Libra Esva uses a multilayer anti-spam engine,which allows it to block 99.97% of spam - Virus Bulletin Spam test July 2010 - with only 0.12% False Positive rate!
These incredible results are achieved by applying  13 successive levels of analysis to every incoming message before being delivered to the final recipient, as illustrated below:

The anti-spam engine Libra Esva uses  is particularly efficient as it filters 98% of email spam at the SMTP protocol level. This means  an infected message is rejected before it's received by the system, with obvious advantages of bandwidth, security and internal resource utilization!

A detailed description of the features of each layer of the Libra Esva anti-spam engine is available in the attached document, viewable here.