What is tarpit?
Tarpit is an option in Spam Blocker. If Tarpit is checked, when an SMTP session is first caught Spam Blocker will check if the client IP is on a DNSBL. If it is it will reject the session, if not, the session will be accepted. This means that SMTP connections are outright refused from blacklisted servers before they can even send email. This increases the total spam capacity of a given server by quite a bit and also saves bandwidth. However, it may increase false positives as all emails from blacklisted servers are rejected. Tarpit events are in the DNSBL Eventlog. Disabling tarpit does not disable DNSBL usage, it only disables the preemptive check during session initiation time. DNSBLs will continue to be checked and positive hits will increase the spam score.
