[zafiro17]

I wish both the K9 and Thunderbird teams all the best. K9 needs some love, and so does Thunderbird, honestly.

I use Aquamail on Android and love it. Great feature set, works great with multiple accounts, lots of configuration options. It's not open source or free and I honestly do not care.

Back in the day it was something like USD 4. Now it's something like USD 25. Still worth it, and I don't mind paying for software if it keeps the developers in business.