XCON: External Domain Name System Resolver Does Not Handle CNAME Records That Point to Other CNAME Records

Microsoft Exchange 2000 Server cannot send messages to remote domains that have a mail exchanger (MX) record that is a pointer to an alias (CNAME) record that is in turn a pointer to another CNAME record instead of being a pointer to an address (A) record.

RFC 2821 (section 3.6) states that domain names must be resolvable to MX records and A records from the domain part of a message. RFC 2821 also permits CNAME records that have targets that can be resolved in turn to MX records or A records.

Not all domains on the Internet comply with the practice that the CNAME record must point to an MX record or to an A record, and these domains may have CNAME records that point to another CNAME record. The design of Exchange 2000 did not account for this possibility.

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.

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, submit a request to 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.
Component: Router

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.
Note Because of file dependencies, this update requires Exchange 2000 Service Pack 3 (SP3). For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

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