"One thing I do remember saying about Outlook 2000 is that you should never install Outlook 2000 on a server running Exchange 2000. By design, Outlook 2000 and Exchange 2000 on the same computer is not supported, and will break things."
However, according to Microsoft, when a developer needs to develop CDO-related application for MS Exchange 2000, CDO 1.2.1 must be installed on the Exchange server, and the only way to install it is to install MS Outlook. Do you still remember what problem might rise when Outlook 2000 is installed on Exchange 2000?
The key here is the version of Outlook. Outlook 2000 definitely should never be installed on your Exchange 2000 Server. For one, the MAPI DLLs get overwritten with the wrong version and that breaks things in unpredictable ways.
But Outlook 2000 is not the only way to get CDO 1.2.1 installed. In fact, the CDO 1.2.1 DLL is installed and registered by default on computers running Exchange 2000. You can find this documented here.
This was first published in February 2002