I subscribe to a fantastic productivity site called Asian Efficiency. The stuff these guys come out with is superb. It's thanks to them and the work they have done that I have implemented the Pomodoro technique for work as well my morning routine which ensures I am as productive as I can be at the times I should be.
This link will take you to their guide on managing email and I encourage you to give it the once over. It's a superb guide and one that I implement almost fully on a daily basis. Remember, the stuff they post isn't meant to be a de facto "You must do this" set of rules, more guidelines for you to think about and implement to best suit your style of working.
Check them out.