A Microsoft guide about how to deploy Exchange 2000 Server clusters said that Exchange 2000 clusters require the Microsoft Distributed Transaction Coordinator (MS DTC) service. Exchange doesn't seem to use any MS DTC functionality, so why is MS DTC required?

Exchange 2000 doesn't use MS DTC. However, Exchange 2000's Collaboration Data Objects (CDO) workflow sink (cdowfevt.dll) requires COM+ when it runs on cluster nodes. COM+, in turn, requires that MS DTC be installed and running. Ergo, installing Exchange 2000 on a cluster requires you to install MS DTC.

The Exchange 2000 installer doesn't install MS DTC for you or even clearly tell you that MS DTC is required for clusters. Instead, you receive an installation log message that states regsvr32 couldn't register cdofwevt.dll. To install MS DTC, run the comclust.exe installer before attempting to install Exchange 2000 on a cluster node.