How do I implement ServicePoint into my feedbackpage

I wanted to make use of this codes to send email to a gmail account after filling up all of the input fields. However, I have been encountering SocketException: No connection could be made because the target machine actively refused it. I have checked the error by adding breakpoint in my visual studio 2017, I have checked that there is error in ServicePoint. What can I do about it?

Codes:

 using UnityEngine;
 using UnityEngine.UI;
 using System.Collections;
 using System.Net;
 using System.Net.Mail;
 using System.Net.Security;
 using System.Security.Cryptography.X509Certificates;
 using UnityEngine.SceneManagement;
 
 public class FeedbackForm : MonoBehaviour {
 
     public InputField senderemail;
     public InputField subject;
     public InputField message;
     public Text error;
 
     public void sendmail_start()
     {
         StartCoroutine(sendmail());
     }
 
     public IEnumerator sendmail()
     {
         yield return new WaitForSeconds(0.0f);
         if (message.text == "" || subject.text == "" || senderemail.text == "")
             error.text = "Please fill in all the fields";
         else
         {
             MailMessage mail = new MailMessage();
 
             mail.From = new MailAddress(senderemail.text);
             mail.To.Add("*******@gmail.com");
             mail.Subject = subject.text;
             mail.Body = "Mail from : " + senderemail.text + " \n----------------------------------- \n \n" + message.text;
 
             SmtpClient smtp = new SmtpClient("smtp.gmail.com", 587)
             {
                 Timeout = 10000,
                 DeliveryMethod = SmtpDeliveryMethod.Network,
                 UseDefaultCredentials = false,
                 Credentials = new NetworkCredential("*******@gmail.com", "*********") as ICredentialsByHost,
                 EnableSsl = true
             };
             ServicePointManager.ServerCertificateValidationCallback =
                 delegate (object s, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
                 { return true; };
             smtp.Send(mail);
             error.text = "The mail is sent successfully";
         }
     }
 
         public void OnBackToMainMenuClick()
         {
             SceneManager.LoadScene("Mainpage");
         }
 
         public void OnClearButtonClick()
         {
             senderemail.text = "";
             subject.text = "";
             message.text = "";
         }
 }

Thanks for your willingness to help if you know how to solve it etc. It would be greatly appreciated.