Message Filtering on Exchange 5.5

I am trying to block email coming in by country-code top-level domains. (ie : .uk, .du, .ru, .jp??etc) on an Exchange server. It would seem what a person would need to do is open up message filtering, click the ?Add? button, type in ?jp? (without quotes) and click OK. This should block mail coming in from the .jp domain, right? Can anyone confirm that by using the message filtering in Exchange 5.5, a mail server can effectively block incoming mail from those domains? (ie: block spam.jp, porn.jp, vol.com.jp, etc)
I would appreciate if the respondent would provide a reference to a book, web page, etc.)