Dim request As WebRequest = WebRequest.Create("http://webservices.tiscali.com/EmailServices.asmx")
request.Method = "POST"
Dim postdata As String = "IsValidEmail?email=mailesistente@yahoo.it"
Dim bytearray As Byte() = Encoding.UTF8.GetBytes(postdata)
request.ContentType = "text/xml"
Dim risposta As WebResponse = request.GetResponse()

Ho pensato di usare questo codice... Non riesco ad ottenere la risposta....