Imperator includes various chat channels you can use as well. Here's the full list of commands and what they do:
/chat global The default chat channel, everyone online can see this.
/chat nation If you are in a nation, this allows you to only talk to your fellow nation members.
/chat town If you are in a town, this allows you to only talk to your fellow town members.
/chat proximity This allows only players within a 50 block radius of you to see your messages.