[Exim] opt in dns blacklisting

This is a multi-part message in MIME format.
--
Hi

I'm planning on adding an opt in dns blacklist filter to my exim setup. I
just want to create a file with list of username@??? address's in
them. The address's in the file are those of people who want there email
checked against a black list. How would I go about getting exim to do this?
--
[ smime.p7s of type application/x-pkcs7-signature deleted ]
--