I've created a usergroup called "Melbourne cruisers", so I can send a mass PM to anyone whio has been on any of our cruises, notifying them of new ones.
Membership of the group is purely voluntary, and people can join or leave the group whenever they want.
If any of the other states would like to setup a similar facility, PM me to discuss it. You'd have to nominate one or more people who would have permission to send messages to the group, as I think it would get annoying if anyone could send mass PMs like that.