Why is this tread marked as SOLVED?
I can't find solution?
Have same problem with zimbra 7 and ubuntu 10.04
Postfix version 2.3 introduces support for Delivery Status Notifications (DSN) as described in RFC 3464.
If you want to disallow all use of DSN requests from the network, use the smtpd_discard_ehlo_keywords feature:
smtpd_discard_ehlo_keywords = silent-discard, dsn
postconf -e "smtpd_discard_ehlo_keywords=silent-discard, dsn"