Produced by the Mozilla Foundation (the same people who brought you the fantastic open source web browser, Firefox) Thunderbird is an excellent free and open source email client. The main reason we like this email application is that it’s compatible with most of the major free web-based email services, so if you use Hotmail, Gmail or Yahoo as an email provider, Thunderbird will enable you to manage your mails from a handy desktop application (you’ll need the free WebMail plugin).
There are, of course, plenty of other reasons to use Thunderbird to manage your emails, whether you use free webmail or have a POP mail account (or both). For a start, Thunderbird offers great tools for organising your mails - a sophisticated folder system, message tagging, and message history navigation that works just like your web browser’s history feature. The application also has strong privacy and security features, something that open source software arguably does better than its commercial counterparts.
Finally, Thunderbird is highly customisable - you can change the look and feel to suit your preferences, and you can choose from a wide range of free plug-ins and add-ons that extend its functionality and make it work the way you want it to.
Thunderbird is available for Windows, Mac and Linux from the project site: http://www.mozilla.com/en-US/thunderbird