We had an article on MSDN a few months ago which used WSE to send SOAP messages over SMTP (affectionately called SoapMail). That article was written with the Tech Preview of WSE 2.0. When the released version of WSE 2.0 came out, we removed all the Tech Preview content. Most we have republished with versions updated for the final release. However the SoapMail article has not been updated.
But a shout out to Damon Cole who ported the previous code over to released WSE 2.0 and put it in a workspace on GotDotNet.