After your domain has been authenticated, you should setup your Email Sending Accounts. The video below gives you an explanation and shows you how to easily set it up.
It is highly recommended that you use an actual working email address with your domain name (ie. [email protected])
If you don't have a custom email address with your domain, that's okay (see video below).
If you decide to setup a custom email address, please contact [email protected] and we can help with that!