Gmane is an archive of public mailing lists, accessible via the web and NNTP. It has been running for nearly 8 years, and now carries around 12000 mailing lists. It runs on Linux and is powered entirely by Free/Open Source software..
One of the services Gmane offers is a free-text search of over 70 million email messages, built using Xapian and libgmime, and running on a single server. In this presentation, you'll learn exactly how this works.