On 3/9/2017 3:16 PM, MRob wrote: > obtained by HELO? Is there something in the tcp connection that > identifies the hostname? Sorry if I misunderstood this part.
The HELO name is not related to and doesn't matter for reject_unknown_client_hostname. Perhaps you were confused by the different context of hostname; client (rDNS) vs. HELO (SMTP). The client hostname is determined by an rDNS lookup of the connecting IP. The resulting rDNS hostname is then looked up, and must resolve to the connecting IP. This is also referred to as Forward Confirmed reverse DNS. You can test reject_unknown_client_hostname and other features using the XCLIENT command to simulate some IP that fails FCrDNS. http://www.postfix.org/XCLIENT_README.html Alternately, you can use "warn_if_reject reject_unknown_client_hostname" and watch the log for warnings. http://www.postfix.org/postconf.5.html#warn_if_reject -- Noel Jones
