Duplication of IMAP messages after power outage

On G4 mirror doors running OSX server we have several times experienced all users getting all their emails again as new unread mails in their imap mailboxes after server crashes, normally after power failures. This has happened ever since the server was installed it has run 10.2.3 and up to 10.2.8 clients use outlook express, mail.app amd entourage, it seems to affect all of them! any ideas? Kerry[/b]