RE: C version of SURBL client?
A while back, I was looking for a command line based Bayesian filter which was compatible with windows and had good performance.
If found the following:
http://www.fourmilab.ch/annoyance-filter/
This program will work on Unix and Windows, is written in C, and does things like decodes base-64 stuff, etc. I don't know the licensing info. However, if the licensing is right, it would be a great place to start for building a C version of SURBL because I think they publish the full source code for anyone to use. Theoretically, someone could start with this source code and build this.
Rob McEwen