ontohub/lib/prevent_mail_interceptor.rb

class PreventMailInterceptor
  RE = /.*@example\.com/

  def self.delivering_email(message)
    unless deliver?(message)
      message.perform_deliveries = false
      Rails.logger.debug "Interceptor prevented sending mail #{message.inspect}!"
    end
  end

  def self.deliver?(message)
    message.to.any? { |recipient| recipient !~ RE }
  end
end