The "e" in email stands for electronic; an apt reference to the way in which mail is sent over the internet electronically, as opposed to the normal physical means. Electronic mail allows for easy and convenient communication over long distances. Modern email operates across the Internet or other computer networks. Some early email systems required that the author and the recipient both be online at the same time, in common with instant messaging. Today's email systems are based on a store-and-forward model. Email servers accept, forward, deliver, and store messages.