Josh Nason writes a concise 5-pointer on what you should do if you feel your email results are diminishing.
My sixth point to add to this list is this… The bottom line is that email marketing is always evolving. If you don’t believe me, then you are doing it wrong, and possibly out of date. There are always new things to think of – be it social media integration, mobile-readiness, conversions, tracking, etc. So, keep up to date with technology by researching constantly.