Want to geek out with me for a few minutes over some numbers? Ok, according to a 2014 study of 1.5 billion emails sent across all industries, the open rate (percentage of emails being opened) is around 23%, and the click-through rate (the percentage of emails that contain a link that is clicked on) is around 4%
Meanwhile, the response rate from direct mail (across all industries) is around 4%. This sounds like they come out about even, until you consider that direct mail campaigns cost more than email campaigns. How much more? A lot.