Server does not support secure connections.

public bool Send()
    {
        string user = ConfigurationManager.AppSettings["email_username"].ToString();
        string password = ConfigurationManager.AppSettings["email_password"].ToString();
        SmtpClient SmtpServer = new SmtpClient();
        SmtpServer.Credentials = new System.Net.NetworkCredential(user, password);
	SmtpServer.Port = 25;
	SmtpServer.Host = "smtp.rediffmail.com";
        SmtpServer.EnableSsl = true;
        MailMessage mail = new MailMessage();
        try
        {

            mail.From = new MailAddress(user, "SUBJECT", System.Text.Encoding.UTF8);
            mail.To.Add(new MailAddress(to));
            mail.Subject = subject;
            mail.Body = message;
            mail.IsBodyHtml = true;
            mail.DeliveryNotificationOptions = DeliveryNotificationOptions.OnFailure;
            mail.ReplyTo = new MailAddress(frm);
            SmtpServer.Send(mail);

        }
        catch (Exception err)
        {	
	return false;
	}
	return true;
    }