You receive a "DNS lookup failure" error message and e-mail messages are returned when you send mail through a Windows Server 2003-based DNS server


When you send e-mail messages to a domain that uses a Microsoft Windows Server 2003-based DNS server, the e-mail messages may be returned, and then you receive a "DNS lookup failure" error message. If you use the nslookup command-line tool to query the DNS server in this scenario, the query operation times out.


This problem may occur if both of the following conditions are true:
  • You use uppercase letters in the name of the destination domain when you send the e-mail message.
  • The resource record is not yet cached on the DNS server.
In this scenario, Windows Server 2003 DNS does not correctly resolve the name of the domain in the question section of the response that is returned from the server. Therefore, Windows Server 2003 DNS does not cache the resource record or send a response that contains the answer to the client. For example, this problem may occur if you send e-mail messages to However, this problem does not occur if you send e-mail messages to


Hotfix information

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.


No prerequisites are required.

Restart requirement

You must restart your computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

File information

The English version of this hotfix has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.

Windows Server 2003

Date Time Version Size File name
19-Dec-2003 18:40 5.2.3790.114 422,912 Dns.exe

Windows Server 2003 64-Bit Edition

Date Time Version Size File name
18-Dec-2003 23:59 5.2.3790.114 1,022,464 Dns.exe IA-64
19-Dec-2003 18:40 5.2.3790.114 422,912 Wdns.exe x86


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section of this article.

More Information

For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

824684 Description of the standard terminology that is used to describe Microsoft software updates