XCLN: Messages with Large Attachments Sit in Outbox

• Microsoft Exchange Windows 3.x client, versions 4.0 and 5.0
• Microsoft Exchange Windows 95 client, versions 4.0 and 5.0

SUMMARY

If Microsoft Exchange is installed in a Token Ring environment and Microsoft Exchange Windows 3.x clients are configured so that the connection to the Microsoft Exchange Server is made via IPX/SPX, the clients might be unable to send messages with attachments larger than approximately 10K. The messages will sit in your Outbox and will never be sent to the Microsoft Exchange Server. At this point, any subsequent messages will also fail to leave the Outbox.

MORE INFORMATION

This behavior can occur as a result of mismatched network packet frame sizes between the Microsoft Exchange client workstation and the Microsoft Exchange Server.

Token-Ring adapters can have network packet frame sizes of more than 16K as opposed to Ethernet, which generally uses 1500 byte frames. Usually the software drivers for Token-Ring cards use a frame size of approximately 4K, but different manufacturers may use different values. In a NetWare environment, if the frame sizes on the computer that is running the Microsoft Exchange Client and the computer running Microsoft Exchange Server do not match, the client will report network errors when sending large e-mail messages or when moving or copying items from the user's Inbox to a public folder. The error text notes the operation that failed and attributes it to "network problems." For example, if the operation being attempted was copying a message from the Inbox to a public folder, the error text would be "An item could not be copied. Network problems are preventing a connection to the Microsoft Exchange Server computer."

To solve this problem, adjust the frame sizes on the server and client to match. When the client Token-Ring driver loads, take note of the maximum packet size that it reports. You will need to set the server's maximum packet size to match this value. For the Token.com driver that ships with NetWare 3.12 and 4.x, the default size that it will report is 4210.

To change the maximum packet size on the server, start the Network application in Control Panel, highlight the Token-Ring adapter card entry, click the configure button, and then change the setting and save it. If you are using the Windows NT driver for IBM Token- Ring, use the registry to configure the Maximum Packet Size. This is a DWORD registry entry with a path of KEY_LOCAL_MACHINE\System\CurrentControlSet\Services\IBMTokx\Parameters (where x is the optional adapter number) and the parameter is MaximumPacketSize. Use the decimal value from the client's driver specification. Restart the server for the new setting to take effect.

For more information on configuring other Token Ring adapters, refer to the manufacturer documentation included with the adapter.

For Windows 95 Clients, to force even length Packets, go to Start, Settings, Control Panels, Network, highlight the "IPX/SPX" transport, click properties, click on the Advanced tab, and set "Force Even Length Packets" value to "yes".