Making a typo in the email or sending it to a wrong person can turn into a real headache or even get you fired. Google has been working for six years to introduce a feature that would allow you to 'unsend' an email. The 'Undo Send' feature gives users from 5 to 30 seconds to cancel the action after they press the send button. At the moment the feature is slowly rolling out to users worldwide and is said to arrive everywhere within two weeks.
Users of the Lab version who had the feature enabled will still have it turned on in the usual version of the app. If you are not one of the testers, the feature is disabled by default, so you need to go to the Settings, open the General Tab, tick Undo Send and set the desired time of delay. The feature is also available in the Android and iOS versions of Gmail, as well as in the Inbox app.
If you often deal with emails, we strongly recommend that you enable Undo Send, as it will certainly pay off in the long run.
Source: Google Apps Updates