User-side script for deleting multiple pages of email in Outlook Web App.

delete-outlook-webmail-inbox.js

/**
 * Paste this in a browser console to automate the processes of clicking
 * "Select All" and "Delete" in OWA. Useful for flushing out abandoned inboxes
 * (from the user side).
 */
(function () {
  document.querySelector('input[type=checkbox]').click();
  document.querySelector('a#lnkHdrdelete').click();
})();