According to the research firm IceGroup, since 1996 the daily volume of employee email has tripled. According to the firm, the average email user now receives between 25 and 50 email messages per day. They project an increase to over 100 emails per day on average within two years. Actually the numbers in this study are a little bit lower than some we've seen in other studies such as the Pitney Bowes study on business communication. Nevertheless, it points up a rising problem in many companies.
Email is so easy to use in most environments that two things happen.
First, nobody gets trained in email. Second, they start sending lots and lots and lots of it. If you haven't done so, consider a basic email tutorial as something that everyone needs to review. It doesn't need to be elaborate. I've developed a simple tutorial that can be accessed with a browser that covers the basics.