ISPCon 2003 Evaluating Spam Control SolutionsBrandendenburg.com 1

1
Email Points of Control
UA User Agent MTA Message Transfer
Agent o originator i intermediate r
recipient

• Accountability
• Filtering
• Enforcement

• Filtering

MTAi1
MTAi2
DNS
2
Evaluating Proposals

• Adoption
• Effort to adopt proposal
• Effort for ongoing use
• Balance among participants
• Threshold to benefit
• Operations impact on
• Adopters of proposal
• Others
• Internet scaling What if
• Use by everyone
• Much bigger Internet
• Robustness
• How easily circumvented

• System metrics
• Cost
• Efficiency
• Reliability
• Impact
• Amount of Net affected
• Amount of spam affected
• Test scenarios
• Personal post/Reply
• Mailing List
• Inter-Enterprise

3
Cascading Control

• Types of Spam
• Accountable
• Legitimate businesses
• Aggressive marketing
• Absence of formal rules
• Rogue
• Actively avoid accountability
• Find a safe haven
• Not always seeking money

• Types of Control
• Legal
• Terminology
• Boundaries
• Whitelist
• Validate sender
• Validate sending policy
• Blacklist
• Arms race
• False positives

4
Be Careful What You Ask For

• Changes to complex systems always have
  unintended, negative consequences
• We must attack spam, but we must attack it
  carefully
• Attacking superficial spam characteristics
  invites an arms race
• Constantly improving tools, but constantly
  failing to reach a stable level of effectiveness
• Adequate solutions for one constituency might be
  inappropriate for another
• Look at their communications styles