It's been a little more than two years since Mozilla announced its plan to turn the K-9 open-source email client on Android to Thunderbird. At the time, the team said that an Android version of Thunderbird has been a popular request, and the company promised a "powerful, privacy-respecting email experience".

While Mozilla Thunderbird has been available on the desktop since 2003, the email client never became as popular as the Firefox web browser, and it will be competing with juggernauts on the mobile space. Thunderbird for Android already nails the basics with support for a wide range of email providers, and a unified inbox option, but for now, the team is more focused on fixing critical bugs with the help of the community.

For K-9 Mail users, a transfer to Thunderbird tool is available in the latest beta version of the app. Mozilla is also working on a transfer feature that will let Thunderbird desktop users transfer their data to the new Android client.

These days, innovation on email clients mostly comes in the form of generative AI features. Microsoft and Google are currently leading the way, though using Copilot in Outlook and Gemini in Gmail is not free.

A mobile version of Thunderbird may still be attractive for people who care about open-source development and others who find Gmail and Outlook too bloated. An iOS version of Thunderbird is still in development at Mozilla, but there's no ETA for it yet.