Very cool to see this being worked on! I have always used IMAP for my work accounts and have been happy with that but I've recently set up as Exchange at my new job and was able to sync my work calendar, which I really liked. While I liked that, having push email was more important to me so I've since reverted back to IMAP set up for this account. If it is helpful, I wouldn't mind downloading the above APK to test. If you already have enough testers, I assume that if everything is well, you'll push the update through for the regular paid app.
Thank you for continuing to support this great app! I've had it since 2013 and absolutely love it.