text: // backscatterer plugin
  
  exports.register = function () {
      this.inherits('dns_list_base');
  }
  
  exports.hook_mail = function (next, connection, params) {
      const user = ((params[0] && params[0].user) ?
          params[0].user.toLowerCase() : null);
      if (!(!user || user === 'postmaster')) return next();
      // Check remote IP on ips.backscatterer.org
      const plugin = this;
  
      function resultCb (err, zone, a) {
          if (err) {
              connection.logerror(plugin, err);
              return next();
          }
          if (!a) return next();
          const msg = `Host ${connection.remote.host} [${connection.remote.ip}] is blacklisted by ${zone}`;
          return next(DENY, msg);
      }
  
      this.first(connection.remote.ip, [ 'ips.backscatterer.org' ], resultCb);
  }
  