Thanks sorry to disagree Camioneur even though you have never had a problem , Microsoft has and admit it is a known problem and have issued a hotfix. i.e
Duplicate e-mail messages are downloaded from a POP3 e-mail server account in Outlook 2003 .
http://support.microsoft.com/kb/885870
How to obtain the hotfix
This issue is fixed in the Outlook 2003 post-Service Pack 1 Hotfix Package that is dated September 13, 2004. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:
885243 (http://support.microsoft.com/kb/885243/ ) Description of the Outlook 2003 post-Service Pack 1 hotfix package: September 13, 2004
As for Windows 7 the RC1 does not have Windows Mail either. I am using it at present.