Hello, I administer multiple independent Nextcloud installations. Every Nextcloud server has his own OpenLDAP server as the only user backend. The Nextcloud installations are federated among themselves and are in the respective trusted servers list.
When a user shares a folder within the Nextcloud server the recipient will get an email notification about that. Recipients from a federated server do not receive an email notification. This should not be since in certain circumstances (most names are to long) the user cannot recognize that some people in the share-search box are "remote" and are treated differently. A user should be able to rely on the recipient to be notified by email