I have a six month old Windows 7 computer, but have kept my old Windows XP PC in case of emergency and for playing the odd game that won't run on the newer operating system. I use Windows Live Mail on the Windows 7 machine, the XP PC runs Outlook Express.
When I boot up the XP PC, it downloads every email I've received since the last switch-on, even if I've already read and replied to them on the other machine. How do I arrange things so that Windows Live Mail becomes my primary email account, and messages aren't stored up to be downloaded by Outlook Express?
It looks as though the XP machine running Outlook Express has been set up to download email via POP3. This downloads messages to your PC, removing them from the mail server. If your computer isn't set up otherwise, this means any new messages that arrive while you're using the XP PC won't be available to your Windows 7 PC.
Your Windows 7 machine, meanwhile, is using IMAP, which leaves a copy of each message on the server. Whatever action you take with each message, for example read, reply or delete, is recorded on the server, so you will see exactly the same information on another PC accessing that account via IMAP. This makes IMAP very fast and allows you to seamlessly access your email from multiple machines.
To fix your problem, you should set up Outlook Express on your XP computer to download mail via IMAP. Check your mail provider's website for simple instructions on how to do so, the exact procedure can vary.