sending email error

Hi all,
             MailMessage message = new MailMessage("from@hotmail.com","to@hotmail.com","example","<h1>Hello Mail<h1>");
                message.BodyEncoding = System.Text.Encoding.UTF8;
                message.IsBodyHtml = true;
                SmtpClient client = new SmtpClient("smtp.mydomain.com", 25);
                client.Credentials = new NetworkCredential("username", "password", "mydomain.com");
                client.DeliveryMeth ...