Hello,
j-chkmail is the filter I developed. It's completely written in C language. It's intended to use very few ressources and be very fast.
Version 1.7 experimental has an interface for SURBL. I'm using it for two months now.
There are two interfaces to SURBL : DNS and local database. DNS based queries are much easier to administrate, but local databases are faster.
For the moment, only queries on local databases are validated. DNS queries is implemented but not yet validated.
j-chkmail is free software, but with downloading is limited to registered users. To become a registered user, you shall accept to identify yourself : name, domain, ..., and have some responsibility on the domain you'll be using it (don't ask a license to hotmail.com, unless you're the hotmail.com system administrator... 8-).
You can check it at :
Best,
Jose-Marcio