I’ve attached a patch that allows prepending broadcast messages with an administrator defined string. I’ve chosen plugin.broadcast.messagePrefix as the name for the new property associated with this. If this property is not set then broadcast messages are not modified.
plugin.broadcast.messagePrefix = "(broadcast) "
Sending message “who ate my lunch?” to email@example.com results in all recipients receiving “(broadcast) who ate my lunch?”.
I hope this proves to be useful for others.