[exim] Exim with AntiVirus

Hi

I am configuring our exim to check the presence of virus on the mail.
I've configure the follow lines in to configuration file:

In global config:

av_scanner = clamd:/var/run/clamav.socket

And in the acl

acl_check_mime:

# Decode MIME parts to disk. This will support virus scanners later.
warn decode = default

  # File extension filtering.
  deny message = Blacklisted file extension detected / Tipologia di file non
autorizzato
       condition = ${if match \
                        {${lc:$mime_filename}} \

{\N(\.exe|\.pif|\.bat|\.scr|\.lnk|\.com|\.reg|\.vbs|\.cmd|\.msi|\.dll|\.)$\N
} \
                     {1}{0}}

  # Reject virus infested messages.
  deny  message = This message contains malware ($malware_name)
        demime = *
        malware = *

accept

In to mine mainlog file I've the follow message for all incoming mails:

temporarily rejected during MIME ACL checks: cannot test demime condition in
MIME ACL
For configure mine exim I've refered to mini-howto of Tim Jackson

How can solve the problem?

Andrea