Gmail script to archive any email thread older than a specified number of days

autoarchiver.js

// Note: Due to the execution timeout google has on scripts, this will only archive 1000-3000 emails. 
// If set as a project trigger with a reasonable frequency, you would only have to bulk archive emails once then the script will archive your emails without timing out.

function RunArchive() {
  ArchiveMail(30);
}

function ArchiveMail(threadAgeThresholdDays) {
  Logger.log('Archiving threads older than %s days ago', threadAgeThresholdDays);
  
  var thresholdDate = new Date(new Date().setDate(new Date().getDate() - threadAgeThresholdDays));
  var thresholdDateString = thresholdDate.getYear() + "/" + thresholdDate.getMonth() + "/" + thresholdDate.getDay();

  var index = 0;
  var batchSize = 100;
  var searchResults = GmailApp.search('in:Inbox before:'+thresholdDateString, index, batchSize);
  
  while(searchResults.length){
    Logger.log('Archiving batch of %s...', batchSize);
    GmailApp.moveThreadsToArchive(searchResults);
    Logger.log(searchResults.length);
    index += batchSize;
    searchResults = GmailApp.search('in:Inbox before:'+thresholdDateString, index, batchSize);
  }
  
  Logger.log('Finished Archiving');
}