We switched to new 2.7.4 (Windows) version, Exchange 2003. So far very good, users are happy

, but I've noticed some e-mails got quarantined by RBL, but when I check IP directly via
http://www.spamhaus.org/zen/ the IP is clean on all 3 lists (SBL, PBL, XBL).
We have only one RBL list configured - zen.spamhaus.org and it is as it was stright after installation, no modifications were done.
Please advise, thanks,
Andrew