I hope that someday I will understand why people like Thunderbird. It is unequivocally the worst e-mail client I have ever used, excepting some early, extremely buggy versions of alpine. I tried it again recently as it is only one of only 3 e-mail clients I found that could do exchange oauth2[1]. It's possible that its interface isn't as objectively terrible as it seems, but it is gratuitously different; if you are g…
I don't know. I've been using it since 2005. Its UI is stable and efficient. Gets the job done and does not get in the way. And it's free software. You are not actually saying what you don't like about Thunderbird so it's hard to oppose anything to your comment. Why Thunderbird should change its UI if it works okay? Gratuitously different from what by the way? And to me, the UIs of Evolution and KMail don't seem that…
Thunderbird is ugly, atrocious on 4K screens, does not group messages by conversation like mail client have in the past 20 years, and insists on listing emails in side-by-side columns instead of using a more compact and space-effective layout like many mail clients in the past 20 years. It's got a menubar, 3 level of toolbars and a burger menu; unnecessary tabs, cramped spacing, and two search fields. It offers XMPP chat and in-browser junk filtering when the former is pretty much dead, and the second is not needed anymore since GMail and its modern competition.
Someone mentioned LibreOffice elsewhere in the comment, and both projects seems stuck in the 2005 UI, UX and feature wise. I actively avoid using them even if I have to resort to using subpar web applications.