Consider the following scenario:

• In a Microsoft Exchange Server 2003 environment, you enable the Sender ID Filtering setting in Exchange System Manager.
• The single-label domain name is invalid.

In this scenario, users receive spam e-mail messages that are sent from a single-label DNS name.

Note To enable the Sender ID Filtering setting in Exchange System Manager, you must configure the setting on the Sender ID Filtering tab in the Message Delivery object properties dialog box.

This problem occurs because the e-mail messages are accepted when they should not be accepted. For example, assume that Exchange Server receives an e-mail message that is sent from example@contoso. In this case, Exchange Server tries to use DNS to resolve "contoso" in order to find the Sender of Policy Framework (SPF) record. However, because there is no DNS entry for "contoso," Exchange Server assumes that the e-mail message was sent from a domain that does not support SPF records. Therefore, Exchange Server accepts the message.

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.

Prerequisites

You must have Microsoft Exchange Server 2003 Service Pack 2 (SP2) installed to apply this hotfix.

Restart requirement

You do not have to restart the computer after you apply this hotfix. However, the IIS Admin Service and all dependent services must be restarted.

Hotfix replacement information

This hotfix does not replace a previously released hotfix.

File information

The English version of this hotfix has the file attributes (or later file attributes) 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 item in Control Panel.

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

Single-label DNS names are names that do not contain a suffix, such as .com, .corp, .net, or .org. For example, "contoso" is a single-label DNS name. A fully qualified domain name (FQDN) is "contoso.com" or "contoso.local."

For more information about the naming schema for Exchange Server software updates, click the following article number to view the article in the Microsoft Knowledge Base: For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:

For more information about Sender ID and about SPF, visit the following Microsoft Web site: