SMTP

This enables the appliance to send emails informing new users once a new WorkSpace is ready and\or if their password is to expire. It is also required for the auto-delete function.
You could use AWS Simple Email Service (SES) to achieve this, or your own SMTP setup. You can test the connection by selecting the lightning icon to the left of the field. For a guide on how to configure SES, please check SES Configuration.