[Exim] Exim & bogofilter

Hello!

    I want use Exim 4 with Bogofilter spam filter. Does anybody did
this? The idea of bogofilter is that it reads message from stdin or from
specified file and returns 0 if message is spam and 1 otherwise. As I
understand I should
use system_filter with contruction like:
if "${run{bogofilter}{}}$runrc" is 0 then
    fail text "Spam is not allowed"
else
    mail
endif

But I can't understand how to redirect message to file or to stdin for
bogofilter

Boris