Code contributions are very welcome, though. On the app settings page, find and tap on the Notifications. Select the app for which you want to change the notification sound. Scroll down and find the Apps or Applications option, then tap on it. Given that the amount of users this affects is getting smaller (because Android 8 has changed the way notifications are configured completely), this is not a high priority issue for me. To change the notification sound for specific apps on Android, follow these steps: Open the Settings app on your Android device. I created an entry for this in our issue tracker: Support custom notification sound on Android 7 and older Playing notification sounds is something that is handled by the system. The app only passes the opaque identifier it gets from the notification sound picker component to the notification system. And it shouldn’t be necessary, because the app never needs to access the notification sound itself. This is very unfortunate, because K-9 Mail no longer requests this permission. It looks like on Android 7 the custom notification sounds are only included in the list if the app has the permission to access external storage. But the list still comes from the system. K-9 Mail 5.800+ now uses a slightly different component to display the list of notification sounds. The app used a system component that would display the available notification sounds for the user to pick one.
K-9 Mail never included support for custom notification sounds itself.
