I don't think you can change the domain length checking on the emailValidator...it's defaulted to allowing 2,3,4 or 6 char's long, without any options to limit that.
The next soltution would be to write a simple regex function that does your email validation instead of using the builtin.
Also, I'd take a look at extending the EmailValidator.as class. Under the public static function validateEmail, there is a condition check being done:
if (lastDomain.length != 3 &&
lastDomain.length != 2 &&
lastDomain.length != 4 &&
lastDomain.length != 6)
You might take a look at overriding that for your uses and creating an extended EmailValidator for your project.