[exim] Exim not allowing mailman command addresses

Hi all,
I am having a mail server running exim4 on Debian Lenny. There is also
a mailman instance on the domain. I have an issue with the setup where
mailman email commands are not accepted by exim. The acl causing this
issue is

<snip>
deny    domains       = +mailman_domains
    !condition    = ${if exists{MM_LISTCHK} {yes}{no}}
        message       = Recipient mailing list unknown
</snip>

This acl was added to deny emails to non-existent mailing lists but
this is denying mailman email command address like
<listname>-request@<list domain>. What could be the problem here?

Thanks & Regards,
Guruprasad