[Mailman-Users] KNOWN_USERS + SpamAssassin discarding lots of mail

I have in my mm_cfg.py :

KNOWN_SPAMMERS = [('X-Spam-Status', 'Yes')]

But for some reason this is discarding lots of mail. Is there some way I can turn up the debugging so I can see why these messages are being discarded? Where do these discarded messages go?

Thanks

Joel Heenan