I use Claws-Mail on Linux (and my wife on Windows). It has a conventional style GUI and is aimed at plain text, but it also can do spelling checking, plus display images, simple HTML, PDFs and more (some with plug-ins).
It doesn’t allow directly composing HTML messages, but you can attach any kind of file you wish. It has lots of other features such as message filtering, configurable toolbars and hotkeys, etc. It allows anti-spam filtering (with add-ons), Perl and Python scripting and can support encrypted email (e.g., using GPG)
One of it’s main advantages from my point of view is that it doesn’t try to be your secretary and organize (i.e., dictate) the way you work. (Even Thunderbird had a bit of that.)
We use Claws-Mail as an IMAP client, so all our mail is kept only on our local Dovecot IMAP server for privacy, but still can be accessed from more than one computer (even remotely, if an encrypted tunnel were used).
Claw-Mail can run on BSD, Linux, macOS, Solaris, Unix & Windows. And (of course) it’s free and Open Source.
1. https://www.claws-mail.org/
2. https://en.wikipedia.org/wiki/Claws_Mail
3. https://9to5linux.com/claws-mail-4-1-adds-text-zooming-in-the-message-view-many-other-new-features
Can it have mu,tiple, accounts? There are 3 of us and we like. To get all our mail in one account with 2 other sub accounts.
Thanks for going to the effort to type all that up.... I looked at Claws the other day Read many reviews on it.
I hate IMAP, and don’t allow the people who have email accounts on my server to use it either. I suppose it has value to government entities, and for businesses that are legally required to keep such records, but to me, it is like buying gold and then letting the seller store it for you.