You can run one on a cloud provider. You’re correct that intelligence orgs probably still can access them, but if you’re that high value of a target then you have bigger problems and / or can afford to build an air gapped system or whatever. If you’re just concerned about other companies mining your messages, self hosting in the cloud solves that.

Reminds me a bit of the old “is your adversary Mossad or not Mossad” decision matrix https://www.usenix.org/system/files/1401_08-12_mickens.pdf