Possible to configure a room to allow remote JIDs?

I’ve been poking around with MUCs, and was wondering if it’s possible to have remote users join MUCs on my server, and if so, how?

So far I haven’t had much luck with having anyone join a MUC on my OF installation that is not an account on my server, and it would be nice if people from other servers can join the MUCs. Am I overlooking something?