Good day! Go to excuse my English) in the general problem is the server installed Zimbra Opensource and there is a problem at all to pile Zimbra desktop but since in Desktop features no confirmation of delivery, I decided to implement with postfix read the manual and found it seemed to me then what I need. Add a line in /opt/Zimbra/postfix/conf/main.cf:
smtpd_discard_ehlo_keyword_address_maps = cidr: /etc/postfix/ esmtp_access
ordered online go to restart the server
send the command sendmail-N success firstname.lastname@example.org and in response to the silence as if sendmail is waiting for the completion of the line.
And accordingly no reports about what that something was delivered to no.