I put up the complete ASF public mail archives as of about 3 weeks ago on Amazon's S3 and have made them public (let me know if I messed up, it is the first time I've done this). I also intend, in the coming weeks, to convert them into Mahout files (if anyone wants to help let me know).
There are 5 files:
The tarballs are organized by Top Level Project name (i.e. Mahout is in the public_l_o.tar file). The tarballs contain GZIP files by date, I believe. I believe the total uncompressed file size is somewhere in the 80-100GB range. That should be sufficient to drive some semi-interesting things in terms of scale, even if it is towards the smaller end of things.
As the ASF has very clear public mailing list archive policies, it is my belief that this data set is completely unencumbered.
From an ORP standpoint, this might make for a first data set for evaluation once we have the evaluator framework in place.