code: public MailRequest newHtmlTemplateMailRequest(String requestId, String subjectTemplate, String htmlTemplateName, Map<String, Object> parameters) {
          return createTemplateMailRequest(requestId, subjectTemplate, htmlTemplateName, true, parameters);
      }
docs: Creates a MailRequest from the specified template.
  The request id is supplied.
  
  @param subjectTemplate  a string that uses the parameters & TemplateEngine to interpolate values
  @param htmlTemplateName the name of the classpath template resource
  @param parameters
  @return an html mail request