The processofflinemessages can be used to make Corrade retrieve offline messages and process them.

llInstantMessage(CORRADE, 
    wasKeyValueEncode(
        [
            "command", "processofflinemessages",
            "group", wasURLEscape(GROUP),
            "password", wasURLEscape(PASSWORD),
            "callback", wasURLEscape(URL)
        ]
    )
);

• This command can be issued to make Corrade process offline messages that may consist of commands and chatter coming from other avatars or the simulator.
• In case the offline messages contain commands, the commands will be executed at the time that this command is issued.