Microsoft KB Archive/285023

= XCON: Internet Mail Service Does Not Follow Time to Live for DNS =

Article ID: 285023

Article Last Modified on 10/26/2006

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APPLIES TO


 * Microsoft Exchange Server 5.5 Standard Edition

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This article was previously published under Q285023



IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry



SYMPTOMS
In Exchange Server 5.5, the Internet Mail Service does not follow the Time to Live (TTL) value in Domain Name Service (DNS) records. When the Internet Mail Service queries DNS for connections, the Internet Mail Service caches up to 1,000 domains (by default), irrespective of the TTL for those records. When the Internet Mail Service is forwarding to a host, it resolves the host name at startup, and never again queries DNS for the value, again ignoring TTL. This behavior makes it difficult to load balance outbound mail properly.



RESOLUTION
A supported fix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Apply it only to computers that are experiencing this specific problem. This fix may receive additional testing. Therefore, if you are not severely affected by this problem, Microsoft recommends that you wait for the next Microsoft Exchange Server 5.5 service pack that contains this hotfix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information about support costs, visit the following Microsoft Web site:

http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS

NOTE: In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The typical support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

The English version of this fix should have the following file attributes or later:

Component: Internet Mail Service

NOTE: Because of file dependencies, this hotfix requires Microsoft Exchange Server version 5.5 Service Pack 4.



STATUS
Microsoft has confirmed that this is a problem in Microsoft Exchange Server version 5.5.



MORE INFORMATION
WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

To give the Internet Mail Service the ability to follow TTL, you need to add the EnableTTL value to the following registry key:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIMC\Parameters

Data Type: REG_DWORD

Value: 0 or 1

The behavior is as follows:
 * EnableTTL disabled (0): Same behavior as before (route DNS lookups are cached indefinitely).
 * EnableTTL enabled (1): Route lookups still cached up to TTL, but DNS lookup is performed again after TTL. Also, routes for which there are no DNS MX records do not get cached at all.

Additional query words: IMS IMC

Keywords: kbhotfixserver kbqfe kbbug kbexchange550presp5fix kbfix kbqfe KB285023

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