Kerio Connect provides the SpamAssassin Bayesian filter as part of the spam filtering mechanism.
This article provides clarifications about SpamAssassin in the context of Antispam licensing.
The Kerio Anti-spam is a paid extension. If you don't have it purchased, the Anti-spam tab will be showing "Kerio Anti-spam advanced filter is not licensed".
However, Apache SpamAssassin filtering is a standalone product functionality, which does NOT require purchasing any extensions. The message filtering will function as a standalone feature. By default, the status will be shown as Learning with appropriate counters for "Messages learned as spam" or "not spam".
For more information about the SpamAssassin learning mechanism, please refer to Bayesian self-learning in Kerio Connect.