Is it possible to prevent an email from being forwarded, or to have sensitive information automatically removed when reply-all/forward is pressed?
For example, a Google Calendar invitation includes a link to directly accept/reject the event. However, if someone clicks reply-all, and they keep the HTML formatting, the link will be shared with everyone else who received the invitation, and they can change the user's RSVP. (Specifically, the email is sent only to you, but has a "To:" header showing all invitees, so the problem remains.)
What can be done to ensure that the recipient does not accidentally share the sensitive link? Would it be possible with some MIME trickery or with a semi-standard header? Or is the best practice to refrain from including such "direct action" links when someone might be tempted to reply-all?