Go in to Exchange administrator and go in to the Connections and Internet mail connection.
Under DELIVERY RESTRICTIONS. Click on list in Reject messages and modify. Then add the users there. They will not be able to use the IMC after you restart the MTA and IMC services.

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P933, 133MHZ FSB, 256M RDRAM
Ultra 160, 18.2GB Cheetah
Gladiac 920, SBLIVE, DVD, FPS SOUND
MS Force Feedback, Cable Modem.
AKA- The ultimate gaming machine.