I am using MAPI through CDO(Collaboration Data Objects)

I give the following piece of code to logOn to a MAPI session

THIS.oSession = CreateObject("MAPI.Session")
THIS.oSession.LogOn()

For logging off , I give the following
THIS.oSession.LogOff()

It takes a lot of time to log On as well as log Off.
Is there any way to improve performance?
Mapisp32.dll and Mdisp32.dll stay in memory for long time before finally unloading.