"Sometimes you might have a need to send an email to somebody but you don’t want it to remain on their computer, for security or personal reasons. Unfortunately, it just isn’t possible using the normal emailing system to send an email to somebody and have it auto delete itself after they have read it or after a certain period of time, just think of the kinds of security issues that would bring.
Although you can’t do it with your normal emails, there is an alternative which is basically the next best option. That is to use a secure web service where you can leave your message, then you email and send a unique link for the message to the other user and they can visit the webpage and view what’s written. The link and the message both expire after viewing or a set period of time meaning your message never existed."