using rbl.snark.net?
You shouldn't be. I'm not. I haven't maintained it for a year! I will update the site if and when I start working on it again.
rbl.snark.net response codes
ip address	reason
127.0.0.2	Previously blacklisted offender
127.0.0.3	Attempted third-party relaying
127.0.0.4	Listed by foreign dnsbl
127.0.0.5	Sender domain does not resolve
127.0.0.6	Host relayed spam, no reverse dns
127.0.0.7	Relayed spam to honeypot address
127.0.0.8	Not currently used
127.0.0.9	Unknown reason

more detailed descriptions
Previously blacklisted offender	This cretin has made it onto an accesslist previous to the rbl list, either because I added him by hand, or because he tried sending mail to a spamtrap address, and was automagically added.
Attempted third-party relaying	Third-party relay attempt blocked by sendmails standard check_relay
Listed by a foreign dnsbl	Listed in a foreign dnsbl, rejected by my mail server
Sender domain does not resolve	Envelope From: address does not resolve
Host relayed spam, no reverse dns	Spam sent to a honeypot address, relays ip address does not reverse resolve
Relayed spam to honeypot address	Spam sent to a honeypot address from this relay
Not currently used	Not currently used
Unknown reason	In the database for unknown reasons.
snark.net and its maintainers assume no responsibility for any application of the data in rbl.snark.net. furthermore all data in rbl.snark.net remains the property of snark.net and its maintainers, and any access to the data is at the requesters own risk. snark.net and its maintainers are not responsible for any losses incurred following any application of the data in rbl.snark.net.