[exim] trouble blacklisting an address

I'm trying to blacklist certain address contained in
/usr/exim/blacklist.senders

using this in acl_check_data:

   warn          log_message = "Blacklisted Sender"
                 senders   = lsearch;/usr/exim/blacklist.senders
   drop          message   = "Sender Blacklisted"
                 senders   = lsearch;/usr/exim/blacklist.senders

It works for most messages, the following one, doesn't seem to work
=====
Return-path: <>
Envelope-to: user@???
Delivery-date: Tue, 01 Feb 2005 15:26:47 -0800
Received: from [213.150.10.2] (helo=smxsat2.smxs.net)
    by mydomain.com with esmtps (TLSv1:DES-CBC3-SHA:168)
    (Exim 4.43)
    id 1Cw7Py-0004Hu-BV
    for user@???; Tue, 01 Feb 2005 15:26:47 -0800
Received: by smxsat2.smxs.net
    with XWall v3.31i ;
    Wed, 2 Feb 2005 00:26:12 +0100
From: System Administrator <postmaster@???>
To: "user@mydomain" < user@mydomain >
Date: Wed, 2 Feb 2005 00:26:12 +0100
X-Mailer: XWall v3.31i
Message-ID: <349921572.1526181343.2772@???>
Mime-Version: 1.0
X-SA-Exim-Connect-IP: 213.150.10.2'
=====

based on that, i'm trying to blacklist "postmaster@???"

either acl_check_rcpt isn't limiting iteself to local domains:
====
   accept  local_parts   = postmaster : mailman
           domains       = +local_domains : 64.207.133.54
====

or i'm reading those headers oddly

any suggestions?