Topic Last Modified: 2006-08-24

The Microsoft® Exchange Server Analyzer Tool queries the Active Directory® directory service to determine whether the configured value for the msExchSmtpPerformReverseDnsLookup attribute has been changed from the default value of False. By default, the msExchSmtpPerformReverseDnsLookup attribute is configured not to perform reverse DNS lookups for incoming messages. If the Exchange Server Analyzer finds that this attribute is set to True, a warning is displayed.

The Perform Reverse DNS Lookup for Incoming Messages option does not have functionality to prevent the receipt of spam e-mail messages. When this option is used, Exchange Server performs a DNS query to resolve the originating Internet Protocol (IP) address of the incoming messages to a host name. Then, the host name is attached to the headers of e-mail messages.

With this feature enabled, you may experience performance degradation because of incorrectly configured DNS records or intermittent connections to the Internet. Therefore, you may want to disable this option when the Internet mail delivery is slower than expected.

To enable or disable reverse DNS lookups for incoming SMTP messages

  1. Open Exchange System Manager.

  2. Expand Servers, expand an Exchange server, expand Protocols, and then expand SMTP.

  3. Right-click an SMTP virtual server (for example, Default SMTP Virtual Server), and then click Properties.

  4. Click the Delivery tab, and then click Advanced.

    • To enable reverse DNS lookups, select the Perform reverse DNS lookup on incoming messages check box.

    • To disable reverse DNS lookups, clear the Perform reverse DNS lookup on incoming messages check box.

  5. Click OK to save the change, and then click OK to exit the SMTP virtual server Properties dialog box.

For more information about the reverse DNS lookup feature in Exchange, see the Microsoft Knowledge Base article 297412, "The 'Perform Reverse DNS Lookup for Incoming Messages' Option Is for Host Name Resolution" (

For more information about SMTP virtual server settings, see the following Knowledge Base articles: