[exim] Greylisting ACL option

Hi Guys

I'm looking to possibly make an option in the ACL below to only greylist
domains written in a flat text file call greylist_domains:

defer message              = $sender_address has been greylisted
        log_message         = greylisted
        sender_domains    = ! +local_domains : ! +relay_to_domains
        set acl_m9            = $sender_host_address $sender_address
$domain
        set acl_m9            =
${readsocket{/var/run/greylistd/socket}{$acl_m9}{5s}{}{}}
        condition               = ${if eq {$acl_m9}{grey}{true}{false}}

Any suggestions would be welcomed.

Thanks
Craig