Email is the electronic equivalent of snail mail. It is a way of sending one or more files (typically text files, but sound, graphics, programs, video files- any kind of file) to a specified user's mailbox (identified by an email address) across a network, or on a single machine.
The first email message was sent in 1971 by Ray Tomlinson, (who also invented the use of the "@" symbol in email addresses.)
From the earliest times Email was the nearest thing to a killer app for the internet until the web took off. Now Email is easily the second most important service after the web, and is still growing in popularity.
The two unique, defining features of email (which the other node's definitions seem to have missed) is first, that it supports the cases where the destination system is not necessarily running when the mail is sent (although the sending system must be running!); and second and most importantly that no prior agreement is required to send the mail.
Other networked services that also send files of data include ftp, some forms of P2P, ICQ. (ICQ is more or less an email system where the emails are kept short but prior agreement is required to send messages to a user).
Cell phone's SMS
(Short Message System) aka
' is a form of email; SMS
texting is the killer app of cell phones
, in Europe and Japan and is growing in America.
Many email systems are currently, in 2003, being plagued with unpopular, criminal and in many cases disgusting spam. More than 50% of mail sent is of this form, and is a real menace- seemingly nothing can stop it.
However, it seems likely that the war on spam will be largely won in the next few years. Promising technical approaches such as Bayesian spam filtering have appeared that filter out over 99% of such email, whilst harming very little wanted mail. Additionally spam is coming under increasing legislative and legal scrutinies which are promising to make spamming millions of email addresses illegal and less cost effective and desirable to spammers.
So, in spite of this threat, at this moment in time it seems likely that some form of email is going to be around for a long time, perhaps longer than snail mail has been around.