Stop Outlook Express from Showing Duplicate Hotmail Messages
The problem is related to selecting Hotmail as your default account and setting Outlook Express to get mail automatically when starting.
The best thing to do is to configure Outlook Express to not download automatically. This will prevent the duplicates. Here's how:
Open Outlook Express, click the Tools menu and click Options.
Click the General tab in the Options dialog box. Remove the checkmark from the Send and
receive messages at startup checkbox.
Click Apply and then click OK.
Close Outlook Express and open it again.
No more duplicates!