Dictionary.net

(Usually "e-mail address") The string used tospecify the source or destination of an electronic mailmessage. E.g. "john@doc.acme.ac.uk".The RFC 822 standard is probably the most widely used on theInternet. X.400 was once used in Europe and Canada.UUCP-style (bang path) addresses or other kinds of sourceroute became virtually extinct in the 1990s.In the example above, "john" is the local part which is thename of a mailbox on the destination computer. If thesender and recipient use the same computer, or the same LAN,for electronic mail then the local part is usually all that isrequired.If they use different computers, e.g. they work at differentcompanies or use different Internet service providers, thenthe "host part", e.g. "sales.acme.com" must be appended afteran "@". This usually takes the form of a fully qualifieddomain name or, within a large organisation, it may be justthe hostname part, e.g. "sales". The destination computernamed by the host part is usually a server of some kindrather than an individual's workstation or PC. The user'smail is stored on the server and read later via client mailsoftware running on the user's computer.Large organisations, such as universities will often set up aglobal alias directory which maps a simple user name such as"jsmith" to an address which contains more information such as"jsmith@london.bigcomp.co.uk". This hides the detailedknowledge of where the message will be delivered from thesender, making it much easier to redirect mail if a userleaves or moves to a different department for example.