1. To open Gmail Go to https://www.gmail.com
2. Click on sign in as shown in the below image

3. Enter your Gmail id and password in the textbox (refer below image)

4. Click the Setting icon as shown in the below image

5. Click on See all Settings as shown in the below image

6. Click on General and select value from the dropdown as shown in the below image

7. View message or undo email send as shown in the below image

Wow!

You can Undo Send easily…