• Mobile

Thunderbird for Mobile April 2025 Progress Report

Here is an update of what Thunderbird’s mobile community has been up to in April 2025. With a new team member, we’re getting Thunderbird for iOS out in the open and continuing to work on release feedback from Thunderbird for Android.

The Team is Growing

Last month we introduced Todd and Ashley to the MZLA mobile team, and now we have another new face in the team! Rafael Tonholo joins us as a Senior Android Engineer to focus on Thunderbird for Android. He also has much experience with Kotlin Multiplatform, which will be beneficial for Thunderbird for iOS as well.

Thunderbird for iOS

We’ve published the initial repository of Thunderbird for iOS! The application doesn’t really do a lot right this moment, since we intend to work very incrementally and start in the open. You’ll see a familiar welcome screen, slightly nicer than Thunderbird for Android and have the opportunity to make a financial contribution.

Testflight Distribution

We’re planning to distribute Thunderbird for iOS through TestFlight. To support that, we’ve set up an Apple Developer account and completed the required verification steps.

Unlike Android, where we maintain separate release and beta versions, the iOS App Store will have a single “Thunderbird” app. Apple prefers not to list beta versions as separate apps, and their review process tends to be stricter. Once the main app is published, we’ll be able to use TestFlight to offer a beta channel.

Before the App Store listing goes live, we’ll use TestFlight to distribute our builds. Apple provides an internal TestFlight option that doesn’t require a review, but it only works if testers have access to the developer account. That makes it unsuitable for community testing.

Initial Features for the Public Testflight Alpha

To share a public TestFlight link, we need to pass an initial App Store review. Apple expects apps to meet a minimum bar for functionality, so we can’t publish something like a simple welcome screen. Our goal for the first public TestFlight build is to support manual account setup and display emails in the inbox. Here are the specifics:

• Initial account setup will be manual with hostname/username/password.
• There will be a simple message list that will only show the INBOX folder messages, with a sender, subject, and maybe 2–3 preview lines.
• You’ll have the opportunity to pull to refresh your inbox.

That is certainly not what you’d call a fully functional email client, but it could qualify for bare minimum functionality required for the Apple review. We have more details and a feature comparison in this document.

In other exciting news, we’re going to build Thunderbird for iOS with JMAP support first and foremost. While support on the email provider side is limited, we start with a modern email stack. This will allow us to build towards some of the features that email from the late 80’s was missing. We’ll be designing the code architecture in a way that adding IMAP support is very simple, so it will ideally follow soon after.

iOS Release Engineering and Localization

We’ve also gone through a few initial conversations on what the release workflow might look like. We’re currently deciding between:

• GitHub Actions with Upload Actions (Pro: very open, re-use of some work on the Thunderbird for Android side. Con: Custom work, not many well-supported upload actions)
• GitHub Actions with Fastlane (Pro: very open, well-supported, uses the same listing metadata structure we already have on Android. Con: Ruby as yet another language, no prior releng work)
• Xcode Cloud (Pro: built in to Xcode, easy to configure, we’ll probably get by with the free tier for quite some time. Con: Not very open, increasing build cost)
• Bitrise (Pro: Easy to configure, used by Firefox for iOS, we’ll get some support from Mozilla on this. Con: Can be pricy, not very open)

For now, our release process is pressing a button every once in a while. Xcode makes this very easy, which gives the release operations more time to plan a solution.

For localization, we’re aiming to use Weblate, just as Thunderbird for Android. The strings will mostly be the same, so we don’t need to ask our localizers to do double work.

Thunderbird for Android

We’re still focusing on release feedback by working on the drawer and looking to improve stability. April has very much been focused on onboarding the new team. I’ll keep the updates in this section a bit more brief, as we have less to explore and more to fix 🙂

• We’ve accepted a new ADR to change the shared modules package from app.k9mail and com.fsck to net.thunderbird. We’ll be doing this gradually when migrating over legacy code.
• Ashley has fixed a few keyboard accessibility issues to get started. She has also resolved a crash related to duplicate folder ids in the drawer. Her next projects are improving our sync debug tooling and other projects to resolve stability issues in retrieving emails.
• Clément Rivière added initial support for showing hierarchical folders. The work is behind a feature flag for now, as we need to do some additional refactoring and crash fixes before we can release it. You can however try it out on the beta channel.
• Fishkin removed a deprecated progress indicator, which provides slightly better support for Android watches.
• Rafael fixed an issue related to Outlook/Microsoft accounts. If you have received the “Authentication Unsuccessful” message in the past, please try again on our beta channel.
• Shamim continues on his path to refactor and move over some of our legacy code into the new modular structure. He also added support to attach files from the camera, and has resolved an issue in the drawer where the wrong folder was selected.
• Timur Erofeev added support for algorithmic darkening where supported. This makes dark mode work better for a wider range of emails, following the same method that is used on web pages.
• Wolf has been working diligently to improve our settings and drawer infrastructure. He took a number of much needed detours to refactor legacy code, which will make future work easier. Most notably,  we have a new settings system based on Jetpack Compose, where we will eventually migrate all the settings screens to.

That’s a wrap for April! Let us know if you have comments, or see opportunities to help out. See you soon!