It is not clear to me if the project is a new mail client based on the old Eudora codebase, or simply making that code portable to MacOS, but anyway, we already have a multiplatform, small but powerful and very fast mail client that shares a lot of concepts taken from the good old Eudora, and ready to be ported to MacOS: Claws Mail.
It's stable and works on most systems and hardware out there, Windows, Linux, BSD, including ARM SBCs (Raspberry PIs, etc). It does work under MacOS, but has to be built locally. If I wanted to make an easy to install Eudora-like mail client for MacOS I'd probably start by contributing to that project for being already very mature on other platforms; I use it on Linux since it was called Sylpheed -that's like 17 years back- and compared to Eudora I used before, from which I could import all email flawlessly, it has been a nice step forward without problems at all.
I used Claws on Linux. What a great little mail client. Software developers love rebuilding stuff for a variety of valid reasons, but one does ponder at the amount of rework done in the name of those reasons.
Interesting… I looked at Sylpheed some years ago and it didn't feel remotely like Eudora, and the Claws screenshots don't suggest very much has changed in the fork.
https://www.claws-mail.org/features.php?section=general
https://www.claws-mail.org/faq/index.php/Installation_and_Co...