Has anyone used DNSBLs behind a mail relay? The MX records for many of our domains point to our border mail relays (running Exim) so all mail received by Zimbra comes from one of those boxes.

This doesn't help the DNSBL as the originating IP will always be our own mail relay.

Is there a way for Zimbra to check the first Received by: IP in the headers, or alternatively I guess I could create an Exim rule that adds a specific header if it's in the DNSBL and get zimbra to increment the spam score if that exists?