mairix is a program for indexing and searching email messages stored in Maildir
(see the documentation section below), MH or mbox folders. 

Some features:
  * Indexing is fast. It runs incrementally on new messages - any particular
    message only gets scanned once in the lifetime of the index file.  
  * The search mode populates a "virtual" maildir (or MH) folder with symlinks
    which point to the real messages. This folder can be opened as usual in
    your mail program.  (Note, if messages are in mbox folders, copies are
    made. Similarly if the virtual folder has mbox format, it is filled with
    copies of the matched messages.) 
  * The search mode is very fast.  
  * Indexing and searching works on the basis of words. The index file
    tabulates which words occur in which parts (particular headers + body) of
    which messages.  
