Taxonomy of anti-spam techniques

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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Message content techniques

• Static filters

• Adaptive filters

SMTP techniques

• Timing and protocol defects

• Greylisting

Network techniques

• DNS blacklists

• Tarpitting and other timing techniques

Whitelist techniques

• Recognizing known correspondents

• Recognizing known responsible parties

Introduction techniques

• Challenges

• Proof of work

• Postage