For deployments that have https://hg.prosody.im/trunk/file/tip/plugins/muc/register.lib.lua#l7 and use https://modules.prosody.im/mod_muc_http_auth.html users can still register to a MUC even if they are not allowed to join. That means they would receive RAI or RMN, for instance.

This module allows sending a message to another MUC room.

    @other-room: hello

The message will appear in the other room as as

    <first-room/You> hello