Dont deliver order and shipments email

order_mailer_decorator.rb

# put at app/mailers/spree/order_mailer_decorator.rb
module Spree
  OrderMailer.class_eval do
    def confirm_email(order, resend = false)
      self.message.perform_deliveries = false
    end

    def cancel_email(order, resend = false)
      self.message.perform_deliveries = false
    end
  end
end

shipment_mailer_decorator.rb

# at app/mailers/spree/shipment_mailer_decorator.rb
module Spree
  ShipmentMailer.class_eval do
    def shipped_email(shipment, resend = false)
      self.message.perform_deliveries = false
    end
  end
end