I recently had the mail icon disappear in the Control Panel of a Vista 64bit machine and I had to setup an exchange account. This is how I found had to get to it.
Open the Control Panel and make sure you have it on Control Panel Home and not Classic View. Then click on the additional options.
When you get to Additional Options you will see the View 32-bit Control Panel, click on this then your mail icon will be available for you to use.
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