GMail Auto-Purge Script

gmail-auto-purge.gs

// The name of the Gmail labels and categories that are to be auto-purged
var GMAIL_LOCATIONS = {
  "label": [
    "<some-label>"
  ],
  "category": [
    "promotions"
  ]
};

// Purge messages automatically after how many days?
var PURGE_AFTER = 60;

// Max to purge in one go
var PURGE_LIMIT = 100;

// If more than PURGE_LIMIT mails to purge, when to schedule the next purge (minutes)
var PURGE_RESCHEDULE_AFTER = 10;

// Email address to send error/debug logs to
var LOG_EMAIL = "<some-email-here>";

// Set to true to always email the execution log
var DEBUG_EMAIL = false;

// How we identify the last trigger set
var LAST_TRIGGER_ID = "GMAIL_AUTO_PURGE_LAST_TRIGGER_ID";

function purgeGmail() {
  var age = new Date();
  age.setDate(age.getDate() - PURGE_AFTER);

  var purge  = Utilities.formatDate(age, Session.getTimeZone(), "yyyy-MM-dd");
  var threads = [];
  
  try {
    // We are processing a max of PURGE_LIMIT messages in a batch to prevent script errors,
    // else it may throw an Exceeded Maximum Execution Time exception.
    for (location in GMAIL_LOCATIONS) {
      for (var i = 0; i < GMAIL_LOCATIONS[location].length; ++i) {
        if (PURGE_LIMIT - threads.length > 0) {
          var search = location + ": " + GMAIL_LOCATIONS[location][i] + " before:" + purge;
          threads = threads.concat(GmailApp.search(search, 0, PURGE_LIMIT - threads.length));
        }
      }
    }
    Logger.log("Got " + threads.length + " threads to delete");

    try {
      // Attempt to clean up the last one-off trigger, since Google won't, and
      // there is a limit on the number of (even expired) triggers you can have.
      var lastTriggerId = PropertiesService.getUserProperties().getProperty(LAST_TRIGGER_ID);
      if (lastTriggerId != null) {
        Logger.info('Got last trigger ID to delete: ' + lastTriggerId);
        var allTriggers = ScriptApp.getProjectTriggers();
        for (var i = 0; i < allTriggers.length; ++i) {
          if (allTriggers[i].getUniqueId() == lastTriggerId) {
            Logger.info('Deleting trigger');
            ScriptApp.deleteTrigger(allTriggers[i]);
            break;
          }
        }
      }
    } catch (e) {
      Logger.log('Failed to fetch/delete last trigger; continuing: ' + e);
    }
    
    // For large batches, create another time-based trigger that will
    // activate the auto-purge process after PURGE_RESCHEDULE_AFTER minutes.
    if (threads.length == PURGE_LIMIT) {
      var trigger = ScriptApp.newTrigger("purgeGmail")
          .timeBased()
          .after(1000 * 60 * PURGE_RESCHEDULE_AFTER)
          .create();
      PropertiesService.getUserProperties().setProperty(LAST_TRIGGER_ID, trigger.getUniqueId());
    }
    
    // An email thread may have multiple messages and the timestamp of
    // individual messages can be different.
    var nDeleted = 0;
    for (var i = 0; i < threads.length; i++) {
      Logger.log("Processing thread " + i+1);
      var messages = GmailApp.getMessagesForThread(threads[i]);
      for (var j = 0; j < messages.length; j++) {
        Logger.log("Deleting message " + j+1);
        var email = messages[j];
        if (email.getDate() < age) {
          email.moveToTrash();
          nDeleted += 1;
        }
      }
    }
    
    Logger.log('Purge complete for ' + nDeleted + ' messages');
    
    if (DEBUG_EMAIL && LOG_EMAIL) {
      GmailApp.sendEmail(LOG_EMAIL, "GMail Auto Purge Debug Logs", Logger.getLog());
    }
  } catch (e) {
    // If the script fails for some reason or catches an exception,
    // it will simply defer auto-purge until the next run.
    Logger.log("Failed to complete purge: " + e);
    if (LOG_EMAIL) {
      GmailApp.sendEmail(LOG_EMAIL, "GMail Auto Purge Error Logs", Logger.getLog());
    }
  }
}