Follow official postfix page (http://www.postfix.org/DSN_README.html) I've:
smtpd_discard_ehlo_keyword_address_maps = cidr:/etc/postfix/esmtp_access cat /etc/postfix/esmtp_access # Allow DSN requests from local subnet only 192.168.1.0/24 silent-discard 0.0.0.0/0 silent-discard, dsn ::/0 silent-discard, dsn I've small lan on 192.168.1.0 and all clients uses a single smtp postfix server. On clients, send the emails with "delivery status notification" option. After sent, postfix send me a delivery status notification: Successful Mail Delivery Report but that email is within postfix queue (why I stopped destination over internet smtp server - purpose test). So, my postfix server always send a delivery status notification also if there's a transmission problem. What's the error? thanks! Pol