(1) A stand-alone mail server that plugs into the network to provide e-mail for an organization. Typically rack-mounted hardware, the device includes software that provides the message store and transfer agent (see mail server and messaging system). Users access their mail with a client program in their computers or via a Web browser. See server appliance and e-mail interfaces.
(2) A device specialized for accessing e-mail that was introduced around the turn of the century. Today's e-mail appliances are typically smartphones. See Internet appliance and Internet server appliance.