Very belated reply, but I've been very happy with Postbox:
https://www.postbox-inc.com/
I use it on both Windows and on Mac. On my Mac, Postbox 5 is managing a local archive of ~20 years of email without problems. On Windows, I'm using the newer Postbox 7, though I use that with IMAP without storing things locally. On the plus side, I love its keyboard shortcuts, that it supports plugins (via some nerdy tweaks) so I can add back an editable Priority column, and I'm surprised to find I actually like the themes feature. The purple Valhalla theme makes me smile every day I use it.
However - there is no calendar feature, and its contacts book features are usable but minimal. I use Google Calendar & Google Contacts for those instead. I wish Postbox could cloud-sync with Google Contacts, or at least with CardDAV, but it doesn't. So it might not work for your needs.
Postbox isn't cheap, it's $79 for a lifetime license. But for me, email is absolutely mission critical, and I think it's a fair price to have the best email experience.