[Exim] filtering during SMTP session

Some time ago I inquired into the possibility of

        message filtering during SMTP session, rather than
        after accepting the entire message and telling remote
        that it was OK.

        For example, if I am able positively identify a message
        as spam after seeing first few lines of the body I would
        prefer to reject it right away.

        I wonder if it was implemented as a feature or a patch
        by the current version.

        Thank you,

--ilya