The author internal id or email must match an employee.

AI generated answer (using internal Slack threads):

Based on the conversations, it appears that the author of an email sent from NetSuite must be an employee. This does not necessarily mean that the employee needs to have login access. You can create an employee without login access and use their email as the author. This will not count against your limited number of licenses. However, you might need to add vicarious email permission on the employee record. If you're getting a

SSS_AUTHOR_MUST_BE_EMPLOYEE

error, it could be due to the author user id not being an integer or not corresponding to an existing employee. ****** Disclaimer: This response was generated by an artificial intelligence assistant based on previous conversations from multiple Slack channels, and may contain inaccuracies or mistakes. ******