For a product in which we need a customer to upload a bulk mailing list, is there a way that the customer can download a template of what the mail list should look like?

You can give site users a template that they can download on the product page.  You would use Assets to do this (Sites > [site name] > Assets).  You would set up the Asset as follows:
 
  • Usage for = Product
  • Product = Product which needs to have the downloadable file
  • Customer can download = True
  • Location of asset = Upload Asset (Then upload the file in the Upload Asset field) or URL to Asset (Then set the location of the asset in the External URL field)
  • External URL - This field appears if "URL to Asset" is selected in the "Location of Asset" field.  Enter the external url of the asset.  It should begin with "http://" or "https://"
  • Generate a thumbnail for the external asset - This field appears if "URL to Asset is selected in the "Location of Asset" field.  Checking this box will cause the system to auto-generate a thumbnail preview for the external asset. 
  • Upload External Asset Image Preview - This field appears if "URL to Asset is selected in the "Location of Asset" field.  Upload an image file here to be used to represent the external asset.  The system will generate a thumbnail preview for the external asset using the file uploaded here.  Please note that the file must be in raster format (.jpg, .png, .gif).
  • Description -  Enter a description of the asset. 
 
This will add the downloadable file to the product page. 
 
For more details on Assets, please review this article: Ch. 058 Assets