A new script was created in order to get around this limitation, which is available here. If no argument is passed to the script, it will return the aggregate numbers for all the zones, and if the zone name is passed in as an argument it will give the numbers for that zone. In both cases it will return two lines. The first is the number of positve hits on the zone, the second line is the total number of requests to the zone.
In order to use the script with mrtg you will have to edit the $statfile variable to point at where rbldnsd is outputting it's stats. For each DNSBL, you have to setup a target in your MRTG config. The target for sbl.spamhaus.org would be:
Target[sbl.spamhaus.org]: `perl /etc/mrtg/rbldnsdstat.pl sbl.spamhaus.org` MaxBytes[sbl.spamhaus.org]: 4800000MRTG should then be run every five minutes using cron.
Title[sbl.spamhaus.org]: RBLDNSD - sbl.spamhaus.org
PageTop[sbl.spamhaus.org]: <H1>sbl.spamhaus.org requests </H1>