Sup is a console-based email client written in Ruby for people who handle large volumes of mail. It brings Gmail-style, thread-centered organization to the terminal.

Features

• Thread-centered archiving, tagging and muting
• Handling of mail from multiple mbox and Maildir sources
• Fast full-text search with a rich query language
• Multiple accounts, choosing the right sender when composing
• Ruby-programmable hooks and automatic tracking of recent contacts

Limitation: Sup does not always play nicely with other mail clients, because not every change can be synced back to the mail source. The wiki describes Maildir syncback.