Previous versions of XEP-0045 suggested sending a warning message to new occupants of a non-anonymous MUC room. The current revision (1.25) says that a status code of "100" must be returned with the user's initial presence, instead. We already do this (in addition to generating the warning message). Receiving the warning message each time the client joins the room can become annoying, especially when reconnections occur frequently (e.g., on mobile devices). So, we omit it, now.
Specify settings that make sense with current ejabberd versions, and use the YAML configuration format. Also, specify the "urn:xmpp:microblog:0" namespace, as that's the microblogging node name currently defined by XEP-0277.