Outlook 2000 Loads New and Old Emails

I have outlook 2000 and a recent problem has developed. My email is routed through an email server run by one of my business partners. The server is an OS X server. He has done everything that has solved previous problems (i.e. rejected passwords by re-creating accounts, etc). But this time I have encountered a new problem. I have my account set to download the emails from the server and then promptly delete them from the server. Now, whenever my computer checks my mail…it downloads all previously downloaded emails again. My account on the server has been rebuilt and the entire server itself has also been rebuilt. This problem only exists on my computer at work as this problem does not exist on my home computer using the same account settings. Is there a problem w/ my computer or email client? How do I fix this?