[linux-elitists] Spam filters

Matthew Palmer mpalmer at hezmatt.org
Thu Mar 26 17:19:31 PDT 2009

On Thu, Mar 26, 2009 at 06:53:41PM -0400, Bob Bernstein wrote:
> On Thu, 26 Mar 2009, Gerald Oskoboiny wrote:
>>> Hiding isn't an anti-spam panacea but, wonderfully enlightening  
>>> discussions of anti-spam flavor-of-the-month aside, what is?
>> Reputation systems.
> Are whitelists properly thought of as "reputation systems?" Or are they, 
> perhaps, the dinosaurs of that family tree?

Theoretically, a whitelist is just a binary-valued reputation system
-- either you're trusted, or you're not.  Practically, they're almost
universally implemented in a spectacularly stupid way (Challenge Response),
or aren't particularly useful in practice due to the need for regular
maintenance by anyone who uses e-mail in any meaningful manner.

The difficulty, in my eyes, for a working global reputation system is
identity.  If you can just dump a bad identity, then it's no barrier to a
spammer.  If you start a new identity at "Evil Spammer" and need to "level
up" from there, then bootstrapping is a pain.

The closest to a functioning reputation system we've got appears to be based
around IP addresses, which are the best identifier available in the SMTP
transaction.  It's still a spectacularly bad one, though, as it doesn't
actually identify the originating actor, both through the "owner" of an IP
address changing over time, and multiple users sharing an IP address.

- Matt

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