How to troubleshoot NDRs with 5.7.1 and 5.7.3 error codes

Symptoms: 1. when sending a mail to blin@mvps.org, you may receive undeliverable message like this:

<mail.chicagotech.net> #5.7.1 smtp; 550 5.7.1 <blin@mvps.org>... Relaying denied. IP name lookup failed (x.x.x.x).

2. Non-delivery reports (NDRs) that contain 5.7.1 or 5.7.3 error codes are associated with Application event log event IDs 1709 and 1710: Event Type: Warning
Event Source: MSExchangeTransport
Event Category: SMTP Protocol
Event ID: 1709
Computer: SERVERNAME
Description: An SMTP client did not authenticate before attempting to send mail. Access was denied. Data: 0000: 05 00 07 80 ...? Event Type: Warning
Event Source: MSExchangeTransport
Event Category: SMTP Protocol
Event ID: 1710
Computer: SERVERNAME
Description: An SMTP client authenticated as user "NT AUTHORITY\ANONYMOUS LOGON" attempted to send as "User.one@domain.edu". Access was denied because the authenticated client does not have permission to Send As this SMTP address. Data: 0000: 05 00 07 80 ...?
The 5.7.3 error code is associated with event ID 1701.

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Possible Causes

Resolutions

Enable relay - Authenticated computers not allowed to relay

Enable Anonymous - Anonymous access to SMTP virtual servers disabled

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