why @ (at the rate of) symbol is used in an email id?
The '@' symbol is used to distinguished between the User ID 'n Domain name (like hotmail,yahoo,rediff etc).
Some more facts about email Email was invented in 1971 by a computer engineer,called Ray Tomlinson, who worked for Bolt Bernek and Newman(BBN)-- the company chosen by the United States Defense Department to build the first internet,way back in 1968 The '@' symbol in email addresses was chosen by Tomlinson because he wanted a keyboard character that didn't occur in people's names.It is said that he just spent just 30-40 seconds to think up the choice of symbol.
You Know the first mail which was sent (between two computer that were actually sitting besides each other),bore the text 'QWERTYUIOP'. the first row alphabets on a QWERTY keyboard