Domains must be registered with Echoworx (our PBE provider) and configured in your PBE-A client profile before they can be used with PBE-Advanced.
Email Security.cloud
Echoworx PBE platform
To register and get your domains configured, you must open a new case to the Global Customer Care with Products - Products Entitlement/Contracts Related.
Note: This step is not required for PBE-Essentials.