[FormatException: Smtp server returned an invalid response.]
   System.Net.Mail.SmtpReplyReaderFactory.ProcessRead(Byte[] buffer, Int32 offset, Int32 read, Boolean readLine) +1066247
   System.Net.Mail.SmtpReplyReaderFactory.ReadLines(SmtpReplyReader caller, Boolean oneLine) +248
   System.Net.Mail.SmtpReplyReaderFactory.ReadLine(SmtpReplyReader caller) +16
   System.Net.Mail.SmtpConnection.GetConnection(String host, Int32 port) +642
   System.Net.Mail.SmtpTransport.GetConnection(String host, Int32 port) +159
   System.Net.Mail.SmtpClient.GetConnection() +35
   System.Net.Mail.SmtpClient.Send(MailMessage message) +1213

[SmtpException: Failure sending mail.]
   System.Net.Mail.SmtpClient.Send(MailMessage message) +1531
   Email.Page_Load(Object sender, EventArgs e) in c:\BegASPNET\Site\WebApplication1\WebApplication1\Demos\Email.aspx.cs:28
   System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) +14
   System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) +35
   System.Web.UI.Control.OnLoad(EventArgs e) +99
   System.Web.UI.Control.LoadRecursive() +50
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +627

public partial class Email : BasePage
{
    protected void Page_Load(object sender, EventArgs e)
    {
      MailMessage myMessage = new MailMessage();
      myMessage.Subject = "Test Message";
      myMessage.Body = "Hello world, from Planet Wrox";

      myMessage.From = new MailAddress("[email protected]", "Sender Name Here");
      myMessage.To.Add(new MailAddress("[email protected]", "Receiver Name Here"));

      SmtpClient mySmtpClient = new SmtpClient();
      mySmtpClient.EnableSsl = true;
      mySmtpClient.Send(myMessage);
    }
}

<system.net>
    <mailSettings>
      <smtp deliveryMethod="Network" from="You &lt;[email protected]&gt;">
        <network host="smtp.virginmedia.com" port="465" userName="[email protected]" password="myPW"/>
      </smtp>
    </mailSettings>
  </system.net>