I think that Outlook as an experience has become significantly worse as o254 has advanced... I understand some of the reasons, such as managing millions of inboxes vs a few dozen on a private server. That said, it's kind of a mess.

I used Thunderbird for years, mostly to keep my NNTP feeds going, at some point, my mailboxes corrupted between versions (the NNTP site I was using didn't work right anymore) and I just kind of gave up at that point. It was in the dark time, before the more recent resurgence of dev activity, but NNTP didn't seem to be even a tangential focus.

I'd love to see a relatively easy open-source server for mail+contacts+calender that allowed the level of visibility, management and sharing that Outlook+Exchange/o365 offers. Right now, I have some of that, but not nearly the same.

Edit: Also, really sick of getting meeting change notifications in Teams for a meeting that is months away... just leave any meeting notifications beyond today/tomorrow in outlook, I don't need them in my workgroup app.