I just imported all my mail from Outlook Express but now all the received dates are set to today's date.
How can I maintain the original dates?
Instead of using the Import feature of Outlook you can use the Export feature from within Outlook Express. The same is true for Windows Mail and Windows Live Mail. This will keep all your dates intact.
For step-by-step instructions see Migrate from Outlook Express or Windows (Live) Mail to Outlook.
Don't use the Import feature of Outlook to import from OE, WM or WLM.