If you are at least a little familiar with concepts of organization and productivity, you should know the term Inbox Zero. If not, I'll give you the basics: after drinking from the source of the book Getting Things Done (GTD, or The Art of Making It Happen), by David Allen, Merlin Mann created the philosophy of keeping your email inbox clean, to the point that there is nothing stressful about it.
This explanation is simple, but the intention is quite noble and works for those who manage to implement it. However, practicing the ideas may not be as easy as understanding the theory.
Fortunately, today there are many email clients whose rich resources make life easier for users, but there are times when even they cannot cope with the high demand of some people. If you handle a lot of emails or would like to boost your productivity even more, get to know the CleanEmail.