Did you check to see if they have a web interface? That's really going to be the easiest way to deal with this, if it's available.
If it isn't, choose Tools |Send/Receive | Send/Receive Settings | Define Send/Receive Groups. Click Edit to edit the All Accounts group. Under Folder Options, choose Download Headers Only. Click OK to save the settings.
Next, you'll press F9 to do a send/receive. This should download just the headers. Delete the one you don't want, and mark the ones you do want to read by right-clicking them and choosing to download each message. Then do F9 again. If this clears the bad message and downloads the good ones, you can go back into the Send/Receive group and make it download the full message again.
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Sue Mosher, Outlook MVP
Author of Microsoft Outlook Programming: Jumpstart
for Administrators, Power Users, and Developers