Hi, <sm...@immi.is> commented:
#An alternative I've been considering is having e-mail clients support #bouncing messages if they are received for an incorrect envelope #address. So you can have an envelope address and a PGP encrypted blob, #and when you decrypt that blob there's a new RFC822 with a new envelope #address and another PGP encrypted blob. If e-mail clients honor a #forwarding agreement on this kind of message, it will be practically #impossible to tell who sent the original message and who is the final #recipient. # #The really hard bit about this is that there are a lot of e-mail clients #out there, and getting them all to support this - even optionally - is #may take some doing. -- If you're checking the envelope address, the check really should be happening on the MTA, not the mail client, because users typically don't "get" envelope addresses (the don't get the whole MAIL FROM or EHLO thing) This makes me think of the extensive and protracted discussions that the email community has had around SPF/Sender-ID and DKIM. Nice starting point: http://www.openspf.org/SPF_vs_Sender_ID -- If you're checking the message body address, that's something that users DO see (and think they "get") but then the question devolves to "which address is the 'right' one?" (see the discussions of "Purported Responsible Address" in RFC4407, just to get your toes wet) -- Forwarding issues have dogged SPF for a long time; rewriting is an option, but that obviously introduces new problems of its own. (See http://www.openspf.org/SRS if interested) -- I'll also say that I have real concerns about any protocol that "bounces" unwanted/unaccepted email (rather than rejecting email at connect time, while the remote MTA is still connected) because of the potential for abuse (e.g., mail bounce attacks against innocent third parties) Anyhow, just a couple of thoughts on this, Regards, Joe _______________________________________________ The cryptography mailing list cryptography@metzdowd.com http://www.metzdowd.com/mailman/listinfo/cryptography