Thunderbird is a freeware email client which helps you organize, customize, secure and protect your email. There is a portable version for Windows (Linux/Unix with Wine) and installable versions for Win/Linux/Unix/MacOS.
This email client includes many features to help you manage your inbox. You can prioritize, find your important email with tags and a find bar helps you find content within your email faster. Choose options to help you be more productive, from the three layout views to the advanced mail filter capabilities.
Thunderbird's top priority is to protect your emails. It keeps them safely stored and protects you from phishing attacks, junk mail, also providing advanced features for email encryption. Thanks to open source process there are hundreds of security experts around the globe working around the clock to keep your email safe.
Finally Thunderbird has an Add-ons manager for extensions and themes, making it even easier for you to customize Thunderbird 2.
Portable version system requirements: Windows 98/Me/2000/XP/Vista/7, Wine on Linux/UNIX
Also you can find installable versions for Windows/Mac OS X/Linux here.
Download "ThunderbirdPortable_2.0.0.23_English.paf.exe" and install portable version into a folder of your choice. Then run "ThunderbirdPortable.exe".