What is Thunderbird used for?

Thunderbird is an experimental GitHub copy of Mozilla's comm-central source tree, which contains the code for the Thunderbird email client. It is a good fit for contributing to Thunderbird development and building Thunderbird from source.

Is Thunderbird open source?

Yes. Thunderbird is open source. Its source code is on GitHub at mozilla/releases-comm-central and is written mainly in JavaScript.

Yes. Thunderbird is open source, so the software itself is free to use.

Can I self-host Thunderbird?

Yes. Thunderbird can be self-hosted on your own server or infrastructure.

What is Thunderbird an alternative to?

Thunderbird is an open-source alternative to Microsoft Outlook, Mailbird, Apple Mail and eM Client. Other open-source alternatives to Microsoft Outlook include Mailspring, Thunderbird for Android and FairEmail.

Is Thunderbird actively maintained?

Yes. The most recent commit to Thunderbird was on 2 October 2026. The project has 195 stars on GitHub.

Thunderbird: open-source alternative to Microsoft Outlook

About Thunderbird

This repository is an experimental copy of Mozilla's comm-central tree, set up so it can be forked on GitHub. Its README is the Thunderbird project README: Thunderbird is an open-source, customizable email client built on the same Mozilla platform that Firefox uses.

To build Thunderbird you need the Firefox repository as well, because the Thunderbird code lives in a comm subdirectory inside the Firefox source tree and the two share a lot of platform code. The README points to a Getting Started guide, a Building Thunderbird guide, a developer website and rendered source tree documentation.

Contributors can join the project's mailing lists, including a moderated planning list for higher-level topics such as future features, and follow the contributing pages on the Thunderbird site. The code is mostly JavaScript, and this repository holds the source rather than the packaged email application.

Key features

Source tree for the Thunderbird email client
Built on the Mozilla platform shared with Firefox
Thunderbird code kept in a comm subdirectory
Developer documentation and build guides
Mailing lists for development discussion

Good fit for

→Contributing to Thunderbird development
→Building Thunderbird from source

Built with: JavaScript
Tags: thunderbird; email-client; mozilla; source-code; javascript; desktop-app

Thunderbird: questions and answers

What is Thunderbird used for?: Thunderbird is an experimental GitHub copy of Mozilla's comm-central source tree, which contains the code for the Thunderbird email client. It is a good fit for contributing to Thunderbird development and building Thunderbird from source.
Is Thunderbird open source?: Yes. Thunderbird is open source. Its source code is on GitHub at mozilla/releases-comm-central and is written mainly in JavaScript.
Is Thunderbird free?: Yes. Thunderbird is open source, so the software itself is free to use.
Can I self-host Thunderbird?: Yes. Thunderbird can be self-hosted on your own server or infrastructure.
What is Thunderbird an alternative to?: Thunderbird is an open-source alternative to Microsoft Outlook, Mailbird, Apple Mail and eM Client. Other open-source alternatives to Microsoft Outlook include Mailspring, Thunderbird for Android and FairEmail.
Is Thunderbird actively maintained?: Yes. The most recent commit to Thunderbird was on 2 October 2026. The project has 195 stars on GitHub.