A combination of thunderbird and mutt.
And bluemail on android...
From Wikipedia, the free encyclopedia
Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).
Distributions include the Linux kernel and supporting system software and libraries, many of which are provided by the GNU Project. Many Linux distributions use the word "Linux" in their name, but the Free Software Foundation uses the name GNU/Linux to emphasize the importance of GNU software, causing some controversy.
Community icon by Alpár-Etele Méder, licensed under CC BY 3.0
A combination of thunderbird and mutt.
And bluemail on android...
Icedove (Thunderbird) works well enough for me. Maybe the reason it's "old fashioned" is because it works well enough that it doesn't need to be changed that often.
In the proprietary software world we're used to UI's being redesigned on a regular basis for no user benefit.
I know it's not an answer you expect but I just use the official web client. I hate how there's 2+ sidebars and a lot of features I don't need in standalone clients. I just need inbox, spam, trash and probably search.
Thunderbird on my pc and the default ios app on my phone for my non proton mail email accounts I just use the proton mail website when I use my proton email
i still have to use windows occasionally, and just run thunderbird on that. When on linux i use aerc because i way prefer terminal applications in general, but also i am lazy and the setup took about three seconds vs. mutt which requires a bit more work.