一段很简单的SMTP邮件发送代码，但就是发送不成功，Gmail用FOXmail可以登录，但下面的代码确会报错：

＂SMTP 服务器要求安全连接或客户端未通过身份验证。 服务器响应为: 5.5.1 Authentication Required. Learn more at      ＂

环境：VS2005 WinForm

请高手帮忙

           System.Net.Mail.MailMessage msg = new MailMessage();
            msg.To.Add("honkang@126.com");
            msg.From = new MailAddress("hkm500@gmail.com", "hkm500", Encoding.UTF8);
            msg.Subject = "hello world mail";
            msg.SubjectEncoding = Encoding.UTF8;
            msg.Body = "hello boy,i see you here";
            msg.BodyEncoding = Encoding.UTF8;
            msg.IsBodyHtml = true;
            msg.Priority = MailPriority.High;
            SmtpClient client = new SmtpClient("smtp.gmail.com",587);
            client.EnableSsl = true;
            client.Credentials = new System.Net.NetworkCredential("hkm500.gmail.com","********");
            try
            {
                client.Send(msg);
                MessageBox.Show("发送成功！");
            }
            catch (Exception ex)
            {
                this.richTextBox1.Text = ex.Message;
            }