Enabling Reverse DNS Lookup

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Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1

If you select this option, the SMTP service will attempt to verify that the client’s IP address matches the host/domain submitted by the client in the EHLO/HELO command. If the reverse DNS lookup is successful, the RECEIVED header will remain intact. If the verification is unsuccessful, "unverified" appears after the IP address in the RECEIVED header of the message. If the reverse DNS lookup fails, "RDNS failed" will appear in the RECEIVED header of the message.

Because this feature verifies addresses for all incoming messages, its use could affect SMTP service performance. Clear the check box to disable the feature.

Important

You must be a member of the Administrators group on the local computer to perform the following procedure or procedures. As a security best practice, log on to your computer by using an account that is not in the Administrators group, and then use the runas command to run IIS Manager as an administrator. At a command prompt, type runas /User:Administrative_AccountName "mmc systemroot\system32\inetsrv\iis.msc".

Procedures

To enable reverse DNS lookup

  1. In IIS Manager, right-click the SMTP virtual server, and then click Properties.

  2. Click the Delivery tab, and click Advanced.

  3. Select the Perform reverse DNS lookup on incoming messages check box.