I had to do some SMTP relay troubleshooting and it wasn't obvious how to view…
If you get the following exception calling a WebSphere web service from your .NET WCF Client (service reference):
System.ServiceModel.CommunicationException: The underlying connection was closed: The connection was closed unexpectedly. —> System.Net.WebException: The underlying connection was closed: The connection was closed unexpectedly.
Try adding this code before the service call:
System.Net.ServicePointManager.Expect100Continue = false;
More info on the 100-Continue behavior from MSDN.