A silly idea for sending a secure message on a Minecraft server ▣-▣-▣-▣-▣-▣-▣
Some servers may have problematic administration. I want to prevent certain users from communicating with each other, even outside the server.
The most logical thing to do in this kind of situation would be to use another platform to communicate, such as Discord, Telegram, etc. It's a good idea, but if you don't want people to find out about your social media accounts, throwaway accounts can be useful.
If the previous two approaches didn't interest you, here's a third one: one-time links and passwords.
Instances of privatebin [https://privatebin.info/directory/] are helpful. They allow you to send messages that can only be accessed once. This way, you can send a password [https://bitwarden.com/password-generator/], and if a staff member intercepts the link, the person you want to talk to won’t be able to access the content, and you’ll know you’re being spied on. If the staff gets the password, just generate a new one and try sending it again.
If the message isn't intercepted, your target contact will receive the password. If they receive the password, send another text—this time, a secure one using the same password they received.
I suggest sharing the link via written books (Here's a tip: don't sign the book—that way it's easier to copy the link), or shortening them and posting them on signs.
The only downside to this method is that if someone with a lot of power on the server impersonates your friend—acting like a skinwalker by mimicking them (same skin and nickname, maybe even the way they talk)—then playing on that server is like living on the edge.
You can do that by sending a link from https://hack.chat/ or https://www.leapchat.org in the password-protected message. Browser-based temporary chat services.
For voice calls, use an instance of Jitsi [such as https://meet.nadeko.net/] or Briefing [https://brie.fi/ng].
Please consider using XMPP. I don't use it myself—since I don't have anyone to use it with—but I like to spread the word.