I like this blog post from lead sloth. It reminds me of the days I worked at Fairfax Media and News Corporation, sending out millions of email newsletters every month. I can say from experience that this article hits the mark. I saw open rates and click rates erode and flatten out when the business did not change anything in terms of its content – ie. the same old thing over and over again with no targeting.
As a result, I initiated a project at News Corp allowing users to customise the content in their email so that it was more relevant to them. By doing so, you not only encourage more engagement, but there is valuable targeting information you glean by looking at the content chosen by the user. The publisher would then truly be able to communicate one to one with that user not only in content but also in direct mesagging, and thus new advertising opportunities emerge.
This way both the publisher and reader wins.