I haven't tried a Challenge/Response system yet, but it would seem to
me that the software should be able to automatically scan all outgoing
emails _and_ automatically add all the To, Cc, and Bcc addresses to
its "white list".

So if I sent an email to a prospective employer (_chuck_@ibm.com),
the C/R software should add Chuck to the white list so that when
Chuck sends an email to me, it does not get challenged.  Doesn't this
eliminate the whole problem of offending people?  And if you subscribe
to a list, add the whole domain (@ibm.com) to the white list.

As to the volume of spam traffic and C/R traffic on the web:  If we
_all_ had C/R software, and used it, and it really did ask questions
that only a human could respond to, wouldn't automated spam become
totally useless, and ineffective, therefore not worth sending?  So the
33% spam and 33% C/R emails would disappear.

Bill Mackin