This isn't Thunderbird. This is a Thunderbird theme.
Normal Thunderbird still gets two to three dozen email subject lines on the screen. I absolutely love it, I've been using it for over 20 years through the rough and through the good. We're in a good period now, and it's been a good period for quite some time.
just tried installing it in case last time I tried it >5 years ago was during the "rough".
I was impressed that it correctly inferred the IMAP and SMTP settings for my custom domain name, but after using it for ~30 seconds random old emails started appearing at the top of the email list, above my latest emails.
Maybe I'll try again in another 5 years.
edit: someone thinks i didn't wait for imap to finish. I did. My latest email appeared at the top. Then 30 seconds later some ancient emails popped up above it, seemingly triggered by scrolling in the email list pane.
Probably the same vendetta they I have against Windows. Every time I try it, I find it so frustrating. So every time I try, I afford it less and less patience.
I get something like that in the initial IMAP sync. Some of my old emails will surface to the top with the current date as today. Never really bothered looking into as it only happens once, but I've been assuming that the date header on those emails were missing.
Yes, I also had that problem and this is exactly the cause. When you resync the mailbox later it gets redated again. It is actually really stupid, because there are only TWO mandatory headers: Date and From. Getting this wrong seams to be really incompetent of the sender software.
Overview, seeing threads with more than a handful of e-mails completely, selection, tagging, dragging, deleting, marking as spam, in general all kinds of bulk actions.
A couple years ago I did run one of early Thunderbird versions in a Windows7 VM and it did look amazing too. TB designers are likely trying to improve UI but most updates are just change how it looks not necessary making it look better or improving UX. Though quick filter is a relatively recent addition if I'm not mistaken and I use it a lot.
Netscape 2.02 or Microsoft Mail client from back then looks amazing by comparison.