In GroupWise 2014 R2, enabling compatibility mode breaks the login page
Press Win + R and type gpedit.msc to load the Group Policy Editor
Navigate on the left pane and expand to Computer Configuration | Administrative Templates | Windows Components | Internet Explorer | Compatibility View
Right-click Use Policy List of Internet Explorer 7 sites and click edit
Change to Enabled and click the Show button
Add the sub domain that should run in compatibility mode
EG: If mail.site.com is added regularly through IE, all sites that have the domain site.com would be added to compatibility mode. With the steps above, mail.site.com can be added and only sites that contain that subdomain will be added to compatibility.
After all domains that need compatibility mode are added, launch a command prompt and type gpupdate /force