stlsailor,

As stated before, your not migrating away from your current system. So backing up the data from your server to re-import to the same server will cause duplicates.

To help remove the duplicates, you can perform a full mailbox export removing everything from the server and importing it again with Do Not Import Duplicates checked. In an Exchange platform 2003 or higher, all duplicated messages should not be imported back to the server. This also has been tested using standard pop services.

Hope this helps.