Error : Receive Duplicate Messages When You Download E-Mail from the Server in Outlook Express

Cause:

'Leave messages on server? is checked in account settings of Outlook Express.
This behavior can occur if the Pop3uidl.dbx file is damaged.
Solution:
SUMMARY
To resolve this behavior, rename the Pop3uidl.dbx file, and then restart Outlook Express. Follow these steps:
Close Outlook Express.
Click Start-> Search and then click For Files or Folders.
In the Search for files or folders named box, type Pop3uidl.dbx, and then click Search Now.
Under Search Results, right-click the Pop3uidl.dbx file, and then click Rename.
Type Pop3uidl.old, and then press ENTER.
Restart Outlook Express