Doubled emails in Outlook is a known bug in Outlook. This bug usually happens up after you've left too much POP mail on our servers for Outlook to handle successfully. The Microsoft explaination and possible fix is here:
There are three possible solutions:
- Follow the Microsoft instructions in the link above and ensure that you have the latest updates and services packs that Microsoft recommends.
- Stop leaving a copy of your email on the server.
- Convert your account from POP to IMAP as IMAP is a big improvement over POP when using more than one computer to check your email.