There is a working prototype of both the general mail over Freenet infrastructure and a POP server which uses it. They are available in CVS. We don't currently have the management infrastructure for things such as nightly source or binary snapshots or even releases. Anyone interested in setting up an installer and some packaging scripts and such could really help things along. In the meantime you can fetch it from CVS, compile it yourself, and follow the configuration instructions to get it working.