The quest for equivalent Exchange

Towards the end of the summer of 2023 my team at MZLA Technologies Corp, the Mozilla Foundation subsidiary that looks after Thunderbird, started discussing a fairly ambitious project: adding support for Microsoft Exchange's APIs. This would turn into an ambitious project that spanned over 2 years and resulted in the first new protocol to be natively supported by Thunderbird in over 20 years. In the first part of this duology, I'll go over the project's big picture, how we defined the project's direction, and the reasoning behind architectural decisions.