I've been working on an email client for about a year to fill the Newton Mail shaped hole in my heart. I put it in the store about a week ago.
Newton Mail: https://en.wikipedia.org/wiki/Newton_(software) Emma Email (my app): https://emmaemail.app
Emma only runs on iOS and only supports Gmail. I have started building it 3 times over the past 5 or so years - because Newton has gone out of business 3 times in that timeframe. The first two times, it was saved by savior companies who bought and revived it, so in those two instances, I stopped working on a "rebuild". The most recent time it went out of business (June/July 2024), it died permanently. Nobody saved it and despite promises from the most recent company that bought / revived it that if it went out of business again, they'd open source it, that never happened. I'm not super upset about that; que sera. Especially after contacting those people (the last company that revived Newton), via reddit about their stack. Sounds like it was a mess of legacy code