gistfile1.js

/*
 * This script goes through your Gmail Inbox and finds recent emails where you
 * were the last respondent. It applies a nice label to them, so you can
 * see them in Priority Inbox or do something else.
 *
 * To remove and ignore an email thread, just remove the unrespondedLabelStr and
 * apply the ignoreLabelStr.
 *
 * This is most effective when paired with a time-based script trigger.
 *
 * For installation instructions, read this blog post:
 * http://jonathan-kim.com/2013/Gmail-No-Response/
 * 
 * label = GmailApp.createLabel(labelName);
 */

// Edit these to your liking.
var unrespondedLabelStr = 'TODO/No Response',
        ignoreLabelStr = 'No Response/Ignore',
        minDays = 2,
        maxDays = 21,
        myEmailAddresses = getEmailAddresses();

function processUnresponded() {
  var threads = GmailApp.search('is:sent from:me -in:chats -filename:invite.ics older_than:' + minDays + 'd newer_than:' + maxDays + 'd'),
          minDaysAgo = new Date(),
          label = GmailApp.getUserLabelByName(unrespondedLabelStr),
          threadsToLabel = [],
          gmailMessageThreads = GmailApp.getMessagesForThreads(threads);

  minDaysAgo.setDate(minDaysAgo.getDate() - minDays);

  // Filter threads where I was the last respondent.
  Logger.log('Checking ' + threads.length + ' threads...');
  for (var i = 0; i < threads.length; i++) {
    var thread = threads[i],
            threadArr = gmailMessageThreads[i],
            lastMessage = threadArr[threadArr.length - 1],
            lastFrom = lastMessage.getFrom(),
            lastMessageIsOld = lastMessage.getDate().getTime() < minDaysAgo.getTime();

    if (isFromMe(lastFrom) && lastMessageIsOld && !threadHasLabel(thread, ignoreLabelStr)) {
      threadsToLabel.push(thread);
    }
  }
  label.addToThreads(threadsToLabel);
  Logger.log('Updated ' + threadsToLabel.length + ' messages.');
}

function isFromMe(fromAddress) {
  for (var i = 0; i < myEmailAddresses.length; i++) {
    var address = myEmailAddresses[i],
            r = RegExp(address, 'i');
    if (r.test(fromAddress)) {
      return true;
    }
  }
  return false;
}

function getEmailAddresses() {
  var me = Session.getActiveUser().getEmail(),
          emails = GmailApp.getAliases();
  emails.push(me);
  return emails;
}

function threadHasLabel(thread, labelName) {
  var labels = thread.getLabels();
  for (var i = 0; i < labels.length; i++) {
    if (labels[i].getName() == labelName) {
      return true;
    }
  }
  return false;
}

function cleanUp() {
  var label = GmailApp.getUserLabelByName(unrespondedLabelStr),
          iLabel = GmailApp.getUserLabelByName(ignoreLabelStr),
          threads = label.getThreads(),
          maxDaysAgo = new Date(),
          threadsToUnLabel = [];

  maxDaysAgo.setDate(maxDaysAgo.getDate() - maxDays);
  Logger.log('Checking ' + threads.length + ' threads for cleanup.');

  for (var i = 0; i < threads.length; i++) {
    var thread = threads[i],
            lastMessageDate = thread.getLastMessageDate();

    // Remove all labels from expired threads.
    if (lastMessageDate.getTime() < maxDaysAgo.getTime()) {
      threadsToUnLabel.push(thread);
    }
  }
  label.removeFromThreads(threadsToUnLabel);
  iLabel.removeFromThreads(threadsToUnLabel);
  Logger.log(threadsToUnLabel.length + ' unresponded messages expired.');
}

function main() {
  processUnresponded();
  cleanUp();
}

Changed the biggest calls to batch operations

Awesome! Mind sending this as a pull request so other people can benefit too? The repo is located here: https://github.com/hijonathan/google-scripts

Hmm, I'm getting this error:

TypeError: Cannot call method "addToThreads" of null. (line 46, file "")