Gmail Undo Send

You can give yourself a little breathing space for reflection when sending an email because Gmail offers an Undo function.

Settings>General>Undo where you can set the delay you want to put in place until messages are sent (or deleted).Between 5-30 seconds.
Scroll to the bottom of the page Save Changes

In future when you send or delete a message you’ll see a bar appear at the bottom of your browser that contains an Undo button. Tap this during the delay period and the email won’t be sent or deleted, giving you a chance to make a better decision.