We have restricted the use of the following CNAME records:
These CNAME records are restricted because they are often needed by your hosting provider to run applications such as email. www is specifically restricted because it is best practice to specify the base domain for www. (Most registrars and hosting providers have already created the www record by default.)
We force you to use a subdomain so that you can build your application on the base domain, and so that we can redirect the referral links to your base domain after you have launched.