A required security operation could not be performed during delivery of this e-mail message. Either the credentials are incorrect, ...

{4}: A required security operation could not be performed during delivery of this e-mail message. Either the credentials are incorrect, or the authenticated user does not have the 'ms-Exch-SMTP-Submit' permission. A lack of the 'Submit' permission results in an authentication failure and not an authorization failure because the server would give away information, making the SMTP server a resource for password guess attacks.