What I have learned so far is that using omemo in xmpp is completely dependant on the client. The server and installed xmpp server software have nothing to do with it.
But is this absolutely true?
My question is:
Can a server admin by some regular means enforce or prohibit the usage of encrypted omemo messages for his server's users?
I am talking about 1to1 chats, no MUCs. Would the answer for MUCs differ?
(by 'regular means' I mean options or functions of the server software, no extreme hacks like analysing the byte stream or sth.)