Eudora

Eudora OSE is the Open Source Edition of one of the internet’s most pioneering and enduring applications. It is a re-imagining and re-implementation of classic Eudora features on top of the Mozilla Thunderbird codebase. It is more than just an extension, as certain functionality required changes to the core of the application. Some of these have been accepted into and become part of Thunderbird, while others are still awaiting acceptance. Eudora OSE integrates so tightly with specific versions of the underlying code that it is highly recommended for users to install the entire application, rather than trying to run the extension on top of Thunderbird.

Download: wiki.mozilla.org/Eudora_Releases