Gmail Expiring Emails Script

script.js

# Based off of http://www.johneday.com/422/time-based-gmail-filters-with-google-apps-script
# See instructions on that page for adding it via script.google.com

function expireEmails() {
  var delayDays = 2 // Enter # of days before messages are moved to trash
  var maxDate   = new Date();
  maxDate.setDate(maxDate.getDate()-delayDays);

  var labelExpiring = GmailApp.getUserLabelByName("Expiring");
  var labelExpired  = GmailApp.getUserLabelByName("Expired");
  var threads       = labelExpiring.getThreads();
  
  for (var i = 0; i < threads.length; i++) {  
    if (threads[i].getLastMessageDate() < maxDate) {
      threads[i].moveToArchive();
      threads[i].removeLabel(labelExpiring);
      threads[i].addLabel(labelExpired);
    }
  }
}