Looking at part of the header of one, I see this;
X-Spam-Flag: YES
X-Spam-Score: 8.692
X-Spam-Level: ********
X-Spam-Status: Yes, score=8.692 tagged_above=-10 required=7 tests=[BAYES_20=-0.74, DNS_FROM_OPENWHOIS=1.13, FH_DATE_PAST_20XX=3.188, TVD_RCVD_IP=1.931, TVD_RCVD_IP4=3.183]
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: base64
X-Mailer: Apple Embedded SMTP Client 1.0
Any ideas on how to allow this? Also, is there a whitelist I can implement?
Found this
Improving Anti-spam system - Zimbra :: Wiki
Perhaps it fits the bill.