IT IS 40 years since American computer engineer Ray Tomlinson put the @ into email addresses, triggering a communications revolution that would forever change the way we correspond. Yet email now faces a mid-life crisis as young people turn to newer forms of communication, such as Facebook and Twitter.

Internal messaging systems have existed since the 1960s but in 1971 Tomlinson was helping build ARPANET for the US Department of Defence and laying the foundations of the modern internet. Tomlinson needed an easy way to send electronic messages between the various computers hooked up to ARPANET. He chose @ - generally referred to as the ''at'' symbol - to designate that a message was intended for a specific user ''at'' a specific organisation. The email protocol continued to develop but, for the next 20 years, it was restricted to academic and military use.

Email is under siege from younger forms of communication. Credit:Peter Riches

The internet was opened up for commercial use in the 1990s and email went mainstream - driven by the rise of internet service providers such as OzEmail and the birth of free webmail services such as Hotmail, Yahoo! and, later, Gmail. Businesses also embraced email, helped by the rise of the BlackBerry and smartphones.

Email had several advantages over existing forms of communication such as phone calls, letters and faxes. Email is fast, cheap, convenient and asynchronous - the latter meaning that, unlike a phone call, the receiver can deal with it when it suits them. Emails are also easier to store, search and archive than reams of paper or ephemeral phone calls that go in one ear and out the other.