The Email Address field generates emails for real domains, so it is entirely possible that some of the generated email addresses will correspond to real users. The only way to prevent this is by changing the domain to one that is known not to exist, or to define your own email address scheme using a Formula field.
One way to alter an email address to ensure it isn't real is to add '.fake' as the top level domain. You can paste the following into the f(x) dialog on any Email Address field to achieve this:
I'll likely make this an option on the email address field itself in the near future.