Description:

mairix is a program for indexing and searching email messages stored
in Maildir, 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.