XFOR: Mail Looping When First Host Cannot Be Reached

ID: Q182406

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:

To prevent looping.

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 XFOR
Version : WINDOWS:5.0
Platform : winnt
Issue type : kbbug