Não consigo enviar e-mail - asp.net c#

        private void SendMail(string sub, string to, string msg)
        {
            try
            {
                SmtpClient client = new SmtpClient();
                client.Host = "hotname";
                client.Port = "hostpassword";

                client.Credentials = new NetworkCredential("email from", "email password");
                client.UseDefaultCredentials = true;

                using (MailMessage m = new MailMessage())
                {
                    m.From = new MailAddress(this.fromEmail);
                    m.Subject = "ModuloIp: " + sub;
                    m.Body = msg;

                    m.To.Add(new MailAddress(to));
                    client.Send(m);
                }

                client.Dispose();
            }
            catch (Exception ex)
            {
                WriteLogFile("SendMail " + ex.Message);
                WriteLogFile("SendMail " + ex.ToString());
            }
        }