Espresso

Espresso is a powerful permissions-based email client designed to completely eliminate spam as you define it from your Inbox.

Espresso's powerful email filter is based on a sophisticated challenge-response system. All messages from approved and trusted senders are immediately accepted. Espresso doesn't rely on deep header analysis, anti-spoofing techniques, heuristics, or Bayesian filters to eliminate spam. It simply looks for the messages you want to receive using sensible, yet powerful rules. With a selection of options available, you decide how to handle messages from unknown senders. Espresso delivers all the email you want to read and blocks all the email you don't want. It's that simple!