Using 8.03

If I send an appt. to an outside user who has Outlook, they receive and all is well. If I cancel the appt., it removes from my calendar, as well as other internal GW users, but not from the outside user(s).

If I send an appt. from Outlook into GW, then cancel, it removes OK from GW calendar.

Is there any way this can work from GW to Outlook?