You have to take a few hours of your life to analyze the ways you use email and determine what parts of your approach aren’t working, and then adjust some of your behaviors.
( Source: TidBITS | It’s Not Email That’s Broken, It’s You )
After trying the Mailbox app, and hoping it would be an email solution, I'm starting to agree with the article above. The app was great, for a week.
To me, it seems the process is too heavily focused on the receiver. It should be flipped to put the emphasis on the sender. If the sender wants the receiver to respond quicker, there should be an opportunity to learn how.
Folks like InBox Pro, are doing some cool things to restructure the way we use email. I think this is closer to the solution.