Is it possible to add domain restrictions to the email address?

[steve-west-m4a]

Is it possible to add domain restrictions to the email address, to validate that the email domain is not one of the free domains (hotmail.com, gmail.com, yahoo.com etc). I know we can use the REGEX but we are limited to a fairly short string to list all of the free domains. A better way to achieve this would be to call an Apex class to check whether the email address is acceptable.