action_mailer.rb

ActionMailer::Base.register_interceptor(BanDisposableInterceptor)

ban_disposable_interceptor.rb

class BanDisposableInterceptor
  def self.delivering_email(mail)
    mail.perform_deliveries = false unless BanDisposableValidator.valid?(mail.to[0])
  end
end

ban_disposable_validator.rb

class BanDisposableValidator < ActiveModel::EachValidator

  DISPOSABLE_DOMAINS =
    JSON.parse(File.read("#{Rails.root}/config/disposable-email-domains.json")) rescue []

  delegate :get_mail_domain, :valid?, to: self

  def validate_each(record, attribute, value)
    error_message = I18n.t 'devise.registrations.messages.invalid_email'
    unless valid?(value)
      record.errors[:email] << error_message
    end
  end

  def self.valid?(mail)
    domain_name = get_mail_domain(mail)
    return false if domain_name.nil?
    !DISPOSABLE_DOMAINS.include?(domain_name)
  end

  private

  def self.get_mail_domain(mail)
    Mail::Address.new(mail).domain rescue nil
  end
end