Google Apps script to cleanup messages from GMail.

gmailCleanup.js

// Inspired in http://www.johneday.com/422/time-based-gmail-filters-with-google-apps-script

// Deletes old marked conversations
function cleanUp() {
  var delayDays = 5; // # of days before messages are moved to trash
  var label = "Delete me"; // label to identify the messages
  var maxDate = new Date(Date.now() - delayDays * 24 * 60 * 60 * 1000);
  var userLabel = GmailApp.getUserLabelByName(label);
  if (!userLabel) {
    return;
  }
  var threads = userLabel.getThreads();
  threads.forEach(function (thread) {
    if (thread.getLastMessageDate() < maxDate) {
      thread.moveToTrash();
    }
  });
}

// Deletes old conversations in selected categories
function batchDeletePromotions() {
  var categories = ["social", "promotions", "forums", "updates"];
  categories.forEach(function (category) {
    GmailApp.moveThreadsToTrash(GmailApp.search('label:inbox category:' + category + ' older_than:2d'));
  });
}