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.