A custom-domain in RefinedSites is a domain of your choice to direct visitors seeking IT support.
With RefinedSites you can get your own custom domain for your support portal, making the experience tailor made for your customers and not leaving them wondering if they are in the right place.
This means that your users can access your portal through any domain you choose.
Setting up RefinedSites directed to your custom domain
Go to JIRA Administration > RefinedSites Configuration, click to configure your RefinedSite.
In RefinedSites Configuration > Custom Domains you'll find the setup.
You'll need your own domain ready, and once you have it, click the edit button, enter the custom domain and save.
Well, working with DNS and domains, it may take a while until the internet knows about this new setup, but once it does you are ready to go and you can access your RefinedSite from your custom domain.