Delete threads from your Gmail mailbox in bulk Raw

DeleteGmailBulk.js

//
// Paste this function into the window at http://script.google.com/ and 
// then click the triangle button in the menu bar to run it.
//
// After the script is finished running (which can take a minute or longer!), 
// go to View -> Logs to view the logs of the script execution. 
//
// Based off of a script I found at https://productforums.google.com/forum/#!topic/gmail/YeQVDuPIQzA
//
function batchDelete() {

  //
  // How many main loops?
  //
  var numLoops = 4;
  
  //
  // How many threads to process at once?
  //
  // The total number of emails deleted will be numLoops * batchSize
  //
  var batchSize = 100
  
  //
  // Total number of messages deleted?
  //
  var total = 0;
  
  //
  // Our starting time
  //
  var startTime = new Date().getTime() / 1000;
  
  for (i=0; i<numLoops; i++) {
    
    Logger.log("Starting search...");
    var threads = GmailApp.search("subject:Nightly Cron Job");
    Logger.log("Search done!");
  
    for (j = 0; j < threads.length; j += batchSize) {

      total += batchSize;
      
      Logger.log("Loop %s: Deleting batch starting at %s", i, j);
    
      GmailApp.moveThreadsToTrash(threads.slice(j, j + batchSize) );
    
      //
      // Calculate seconds elapsed and average number of threads deleted per second.
      //
      var time = new Date().getTime() / 1000;
      var diff = time - startTime;
      var rate = total / diff;
      
      Logger.log("Deleted total of %s threads (%s threads/sec)", total, rate);
    
    }

  }
  
}