Tried this command, said there were none in the sector. Then I went and stood next to a mailbox and got the same result. How do you make this function?

It functions off the updated database values (the launcher fetches an update the same time it uploads your information) For some reason, some of the mailboxes aren't detected and we've been looking into it.

One thing to try for now is '/mf inn'. Hopefully we'll have it fixed for burning crusade, as some of the location code had to be updated.