@b It's a rule. You must trust your sysadmin. Trust me. I am one.
I *COULD* read all the email and private files on any of my servers. Do I? No. I have ethics.
"And you could be fired for doing so."
Yeah, if I was caught doing it. But I RUN THE SERVER. If I was that unethical I wouldn't have problems covering up my actions.

If you don't trust the person/people running your server, don't put sensitive information on that server.

It's not a Mastodon-specific thing.