Delivery Status Notifications (DSN) are messages generated by a mail server to notify the sender that the email has been delivered to the destination mail server.
Problem is, many systems sending email messages are doing DSN requests, but are automated systems and dont accept email messages. This results in your mail server getting clogged with junk outbound email messages, and/or your mail server gets added to a black list.
A quick way to detect if your MX is handling DSN is to telnet to port 25 on the server then type in
and you should see something like
220-mx1.mydomain.com ESMTP Postfix ehlo localhost 220 mx1.mydomain.com ESMTP Postfix 250-mx1.mydomain.com 250-PIPELINING 250-SIZE 154337280 250-VRFY 250-ETRN 250-STARTTLS 250-ENHANCEDSTATUSCODES 250-8BITMIME 250-DSN 250 CHUNKING
The above server supports DSN as you can see the line “250-DSN”
To disable this on a Zimbra 8 server ssh to the server, then
su zimbra postconf -e "smtpd_discard_ehlo_keywords=silent-discard, dsn" postfix reload
Now it is disabled