Email is by far the best-converting channel in ecommerce, with an average conversion rate of 3.6%.
This is miles ahead of Google Adwords (1.75%) and Facebook Ads (1.42%).
And the ROI is incredible. For every dollar you invest in Email Marketing you get $38 in return. Top performers report an ROI of over 70:1.
More in this article: http://blog.compass.co/a-quick-guide-to-email-marketing-for-ecommerce/