[Exim] Spam Filtering Question

Can anyone recommend a spam filter I can use with exim that will deliver
spam to a mailbox or a subfolder of inbox (for IMAP collection) that will
work with exim?

I have exim running off mysql and have tried an ACL based spam filter (to
reject at smtp data time) but didn't like it cos you have no way of knowing
what is being rejected/filtered.

Any advice gratefully received.

Adam