Have you ever regretted an email seconds after you hit “send”? Gmail’s new app feature, Undo Send, helps you recall an email within 30 seconds of being sent. You can also undo deleting a message as well as archiving one. The feature has been around in a beta version since 2009 but only recently became an official mobile setting. To activate, hit the General tab in Gmail settings, or simply update your mobile app and reload. google.com.