gmail-purge.js

// The name of the Gmail Labels that are to be purged
var GMAIL_LABELS = [
  "list",
  "of",
  "labels",
  "to",
  "purge",
];

// Purge messages automatically after that many days
var PURGE_AFTER = "365";

/*
  Originally from http://labnol.org/?p=27605, adapted
  to support a list of labels instead

  Add this file to your google drive, set your labels
  and the TTL and add a trigger to run it every 2 hours.

  If you have very old threads it's best to purge them
  manually first, otherwise you'll run into rate-limiting
  issues quickly:

  - search for "label:<label> before:2014-07-05"
  - select all
  - delete
 */

function purgeGmail() {
  var age = new Date();
  age.setDate(age.getDate() - PURGE_AFTER);
  
  var purge  = Utilities.formatDate(age, Session.getTimeZone(), "yyyy-MM-dd");

  for (var k=0; k<GMAIL_LABELS.length; k++) {
    var search = "label:" + GMAIL_LABELS[k] + " before:" + purge;
  
    var threads = GmailApp.search(search);
    
    if (threads.length == 0) {
      Logger.log("Nothing to delete in " + GMAIL_LABELS[k]);
    }
    for (var i=0; i<threads.length; i++) {
      var messages = GmailApp.getMessagesForThread(threads[i]);
      for (var j=0; j<messages.length; j++) {
        var email = messages[j];
        if (email.getDate() < age) {
          Logger.log("Deleting " + email.getSubject() + " from " + email.getFrom());
          email.moveToTrash();
        }
      }
    }
  }
}