code: def post_signup(self, user, login_user=None, send_email=None):
          
          self.signup_signal.send(self, user=user)
  
          if (login_user is None and self.options["login_user_on_signup"]) or login_user:
              self._login(user, user.signup_provider)
  
          to_email = getattr(user, self.options["email_column"], None)
          if to_email and ((send_email is None and self.options["send_welcome_email"]) or send_email):
              template = "users/welcome.txt" if self.options["send_welcome_email"] == True else self.options["send_welcome_email"]
              current_app.features.emails.send(to_email, template, user=user)
docs: Executes post signup actions: sending the signal, logging in the user and
          sending the welcome email