Microsoft Knowledge Base Article 914255 contains the following summary and introduction:
SUMMARYMicrosoft Exchange Server 2003 and Microsoft Exchange 2000 Server use routing groups to provide messaging services in an organization. Therefore, when you experience message delivery issues, one of the critical areas that you must troubleshoot is the communication failure between routing groups.
If you do experience messaging delivery issues, you can use the Winroute tool to start troubleshooting the issues. If the following text entry is adjacent to a deleted routing group, it indicates a routing entry that has not been flushed from the routing engine cache:
After you use the Winroute tool, you can use the Remonitor tool (Remonitor.exe) to further troubleshoot messaging delivery issues. This article describes how to use the Remonitor tool in this scenario.
INTRODUCTIONMicrosoft has released the Remonitor tool to clear the cache for the routing engine. The Remonitor tool lets you fix problems with stale routes without having to shut down and restart all Microsoft Exchange servers at the same time. In the versions of Microsoft Exchange Server that are earlier than Exchange 2000 Server, you had to shutdown and restart all the Exchange servers at the same time to force concurrent destruction of the Organization object from inside the Reapi.dll file on all the Exchange servers in the organization.
Important We recommend that you run the Remonitor tool under the guidance and supervision of Product Support Services (PSS).