I don't think that's really a legitimate question. If you tell a friend e.g. your email address, you willingly give up the control you had over that piece of i

I don't think that's really a legitimate question. If you tell a friend e.g. your email address, you willingly give up the control you had over that piece of information, and accept that he now knows your email address. What you're expecting is that you can control when your friend forgets the information you voluntarily gave him. I doubt that's a legitimate expectation.