To be clear, what I would like to see in an MUA that addresses the use case Brian described is that it is just a new mime encoding that allows a message to be pieced together from a collection of signed attachments. So in this message, the mail would be encoded as two parts. The first would be the complete message you wrote, with its signature. The second would be the text I have written here. The quoted text above would be represented as a reference to the attached message. This should be very easy to accomplish in the UI—the UI should look exactly like the current UI. It's just a tweak to how copy, cut and paste work. There's no reason to get rid of MIME—I think it's a pretty good solution. I mentioned the other solutions not because I prefer them but because they exist and do demonstrate that replacements for IETF standards can and do catch on in the marketplace, and that we ought not to just be smug about how great SMTP, RFC822 and MIME are and pretend that we don't have competition.
S/MIME handles this case pretty well, but I've never seen anything other than a list manager such as Mailman wrap signed parts together.
Regards, John Levine, johnl@xxxxxxxx, Primary Perpetrator of "The Internet for Dummies", Please consider the environment before reading this e-mail. http://jl.ly
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