About Other Handlers

A handler is any COM object that exposes (implements) the IExchangeEventHandler interface and advertises (is registered under) the COM category CATID_ExchangeEventSink.

Other types of handlers could include those that can run Microsoft Visual Basic version 5.0 programs, JavaScript, Java VM code, and C++ code in addition to JScript or VBScript provided by Microsoft. Handlers can currently only be authored in C/C++.
The mechanism for processing folder events with custom handlers is similar to that used with the Microsoft Exchange Scripting Handler, as shown in the following diagram.