Rails 3, Unknown validator: 'EmailValidator'

This error occures, because rails loads model file before your validation file

Try to require your validation file manually at the start of your model file

require_dependency 'validators/email_validator.rb'

If you place your custom validators in app/validators they will be automatically loaded without needing to alter your config/application.rb file.

Resource: Where should Rails 3 custom validators be stored? (second answer)