Keeping your chats secure is a good idea, but end-to-end encryption is just the beginning of the list of options to consider when picking a messaging app.
I can almost guarantee you they are using it through a VPN or they have a western SIM card. If not I’d love to know what server they use, as I’ve tested this a bunch of times on several public and private servers and it’s always the same result. If it isn’t blocked on day 1 it will be blocked quickly.
This is odd because I know a few mainland Chinese people that use XMPP without problems (and afaik without a VPN).
Sounds like your server got blocked for another reason?
I can almost guarantee you they are using it through a VPN or they have a western SIM card. If not I’d love to know what server they use, as I’ve tested this a bunch of times on several public and private servers and it’s always the same result. If it isn’t blocked on day 1 it will be blocked quickly.