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.