Google App Script for Gmail Auto Archiving

Code.gs

/* Paste this code in scrip.google.com.
 * You have to manually add a (daily) trigger:
 * Edit -> Current project's triggers -> Add trigger */
function RunAutoArchive(){
  var threadCount = 0;
  
  // All read emails older than 1 month will be archived
  var searchQuery = 'label:read in:Inbox older_than:1m';  
  var threads = GmailApp.search(searchQuery);
  threadCount = threads.length;

  if(threadCount > 0){
    // Split the array in chunks of 100 because of Google's limit
    var i, threadChunk, chunk = 100;
    for (i=0; i<threadCount; i+=chunk) {
      threadChunk = threads.slice(i,i+chunk);
      GmailApp.moveThreadsToArchive(threadChunk); // Do the archiving
      GmailApp.refreshThreads(threadChunk);
    }   
  }
  return threadCount;
}