function GetGmailContacts() {
  // get all contacts
  var contacts = ContactsApp.getContacts();

  // assign object for contact group
  var group = ContactsApp.getContactGroup('ToBeDeleted');

  // loop through each contact
  for (var i = 0; i < contacts.length; i++) {
    // get current email address
    email = contacts[i].getPrimaryEmail();

    // check if email is not null
    if (!(email == null)) {
      // check message count
      count = GmailApp.search('from:' + email).length;

      // if count is zero or null then add that user to Group called Blacklist
      if (count == 0 || count == null) {
        // add this user to the "ToBeDeleted" contact group
        group.addContact(contacts[i]);
      }
    }
  }
}