Multiple emails - when CC'd

[Jason]

I have a customer who, who has 5 PC's on their network - they are using Exchange 2003 Small Business and Outlook 2000 clients. Whenever an external mail sender sends and email anc copys 2 or more people each person will recieve more than 1 email. e.g. an email is sent to 3 people, each person will receive 3 copies of that mail

Any Ideas

Your help is greatly appreciated