Notmuch -- Just an email system

Notmuchmail helps to do fast, global-search and tag-based email system to use within your text editor or in a terminal. "Not much mail" is what Notmuch thinks about your email collection. Even if you receive 12000 messages per month or have on the order of millions of messages that you've been saving for decades. Regardless, Notmuch will be able to quickly search all of it. It's just plain not much mail.

"Not much mail" is also what you should have in your inbox at any time. Notmuch gives you what you need, (tags and fast search), so that you can keep your inbox tamed and focus on what really matters in your life, (which is surely not email).