Topic Last Modified: 2006-05-03

The Microsoft® Exchange Server Analyzer Tool performs a Domain Name System (DNS) lookup to retrieve the Mail Exchanger (MX) records for a domain. If the MX records are successfully retrieved, the Exchange Server Analyzer then performs a DNS lookup to retrieve the Host (A) records of the servers that the MX records point to. If the DNS lookup operation does not return an IP address for any one of those Host (A) records, the Exchange Server Analyzer displays an error.

This error indicates that the DNS Host (A) record appears to be missing for the server. This error may cause messages destined for remote domains to back up in the Exchange server Remote Delivery queues. This error may also cause other routing or service delays.

The DNS lookup of the Host (A) record for an MX record can fail for the following reasons:

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:

  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" (

  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:

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