Probably the permissions are set too loosely in Active Directory.

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Sue Mosher, Outlook MVP
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Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers
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>I Cannot prevent Outlook 2003 users on Exchange 2003 from viewing other
>users
> calendar. I set the permissions to none on those calendars but these users
> can still view and even make changes. What am I missing on the exchange
> server to make this work as intended?