Email never be a guaranteed service. If you send a $20 item in plain mail,it is at no fault at either side if lost. If a $20k value item is lost in transit of a non-registered mail, (even registered, but not insured), what recipient to do with it? Email is a little bit different - information instead of real items is sent. Given the nature of email - unreliable, it is up to one side (the sender or the recipient, in most cases, the sender) to follow up with it. If recipient demands getting a critical email and he suspect it might have been sent from sender, he shall follow up.