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. Notmuch integrates very well with the mutt client for fast and efficient searching in all your mails.