Small home network

I have a small home network consiting of a server running 2003 and laptop and
a desktop.
After so called setting up from the supplier!! I also run exchange to handle
my email.
the problem I have is that all email gets sent to every pc which i dont want
as each is only suppose to recieve the mail for that perticular user.
E.g. Laptop for Jasons mail\ and desktop for Lindas mail.
Please help