Hello,
As already mentioned in the previous reply to your post, this is by design in Backup Exec. For more information and suggestions, refer to the following technotes:
Title: Do the restore options "Restore Over Existing Files," "Skip if File Exists," or "Skip if Existing File is More Recent" have any affect when restoring Microsoft Exchange mailboxes?
http://support.veritas.com/docs/191920
Title: Upon completing a restore of an Exchange Mailbox, the mailbox has duplicate mail messages.
http://support.veritas.com/docs/237260
Hope this information helps. In case of any more doubts, do write back to the forum.
However if we do not receive your update within two business days, this post would be marked ‘assumed answered’ and would be moved to ‘answered questions’ pool.
Regards.