Message tracking providing you have it turned on.
Ok not much help if you need to get stats on something a user has
already sent, but the following might be useful to look at implementing
for the future.....
"SQL Server 2000 Report Pack for Microsoft Exchange"
The SQL Server 2000 Report Pack for Microsoft Exchange is a set of 13
Microsoft SQL Server 2000 Reporting Services reports that work with a
Microsoft Exchange sample reporting database.

With the Report Pack, you have the choice of using the sample reports
either as-is or as templates for designing new reports using the SQL
Server Reporting Services Report Designer.

This Report Pack includes the following reports:
Current - All Mailboxes (By Folder)
Shows folder statistics over all folders. Tip: Be on the lookout for
especially large mailboxes.
Current - Folder Tree Sizes (By User)
Shows the folder tree and size of items contained within each folder of
a specific user's folder. Drill down for breakdown. Tip: Find the
largest folders and the largest items so you can free up space.
Folder Tree Sizes (All)
Shows the folder tree and size of items contained within each folder
for all user's folders since the last extraction. Drill down for
breakdown. Tip: Find the largest folders and the largest items so you
can free up space.
Outgoing - Sent E-mails for User (Plain Table)
Compares the number of items found in users' Sent Items box. Tip: The
highest send the most e-mail, which often correlates to the hardest
workers.
Outgoing Sent E-mails for User (With Graph)
Compares the number of items found in users' Sent Items box. Tip: The
highest send the most email, which often correlates to the hardest
workers.
Outgoing Sent E-mails for User (With Bar Chart)
Compares the number of items found in users' Sent Items box. Drill down
for breakdown. Tip: The highest send the most email, which often
correlates to the hardest workers.
Outgoing - Busy Receivers of Our E-mail
The top 50 people who were sent email from members of our organization.

Incoming - Received E-mails for User (By Date)
Compares the number of items found in users' Sent Items box. Drill down
for breakdown. Tip: The highest receive the most e-mail, they probably
stress out the most.
Incoming - Busy Receivers of Incoming E-mail
Shows how many emails were received into peoples' inbox.
Outgoing - By Keyword
Examines the content of mail items to indicate which key phrases are
being used by employees based on items in their Sent Items folders.
Tip: Configure with your product names to see the e-mail activity by
product.
Outgoing - Largest E-mail Senders
Shows the people who sent e-mail with the largest sizes.
Extraction Log (All Records)
Shows all of the Extraction Log records, including time to extract data
from Exchange and store to the database for each user.
Extraction Log (Last Extraction)
Shows the Extraction Log records for the most recent extraction,
including time to extract data from Exchange and store to the database
for each user.

http://www.microsoft.com/downloads/details.aspx?FamilyId=108C2B01-2CC9-4A84-A669
-EB22533FA5E2&displaylang=en

The Quest message stats is a cool tool also.