I just got my new weekly chart from Marketing Sherpa, and saw proof that email open rates have been declining rapidly for the past few years. Many technical / analytical marketers have known this for a while, but it is always great to have objective data to back it up. The chart is pretty clear. But there are actually two major factors driving the data. First, there are some trends about email as a medium that work to lower open rates in general. Second, changes in technology are making it more and more difficult to get reliable open rate data.