Even in the XP Mode, the security issues are still there. Your user, even though he doesn't want to, really needs to change. I know its hard for some to let go of something they are comfortable with but its time to change. I used to manage a large network and many users felt the same way when there was an update or new program - they wanted their old comfortable programs, but after the "learning period" they were happy with it and didn't want to go back.
One alternative, which is not a major shock would be to find a (legal) copy of Office 2003 Professional, that has Outlook. Outlook 2003, which is very similar to Outlook Express, works under Win 7 and Win 8. Most of Office 2003 is not really supported anymore but I still get security updates for Outlook 2003. http://www.evaluesoftware.com/index....FQGvnQodHxAAAA