XCLN: Transmitting Over SPX via Dialup Connection

There are two known problems with Exchange 95 clients transmitting messages using SPX over dialup connections. The second problem will not be seen until the first is resolved.

The first problem encountered appears as the following error in Windows 95: Nwlink.vxd is accepting packets larger than max frame size. The exception causes the machine to hang. For more information, please see the following article in the Microsoft Knowledge Base: The second problem:

The real problem is exposed once the Nwlink.vxd problem is remedied. The Microsoft Exchange Windows 95 client will hang when attempting to transmit a packet greater than 1160 bytes over a dialup connection using SPX.

This occurs because Wsipx.vxd submits a larger frame than is supported. SPX checks the max NDIS packet frame size against the max frame size for the connection and fails. NDIS packet frame size is 1497 bytes and max frame is 1160. For more information, please see the following article in the Microsoft Knowledge Base:

Connect to the Microsoft Exchange Server before launching the Microsoft Exchange client.

Microsoft has confirmed this to be a problem in Windows 95. A supported fix is now available, but has not been fully regression-tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft recommends that you wait for the next Service Pack that contains this fix. Contact Microsoft Product Support Services for more information.