On campus, we use Microsoft Outlook for faculty/staff e-mail. Students can use the Outlook Web Access, or can set up any e-mail client (including things like mail on mobile devices like iPhones).
Some people want to use Outlook Express. That's fine, except that you have to be careful of the settings.
Outlook Express defaults to using POP3 e-mail. That's not uncommon and fine to use in most cases. But Outlook Express is a bit behind the times: the default is to move all e-mail from the server to your hard drive.
If you're not careful, all the mail in your inbox will move to your hard drive -- and be removed from the server. In the days before portable computing, fast connections, and cheap memory, this made sense. It was much more convenient to store your e-mail on your hard drive.
Nowadays, people want to keep e-mail on the server so it's available from anywhere. If you use Outlook Express with its default settings, your mail will no longer be on the server, and it isn't easy to restore it.
If you do want to use Outlook Express, check in the settings so that it leaves a copy of the message on the server. I'm not sure if that's part of the usual setup, so you may have to go into the settings and change it before connecting to the Internet.
We've seen several cases of people inadvertently deleting everything from the server. If you want, you can use Outlook Express (though there are better mail clients out there), but don't make that mistake.