Datto Drive restricts the use of a subdomain name to one unique email domain.
For example, this means that when you register your first account with the email domain @johnspizza.com, nobody else can create a Datto Drive account with the @johnspizza subdomain. This prevents the creation of duplicate subdomains. When you click the link to request access, Datto Drive sends an email to the user who first registered the subdomain. This email asks for access to create an account on that subdomain.