docs: def _verifySender(self, sender):
          """
          Verify that this sender is valid.
          """
          if self.store.findFirst(
              LoginMethod,
              AND(LoginMethod.localpart == sender.localpart,
                  LoginMethod.domain == sender.domain,
                  LoginMethod.internal == True)) is None:
              raise BadSender(sender.localpart + u'@' + sender.domain,
                              [lm.localpart + u'@' + lm.domain
                               for lm in self.store.query(
                          LoginMethod, LoginMethod.internal == True)])