The "free" version of outlook that replaced Mail is so bad that it made me finally switch to Thunderbird and I don't see myself going back anytime soon.
The only thing I'm missing sometimes is the Copilot integration, but copy and paste with Thunderbird is still faster than using Copilot in Outlook...
When I was using Thunderbird on Windows back years ago, i abandoned it in a week because it was absolutely slow when fed with years of archives as compared to Outlook 2010. Seeing recs for Thunderbird recently says something for sure.
Apparently, they did a rework of the interface a few years ago.
https://github.com/thunderbird/developer-docs/blob/master/th... and https://blog.thunderbird.net/2023/02/the-future-of-thunderbi...
I don't even think Thunderbird has gotten any significant speed improvements over the years (unlike Firefox). The only real reason it's gotten better on that front is that processors and I/O have gotten faster. Meanwhile, Outlook as managed to take every morsel of improved hardware, and squandered it.
I've never had problems with Thunderbird on that front, but then again, I've never had email accounts with 100k emails archived.
I really like Betterbird. It's basically ESR Thunderbird + a few fixes.
If you want mail to just work and updates going smoothly it's the solution.