How to Undo the Sent E-mail in Gmail

Enable The Undo option In Gmail

Have you ever worried about the important e-mail sent to the wrong person.
Do you know that we undo the sent e-mail i.e we can retrieve the sent e-mail before he/she reads the e-mail..This option is available in Gmail.
Enabling the Undo Option In Gmail

First Login to your G-mail Account
And then right hit on the wheel button (Settings).

After Hitting on the "Settings" by default "General" Tab opens