Public Class Form1

    Const postPage As String = "http://www.somesite.com/cgi-bin/whatever.cgi"

    Private Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles Button1.Click
        SubmitForm()
    End Sub

    Private Sub SubmitForm()
        Dim headerVars As String = "email=" & TextBox1.Text & "&item2=value2&item3=value3"
        Dim bytes As Byte() = System.Text.Encoding.UTF8.GetBytes(headerVars)
        Dim req As HttpWebRequest = DirectCast(WebRequest.Create(postPage), HttpWebRequest)
        req.Method = "POST"
        req.ContentType = "application/x-www-form-urlencoded"
        req.ContentLength = bytes.Length

        Using requestStream As Stream = req.GetRequestStream()
            requestStream.Write(bytes, 0, bytes.Length)
        End Using

        Using response As HttpWebResponse = DirectCast(req.GetResponse(), HttpWebResponse)
            If response.StatusCode <> HttpStatusCode.OK Then
                Dim message As String = String.Format("POST failed. Received HTTP {0}", response.StatusCode)
                Throw New ApplicationException(message)
            Else
                MessageBox.Show("Success!")
            End If
        End Using
    End Sub

End Class