code: def send_email(self, register_user):
          
          try:
              from flask_mail import Mail, Message
          except Exception:
              log.error("Install Flask-Mail to use User registration")
              return False
          mail = Mail(self.appbuilder.get_app)
          msg = Message()
          msg.subject = self.email_subject
          url = url_for(
              ".activation",
              _external=True,
              activation_hash=register_user.registration_hash,
          )
          msg.html = self.render_template(
              self.email_template,
              url=url,
              username=register_user.username,
              first_name=register_user.first_name,
              last_name=register_user.last_name,
          )
          msg.recipients = [register_user.email]
          try:
              mail.send(msg)
          except Exception as e:
              log.error("Send email exception: {0}".format(str(e)))
              return False
          return True
docs: Method for sending the registration Email to the user