Devise validate email property with exclusion of words and #myapp.com - ruby-on-rails

Question

Trying to validate the email field in a rails devise app with a word exclusion.
validates :email, :exclusion => {:in => ["admin", "root",,
:message => "is reserved"}
Wich works great on the :username field but not on the email.
I suspect that Devise is "taken over" the validation of the email field and I need to super/ overrule the registrations controller of Devise.
How could I:
Prevent emails with words based on an :exclusion
Prevent emails with #myapp.com so users don't use the domain the app runs on.

Answer 1

You can always write custom validations to achieve what you want. Example from the guide:
The easiest way to add custom validators for validating individual
attributes is with the convenient ActiveModel::EachValidator. In this
case, the custom validator class must implement a validate_each method
which takes three arguments: record, attribute and value which
correspond to the instance, the attribute to be validated and the
value of the attribute in the passed instance.
class EmailValidator < ActiveModel::EachValidator
def validate_each(record, attribute, value)
unless value =~ /\A([^#\s]+)#((?:[-a-z0-9]+\.)+[a-z]{2,})\z/i
record.errors[attribute] << (options[:message] || "is not an email")
end
end
end
class Person < ActiveRecord::Base
validates :email, :presence => true, :email => true
end

Answer 2

After checking if it is an e-mail, I would split the two validations. One for exclusion, and other for domain. You can retrieve the current domain when using passenger.
validate :email_username_is_not_on_blacklist, :email_domain_is_allowed
EXCLUDED_USERNAMES = "admin", "root"
EXCLUDED_DOMAINS = "myapp.com"
def email_username_is_not_on_blacklist
user, domain = email.split("#")
errors.add(:email, "E-mail user is not allowed") if self.class.EXCLUDED_USERNAMES.include?(user)
end
def email_domain_is_allowed
user, domain = email.split("#")
errors.add(:email, "E-mail domain is not allowed") if self.class.EXCLUDED_DOMAINS.include?(domain)
end