After a long period of six years Google finally graduated ‘Undo Send’ feature from Labs to its main settings in web version of Gmail( for mobile user this feature is also available in Inbox App). So if you have sent a mail by mistake or if missed something in mail or if you have second thoughts immediately after sending, then ‘Undo Send’ is life saving for you. As name suggests ‘Undo Send’ will cancel sending of your mail. Gmail just delays the sending of mail for seconds you set in setting’s ‘Send Cancellation Period’ option. So if you changed your mind after sending a mail then you will definitely like this feature, as now you can revert back sending of your mail if you immediately clicked ‘Undo Send’ showing at Top within set time frame.
Gmail disabled the ‘Undo Send’ feature by default. To enable the ‘Undo Send’ feature, Gmail users need to click onto Settings, then under the General tab tick the ‘Enable Undo Send’ . There User can set ‘send cancellation period’ from 5 seconds to 30 seconds. Gmail will delay the sending of mail for the time you set here. So you can cancel your mail within this time frame. After sending a mail Gmail will show a message for ‘Undo Send’ at top of Gmail Inbox for the set time frame. If you clicked that ‘Undo send’ after sending a mail within set time frame then Gmail will not send your mail.
In April 2018 Google launched new Gmail with completely new design. In new Gmail Undo feature is enabled by default and you can’t turn it off. You can just set the “Send Cancellation Period” according to your requirement.
To Unsend email, Gmail shows the box in left bottom side to Unsend email just after you sends email.