Thunderbird
Thunderbird is a free, easy-to-set-up email application made by The Mozilla Foundation that is fully customisable and loaded with great features.
The Mozilla Foundation are a non-profit organisation that promote openness, innovation and opportunity on the Internet by engaging in unique partnerships with some of the world’s leading brands and non-profits, as well as with technology, content and service providers.
Thunderbird offers support for user privacy and remote image protection, supports the Do Not Track option and protects you from email scams which try to trick users into handing over personal and confidential information by indicating when a message is a potential phishing attempt.
At the heart of Thunderbird is an open source development process.