The technology behind the patent.

What the patent covers

The claims describe a mail-receiving system that evaluates a connection against a layered set of policies during the SMTP dialogue, where each layer can terminate the session with a permanent error before the message body is transmitted, and where policy is resolved per recipient, so two recipients on the same server can receive different answers to the same sender.

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Why it is different from a content filter

A content filter is a classifier: it receives a message and estimates whether it is spam. The patented approach is a policy engine: it answers a sequence of yes or no questions about the session, each based on a verifiable fact, and refuses at the first no. The two are complementary, and Spamjadoo includes a classifier for what passes, but the order matters. Refusing first means the classifier sees a fraction of the traffic and the receiver never stores what it refused.

Per-recipient policy

Because the decision is made at RCPT TO, the engine knows exactly who the message is for before deciding. That is what allows JMail aliases to carry their own rules, and what lets an ISP run different policy for each tenant without running separate servers.