'Reverse the send action, shortly after accidently clicked the 'send' button .'
2. Set the ‘send cancellation period’
3. Right after the email is sent, you will see an undo button
4. Click the button to withdraw the email
(The email is actually not sent during the undo period, there is no way to reliably unsend an email once it is actually out.)
Demo Video (Undo Send)