A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
messages from an author to one or more recipients. Modern email operates across the Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
or other computer network
A computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information....
s. Some early email systems required that the author and the recipient both be online at the same time, in common with instant messaging
Instant Messaging is a form of real-time direct text-based chatting communication in push mode between two or more people using personal computers or other devices, along with shared clients. The user's text is conveyed over a network, such as the Internet...
. Today's email systems are based on a store-and-forward model. Email servers accept, forward, deliver and store messages.