However, the State Department networks are such an obvious target that I would be shocked to find that their IT groups were completely free of Chinese/Russian/Israeli agents. Would you be willing to bet that the Italians didn't have somebody snooping on SoS messages too?
Security by obscurity: set up your own server that they don't know about. (Although after the first few messages somebody will figure it out...) It is just lagniappe that the records are under your control and any dicey quid pro quo agreements can be kept out of the public eye.
I wonder how many others do the same.