Ask HN: Recommendations for macOS Mail Client

I'm looking for recommendations for macOS mail clients for a friend who's just got their first Mac. Their requirements are:

- Configurable to not mark emails as read when viewed on the preview pane (which rules out Apple Mail, which otherwise would be suitable)

- Support for using iCloud Contacts (and iCloud Calendar if it includes calendar functionality), ideally by using the system contacts and calendar, though adding iCloud through CardDAV and CalDAV would also be acceptable

- Free or a one-time purchase (no subscriptions)

- No mandatory cloud features (optional is fine as long as it's able to be turned off)

Any suggestions?