Thought I would share this problem I ran into and the solution incase anyone else has it. Running Mailman 2.1.20 on Ubuntu 16 and a recent update to postfix stopped my lists. In my syslog I was seeing a message similar to: Oct 24 16:43:59 mailman postfix/smtpd[18686]: NOQUEUE: reject: RCPT from mailman.ihmc.us[184.182.233.xxx]: 451 4.3.0 <user@ihmc.us>: Temporary lookup failure; from=<podcast-bounces@mailman.ihmc.us> to=<user@ihmc.us> proto=ESMTP helo=<mailman.ihmc.us> As it turns out Postfix 3 tightened up on relaying. In my postfix/main.cf I had both mynetworks_style = subnet mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128 I finally found at <http://www.postfix.org/BASIC_CONFIGURATION_README.html <http://www.postfix.org/BASIC_CONFIGURATION_README.html>> that if mynetworks is present then mynetworks_style is ignored. So I commented out mynetworks and changed mynetworks_style = host and now mail from lists is being delivered again. Hope this helps someone else.

Alan M Ordway