The msexchange.org Web site s Software section contains a pretty good database of content management products, including links to vendor Web sites and product reviews.
Exmerge s documentation describes how it works, and what you can do with it, in more detail than I ve gone into here. Look for the Exmerge.doc file in the Support\Utils\I386\Exmerge\ directory of your Exchange product CD.
The Microsoft Developer Network (MSDN) Web site has a great deal of technical information on the workings of Exchange s event sink mechanism; see http://msdn.microsoft.com/library/en-us/cdosys/html/_cdosys_smtp_nntp_transport_event_sinks_with_cdo.asp .
Sue Mosher s Slipstick Systems Web site includes a page that describes content control and management solutions; see http://www.slipstick.com/addins/content_control.htm .