It's from a knowledge base article No 284404 (Can't paste in the link).
When you log on to Outlook 2002 by using a profile that contains two Post Office Protocol (POP3) accounts, you may be prompted to provide a password for one of the accounts, and you may receive duplicate e-mail messages from the accounts.
This behavior can occur if your Outlook profile contains two Internet accounts that both point to the same POP3 server.
To resolve this issue, turn off e-mail reception for one of the POP3 accounts:
In Outlook, on the Tools menu, point to Send/Receive Settings, and then click Define Send/Receive Groups.
Double-click the group that contains the two POP3 accounts, and under Accounts, click one of the POP3 accounts.
Click to clear the Receive mail items check box.