Don't worry undo sent mail in-GMail

Google have a feature to undo sent email for a period of preset time. To use this feature you need to enable Undo send lab from Google labs.

To enable the lab:

1. Click the  gear in the top right.
2. Select Settings.
3. Click the Labs tab.
4. Find the "Undo Send" lab and select the Enable radio button.
5. Click Save Changes at the bottom of the page.

This feature can't pull back an email that's already gone; it just holds your message for five seconds so you have a chance to hit the panic button. 

Naresh Sameneni