I recently had to lock down a Windows 2008R2 remote desktop server (terminal server)
One of the requirements was to show only some control panel items, a setting that can be achieved using the Group Policy setting "Show only specified Control Panel items" (under Policies > Administrative Templates > Control Panel), but that setting requires the applet's canonical name, like Microsoft.Mouse. All applets included with Windows have their own canonical names, found in this article
I couldn't find the mail icon's canonical name anywhere, and eventually found out that writing down the applet's filename - mlcfg32.cpl is enough.