Email Discovery and Compliance is a free eBook available for free (registration required) at the Windows IT Pro site, authored by Devin Ganger.
"Modern corporate messaging systems are no longer just about email. They also provide collaboration and an enterprise-wide repository of knowledge. Messaging data has become a vital asset for any organization. Within the past few years, a series of wide-reaching federal regulations have reshaped the corporate environment and focused unprecedented attention on the corporate messaging infrastructure and the data it carries. It seems that hardly a month goes by without another high-profile lawsuit demonstrating the critical importance of managing messaging data.
You know you need to manage your email data; how do you do it? What steps are you taking? What additional measures should you enact? What shouldn't you do? This ebook answers these questions and helps you get control of your vital messaging data. We assume that you have Microsoft Exchange."