If both the bodytemplate and body fields are present, the body of the message will be included as normal, and the template will appear at the bottom of the email. If you specify a template, custom fields must be dealt with by your template, as they will not be included at the end of the email. The recipient of the email message generated by this gateway can be specified using any one of several methods. Recipients can also be specified via a 'mailto' field in the HTML form itself. This allows you to do fun things like using a single form to send mail to one of several email addresses.
Online help is available.