[exim] $run in data acl

Hi

I want to call pyzor in the data acl to check for spam.
However, I don't know how to pass the mails content to pyzor. I don't know
how to access the data file.
Neighter $MESSAGE_ID inside the called script nor the ${message_id} seem to
work...
If I could get some of this, I could read
/var/spool/exim4/input/$MESSAGE_ID-D

How can I get the mail data inside the data acl ?

Regards,
Steffen