DOCUMENT:Q285023 11-JUN-2002 [exchange] TITLE :XCON: Internet Mail Service Does Not Follow Time to Live for DNS PRODUCT :Microsoft Exchange PROD/VER::5.5 OPER/SYS: KEYWORDS:exc55 kbExchange550preSP5fix ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Exchange Server, version 5.5 ------------------------------------------------------------------------------- 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: Q256986 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 described in this article and should be applied only to systems experiencing this specific problem. This fix may receive additional testing at a later time, to further ensure product quality. 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 fix. 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, please go to the following address on the World Wide Web: http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS NOTE: In special cases, charges that are normally incurred for support calls may be canceled, if a Microsoft Support Professional determines that a specific update will resolve your problem. Normal 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 +----------------------------+ | File name | Version | +----------------------------+ | Msexcimc.exe | 5.5.2654.52 | +----------------------------+ NOTE: Because of file dependencies, this hotfix requires Microsoft Exchange Server version 5.5 Service Pack 4. STATUS ====== Microsoft has confirmed this to be 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 : exc55 kbExchange550preSP5fix Technology : kbExchangeSearch kbExchange550 kbZNotKeyword2 Version : :5.5 Issue type : kbbug Solution Type : kbfix ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2002.