What is a addon domain? An addon domain allows you to add another domain to your existing account and direct that domain to a subfolder. For example, a photographer might have a domain camera.com and wish to set up another domain on their account called photos.com, but have photos.com show different content than the master domain. In that case, photos.com would be set up as an addon domain, pointing to the folder /photos under the main site. Visitors to photos.com would only see that URL in the address bar of their browser.