Have you ever seen a mistake in your email right the moment you click “Send”? Google has officially added an Undo feature in Gmail. If you make a typo or regret sending a message, you can undo the action by enabling "Undo send." This setting gives you the option to take back a message you just sent.
To enable Undo Send:
If you had Undo Send turned on in Gmail Labs, your Undo Send setting will be on by default.
Note: To give you time to undo, Gmail delays sending the message for a few seconds. So if you don't select "Undo" within the time limit, your message will be sent. "Undo send" may not work if you experience connection issues.