This is how it used to be. Also it used to be that when you recalled a messaged the recipient received an e-mail saying "so and so would like to recall a message" leaving the recipient the option to accept or reject. Times have changed and now a message can be deleted outright sending a command using the RFC822 message ID on the email to delete it outright. Which is not strictly a gmail thing but it is certainly implemented by gmail.That only applies if the SENDER was using the option with their gmail or maybe Microsoft Outlook account and I believe it must be done within about maybe 60 seconds max I believe after sending. And even then it's not 100% reliable.