Great little command line utility to index and search Maildir, MH or MBOX formatted mail folders. It creates a new mail folder with the results linked back to the mail so works transparently in any mail client that uses one of these formats for mail storage.
See: http://rajasuperman.blogspot.com/2007/07/using-mairix-through-procmail.html for an example of using with Procmail and Dreamhost.
Posted from Diigo. The rest of my favorite links are here.