The remote certificate is invalid according to the validation procedure.

public void SendMailNew(string mailTo, string Body, string Subject, string filepath)
    {
        try
        {
            MailMessage msg = new MailMessage();
            msg.IsBodyHtml = false;
            msg.Subject = Subject;
            msg.Body = Body;
            msg.From = new MailAddress("xxxxxxxxxxxxxxxxx");
            string[] multiId = mailTo.Split(';');
            foreach (string mailid in multiId)
            {
                if (mailid.Length != 0)
                {
                    msg.To.Add(new MailAddress(mailid));
                }
            }
            msg.Attachments.Add(new Attachment(filepath));
            SmtpClient smtp = new SmtpClient();
            smtp.Host = "Smtp.gmail.com";
            smtp.Port = 587;
            smtp.EnableSsl = true;
            string Password = ConfigurationManager.AppSettings["SMSPASSWORD"];
            NetworkCredential nc = new NetworkCredential("xxxxxxxxxxxxx", Password);
            smtp.Credentials = nc;
            smtp.Send(msg);
           
        }
        catch (Exception ex)
        {
            throw ex;
        }
    }