Any chance to fork the old version as a new (paid) app?

[MonkeyMatt]

You can continue using 5.600 for free:

How to downgrade to an earlier version?

Android does not support downgrading an app. So you have to uninstall the app, then install the old versions you want to continue using. Before doing that, you probably want to export your settings, though. Export K-9 Mail settings Open the drawer Select Settings Select Export settings Tap the Export button Select a destination and tap the Save button Disable auto update in Google Play Open the Play Store app Go to the details page of K-9 Mail Open the “three dots” menu in the upper rig…

The old version targets an old version of android so can no longer be uploaded to the google play store unless some big rework is done to meet the play store rules