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

{4}: A required security operation couldn't be performed during delivery of this e-mail message. Either the credentials are incorrect, or the authenticated user doesn't have the 'ms-Exch-SMTP-Submit' permission. A lack of the 'ms-Exch-SMTP-Submit' permission results in an authentication failure and not an authorization failure. This is to prevent the server from giving away information, making it a resource for password guess attacks.