The problem is that during upgrade, script replaced two lines in /etc/postfix/main.cf file: smtpd_client_restrictions = and smtpd_recipient_restrictions = with some default values . The rest of the settings in this files was unchanged. I made some customization in those lines. I did upgrade by running ispconfig_update.sh script. In september I made upgrade from 188.8.131.52 to 184.108.40.206 Yesterday I made upgrade from 220.127.116.11 to 18.104.22.168 and in both cases I did have the same problem with Postfix. Please make changes to ispconfig_update.sh that during next upgrade it will not replace those two lines any more. Thank you.