Returns the number of objects selected in the active window. Selections can only be made in windows that display containers.
See IExchExtCallback : IUnknown.
HRESULT GetSelectionCount(
ULONG FAR * lpceid
);
The IExchExtCallback::GetSelectionCount method is used to return the number of objects selected in the active window. The window is determined by the context in which the extension object is installed.