C# error in sending mail : A connect request was made on an already connected socket
using (MailMessage mail = new MailMessage())
{
    using (SmtpClient mailer = new SmtpClient("smtp.server.com"))
    {
        Console.Write("Sending mails...");
        mail.From = new MailAddress("from@mail.com");
        mail.To.Add("myaddress@mail.com");
        mail.Subject = "test-subject";
        mail.Body = "test-body";
        mailer.Port = 25;
        mailer.Credentials = new System.Net.NetworkCredential("from@mail.com", "from-password");
        mailer.EnableSsl = true;
        try
        {
            mailer.Send(mail);
            Console.WriteLine("Mail sent");
        }
        catch (Exception e)
        {
            Console.ForegroundColor = ConsoleColor.Red;
            Console.WriteLine("rCannot send mail, an error occured : {0}", e);
            Console.ResetColor();
        }
    }
}

Cannot send mail, an error occured : System.Net.Mail.SmtpException: Failure sending mail. ---> System.Net.WebException: Unable to connect to the remote server ---> System.Net.Sockets.SocketException: A connect request was made on an already connected socket 200.200.200.200:25
   at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress)
   at System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Int32 timeout, Exception& exception)
   --- End of inner exception stack trace ---
   at System.Net.ServicePoint.GetConnection(PooledStream PooledStream, Object owner, Boolean async, IPAddress& address, Socket& abortSocket, Socket& abortSocket6, Int32 timeout)
   at System.Net.PooledStream.Activate(Object owningObject, Boolean async, Int32 timeout, GeneralAsyncDelegate asyncCallback)
   at System.Net.PooledStream.Activate(Object owningObject, GeneralAsyncDelegate asyncCallback)
   at System.Net.ConnectionPool.GetConnection(Object owningObject, GeneralAsyncDelegate asyncCallback, Int32 creationTimeout)
   at System.Net.Mail.SmtpConnection.GetConnection(ServicePoint servicePoint)
   at System.Net.Mail.SmtpTransport.GetConnection(ServicePoint servicePoint)
   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 TestApp.Program.Main(String[] args) in D:DesktopTestAppTestAppProgram.cs:line 290