DOCUMENT:Q182406 04-APR-1999 [exchange] TITLE :XFOR: Mail Looping When First Host Cannot Be Reached PRODUCT :Microsoft Exchange PROD/VER:WINDOWS:5.0 OPER/SYS: KEYWORDS:kbusage ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Exchange Server, version 5.0 ------------------------------------------------------------------------------- SYMPTOMS ======== When there are two servers listed in an Exchange record and the first host is not available, the server then looks to itself to receive the messages. This is not desirable due to the potential of looping. STATUS ====== Microsoft has confirmed this to be a problem in Microsoft Exchange Server version 5.0. This problem has been corrected in the latest U.S. Service Pack for Microsoft Exchange Server version 5.0. For information about obtaining the Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces): S E R V P A C K MORE INFORMATION ================ An SMTP host should deliver messages destined for a remote host to itself. After you perform an Exchange record query, if one of the Exchange hosts is the host doing the query, it must remove itself and all Exchange hosts with a weight equal to its own from the list. This is done for two reasons: 1. To prevent looping. 2. To avoid message backward flow (that is, messages moving to a less preferred Exchange host). The Internet Mail Service handles this as long as it is running on a host with one network interface card (NIC) that has one IP address. ====================================================================== Keywords : kbusage Technology : kbExchangeSearch kbExchange500 kbZNotKeyword2 Version : WINDOWS:5.0 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 1999.