It has been a quite an issue that you by mistakenly send an important email to the wrong person. Google is reportedly been testing the ‘Unsend’ option for quite a time now, say almost 6 years.
Using the Undo feature on Gmail, the user would be able to take back the Email he just sent. User can cancel the sent email after the minimum of maximum of 10 seconds time period. Now comes the tricky and the unliked part. User’s who want to avail this opportunity would have to wait more then the rest of the world to send an Email. You can adjust the window for which you can cancel the sent Email. More the Undo window, more time the mail would take to send.
How can you enable it? Its easy, just open the Gmail (In App) settings and click on General tab, and boom there you see the most awaited option of Gmail that would totally save you from inevitable situations.