Sending Email is timing out

MailAddress fromAddress = new MailAddress("testmail@interwebs.com");
            MailAddress toAddress = new MailAddress("domlennonza@gmail.com");
            string subject = "Test Subject";
            string body = "Test Message";

            SmtpClient client = new SmtpClient
            {
                Host = "mail.mymailserver.co.za",
                UseDefaultCredentials = false,
                Credentials = new NetworkCredential("username", "password")
            };

            using (MailMessage mm = new MailMessage(fromAddress, toAddress))
            {
                mm.Subject = subject;
                mm.Body = body;
                client.Send(mm);
            }