I notice that with the zen.spamhaus.org RBL, there's the following disclaimer :

"Because ZEN includes the XBL and PBL lists, do not use ZEN on smarthosts or SMTP AUTH outbound servers for your own customers (or you risk blocking your own customers). Do not use ZEN in filters that do any ‘deep parsing’ of Received headers, or for anything other than checking IP addresses that hand off to your mailservers."

Ok, I'm not a smarthost, and I assume Zimbra doesn't do deep parsing of the received headers.

However, I've got a standard Zimbra 6.0.5 server that is used by out-of-office users that make use of SMTP AUTH (from their homes, hotels, airports, etc.). In Zimbra, does that mean that authenticated SMTP users will get blocked by the zen.spamhaus.org RBL because the IP of the internet connection they're on may be blocked? Or is it smart enough to exempt authenticated users from the RBL lookup?