We’re back with another progress report as we continue improving K-9 Mail for its transformation to Thunderbird for Android! We spent most of the previous month preparing for a new stable release. In April 2023, we finally published K-9 Mail 6.600.

K-9 Mail 6.600

Along with a couple of new features, a lot of changes and bug fixes went into the new K-9 Mail version. However, space for release notes in app stores is very limited. So we went with this list of changes:

  • Redesigned the message view screen; tap the message header containing sender/recipient names to see more details
  • Added a setting for three different message list densities: compact, default, relaxed
  • Added better support for right-to-left languages when composing messages
  • Search now also considers recipient addresses
  • Fixed a bug where notifications would sometimes reappear shortly after having been dismissed
  • IMAP: Fixed a bug where sometimes authentication errors were silently ignored
  • Various other small bug fixes and improvements

Missing home screen widgets

After learning that an old bug in Android had finally been fixed in 2021, we changed the app to disable home screen widgets by default and only enable them after the user had added at least one account to K-9 Mail.
Of course we limited this to Android versions that should include the fix. However, this didn’t quite work as intended and existing home screen widgets disappeared on some devices. So we reverted the change in K-9 Mail 6.601.

K-9 Mail 6.7xx

With the stable release out the door, it was time for a new series of beta releases to test early versions of features and fixes that should go into the next stable release.

Bug fixes

The first beta version (6.700) didn’t include any new features, but fixes quite a few bugs (mostly obscure crashes).

IMAP ID extension

The GitHub user wh201906 contributed code to add support for the IMAP ID extension (thank you). It is used by an email client to send information about itself to the IMAP server. In turn, the server responds with some information about itself (name, software version, etc).

Unfortunately, some email providers reject clients not using this extension, even though the specification explicitly states the extension must not be used for that purpose. To make K-9 Mail work with such email providers without users having to change a setting, we decided to enable this functionality by default. Also, because we want to align our default values with Thunderbird, and it’s enabled there by default.

The information sent to the server is limited to just the app name – “K-9 Mail”. If you wish, you can disable this feature under Settings → <Account> → Fetching mail → Incoming server → Send client ID.

Next: Improved account setup

The main goal for the next stable release is to improve the account setup experience. Many new users are struggling with setting up an account in K-9 Mail. That’s because K-9 Mail only supports automatic account setup for a handful of large email providers. For all other email providers users have to manually enter the email server settings. And this can be a very frustrating experience.

Ideally, users only have to provide their email address and the app will figure out the rest. We’ll be adding support for Thunderbird’s Autoconfig mechanism which aims to deliver just this user experience.

Hopefully, we’ll be able to ship a first version of this in a beta release in May.


In April 2023 we published the following stable releases:

… and the following beta versions:

If you want to help shape future versions of the app, become a beta tester and provide feedback on new features while they are still in development.

This progress report was also published in the Thunderbird blog.