Sounds like you'll want to check what delegates that one user has set up.

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Sue Mosher, Outlook MVP
Author of Configuring Microsoft Outlook 2003
http://www.turtleflock.com/olconfig/index.htm
and Microsoft Outlook Programming - Jumpstart for
Administrators, Power Users, and Developers
http://www.outlookcode.com/jumpstart.aspx
> When one of the users in my netwerk sends an invitation to other users, the
> acceptances of the this appointment are spread all over the network. All
> users in the network are overloaded with acceptances of the invitation. These
> users do not have anything to do with this appointment.