XCON: Event ID 9318 Occurs Within Site When Servers Operate over a WAN

When you review the Event Viewer application log for Microsoft Exchange Server 5.0 Service Pack 1, you notice that the message transfer agent (MTA) is logging Event ID 9318 at random intervals. The entry is similar to the following example, though the index and Microsoft Windows NT error code numbers vary:

This behavior can occur when you have more than one server in a site, but the servers are connected across a wide area network (WAN) rather than a local area network (LAN). Event Viewer logs this event when WAN traffic is heavy or when network connectivity is unstable.

To work around this problem, follow these steps:

1. Open the MTA Site Configuration Properties dialog box, and then click the Messaging Defaults tab.
2. Type 15 in the Checkpoint Size (K) box.
3. Type 90 in the Recovery Timeout (sec) box.
4. Type 3 in the Window Size box.

NOTE: If most of the WAN is regularly experiencing heavy traffic, this workaround may not completely alleviate the problem. It may be necessary to redesign the Exchange Server organization.

Checkpoints are markers for data transmission. The checkpoint size is the amount of data that is to be transferred before a checkpoint. If a transmission error occurs and the message must be transferred again, the transfer can resume from the most recent checkpoint. The default checkpoint amount is 30 kilobytes.

The recovery timeout setting is used for specifying the amount of time after a transmission error occurs that the MTA waits for a connection before deleting all checkpoints and restarting the transfer from the beginning. The default time is 60 seconds.

The window size indicates the number of checkpoints that can go unacknowledged before data transfer is suspended. The window size determines the amount of resources that are set aside for the receiving station. It is only useful to set a window size when the checkpoint size is set to something greater than zero. The default window size is 5.