We often get asked how many people participate in the project.
Leading the project is Jörg, who served as Thunderbird's first employee as well as maintainer and release engineer from 2016 to 2019. In addition, a seasoned Thunderbird contributor has provided many of the improvements. There are people who send the occasional patch, they are not always visible on GitHub since we commit their work after revision.
Others maintain platform distributions such as Flatpak, Arch Linux, Winget, and Chocolatey, and one volunteer compiles for the ARM processor of Android devices.
We have translators for Czech, Italian, Japanese, Dutch, Polish, Portuguese, Russian, Ukrainian, Swedish and Chinese (listed in alphabetical order by locale code).
We're in personal contact with many of our users who point out bugs, motivate improvements, do testing, and also file upstream bugs on Thunderbird's bug tracker Bugzilla. Sometimes the Thunderbird folks get interested in those bugs and we can include their fixes earlier than they do.
Our project is rather humble, we don't have the many millions the Thunderbird team can rely on. We don't have ~50 staff (amongst them four directors, nine managers, one coordinator and five "specialists"), and we don't have access to the Mozilla server farm used in Mozilla's automation.
Our hardware is rather humble: One Windows build machine, a fast Asus NUC 15 Pro Plus (see picture), and two Mac Minis (Intel + Silicon) for the Mac builds. Linux is compiled in a VM on Windows. This setup makes the project quite flexible; over the years we've shipped releases from three countries on two continents.