Journaling in MS Exchange

Journaling is the ability to record all communications in an organization. E-mail communications are one of many different communication mechanisms that you may be required to journal. Therefore, journaling in Exchange has been developed to enable the messaging administrator to feed messaging data into a larger journaling solution, while using minimum overhead.

http://www.microsoft.com/technet/prodtechnol/exchange/2003/library/journaling.mspx

How to Enable the "Message Journaling" Function for an Exchange Server Mailbox Store

http://support.microsoft.com/default.aspx?scid=kb;en-us;261173&Product=exch2k

Selective for MS Exchange 2000/2003