smtp irule for access control

basically I have a new rule set that implements a whitelist, a blacklist and a greylist however one part I am missing is the dnsrbl ability in milter-greylist that now I have to figure out any one have any ideas?

My irule is as so

 
when RULE_INIT {
  set static::debug 1
}

when CLIENT_ACCEPTED {

if { [class match [IP::remote_addr] equals  smtp_relay_allowed ] } {
    log local0. "Node  IP address is: [IP::remote_addr] whitelisted as smtp_relay_allowed"
    snatpool smtp_mailpool
   }
if { [class match [IP::remote_addr] equals  smtp_spambot_reject] } {
    log local0. "Node IP address is: [IP::remote_addr] rejecting due to data group smtp_spambot_reject"
    reject
   } else {
   snatpool untrust_smtp_mailpool
   }
}

so the above allows smtp to pass into a whitelist from internal sources, to drop bad known spammers and then pass anyone else to a snatpool ip range that gets evauled by milter-greylist, however I would like to also account for stuff like

dnsrbl "PBL" zen.spamhaus.org

acl greylist dnsrbl "PBL" delay 66m