Redirecting another domain to your site
Your Site Builder site can only use a single URL, however it is possible to set up Domain Forwarding on your DNS zone to redirect other domains to your Site Builder URL through DNS settings.
For example, if you have these domains registered:
You can configure your DNS zone to redirect these requests to www.sitebuilder.com.
The redirection can be created by logging in to the Domain Registrar's of the domain you'd like to redirect, and utilizing their web interface to enable domain forwarding, pointing to the domain of your choice.
As each interface is different, you may need to contact the support team for that Domain Registrar in order to get help on how to enable Domain Forwarding.