The QueryRelease method does any cleanup that is necessary before the Microsoft Exchange Client unloads the custom action DLL from memory.
HRESULT QueryRelease(
VOID
);
None.
Return NOERROR if the command completes successfully; otherwise return E_FAIL. Note that the Microsoft Exchange Client will unload the custom action DLL from memory regardless of the return value.
The Microsoft Exchange Client invokes this method so the custom action DLL can release any memory or perform any other housekeeping chores before the DLL is unloaded from memory.