Undo a sent message in Gmail

If you change your mind after you press mail "Send" button , there's a feature that will help you to  Undo the sent message.  To enable this feature;

• First you login into Gmail account
• Click the link "Settings "
• Click the tab "Labs" and you can see a list of options from which you select the option "Undo Send" and make its radio button "Enable" and "click Save"

  

After enabling the feature, Gmail will show an "undo" link when you send a message. it is seen on the side of "Your message has been sent" message. 

You have to react quickly because the link disappears in 5 to 10 seconds and there's no way to bring it back. If keyboard shortcuts are enabled in your Gmail account, a better option than clicking on "undo" is to press "z". When you undo sending a mail, Gmail saves it as a draft and you can continue editing the message or discard it.