indexes and searches email in locally stored email

 mairix is a program for indexing and searching locally stored email messages.
 mairix supports Maildir, MH folders, and mbox formats.
 .
  * 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 folder with symlinks
  which point to the real messages. This folder can be opened as usual
  in your mail program.
 .
  * 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.