Have you ever sent an email and then immediately regretted sending it? If you are using Gmail as your mail client, you can do just that with an interesting but buried option in Gmail settings.
To enable this feature, go to Mail Settings in Gmail (upper right corner, under the gear icon). Navigate to the "Labs" tab. In the labs search box, look for "Undo Send" and choose Enable, then save. Now in Mail Settings you will see an option to "Undo Send: Send cancellation period: __ seconds." Enter the number of seconds that Gmail will allow you to change your mind in the future (try 10 seconds).
With this enabled, the next time you send an email, you’ll be able to “Cancel” it from being sent out, as long as it is within the time frame you specified.