Move to trash read email labelledd, or sub-labelled, by a specific string. (in this case Geeks).

autocleanup

function processLabel(label) {
  var data = GmailApp.getUserLabelByName(label).getThreads();
  for (var i=0; i < data.length; i++) {
    if(!data[i].isUnread() && !data[i].hasStarredMessages()){
      data[i].moveToTrash();
    }
  }
};

function deleteOldMessages(){
 GmailApp.getTrashThreads()
 var labels = GmailApp.getUserLabels();
 for (var i = 0; i < labels.length; i++) {
   if(labels[i].getName().indexOf("Geeks/")===0){
     processLabel(labels[i].getName());
     Logger.log("label: " + labels[i].getName());
     Utilities.sleep(1000);
   }
   
 }
}