[exim] I cannot get demime file extension blocking working

Hi,

I have this simple ACL:

acl_check_data:
        deny    message = This message contains an unwanted attachment
type.
                demime =
bat:btm:cmd:com:cpl:dll:exe:lnk:msi:pif:prf:reg:scr:vbs:url:cab:mp2:mp3:mpeg:msi:wma:wmv:zip

It doesn't seem to do anything and I can't see any reference to it
when running in debug mode. Is there something else I have to do to
get acl_check_data enabled?

Thanks,
Adrian.