Looking for a map of 2019? You’ve come to the right place.
After a month of testing, I’ve found a proper email client. It meets my requirements – runs on Android phone, works with a blended IMAP/POP server, connects only when necessary to poll mail, has reasonable controls.
The winner is: K-9 email. Free, open-source, supports all that I need, free, can auto-thread received mail, easy to operate, and well-documented for advanced features.