From Mercury Systems summary:

Do you know how many messages your organization sends each day, week or month using Microsoft Exchange e-mail ? Can you measure the cost of system messages like directory replication?

Your Microsoft Exchange e-mail service does not provide you with any analysis or report. You cannot analyze the utilization of your electronic mail, measure the flow of traffic, nor establish an internal cost of utilization.

Where I work, there is a struggle going on about email centralization vs distribution. Unfortunately, we can guess that a large majority of email (say 90%) is internal, that there are high morning peaks, .... but we have no hard figures. If we had this tool, we could have hard figures for our decision making. We are moving from ccMail.

If your organization uses Exchange, strongly consider getting and maintaining traffic data.

Related tip:

Disable Exchange server DNS Reverse Lookups

Microsoft's Notes from the Field are excellent.