Here is an interesting article from itmanagement.com explaining the top 5 benefits that come with a good email management solution:

For the individual user, email management usually refers to the process of moving messages from their inbox to the appropriate archive folder. If they make a mistake in that filing, it generally isn't a big deal. However, for business entities, managing email effectively can have a significant impact on their bottom line. Read on for five of the top email management benefits.

1. Increased Productivity

Take just one issue that email management addresses: spam. According to the National Technology Readiness Survey, an annual survey conducted by Center for Excellence in Service at the University of Maryland's Robert H. Smith School of Business and Rockbridge Association, the economic impact from time wasted deleting spam was estimated to be $21.6 billion in 2004. According to Iron Port, an email management vendor, there were roughly 86 billion spam messages per day in the month of November, 2006, up from 5 billion per day in June of 2006. Considering the huge economic impact in 2004 of a relatively smaller amount of spam, having an effective spam solution in place can greatly increase your business' productivity. And handling spam is only one part of what email management systems do.