Jean-Christophe Bandini wrote:
then whitelist become _more_ expensive to maintain than
blacklist because as you said above there are 'massively
more non-spammer than spammer'
The relative expense depends on whether you are speaking
globally or locally. While there are many more non-spammer servers than
spammer's servers, for many receivers of email, they are exposed to more
spammer servers than non-spam servers. The number of non-spam servers is
limited to some number equal to or less than the number of
correspondents that the user has. The number of spam servers, however,
is typically very large for any user who receives spam. Thus, one can
argue that at the individual level, maintaining whitelists is much
cheaper than maintaining blacklists.
On a more global level, it is clear that maintaining whitelists
is going to be more expensive. An ISP or listing service needs to be
able whitelist *all* of the unique machines that are on the aggregated
whitelists of all the individual users. In that case, the number of
whitelisted machines will probably greatly exceed the number of
blacklisted machines.
So, yes, at the "global" level, whitelists would be larger than
blacklists, however, at a "local", individual user leve, the whitelists
would probably be smaller than the blacklists.
bob wyman
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