notmuch (fast mail indexer for maildir)

Notmuch is an answer to Sup. Sup is a very good email program written

by William Morgan (and others) and is the direct inspiration for

Notmuch. Notmuch began as an effort to rewrite performance-critical

pieces of Sup in C rather than ruby. From there, it grew into

a separate project. One significant contribution Notmuch makes

compared to Sup is the separation of the indexer/searcher from

the user interface. (Notmuch provides a library interface so that

its indexing/searching/tagging features can be integrated into any

email program.)