[Scottn1]

Another is The Bat!. I've personally been using this email client for PC for 10 years now. https://www.ritlabs.com/en/

It has extremely powerful filtering, multiple inboxes for all my accounts (I prefer to deal with them separately rather than the unified inbox trend), IMAP and recently redone outlook.com/Exchange pipeline, can encrypt local store, and it's very customizable (can have it do threading/conversation for example). Reminds me of the old Opera in this regard.

The UI is a bit dated imo as it has stayed true to it's same look the whole time I've used it and skipping the modern trend of Outlook-like email client looks, but this to me is part of it's appeal. Once you get used to it.