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Abstract

We present Active Spam Killer (ASK), a program that attempts to validate unknown senders before allowing delivery of their message. Validation occurs by means of a challenge reply sent to senders who are not yet known to the system. Messages are kept in a queue pending confirmation until the sender replies to the challenge. Further messages coming from confirmed senders are delivered immediately. In a sample of 1000 spam mails, ASK was 99.7% effective at blocking spam, resulting in only 3 spam messages being delivered. Other programs' best ratios were 97.8% or as many as 22 spam messages delivered.