- Added support for setting the notification vibration pattern on Android 8+
- Added support for setting a custom notification light color on Android 8+
- Added a setting to configure the notification sound on Android 8+ (because some vendor-specific Android versions removed this feature from their user interface)
- Restore 'new mail' notifications when the app is restarted
- Open message from notification in Unified Inbox if possible
- Hide sensitive information when sync and error notifications are displayed on the lock screen
- Added a setting to suppress notifications for chat messages
- Don't create notifications when manually refreshing the message list
- Don't show notifications for new messages when syncing a folder for the first time
- Removed the "hide subject in notifications" setting; use the "lock screen notifications" setting instead
- Fixed back button behavior when opening a single message from a notification
- A lot of other fixes related to notifications
- Added support for entering Reply-To addresses when composing a message
- Optionally show starred message count in side drawer
- Require the user to authenticate before unmasking server passwords
- Added a menu option to export the debug log under Settings → General settings → Debugging
- IMAP: Removed setting to enable remote search (it's now enabled by default; still requires an additional button press)
- Numerous other bug fixes and improvements (see change log entries for 5.9xx)