mail server continuously downloads mail

Hi,
My client uses a local dial up account to access e-mail. Whenever he logs on to download his mail using Outlook Express the local ISP mail server starts downloading around 50 e-mails from people and sources he does not know. When he logs into his e-mail server through a web based retrieval site that the ISP told him to use it shows the folder is empty. There are no viruses,I ran scan with updated defs. I emptied all temp and temp int folders along with history, recent, cookies. I checked the add remove programs for any spyware or other programs I recognized as bad. There was nothing I did not recognize as known safe.
Any thoughts???