GMail Introduces Undo Send

Undo Send has just been added to Gmail. It doesn’t mean that you can reclaim an email that has been already sent. Instead, it is waiting for 5 seconds during which you can cancel the action of sending the email. After those 5 seconds, you mail will be sent, even if you close the window or if you computer reboots.

To enable the feature, go to Gmail Labs and click the “Undo” link.