Duplicate email message in Note book

Since I hook my Notebook into the network domain in my office, all the problems came out. I’m using PCMCIA network card to connect my Notebook to the LAN.

The problems is when I’m using Outlook Express 5.0 to retrieve my email, it always keep receiving the same email. (until 5-8 copies). WE do not have an Exchange server.
Pls help me to solve this!