Mark as read script based on http://mikecr.it/ramblings/marking-gmail-read-with-apps-script

mark_as_read

function markArchivedAsRead() {
  var threads = GmailApp.search('label:unread -label:{inbox, Unsnoozed}');
  for (var i=0; i<threads.length; i++)
  {
    var messages = threads[i].getMessages();
    var markUnread = 1;
    for (var j=0; j<messages.length; j++)
    {
      if (messages[j].isInInbox())
        markUnread = 0;
    }
    if (markUnread)
      threads[i].markRead();
  }
};