“Notmuch mail” is a fast, powerful, global-search and tag-based email system that you can use in your Linux text editors or terminal. Its development was highly influenced by Sup, and it offers performance enhancement to several Sup features.
It is not much of an email client, therefore, it does not receive emails or send messages but simply allows users to search quickly through a collection of emails. You can think of it as a library interface to extend an email program for fast, global and tag-based email searching functionality.
Notmuch has the following notable features:
Does not support IMAP or POP3 protocols
No mail composer
Supports tags and fast search
No user interface
Uses Xapian to perform its major task, hence “not much”
Supports several command-line utilities, email clients and wrappers for Emacs, vim text editors
Also supports Mutt integration script