Localization? One of the screenshots is clearly in a uk locale where it's a wastebin, not trash? However... that screenshot is still connected to a server where the trash folder is named trash. Changing the name of server folders is gross, regardless.
> - Each of the "reply", "forward", etc buttons are all menu dropdowns. Each menu is a small click target. Why isn't this just an overflow menu? Why can't these be customized?
How can you tell it can't be customized from the screenshots? I think it's setable in the preferences, but it's been along time since I used Claws. I don't remember drop downs next to the reply buttons (and can't fathom why they'd be there) either, though. Maybe some address selection? They can still be buttons and have drop downs next to them, though. That's nice for reply, and then have a reply all in a drop down next to it, because reply all is terrible, but sometimes needed. (Actually, in a perfect world, it might be nice to carry all the address info into the draft and be able to select people to send to later, but that's a change in substance, and has issues when you're saving drafts on imap and restoring them later)
> - The "connected" icon at the bottom appears to be stolen from an ancient Mozilla build (though I'm unsure of the origin). Is that truly the best visual indicator for connectivity in the year 2022?
I mean... You click on it, and get disconnected operations. You could update it, but why? It works, it's clear if you've used it. It's unobtrusive if you don't.
> - The inbox shows the file size of emails in two separate places, with a precision that goes down to tens of bytes. Why?
I see three sizes in the main view, one for the list, one for the whole inbox, one for the currently selected items. This is pretty handy if you are trying to clean up mail to manage a storage quota, which is fairly important for people who have a storage quota. I don't remember if Claws uses three significant figures for size or two digits after the decimal place. We can't really critique this without more information.
- The same icons are recycled in multiple places, like queue and outbox. Why can't they get more icons? Why aren't they distinct?
- Why is it called "trash" AND "wastebin" in the same place, with two different styles of icon?
- Each of the "reply", "forward", etc buttons are all menu dropdowns. Each menu is a small click target. Why isn't this just an overflow menu? Why can't these be customized?
- The "connected" icon at the bottom appears to be stolen from an ancient Mozilla build (though I'm unsure of the origin). Is that truly the best visual indicator for connectivity in the year 2022?
- The inbox shows the file size of emails in two separate places, with a precision that goes down to tens of bytes. Why?
Your idea of good or bad UI doesn't consider that this UI already has things that could be net improved without actually removing or changing functionality. "Designed" implies that thought went into how it's used and looks. Nobody is advocating making it look like Material UI.