Warning banner for incoming external emails

[asnead]

Greetings,
Does Zimbra offer any method of creating a warning banner for all incoming external email messages? One of our higher ups saw this on a colleague's email and wants it implemented sooner rather than later.
I have not found any mechanism for doing this, and the only hit I got on a forum search was asking the same question. (viewtopic.php?t=60663) I am not a seasoned Zimbra admin, though, so it is certainly possible I missed it.
If the answer is that the feature is not yet there then that is fine, I just need to confirm it either way.