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.

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summary: Remote Roster Management
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Introduction
============

This module adds support for [XEP-0321: Remote Roster Management] which
is commonly used to allow components such as transports to modify the
rosters of local users.