• Major redesign of the user interface
• Temporarily disabled Push (IMAP IDLE) until we can make it work reliable; your accounts will be polled every 15 minutes instead
• Deprecated support for the WebDAV protocol; new accounts can no longer be added
• K-9 Mail now requires Android 5.0 and newer
• Added support for Autocrypt setup message
• Added support for encrypted subjects
• Allow installation on external media (Android 6+ with adopted storage)
• Removed the broken option to store the message database on external storage
• Removed the 'remote control' interface third-party apps could use to change some settings in K-9 Mail
• Fixed a lot of bugs and probably introduced some new ones. Please report bugs.