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Duplicate Messages in Outlook 2002
Outlook downloads messages from a Post Office Protocol 3 (POP3) server again, after it empties the Deleted Items folder--even if you have both the "Leave a copy of messages on the server" and the "Remove from server when deleted from Deleted Items" options enabled on the POP3 account.
This problem occurs because a background synchronization took place at the same time, or just after the "Deleted Items" folder was emptied. This is an issue with the order in which Outlook carries out the deletion from the server and the downloading of messages.
Unfortunately there is not an available workaround for this problem, other than not to begin a synchronization at the same time that the "Deleted Items" folder is emptied. This issue does not result in data loss (other than messages that you instructed Outlook to delete). The duplicate messages will simply need to be deleted manually.