'553' error?

[Mike Nolan <nolan @ celery . tssi . com>]

Is this a variation on the anti-spam relaying blocking problem that we've 
discussed recently?  (And is there a list of the various error codes 
somewhere?)

> ... while talking to mail.kcinter.net.:
> >>> RCPT To:<xxxxxx@mail.kcinter.net>
> <<< 553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)
> 550 <xxxxxx@mail.kcinter.net>... User unknown
--
Mike Nolan