NekoProxy

That's a plugin that can build a bridge between two minecraft servers to allow players talking with the another server, although the player don't want to join the target server.

If you want to run this plugin, you need to create a extra public port(Such as 8081).

You have to edit the config file for connection. You can find primary "config.yml" in plugins/NekoProxy folder after you reboot your server. That's a example for config:

If your server use NAT, you need to create a NAT proxy to open the internal port to public.

Theoretically, the plugin support all the minecraft version from 1.21 to 1.21.11, but the version between 1.21.3 and 1.21 wasn't tested. If you decide to try, remember that you can't get support from everywhere.

Certainly, you can also connect version 1.21.x with 1.12.2.

When connect successfully, you can set a priefix "_" before your sentence to send, then that sentence will be sent to target server. If process finished, the system will change the _ to * on local.