Mairix is a tool for indexing and searching words in locally stored mail. It was written by Richard Curnow and is licensed under the GPL. Mairix comes with most popular GNU/Linux distributions, but it also runs under Windows (with cygwin), Mac OS X and Solaris. The homepage can be found at http://www.rpcurnow.force9.co.uk/mairix/index.html
Though mairix might not be as flexible as other search tools
like swish++ or namazu, which you can use via the
nnir back end, it has the prime advantage of being
incredibly fast. On current systems, it can easily search through
headers and message bodies of thousands and thousands of mails in
well under a second. Building the database necessary for
searching might take a minute or two, but only has to be done
once fully. Afterwards, the updates are done incrementally and
therefore are really fast, too. Additionally, mairix is very easy
to set up.
For maximum speed though, mairix should be used with mails
stored in Maildir or MH format (this
includes the nnml back end), although it also works
with mbox. Mairix presents the search results by populating a
virtual maildir/MH folder with symlinks which point to
the “real” message files (if mbox is used, copies are
made). Since mairix already presents search results in such a
virtual mail folder, it is very well suited for using it as an
external program for creating smart mail folders, which
represent certain mail searches.