This is Grendel -- a Java mail/news client. The grendel.storage.intertwingle package implements some of the ideas in <http://www.mozilla.org/blue-sky/misc/199805/intertwingle.html>. There are lots of spiffy ideas in intertwingle but the one focussed on here is just to keep a global database optimized for interesting searches across all folders. See http://www.mozilla.org/projects/grendel/ for more info.