Gmail has added an undo send feature to its general settings on web. Announced on June 22, 2015, the feature was created in a bid to cancel mails with errors or retract mails that should never have been sent (you should never have sent that hate mail to your ex).
Under Gmail settings, the undo send feature is turned off by default for those not currently using the Labs version but can be changed . People using the labs version have their undo feature setting turned on by default.
Gmail has given you a chance to repent from sending unpalatable emails to people but it is best you start counting before you hit ‘send’.