The SMTP server requires a secure connection or the client was not authenticated. The server response was: Authentication required in Dynamics 365 Finance / Dynamics AX

 I was getting the below error while try to send a test email through email parameters after updating SMTP details.

The SMTP server requires a secure connection or the client was not authenticated. The server response was: Authentication required

Solution

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-> After updating the SMTP detail refresh the application page and try again

-> If the above steps does not work, login with send as email address (ex: noreply@abc.com) and update the SMTP details and send a test email.