Mairix is a tool for indexing and searching words in locally stored mail (see: http://www.rpcurnow.force9.co.uk/mairix/index.html).
With the package mairix.el, you can call mairix from within Emacs to search and index your mails. Currently, Rmail, Gnus and VM are supported to display the search results (mbox format). However, mairix.el tries to be pretty general so that it should be easy to integrate other Emacs mail programs as well. For details, see the documentation and the source.
Attention Gnus users: if you use Gnus with Maildir/MH, use the native back end nnmairix.el instead. See GnusMairix for details.
mairix.el is currently in CVS (see EmacsFromCVS) but it also works with Emacs 22. You can always get the latest version here:
The info file for mairix.el can be found here:
You can also read the docs online: