silently discarding infected messages

Hi all

I'm trying to use exim's 'discard' ACL verb to silently reject messages
containing virusses.  Up to now I have used 'deny' which has the unwanted
effect of causing a bounce message to be generated by the upstream MTA.

Here's my complete data ACL:

check_message:

  # Skip anti-virus and spam checking if sending host is local
  accept  hosts = +relay_hosts
  accept  authenticated = *

  deny    message = This message contains malformed MIME
          log_message = R=<$recipients> malformed MIME ($demime_reason)
          demime = *
          condition = ${if >{$demime_errorlevel}{2}{1}{0}}

  # Use discard instead of deny to silently accept virusses and delete them.
  # The defer_ok causes the message to get through in case scanner is down.
  discard log_message = R=<$recipients> contains virus ($malware_name)
          demime = *
          malware = */defer_ok

  deny    message = This message contains an attachment we do not permit (.$foun
d_extension)
          log_message = R=<$recipients> contains attachment (.$found_extension)
          demime = bat:com:exe:pif:scr:vbs

  warn    message = X-Spam-Score: $spam_score
          condition = ${if <{$message_size}{80k}{1}{0}}
          spam = exim:true

  warn    message = X-Spam-Report: $spam_report
          condition = ${if <{$message_size}{80k}{1}{0}}
          spam = exim:true

  # Add new subject header if spam score exceeds spamd's threshold.
  # This header is temporary and is rewritten as the subject header in
  # the system filter.
  warn    message = X-New-Subject: [SPAM?] $header_Subject:
          condition = ${if <{$message_size}{80k}{1}{0}}
          spam = exim/defer_ok

  accept

The problem is that the log_message clause appears to be ignored.  When an
infected message arrives, the exim_mainlog shows

2004-08-17 10:03:08 1Bwzs3-0004A4-63 => blackhole (DATA ACL discarded 
recipients)

I'd like to be able to log the message recipient(s) and the name of the virus.
The exim spec seems to indicate that log_message should work with discard, but
it doesn't seem to work for me.

Any ideas?  Is there a better way to achieve what I'm after?

(Using exim-4.34 and the corresponding exiscan-acl).

Andrew Gay