Microsoft KB Archive/182406

= XFOR: Mail Looping When First Host Cannot Be Reached =

Article ID: 182406

Article Last Modified on 10/28/2006

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APPLIES TO


 * Microsoft Exchange Server 5.0 Standard Edition

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This article was previously published under Q182406





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: kbbug kbfix kbusage KB182406

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