Topic Last Modified: 2006-05-04

The Microsoft® Exchange Server Analyzer Tool performs a Domain Name System (DNS) lookup to retrieve the Host (A) records of remote servers that the Exchange server is trying to send messages to. If the DNS lookup operation does not return an IP address, the Exchange Server Analyzer displays an error.

This error indicates that the DNS Host (A) record appears to be missing for the remote server. This error may cause messages to back up in the Exchange server Remote Delivery queues.

The DNS lookup of the Host (A) record from the remote server can fail for the following reasons:

• The DNS server is down or not responding because of a network failure or other reasons.
  
  
• The Host (A) record for the remote server is missing from the DNS server because the record is unavailable or is incorrect.
  
  
• The DNS server is not configured to enable dynamic host record updates.
  
  

To verify that the DNS server is online and that the Host record is present

1. Verify that the DNS server is running by doing one or more of the following checks:

   • Look at the DNS server status from DNS Administration program on the DNS server.
     
     
   • Restart the DNS server. For more information, see "Start, stop, pause, or restart a DNS server" (http://go.microsoft.com/fwlink/?LinkId=62999).
     
     
   • Verify the DNS server responsiveness by using the nslookup command. For more information, see "Verify DNS server responsiveness using the nslookup command" (http://go.microsoft.com/fwlink/?LinkId=63000).
     
     

2. Use nslookup to verify that the Host (A) record exists on the DNS server. For more information, see "To verify A resource records exist in DNS" (http://go.microsoft.com/fwlink/?LinkId=63001).

3. If the Host (A) resource record does not exist, manually add or modify the A resource record or configure the DNS server to enable dynamic record updates:

   • Manually add an A resource record. For more information, see "Add a resource record to a DNS zone" (http://go.microsoft.com/fwlink/?LinkId=63002).
     
     
   • Manually modify an A resource record. For more information, see "Modify an existing resource record" (http://go.microsoft.com/fwlink/?LinkId=63014).
     
     
   • Configure the DNS server to enable dynamic host record updates. For more information, see Microsoft Knowledge Base article 816592, "How to configure DNS dynamic updates in Windows Server 2003" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=816592).
     
     

• For information about how Exchange Server 2003 uses DNS to resolve external IP addresses, see "Transport Dependencies for Exchange Server 2003" in the Exchange Server Transport and Routing Guide (http://go.microsoft.com/fwlink/?LinkId=47579).
  
  
• For information about DNS name resolution, see Microsoft Knowledge Base article 322856, "How to configure DNS to use with Exchange Server" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=322856).
  
  
• For information about how to troubleshoot DNS, see "Troubleshooting DNS" (http://go.microsoft.com/fwlink/?LinkId=63003).
  
  
• For information about Exchange Server 2003 system monitoring, see "Chapter 3: System Monitoring with Exchange Server 2003 Management Pack" in the Exchange Server 2003 Management Pack Guide for MOM 2000 SP1 (http://go.microsoft.com/fwlink/?LinkId=47573).
  
  
• For information about Host (A) resource records, see "Managing Resource Records" (http://go.microsoft.com/fwlink/?LinkId=63004).
  
  

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