I recently followed the wiki advice located here...
Except instead of the listed RBL's, I just listed one, the Spamhaus Zen RBL which combines all their lists into one and is located at zen.spamhaus.org as follows...
It did not give me any error messages and I rebooted the server. I expected to be given some indication in the admin interface that this was now active but I can't see anything different. Is there anything else I need to do to activate this RBL or is it now just silently working away?
zmprov mcf zimbraMtaRestriction reject_invalid_hostname zimbraMtaRestriction reject_non-
fqdn_hostname zimbraMtaRestriction reject_non_fqdn_sender zimbraMtaRestriction