Indeed they do use 11x but it’s still a possibility to cause issues. It’s entirely possible to manage a fleet of IPs across a net but it takes a solid plan organization plan. My company is big on the acquiring companies game where IP overlaps are a perpetual challenge when merging sites in and you need a mess of snat/dnat conversions to keep routing from getting in a knot.
There’s a function built into Thunderbird to create keys, and I think publish the public cert directly to the MIT repo.