They claim it in the article, and in a few other publications, but I haven’t seen anything that explicitly confirms, from sunbird, that this is the case, including on their website. They also make claims on their website that conflict with that architecture, as I don’t believe it would be possible to E2E encrypt messages like they claim they do. I kinda wonder if the Mac Mini claim is an assumption that everyone just ran with, without confirming that it’s true. I could be wrong though, I’ll gladly eat my words if anyone has a primary source to cite, but that architecture and business model just doesn’t appear to be compatible with their claims.