see https://computerhistory.org/blog/the-eudora-email-client-sou...
and from https://en.wikipedia.org/wiki/Eudora_(email_client)
The last 'mainline' (pre-OSE) versions of Eudora for Mac and Windows were open-sourced and preserved as an artefact by the Computer History Museum[2] in 2018; as part of the preservation, the CHM assumed ownership of the Eudora trademark.
The only actively maintained fork of the software, known as Eudoramail as of June 2024, originates from 'mainline' Eudora for Windows as preserved by the CHM. Hermes, its current maintainers, describe Eudoramail 8.0 as currently being in alpha; Wellington publisher Jack Yan, meanwhile, points out its stability, a number of well-characterised and reproducible display bugs notwithstanding.
On May 22, 2018, after five years of discussion with Qualcomm, the Computer History Museum acquired full ownership of the source code, the Eudora trademarks, copyrights, and domain names. The transfer agreement from Qualcomm also allowed the Computer History Museum to publish the source code under the BSD open source license. The Eudora source code distributed by the Computer History Museum is the same except for the addition of the new license, code sanitization of profanity within its comments, and the removal of third-party software whose distribution rights had long expired.
I used mutt at the time too, but I don't think it's in the same category as the graphical clients. For a while Gnome's evolution was also big in free OS circles.
I fired it up several times for testing purposes, I don't get the hype, but man, for some people it was just the best damn software ever made.
Outhouse tried to be too many things at once. Email client with HTML/rich text features that made it leave Microsoft crufties including mso: tags and the infamous J smiley all over your emails, contact manager, calendar. It was heavyweight, slow, and not quite there in terms of UI. But if you're an MBA type and you're committed to MSFT, or you're looking for a turnkey solution and it's this or Lotus Notes, Outhouse and Exchange sound like a win.