I'm having the same problem
I'm having the same problem. I know it's not spam (in my case, at least) because the messages are coming from friends who swear that they sent their email only once. It's just 2 emails in particular. None of the repeat emails have come from strange email addresses.
I have SpamDetective which lets me delete spam before I download it and I use Outlook after first checking my email with SpamDetective. I have Norton Antivirus and I ran a full scan yesterday, and it picked up a couple of viruses in my SpamDetective trash list (in spam emails that I never downloaded).
Norton deleted the emails from my trash list, but today I'm still having the same problem. I received multiple copies of the same exact 2 emails once again!
It's really making me crazy! It's so frustrating!