Exchange 2007 anti spam

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I set up the anti spam filters on my exchange server 2007 yesterday (operates as hub, client access etc) and then configured the IP block list to access the spamhaus.org block list. From this moment on it seemed to block every mail coming in and sent a return message that their ip address is on the block list.

Do any of you exchange gurus have an idea why this might happen?

I've also heard that exchange 2007 might download a microsoft spam filter/block list like it does for outlook but can anyone confirm this?