Symantec Messaging Gateway does not deliver to an external domain, and the Message Audit Log (MAL) shows a final delivery status with the "554 5.7.1" code.
SMTP code "554 5.7.1" is a rejection from the Recipient Domain. SMTP code "554 5.7.1" means 'Not allowed'. The address in '
Mail From' appears to have insufficient submission rights, or is invalid, or is not authorized with the authentication used; the address in an RCPT TO command is inconsistent with the permissions given to the user; the message data is rejected based on the submitting user. A 5xx level status code indicates a "terminal" status and SMG will not attempt to redeliver the message.