No delivery to &1, authentication required

What causes this issue?

The message was processed successfully in the SAP system. The mail
server that is supposed to receive the message for further processing
requires authentication. The SAP system does not support this procedure.
As a result, the message was not delivered to recipient &V1&.


Information from External System
IF &V4& <> ''
&V4&&V3&
ELSE
<No information available>
ENDIF

How to fix this error?

The administration settings must be changed. The specified mail server
must not request authentication.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.