For centuries ,the only form of written correspondence was the letter .Letters were ,and are ,sent by some form of postal service ,the history of which goes back a long way. Indeed ,the Egyptians began sending letters from about 2000 BC, as did the Chinese a thousand years later.        Of course ,modern postal services now are much more developed and faster ,depending as they do on cars and planes for delivery .Yet they are still too slow for some people to send urgent documents and letters.        The invention of the fax machine increased the speed of delivering documents even more .When you send a fax ,you are sending a copy of a piece of correspondence to someone by telephone service .It was not until the early 1980s that such a service was developed enough for businesses to be able to fax documents to each other.        The fax service is still very much in use when copies of documents require to be sent ,but ,as a way of fast correspondence, it has been largely taken the place of by email. Email is used to describe messages sent from one computer user to another.        There are advantages and disadvantages with emails. If you send someone and email, then he will receive it extremely quickly. Normal postal services are rather slow as far as speed of delivery is concerned.        However ,if you write something by email ,which you might later regret ,and send it immediately ,there is no chance for second thoughts. At least ,if you are posting a letter you have to address and seal the envelope and take it to the post box .There is plenty of time to change your mind. The message is think before you email! It can be inferred from the text that_.
the fax service had been fully developed by the 1980s letters have been used in prefix = st1 /Chinafor about 1,000 years the fax machine was invented after the 1980s letters have been used in Egyptfor about 2,000 years