Fast system for indexing, searching, and tagging email. Even if you
receive 12000 messages per month or have on the order of millions of
messages that you've been saving for decades, Notmuch will be able to
quickly search all of it.
Notmuch is not much of an email program. It doesn't receive messages
(no POP or IMAP support). It doesn't send messages (no mail composer,
no network code at all). And for what it does do (email search) that
work is provided by an external library, Xapian. So if Notmuch
provides no user interface and Xapian does all the heavy lifting, then
what's left here? Not much.