Source : Free On-Line Dictionary of Computing

electronic mail address
     
         (Usually "e-mail address", rarely "e-dress",
        "e-ddress") The string used to specify the source or
        destination of an {electronic mail} message.
        E.g. "[email protected]".
     
        The {RFC 822} standard is probably the most widely used on the
        {Internet} though {X.400} is also in use in Europe and Canada.
        {UUCP}-style ({bang path}) addresses or other kinds of {source
        route} became virtually extinct in the 1990s.
     
        In the example above, "john" is the {local part} which is the
        name of a {mailbox} on the destination computer.  If the
        sender and recipient use the same computer, or the same {LAN},
        for electronic mail then the local part is usually all that is
        required.
     
        If they use different computers, e.g. they work at different
        companies or use different {Internet service providers}, then
        the "host part", e.g. "sales.acme.com" must be appended after
        an "@".  This usually takes the form of a {fully qualified
        domain name} or, within a large organisation, it may be just
        the {hostname} part, e.g. "sales".  The destination computer
        named by the host part is often a {server} of some kind rather
        than an individual's {workstation} or {PC}.  The user's mail
        is stored on the server and read later via {client} mail
        software running on the user's computer.
     
        Large organisations, such as universities will often set up a
        global {alias} directory which maps a simple user name such as
        "jsmith" to an address which contains more information such as
        "[email protected]".  This hides the detailed
        knowledge of where the message will be delivered from the
        sender, making it much easier to redirect mail if a user
        leaves or moves to a different computer for example.
     
        (1996-10-22)