How to enable recall/undo send feature
To configure the Undo Send feature (and make sure it’s enabled):
1. Click the gear icon in the top-right corner of your Gmail screen.
2. Click “Settings.”
3. Select the “General” tab, and navigate to “Undo Send.”
4. Check the “Enable Undo Send” radio button.
5. Using the dropdown menu, extend the cancellation period from 5 to 30 seconds.
6. Scroll down and click “Save Changes.”
After this feature is enabled you can recall emails that you mistakenly sent. If this feature isn't enabled when an email is mistakenly sent than it cannot be recalled