Most of us are using Gmail, but still we are not aware of amazing feature of this. Gmail launched a feature named "Undo Send" . You will get this feature in Labs tab. Gmail labs have many cool features , so one of the feature, undo send allow us to undo the sent emails even after 30 seconds of pressing the send button. If you pressed the send button and later on noticed that you made a mistake, then you can straight away press the undo button and the email will be saved in draft folder.
Follow the Steps :
Press wheel Icon on the top right portion of Gmail page.
Write Undo in the Search box then click Enable button and click on save changes.
Now Compose a E-Mail and when you click the send button you will notice a pop up as shown in the below image.
When you press the undo button your email will get saved in the draft folder. This undo button will remain on the screen for 5,10,20, or 30 seconds.