Mailfilter is available in many different pre-compiled binary packages for various platforms. The requirements to merely run any of these are relatively little. However, if you want to compile the program's source code yourself, then your system must provide a few additional utilities and features.
Requirements to merely run Mailfilter:
Additional Requirements to compile the Source Code:
Also note that packages are already shipped with many systems, such as Debian, Mandriva, Fedora, and various BSDs. If you run any of these systems, then you may not need to compile from source at all.