MessageHandler An interface representing a message handler. 
MessageHandlerContext Well-behaved MessageHandler implementations should use as much as possible this interface to create approprate entities. 
MessageHandlerErrorCollector Message handlers should report here what they are doing Depending on the context in which handlers are run (either normal production run as from a scheduled service or in a test mode - a dry run - from UI) this information can be transparently routed to appropriate place. 
MessageHandlerExecutionMonitor This is extension to MessageHandlerErrorCollector interface for with a few reporting methods around Messages. 
MessageHandlerFactory This call is going to be moved away from API into JIRA Mail Plugin. 
MessageUserProcessor A set of User-related util methods which can be useful while processing Message objects. 


DefaultMessageHandlerContext This class has been made public only to allow easy unit testing by tests from other packages.