We have found that Internet Explorer Versions 7 and 8 have compatibility viewing issues with our webmail client. 

Microsoft's article on compatablity view

If you are using Internet Explorer 8 you can change the compatibility view 
(Tools -> Compatibility View) this should clear up the problem. There is no compatibility mode in Internet Explorer 7, however; you can use our "Lite Web Client" and that will allow you to view your email. Other options are to download and run a different browser: 

Google Chrome | Mozilla Firefox