Archive read emails from a particular Label

moveReadLogglyMailsToArchive.gs

function moveReadLogglyMailsToArchive() {
  // Get all inbox emails (the label is applied by a filter matching all incoming conversations)
  var label = GmailApp.getUserLabelByName("[Loggly Autoarchiver] Inbox");
  if (label === null || label === undefined) {
    // abort
    return -1; 
  }

  var threads = label.getThreads();
  
  for (var i = 0; i < threads.length; i++) {
    // only archive read emails
    if (! threads[i].isUnread())
    {
      // remove archiver's inbox label
      threads[i].removeLabel(label);
      // but add the archiver's archive label
      threads[i].addLabel(GmailApp.getUserLabelByName("[Loggly Autoarchiver] Archived"));
      // move to archive eventually
      threads[i].moveToArchive();
    }
  }
}