Export failed, how to avoid duplicate mail

Hello

I am in the process of exporting back archives to users mailboxes, but one of the users just faild exporting the mail. I got the error "Processing aborted due to an unrecoverable error.". This has happened to me before, so I guess it is something that just happens once in a while.

The issue at hand is that it managed to export 18000 e-mails before it failed, how do I avoid exporting these 18k e-mails back when I try to export it again? I really dont want the user to have duplicates of 18k mails.

Regards

Anders Helgesplass