) by Return Path, which also offers recommendations. Among respondents who measure their campaigns, 40 percent say email earns the highest ROI, followed by search (28 percent) and direct mail (18 percent). Revenue per campaign is the most-utilized email-marketing success metric, used by 39.8 percent; file size is a close second with 38.3 percent keeping tabs; and revenue per email third at 25.8 percent. Some 35 percent do not set clear success metrics.

All the more reason to get the email campaign optimized.