Gmail allows you to cancel a sent email, but it’s default may be too short a time for you. You can extend the cancellation period up to 30 seconds, which should be plenty of time to stop an email that you’ve changed your mind on.
1. Go to Gmail and login to your account.
2. Go to the upper-right corner and select Settings.
3. On the General tab, go to the Undo Send section.
4. Make sure that the Enable Undo Send checkbox is selected.
5. Use the Send cancellation period dropdown and select the desired amount of seconds. Options are 5, 10, 20, and 30 seconds.
6. Click the Save Changes button.