Duplicate mails in Outlook 2007

You may be receiving duplicate mails because of two accounts created in Microsoft Outlook 2007 that are pointing to the same POP3 server. I have searched and found a few steps to resolve your issue. I suggest that you follow the steps provided below:

1. Launch Microsoft Office Outlook 2007.
2. On the “Tools” menu, point to “Send/Receive” and then point to “Send/Receive Settings”.
3. Click on “Define Send/Receive Groups.” 
4. Double-click the group that contains the two POP3 accounts, and under “Accounts”, click one of the POP3 accounts.
5. Click to clear the “Receive mail items” check box.

If the issue persists, I suggest that you contact your Internet Service Provider since they would be your first point of contact in resolving the issue.