Are you saying that you are receiving multiple instances of a message via
POP3 or you having problems sending? In either case, it sounds like you
might have an internet security related product that is scanning e-mail. I
would try disabling the e-mail scanning portion or uninstall/reinstall the
product w/out e-mail integration.
The other thing that can introduce duplicate messages is if you have 2 or
more accounts in Outlook defined that check the same mailbox.