Topic Last Modified: 2006-05-17

The Microsoft® Exchange Server Analyzer Tool queries the Domain Name System (DNS) servers it uses for the mail exchanger (MX) records of remote domains that Exchange sends to.

If the Exchange Server Analyzer cannot retrieve MX records for a remote domain from the DNS servers it uses, the Exchange Server Analyzer displays a warning.

This warning indicates that the DNS MX records appear to be missing for the remote domain.

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 (A) record.

If MX records for remote domains are missing, this may cause messages destined for the remote domains to back up in the Exchange server Remote Delivery queues in addition to other routing or service delays.

The DNS lookup of the MX records can fail if the DNS server is down or unreachable because of a network failure or for other reasons.

To verify that the DNS server is online and that the MX 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 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 (

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