The extension point IncomingMessageAnalyzer is a java interface that can be implemented by CorePlugins to analyze IncomingMessages before or instead of being analyzed by the knowledge base.
Your plugin receives an IncomingMessageAnalyzerInput that provides additional information about the incoming message and the analyze results of preceding plugins.
Your plugin can add AnalyzerDecisions (e.g. CategoryAnalyzerDecision) as a result of the Analysis and may add additional data to the storage of the ticket, that will be created after the message has been successfully processed.
Alternatively you can just pass transient data via the IncomingBindings to other plugins or the knowledge base.