--On Tuesday, September 10, 2013 08:09 +1200 Brian E Carpenter <brian.e.carpenter@xxxxxxxxx> wrote: >... > True story: Last Saturday evening I was sitting waiting for a > piano recital to start, when I overheard the person sitting > behind me (who I happen to know is a retired chemistry > professor) say to his companion "Email is funny, you know - > I've just discovered that when you forward or reply to a > message, you can just change the other person's text by typing > over it! You'd have thought they would make that impossible." There is another interesting detail about this in addition to the part of it addressed by the brothers Crocker. When MIME was designed, there were a number of implicit assumptions to the effect that, if an original message was included in a reply or a message was forwarded, the original would be a separate body part from the reply or forwarding introduction. Structurally, that arrangement not only would have preserved per-body-part signatures but would have largely avoided a number of annoyances that have caught up with us such as an incoming message that uses different charset values than the replying or forwarding user is set up to support. Obviously, that would not help with replies interleaved with the original text, but that is a somewhat different problem (although it might take a bit of effort to explain the reasons to your chemistry professor). When things are interleaved, preventing charset conflicts, modification of quoted text, and other problems is pretty much impossible, at least, as Dave more or less points out, if the composing MUA is under the control of the user rather than being part of a centrally-controlled environment that can determine what gets typed where. It didn't work out that way. Indeed, more than 20 years later, forwarded messages and "reply with original included" ones are the primary vestiges of the popular pre-MIME techniques for marking out parts of a message. Perhaps we should have predicted that better, perhaps not. But the reasons why "make that impossible" are hard are not just security/ signature or legacy/installed base issues. best, john