cleanup_gmail.js

function deleteFromGmail(search_query) {
  let batchSize = 100;
  let threads = GmailApp.search(search_query);
  for (slice_index = 0; slice_index < threads.length; slice_index += batchSize) {
     GmailApp.moveThreadsToTrash(threads.slice(slice_index, slice_index + batchSize));
   }
}

function deleteOldSocialMailsFromGmail() {
  // Delete 6 months old Social Emails
  deleteFromGmail("category:social older_than:6m")
}

function deleteOldPromotionsMailsFromGmail() {
  // Delete 6 months old Promotions Emails
  deleteFromGmail("category:promotions older_than:6m")
}