envoyer un e-mail avec C#

Bonjour:

j'essaye d'écrire un petit programme permettant d'envoyer un e-mail avec C#,
j'ai fait une petite recherche, j'ai trouvé un morceau de code, que j'ai
légèrement modifié comme suit:


using System;
using System.Windows.Forms;
using System.Net.Mail;

public class sendmail
{
public static void Main(string[] args){
MailMessage mail = new MailMessage();
SmtpClient SmtpServer = new SmtpClient("smtp.mail.yahoo.fr");

try{
mail.From = new MailAddress("xyz@yahoo.fr");
mail.To.Add("xyz@yahoo.fr");
mail.Subject = "Test Mail";
mail.Body = "This is for testing SMTP mail";

SmtpServer.Port = 465;
SmtpServer.Credentials = new System.Net.NetworkCredential("xyz",
"4589");
SmtpServer.EnableSsl = true;

SmtpServer.Send(mail);
MessageBox.Show("mail Send");
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());
System.Console.Error.WriteLine(ex.ToString());
}
}
}

J'ai compilé avec la commande:
"d:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\csc"
e:\my_data\prog\c#\sendmail.cs

resultat OK, sendmail.exe généré.

Mais quand je lance "sendmail", j'obtiens les erreurs suivantes:

System.Net.Mail.SmtpException: Failure sending mail. --->
System.IO.IOException:
Unable to read data from the transport connection: An existing connection
was f
orcibly closed by the remote host. ---> System.Net.Sockets.SocketException:
An e
xisting connection was forcibly closed by the remote host
at System.Net.Sockets.Socket.Receive(Byte[] buffer, Int32 offset, Int32
size,
SocketFlags socketFlags)
at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset,
Int32 s
ize)
--- End of inner exception stack trace ---
at System.Net.Sockets.NetworkStream.Read(Byte[] buffer, Int32 offset,
Int32 s
ize)
at System.Net.DelegatedStream.Read(Byte[] buffer, Int32 offset, Int32
count)
at System.Net.BufferedReadStream.Read(Byte[] buffer, Int32 offset, Int32
coun
t)
at System.Net.Mail.SmtpReplyReaderFactory.ReadLines(SmtpReplyReader
caller, B
oolean oneLine)
at System.Net.Mail.SmtpReplyReaderFactory.ReadLine(SmtpReplyReader
caller)
at System.Net.Mail.SmtpConnection.GetConnection(String host, Int32 port)
at System.Net.Mail.SmtpTransport.GetConnection(String host, Int32 port)
at System.Net.Mail.SmtpClient.GetConnection()
at System.Net.Mail.SmtpClient.Send(MailMessage message)
--- End of inner exception stack trace ---
at System.Net.Mail.SmtpClient.Send(MailMessage message)
at sendmail.Main(String[] args)

Quelqu'un aura une idée où est-ce l'erreur?

Merci d'avance

Maurice