Taxonomy of anti-spam systems. version 03.
3/20/2003
Author: Paul Judge

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1.	Spam Prevention Approaches - These systems aim to prevent the spread
of spam messages. This includes protection systems and deterrence systems.

	a)	Spam Protection (to shield from exposure)
		i)	Whitelists
			(1)	Basic
			(2)	Verified
				(a)	Authenticated sender identity
				(b)	Token supported
				(c)	Disposable email addresses 
		ii)	Challenge/Response systems
			(1)	Basic
			(2)	Human verification (i.e. turing tests)
		iii)	Consent Tokens (a priori consent)
			(1)	Proof-of-work (i.e. hashcash)
			(2)	Stamps
		iv)	Don't receive messages, just notification (i.e.
IM2000)

	b)	Spam Deterrence Approaches - (to discourage from acting)
These systems aim to deter spamming activities. In most areas of life, deterrence is achieved by introducing the ability to identify and track wrongdoers. These systems provide input to certain spam reaction techniques such as charging, legal prosecution, malicious response, and feedback to reputation systems.

		i)	Authentication
		ii)	Tracking
		iii)	Non-repudiation

2)	Spam Detection 
	a)	Human determination
		i)	Collaborative filtering (i.e., razor) 
	b)	System Determination
		i)	Who is it from? 
			(1)	Blacklists
			(2)	Reputation systems
		ii)	What's in it? (Content Filtering)
			(1)	Static lists 
			(2)	Learning methods 
		iii)	How was it sent?
			(1)	Forged info?  (i.e. reverse DNS, domain
lookup, verify email address on calling server, verify message on sending server,reverse MX record)
			(2)	Envelope characteristics; delivery path
information 
			(3)	Quantity? (i.e. DCC)

3)	Spam Responses - These are the different approaches that can be
taken upon receipt. 

	a)	Accept
	b)	Quarantine
	c)	Reject
	d)	Drop
	e)	Label
	f)	Challenge
	g)	Limit Rate
		i)	Ingress
		ii)	Egress
	h)	Feedback 
		i)	to detection systems i.e. blacklists, reputation
systems, learning content filtering methods
		ii)	to other response systems
	i)	Charge
		i)	Confirmed payment (i.e. Bonded Sender, Trusted
Sender)
		ii)	Pursue payment (i.e.Habeas)
	j)	Legal Prosecution
	k)	Malicious response (e.g., teargrubbing and hackback)