To enroll devices by entering an email address, make a TXT entry in the DNS database for the domain(s) desired. The method for this can vary based on the DNS solution, so check with your DNS documentation for more information on doing this.
For Apple iOS devices (iPhone, iPad, etc) create the entry as:
For Google Android devices, create the entry as:
Currently, there is no option for Windows Phone (7.5) devices to enroll using email and DNS records, due to limitations in the phone operating system. This might change with future releases of Windows Phone.