Like many of the products in this review, Katharion's uses a multilayered analysis, including Bayesian and heuristic filters and blacklists, and open-relay databases to arrive at an overall probability that a message is spam. The company leases space in data centers on the East and West Coasts for redundancy and high availability and provides multiple MX entries to its customers to ensure mail is delivered.
Katharion Anti-Spam had the highest false-positive rate and also the lowest false-negative rate of the Top 10 vendors we tested, which means that its default spam threshold was more aggressive than the other products we tested. We could set the spam threshold to one of four levels of aggressiveness: very high, high, medium and low, and we were able to determine how we wanted detected spam to be handled. For our accuracy test we tagged it as spam and sent it on to the intended recipient for additional processing using mail server rules. Alternatively, we could have deleted it, directed it to Web mail (hosted by Katharion or locally), or returned it to the sender. Anti-Spam can be configured so that users have the same control over the fate of spam addressed to them as admins have for their domains. By logging on to the Web-based control panel, users can also manage their own whitelists and blacklists.
Katharion Anti-Spam for Businesses. Katharion, (866) 667-7266, (310) 571-3200. www.katharion.com 
Espion's Interceptor is an open-source-software-based appliance that makes use of some well-known open-source products. But Interceptor's lack of clustering, virus scanning and distributed administration moved it to the bottom of our report card. Espion assured us that its next release, which should be available by the time you read this, will include ClamAV for virus scanning, and the following release will include clustering.
The Interceptor sanitizes e-mail by correcting malformed messages that can contain malicious code, then using deterministic and predictive filters along with real-time blacklists to score a message on its spaminess. Espion includes a long list of attachment filters; we were able to add new attachment extensions and delete existing extensions using the Web-based management interface.
Espion includes a well-designed spam quarantine and digest mechanism. We easily retrieved ham from quarantine by clicking on a link in the HTML-based quarantine digest message. Administrators can designate trustworthy users to help train the Bayesian engine by marking false positives in the quarantine area. False negatives can be placed in a mailbox set up to provide additional opportunities for training the Bayesian filter.
