the device:some native device characteristics make it difficult to inter-act with e-mail.for example,a device without a touchscreen can make clicking on a link frustrating or even impossible. even if you know the capabilities of every device used by every one of your customers and you can somehow keep that information updated when your customers change to another device, it's next to impossible to design an e-mail that allows seamless interaction on every device. besides that, it's not practi-cal to design a different e-mail for every device. that defeats one of the main benefits of e-mail, which is mass delivery.