Michael Hyatt writes a very useful post: Taming Your E-Mail Inbox – based on suggestions in a book by David Allen – “Getting Things Done”.
The most unproductive thing you can do when it comes to e-mail is to read the same messages over and over again. This has the effect of doubling, tripling, or even quadrupling your workload. Instead, you should read each message once, then decide what to do with it. Read-decide. Read-decide. This is the pattern of effective e-mail processing. The goal is to end up with an empty inbox daily or, at the very least, every couple of days.