Taxonomy of anti-spam techniques

From ASRG

Many people have invented many anti-spam techniques over the past decade. And a lot of the techniques keep being reinvented. Our goal here is to list all the anti-spam techniques we know, both the good ones and the bad ones.

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Contents 1 Message content techniques 2 SMTP techniques 3 Address management 4 Network techniques 5 Whitelist techniques 6 Message validation techniques 7 Introduction techniques 8 Administrative techniques

Message content techniques

• Static filters

• Adaptive filters

• URL filtering

SMTP techniques

• Timing and protocol defects

• Greylisting

• Callbacks

• Rate limits

• SMTP pull

Address management

• Tagged addresses

• Code words

• Disposable addresses

Network techniques

• DNS blacklists

• DNS validation

• HELO/EHLO Pattern Matching

• Tarpitting and other timing techniques

Whitelist techniques

• Recognizing known correspondents

• Path validation
  • Path validation manual techniques
  • SPF (Sender permitted from)
  • Sender-ID
  • SRS (Sender Rewriting Scheme)

• Marking valid mail client hosts

• Signatures

• Subject keywords

Message validation techniques

• Cryptographic signatures

• Signature callback

Introduction techniques

• Challenges

• Proof of work

• Postage

• Attention bonds* Path validation manual techniques

• SPF (Sender permitted from)

• Sender-ID

• SRS (Sender Rewriting Scheme)

• Captchas

Administrative techniques

• No spam notices

• Do not spam lists

• Abuse Reporting