Topic Last Modified: 2007-05-10

The Microsoft Exchange Analyzer Tool performs a Domain Name System (DNS) lookup to retrieve the Mail Exchanger (MX) records for a domain. If the Exchange Analyzer cannot retrieve MX records for a domain from the DNS server, the Exchange Analyzer then tries a DNS lookup to retrieve the Host (A) records of the domains that the Exchange server is trying to send messages to.

The Exchange Analyzer displays an error if the following conditions are true:

This error indicates that the DNS Mail Exchanger (MX) and Host (A) records appear to be missing for the domain and servers. This error may cause messages destined for remote domains to back up in the Exchange server Remote Delivery queues in addition to other routing or service delays.

To determine mail hosts, the sending Exchange server checks for an MX record. Next, the sending server resolves the MX record to an IP address by checking for an address record (A record).

The DNS lookup of the Mail Exchanger (MX) and Host (A) records can fail for the following reasons:

To verify that the DNS server is online and that the MX and Host records are 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 the DNS Administration program on the DNS server.

    • Restart the DNS server. For more information, see "Start, stop, pause, or restart a DNS server" (

    • Verify the DNS server responsiveness by using the nslookup command. For more information, see the instructions in "Verify DNS server responsiveness using the nslookup command" (

  2. Use nslookup to verify that the Mail Exchanger (MX) records are configured correctly. For more information, see "How to Use Nslookup to Verify MX record configuration" in the "Verifying DNS Design and Configuration" section of the Exchange Server Transport and Routing Guide (

  3. 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" (

  4. 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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