> Apple ruined their IMAP client ("Mail") a few years ago

Please elaborate on this point. I’d like to know how it was before and how it is now.

> so now that world is basically Outlook and Thunderbird, and I'm sure I don't need to describe why Outlook is unacceptable.

Please also elaborate on why Outlook is unacceptable. I like hearing different perspectives.

I personally don’t use Outlook and don’t like it because it pushed a lot of non-standard things (for want of a broader and better word), is actually slow and painful to use, and exists to satisfy Microsoft’s agenda to make everything proprietary (AFAIK Outlook365/Microsoft365/Exchange Server by default disables IMAP, SMTP and POP citing those as insecure even though they’re usable with OAuth2).