HES/HES - Inbound Filtering denies emails for non-existent users and does not send NDRs for emails rejected using Active Directory Sync Client or Directory Management.
During the SMTP connection between the sender’s mail server and HES mail server, HES/HES - Inbound Filtering sends an SMTP Error back to the sender’s mail server instead of an NDR. It is up to the sender’s mail server to send an NDR back to the sender.
Apr 18 21:55:22 in01 postfix/smtpd[52897]: NOQUEUE: reject: RCPT from unknown[undisclosed IP Address]: 554 5.7.1 <undisclosed recipient email address>: Recipient address rejected: Access denied; from=< undisclosed sender’s email address > to=< undisclosed recipient email address > proto=SMTP helo=<p1186-ipbf206oxxxx.xxxxx.domain.com >