Brad Knowles explained:
    Indeed.  We need to be careful about the SMTP Response Codes that we 
issue on a hashcash-enabled MTA.
problem.  You are looking at the hashcash model in a classic but fundamentally 
flawed way.  I have a very different insight which camram takes heavy advantage 
of.  This insight is that e-mail really consists of two protocols, the transport 
layer (SMTP) and the content interpretation layer (headers and body).  By 
recognizing that you only need to change the interpretation layer to include 
stamps or certificates or whatever, the problem is simplified.
camram puts all of its efforts into the interpretation where because that's 
where you need to make the decisions about spam.  Now you may want to have some 
additional authentication features at SMTP layer but that is completely 
independent and orthogonal to what camram does.
camram implements electronic stamps.  Stamps go on the envelope and are 
associated with the message independent of how you get it there.
although I have discovered that server side filtering and stamp generation 
really needs to know who is okay and who is not for sending messages.  It's 
probably going to require either multiple interfaces (for enterprise) or 
SMTPAUTH for the general ISP case.
    That sounds like an interesting first-pass, yes.  Of course, this 
would have to be integrated into the default version of SpamAssassin 
that everyone installs (and other filtering agents), in order for 
something like this to be of value.  Otherwise, you're calculating this 
stuff and stamping your messages with it for nothing.
well, that's is what will be happening with camram 0.2.  All messages classified 
as "yellow" (neither spam nor ham) will be triggering postage due notices.  So 
with no stamps, it's what you describe.
there is a problem with setting up a response only environment and that is 
determining when to start generating stamps.  If we implement automatic postage 
due response handling in the very beginning, then once you hit the 10 percent 
threshold for postage due notices vs. outbound mail, then it might be possible 
to do that.  It would also have the advantage of giving folks chance to 
establish a white list and minimize stamp generation from the get go.
anyway, this is definitely getting into the implementation realm and I encourage 
you to sign up for the camram mailing list (it's low-volume, believe me) and 
start making this shared vision real.
---eric
PS, I've been living with stamp generation for the past four months on a Pentium 
II/333 in foreground mode and it doesn't suck too bad although it would be 
better in the background.  Check the headers.
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