If the government is on your list of threats you need a lot more than "private mail server".
If I were to live in the US, I would know when my server went missing. With Google or other cloud-providers they can do it behind your back.
> If it's located outside the US it's a valid target for all the TLAs.
And then can't seize it. It's physically secure. It may not be bullet-proof security-wise (what is?) but they can't rubber-stamp their way into it.
And for some people that's quite an important aspect.
We can, and we definitely should.
I mean, if you have a remote server- it's lawful for them to snoop (by their own law), but it certainly makes it harder, to gain access and maintain access- as these systems may be wildly different and hosts will be varying degrees of paranoid.
On a server owned by somebody else, which the US government can fully spy on, seize and lock down at a whim.
Now try that with a privately owned and administered server.