ReplyUnknownCommand is a TIdReply property that represents the response code and text used when an unknown command is received during execution of a client connection. 

ReplyUnknownCommand is used during execution of the client connection task when COmmandHandlersEnabled contains True. Methods in the server are used to read the command and optional data from the client connection context. If a valid TIdCommandHandler instance in CommandHandlers cannot be located for the values read from the client connection, values in ReplyUnknownCommand are used to generate the response written using the IOHandler for the client connection. 

The default values in ReplyUnknownCommand are assigned during initialization of the component, and includes the following response code and text: 

Resources allocated to the ReplyUnknownCommand property are freed in Destroy.

TIdReply 

TIdCommandHandler 

TIdCommandHandlers 

COmmandHandlersEnabled 

Destroy