The remote certificate is invalid according to the validation procedure_Sendmail

//Sending Mail From Asp.net

             System.Net.Mail.MailMessage mail = new System.Net.Mail.MailMessage();

            mail.To.Add(to);

            mail.From = new MailAddress(from, from, System.Text.Encoding.UTF8);

            mail.Subject = "subject";

            mail.SubjectEncoding = System.Text.Encoding.UTF8;

            mail.BodyEncoding = System.Text.Encoding.UTF8;

            mail.IsBodyHtml = true;

            mail.Priority = MailPriority.High;

            

             mail.Body = "test mail";

            SmtpClient client = new SmtpClient();

            // this line will solve problem

            ServicePointManager.ServerCertificateValidationCallback = delegate(object s, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors) { return true; };

            client.Credentials = new System.Net.NetworkCredential("mail Id", "password");

            client.Port = 587;

            client.Host = "smtp.gmail.com";

            client.EnableSsl = true;

            try

            {

                client.Send(mail);

            }

            catch (Exception ex)

            {

                Exception ex2 = ex;

                string errorMessage = string.Empty;

                while (ex2 != null)

                {

                    errorMessage += ex2.ToString();

                    ex2 = ex2.InnerException;

                }

                

            } // end try