... until something that you are required to know (that was sent in the AMP part of the email) is not in the plaintext version of the email. Happened many times

... until something that you are required to know (that was sent in the AMP part of the email) is not in the plaintext version of the email. Happened many times with HTML, and now there is another layer where that will happen. Is people or the communication what stops working, and then the involved system, not a piece of software by itself.