OnCommandHELP is a TBasicHandler event handler property that represents the event handler signalled when executing the SMTP HELP command verb using a CommandHandler. 

OnCommandHELP implements the processign needed to send the list of commands supported by the SMTP server to an SMTP client connection. 

The server implementation must assign a procedure to the OnCommandHELP event handler to allow responding to the event notification. When OnCommandHELP is unassigned, the text in Messages.ErrorReply is sent to the client connection. 

OnCommandHELP can be used to request more specific help detail by including an optional parameter value in the TIdCommand.Params found in ASender.

TBasicHandler Messages TIdCommand