If it prints other documents, then you know it's working. You didn't say what email client you're using, but have you gone into the settings of the program and designated a printer to use for printing email.
Then it either isn't installed or the printer is faulty. Is this a known working printer? Did you install the proper drivers for it? Try looking in Control Panel / Printers and faxes and see if it's listed. If you see it, right click it and see if you can print a test page to see if it's working.
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