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. The Exchange Server Analyzer then performs a DNS lookup to retrieve the Host (A) records of the remote domains.

If the Exchange Server Analyzer DNS lookup operation does not return MX records for the remote domains but can subsequently retrieve Host (A) records for the same remote domains, the Exchange Server Analyzer displays a warning.

In this situation, after failing to retrieve the MX records, Exchange Server may try to send mail to the servers that the Host (A) records point to. It very important that those Host (A) records point to the correct mail servers.

Some domains may configure their Host (A) records to point to an Internet Service Provider (ISP) which, although it may have valid mail servers, might not be the authoritative mail server for the intended recipient. In this case the mail will be rejected.

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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