I'm running zimbra zcs for a few months now without any problems. but lately im getting this header when sending emails:

Received: from ***** (***** [])
by ****** (Postfix) with ESMTP id E461A3AC884
for <********>; Thu, 18 Sep 2008 11:21:50 +0200 (CEST)

which causes various spamfilters on the receiving end (eg. spamassassin with RCVD_ILLEGAL_IP) to complain!

Does anyone can give advice on what caused this bahaviour and what to do?