I used Astro for a while and like it, but it is missing several features like color coded unified inbox, differentiated read receipts by email address (knowing who actually read an email sent to multiple people is helpful). I also found a few ‘features’ in Astro pretty annoying without the ability to turn them off, such as push notifications for read receipts. The ‘ai’ is also pretty bad and useless. Also, Astro does not have a Windows program, only iOS & Mac.
I have switched to Missive which has apps for iOS, Mac, & Windows. It seems to have all features of Newton, but it does require a subscription to unlock all features such as downloading full email history, which is a bit annoying. I wish something cheaper existed, but it doesn’t. I’ve tried literally every alternative out there like Spark, Polymail, Airmail, Astro, etc. I’ll keep looking if anything cheaper comes along that is as good as Missive