I used TB for a decade or more, then in the end quit, because it was bloating too much. It was a browser doing email, not an email client.
I then used Claws for a while, but came to really dislike it - lots of small UI issues.
Then I wrote my own email client in Python, Postgres for store, Apache/HTML front-end. That's been fantastic. Python does all the heavy lifting, you need to design a decent database.
Now I add features as I need them - few days I added the ability to specify how many times an email should be sent, when you need to spam the recipient for some reason (say, a company which is spamming you and is not responding in a reasonable or timely manner to GDPR requests).
The basic client design I've not seen elsewhere - but I've not used many clients so it may very well exist. There's a single inbox of email, and you define sets, and a set defines what is shown. So you don't move emails around between folders, you define what's shown, and you can have multiple sets concurrently - so for example, "inbound", "last 24 hours".
There are also a bunch of other small features which I've had in time for a long time but have never seen. For example, the from/to addresses have the localpart and domain separately, so you can order by domain. There's immediate in-page filtering, too, for each column, so you can just enter a few letters of what you know is the origin domain and bingo, there you go.