Exchange 2003 sending calendar messages to all instead of single recipient

We have a situaltion which I am not sure how to go about fixing.

We use Exchange 2003 and Outlook 2003.
When a person sets up a meeting in the Outlook calendar with one person required and sends the notice of meeting to that person, all people in the office get the notice. I know that it is probably something very simple but I can’t seem to locate it. Does anyone have any idea how to stop this?