CommandHandlersEnabled is a Boolean property that indicates if command handler instances have been assigned for the server. When CommandHandlersEnabled is set to True, the TIdCommandHandler instances are used to respond to commands and data received from an executing client connection. 

The default value for CommandHandlersEnabled is IdCommandHandlersEnabledDefault as assigned during initialization of the component. 

Override the InitializeCommandHandlers method to assign the default command handlers at runtime (during activation of the server), or assign TIdCOmmandHandler instances (at designtime) using the IDE. 

Use OnExecute, when CommandHandlersEnabled is False, to provide alternate event handling for the execution of client connections to the server.

CommandHandlers 

TIdCommandHandler 

OnExecute