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It's awesome that they implement an email client. (hopefully open source) Opera Mail and Thunderbird were good free email clients, but now discontinued. What options are there (PC)? Outlook, Windows 10 Mail, Windows Live Mail/Outlook Express, Thunderbird, IBM Notes, OSX Mail. Ideally, I would like an email client that is as powerful as Outlook, has the UI of Google mail (especially the conversation view), has superb…
I like Postbox, which is a commercial fork of Thunderbird. Seems to hit most of your needs (not sure about the conversation view as I always turn off threads) and has some of the keyboard shortcuts of GMail. Definitely lets you store emails on disk / offline. Alas version 4 has been less stable than version 3 was. (Not free, but $20 is pretty cheap.)
Given that, I was going to wait until PB4 is no longer officially supported and make a full switch over to Thunderbird.