May I summarize this conversation, please?

 People,

    I'd like to take a moment and review what I think we've learned from 
these discussions.  I am not even going to try to figure out who gets 
credit for what.  Please correct me if I am wrong

    The problem with SPAM can be solved if we solve four subproblems: 
identification, authentication, authorization, and trust

    * At this point, we can uniquely identify the sender of a mail
      message using their E-mail address and their MTA host name and/or
      MTA IP address.   
    * However, we cannot authenticate that a message actually came from
      the person the message identifies as the sender.  This is so for a
      couple of reasons: 1) SMTP makes no guarantee that the sender
      identification is either honest or accurate. 2) a corrupt or
      incompetent MTA sysadmin can break any system that we care to
      implement.  3) My intuition tells me that a corrupt or incompetent
      UTA sysadmin can break any system, if no other method than
      telnetting to the MTA.  I think we are in agreement that this
      situation will not change without changing the SMTP protocol and
      we are reluctant to do that.
    * Several methods of authorizing messages have been proposed or
      implemented.   These methods can be grouped into internal
      examination methods and external examination methods.  Internal
      examination methods include keyword recognition systems,
      statistical analysis systems, Bayesian analysis, reputation
      systems, and other techniques that border on A.I.  External
      examination methods include whitelists, blacklists,
      challenge/response mechanisms, and counting sent/received message
      ratios.
    * Trust is defined as anthing which will break the system if it
      doesn't work right.  I think we have decided that we cannot trust
      the sender of an E_mail message.  I think we are reluctant to
      trust an impartial third party e.g. Verisign because of concerns
      that the third party will not be trustworthy in any of a number of
      ways.  Ideally, the trust mechanism should be in the receiver's
      MTA.  Since an MTA can handle a lot of messages, the computational
      cost should be low.


We've had several (frustrating at times) discussions about some good 
ideas that do not work.  Whitelists and blacklists suffer from the 
problems of insufficient granularity, timeliness, and spammers 
frequently create new identities.  If we could solve the authentication 
problem, then blacklists and whitelists might work.
Internal examination methods tend to be compute intensive, and the cost 
of examining a message to see if it is spam is high.  Furthermore, a 
spammer could run his/her message through the system, and modify the 
text until it was accepted.
Challenge/Response was rejected because it was perceived as being hard 
for the visually challenged.  Was that really the reason or is there 
something else I have forgotten?
Reputation systems were rejected (I think that is the consensus) because 
it is not clear that past behavior is a good predictor of future 
behavior: the Russell Chicken scenario.  Also, crooks sometimes go straight.
Multiple indicators have been proposed, but I do not understand how they 
would work in practice.  If the internal examination system felt there 
was a high probability of spam and the sender has a reputation for 
sending spam, then probably the message is spam.  But if we cannot 
authenticate that the spammer is who he or she says he or she is, then 
is the reputation meaningful?  What if the internal examination system 
and the external examination system disagree?  And does multiple 
indicators have sufficient accuracy in prediction to justify the extra 
cost of calculation?


Have I missed anything important?  I have not always understood the 
arguments going back and forth.


Now, I would like to get on my soapbox for a moment.

I think that the inability of the receiver to  authenticate the sender 
of an E-mail is a fatal flaw.  I believe that SMTP as it currently 
exists, will either have to be extended to allow or force the sender to 
authenticate, or else will have to be rewritten from scratch.  I think 
that extending SMTP is outside the scope of our charter as I understand 
it.   I am **very** reluctant to advocate throwing away SMTP and 
starting from scratch, because I look at the success IP V6 has (not) had 
penetrating the market.  We must be evolutionary not revolutionary.

And I am afraid we're going to have to patent whatever we come up with 
to prevent anybody else from patenting it and stealing it.  Blech!

I am now getting off of my soapbox.



Sincerely yours,



Jeff