I notice security companies such as Rapid 7 prevent people signing up with either free email accounts, or accounts provided by ISPs: ...
In a registration form the user is asked for his e-mail address. The e-mail address will be validated for the correct format (e.g. at the least contains @) and I'm considering checking if it's already ...
Most hosting companies, such as mine (hostgator) give the following notice when providing a contact email: Email address that you can be contacted at. This should be an email address that is not ...