I've got an odd one. I've got a single user that will start receiving 2 identical copies of emails. He's using Outlook 2000 via imap. A send/receive runs and double copies come in. When send/receive runs again a minute later, the copies go away. Looking in webmail only ever shows 1 copy of a mail.
I've got multiple users on Outlook 2000, but he's the only one reporting this issue. I think I solved it before by deleting the local mail account and recreating it. But the problem has crept back up recently. And I'd rather not have to recreate his account in Outlook every month or so.