The Free On-line Dictionary of Computing (30 December 2018):
electronic mail address
(Usually "e-mail address") The string used to
specify the source or destination of an electronic mail
message. E.g. "email@example.com".
The RFC 822 standard is probably the most widely used on the
Internet. X.400 was once used 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
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 usually 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
"firstname.lastname@example.org". 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 department for example.