OnCommandVRFY is a TBasicHandler event handler property that represents the event handle signalled when executing the SMTP VRFY command using CommandHandlers. 

OnCommandVRFY allows the SMTP server to verify that the TIdCommand.Params value specified in ASender contains a valid user name or email address for a mailbox on the SMTP server. 

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

TBasicHandler Messages TIdCommandHandlers TIdCommand