In addition to the main domain, you can add an unlimited number of redirects to your Box.
In the Box overview, click on the pencil icon next to the section heading Redirects. A plus symbol entitled Add redirect will appear. Click on the plus symbol, enter your chosen domain and confirm your entry by selecting Save all.
The next steps depend on where your domain is hosted:
The article External domain: Update DNS records explains the steps involved if your domain is hosted by another provider.
Follow the steps in Connect a RAIDBOXES domain to your Box if your domain is hosted by us.