A question every salesperson asks. Experian did a study of email marketing in 2012, and came up with some interesting gems:
Users are active at night with almost 22% open rates between 8-12pm and 18% from 12-4am (must be more insomniacs than we thought!)
Saturday and Sunday open rates are close to 18%, most likely due to people having more free time and a a lack of competition.
I'm trying out some new techniques around promoting my book, and my lesson so far is this: Experiment. Most email programs enable you to track open and click-thru rates, so watch these closely and compare results. When you find something that works, stick with it and share it with your fellow sales pros!