Hi JulieCRC,
Base on my knowledge , you can achieve your goal with exchange audit feature, or viewing Mailbox Resources in Exchange Server.
Here are some KB article for your reference
How to monitor mailbox access by auditing or by viewing Mailbox Resources in Exchange Server
http://support.microsoft.com/kb/867640
White Paper: Configuration and Mailbox Access Auditing for Exchange 2007 Organizations
http://technet.microsoft.com/en-us/library/ee331009(EXCHG.80).aspx
This post appears to be related to Exchange. For peer experience and suggestions, you may wish to post to the Exchange Server Forum . This will provide access
to others who read the public newsgroups regularly who will either share their knowledge.
http://social.technet.microsoft.com/Forums/en/category/exchangeserver/
Thanks.
Tiger Li