[DaveWalk]

As usual, I came here to look for recommendations :) I have been enjoying Mailspring[0], an OSS fork of Nylas Mail (RIP). I came across it while looking for the closest thing to Google Inbox (RIP also). Mailspring is cross-platform.

[0]:https://getmailspring.com/

[paulcarroty]

It's free, but not open source.

[DaveWalk]

I thought this was the source? https://github.com/Foundry376/Mailspring

Or are you referring to the cloud aspects of Mailspring, like read receipts etc?