Mailbox unavailable. The server response was: 5.7.1 Unable to relay for

Mailbox unavailable. The server response was: 5.7.1 Unable to relay for

private void SendMAil()
    {
        NetworkCredential loginInfo = new NetworkCredential("info@syndromeindia.com", "troikainfo");
        MailMessage msg = new MailMessage();
        msg.From = new MailAddress("info@syndromeindia.com");
        msg.To.Add(new MailAddress("jr@syndromeindia.com"));
        msg.Subject = "Demo";
        msg.Body = "Code of vidya";
        msg.IsBodyHtml = true;
        SmtpClient client = new SmtpClient("syndromeindia.com");
        client.EnableSsl = false;
        client.UseDefaultCredentials = false;
        client.Credentials = loginInfo;
        client.Send(msg);
}

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