In 2025, Thunderbird did something it hasn't done in over 20 years, since before even its first stable release in 2004: it grew built-in support for a new email platform. This new platform is Microsoft Exchange, the backbone of some of Microsoft's biggest communications and productivity tools.

This talk will briefly go over the step we took to try to define how to support new platforms and protocols in an old code base, and the challenges we encountered as we worked our way towards full email support for Exchange in Thunderbird.