Date: Fri, 5 Aug 1994 22:11:59 -0700 From: Hal <hfinney@shell.portal.com> To: cypherpunks@toad.com Subject: Re: Remailer ideas References: <9408051709.AA14763@ah.com> . . . A copy of outgoing email could be kept, acknowledgements received on receipt, and the email deleted or re-transmitted as needed. Serial numbers would distinguish retransmissions so that redundant resendings (where the packets "crossed in the mail", so to speak) would be dropped. All this was designed in an afternoon in Xmodem. It's conceptually easy. The hard part is getting a standard and getting people to build it into their Mail User Agents. I think that many of the simple cases are conceptually easy, but even slightly complicated ones are non-trivial. For example, I tend to include Return-Receipt-To: lines in my messages, so I get a bunch of responses. Interpreting those responses and deciding what action would be appropriate raises some interesting questions, not the least of which is ``What does it mean for a message to be successfully delivered to the cypherpunks list?''. Just as an example how easily the issue can become confused, I'll throw in, ``How is the meaning of successful delivery affected by changes in list membership during transmission?'' Considering that some of the addresses to which cypherpunks is distributed are also distribution lists, any list related problems are multiplied. Practical issues make this whole thing more difficult. The ``getting people to build it into their Mail User Agents'' part in particular. The idea of a Return-Receipt-To: field has been around for a while, but the semantics have never been pinned down. Some mailer daemons generate replies meaning that the bits were delivered. Some readers (MUAs?) generate replies based on end-user actions. This thread of discussion got me thinking about a really sick thought though: Using email messages to represent UDP packets. Rick